Supply Chain - Wastewater Treatment - Preliminary Treatment

One of South West Water’s aims is for everyone to feel confident about the water at their favourite beach, river, or lake. The Inlet Enhancement Projects programme of work was put in place to ensure that all flows coming into sewage treatment works under normal conditions are screened down to 6mm 2D and that the storm spills were screened down to 10mm. As part of this programme, Galliford Try was engaged to deliver 10 projects across Devon for the enhancement of the inlet works and install new automated preliminary screens with manually screened bypass channels and associated LCPs for control. Planning and design

Following a full review and selection process for a preferred screen provider to ensure that the correct product was selected for the application, South West Water and Galliford Try, supported by the civils design arm of Fishtek Consulting, selected Haigh Engineering Ltd as the main supply partner.

Galliford Try worked collaboratively with Haigh Engineering to discuss the specific requirements for each of the sites individually. This included a programme of site visits to gather information about the existing structures and hydraulic profiles that were to be adapted. After this, Galliford Try held numerous design review meetings with South West Water’s key stakeholders, including the operational area managers, to discuss the best specific application that were developed with the delivery partners for each of the sites along with design flow rates.

[caption id="attachment_11530" align="alignnone" width="1200"] The new screen, LISEP and grit trap at Moreleigh STW - Courtesy of Galliford Try[/caption] Locations

The 10 wastewater treatment works are:

East Ogwell STW Compton and Marldon STW Drewsteignton STW Diptford STW Moreleigh STW Whiddon Down STW Cornworthy STW Zeal Monachorum STW Parkham STW Bridford STW

The sites were batched - 3 sites at a time - with South West Water and Galliford Try prioritising those which would gain the most benefit from the scheme. Fishtek Consulting was engaged as designers to look at the civils detailed design and to model each of the sites with the new screens in place.

Each site had its own complications as Galliford Try had to manage flows through to the rest of the site. With each site being different in nature of hydraulics, there was a varied approach to be taken; whether that be pumped flows or gravity flows into the site.

Another challenge to each project was the selected screen, as some of the screens come as a package screen with bypass included and all that was required was a level foundation, whilst some screens sat in the channel, meaning that Galliford Try and CR Civil Engineering had to break out existing channels and benching to facilitate the installation of the new screen and associated equipment.

Construction

Where possible, construction was scheduled for the dryer months to minimise the impact on the performance of the site and risk of delays due to high flows. After initial site set-up, the first task was to set up over pumping or a bypass on each site which was agreed up front with the client and a process risk assessment put in place for the duration of the works. Once this was set-up, the deconstruction of some of the existing inlet structures could be undertaken to form a new base slab or a new benched inlet for the screen to sit.

Once the new screen was installed with all relevant ducting in place to take power and control cabling, commissioning engineers from Galliford Try and Haigh Engineering Ltd set the parameters for the new screen and ensure the process worked as it should.

[caption id="attachment_11536" align="alignnone" width="1200"] Drewsteignton STW screen in foreground and LISEP tucked behind - Courtesy of Galliford Try[/caption] Inlet Enhancement Projects: Supply chain - key participants Project delivery: Galliford Try Civils design: Fishtek Consulting Civil engineering: CR Civil Engineering Electrical installation: AGT Electrics Screen supplier: Haigh Engineering Ltd Pumping: Pump Supplies Ltd Innovations

Galliford Try used a specialist expanding grout for the controlled breaking out some of the civils structures on some of the sites. The process required small holes to be drilled into the structure and then the grout was mixed and poured into the holes. This took 18 hours to work and expand. The slow expansion then broke each structure away with minimal dust, noise, and risk due to the lack of potential for flying debris. In addition, this methodology significantly reduced hand and arm vibration exposure.

[caption id="attachment_11533" align="alignnone" width="1200"] East Ogwell STW: (left) overall view of inlet and (right) new screen in place - Courtesy of Galliford Try[/caption] Risk management

Primarily, a lot of the design was undertaken up front with multiple visits to site to confirm what was required and at this stage high risk tasks were either worked around or agreed upon up front. Risks were further mitigated by good planning and communication with all parties on site. Any risks that did occur were communicated back to the client for further instruction.

Results Cost savings: Galliford Try added value by minimising costs on equipment and man hours on each project as the projects were repetitive and design did not change much. Through multiple sites and screens of the same nature, efficiencies were gained. The use of Galliford Try`s in-house capabilities to fabricate and produce the control panels benefited the overall programme of works. This enabled a succedent programme of works to be maintained throughout with zero incidents on site. Carbon savings: With the sites being in close proximity there were carbon savings on travel and by ordering multiple units at the same time, there were carbon savings in the delivery of plant to sites. Health & Safety: Minor works health and safety plans were produced along with all site information compiled on site. Zero accidents or incidents were reported over an average of 810 man hours per site Engagement

Galliford Try was heavily engaged with operations through pre-construction to delivery and closeout, ensuring that all snag items were closed out efficiently and the end user was happy with the solution provided.

Hawkchurch is a small village on the Devon/Dorset border, 3 miles north-east of Axminster and 4 miles north of the fishing town of Lyme Regis. The existing sewage treatment works was constructed in the 1980s and serves a population of around 500. It was typical of the era, with an old style Dortmund tank with percolating filter and humus tank off the back end. Final effluent is pumped from the site to an outfall into the Blackwater River. The project driver was to reduce the number of unconsented spills to the environment by providing a capacity of 45m3 storm storage and inlet works screening to remove solids and enhance the operation of the works. Project scope

At the scoping stage, Galliford Try worked closely with South West Water to establish the most cost-efficient solution when considering both operational expenditure (OPEX) and capital expenditure (CAPEX) to ensure South West Water achieved the best whole life costs. From this exercise it was established that the scope outlined below was to be included for construction on site:

A new above-ground concrete storm tank with capacity of 45m3 (exceeding the EA’s required storage volume of 40m3). New access platform to span the storm tank for washing down of the storm tank. New LCP for the control of duty/standby pump for return of effluent within the storm tank. One Jacopa wave screen to be installed on the overflow from the storm tank. One new HAIGH 590 series, 6mm 2D mechanically cleaned screen and 10mm 1D hand raked bypass screen from Haigh Engineering to be installed within existing inlet channel. The site

Access to site was challenging, as the site was only accessible via one narrow road with infrequent passing places for the larger vehicles required to get construction equipment and materials to site. Additionally, the footprint of the site was only 880m2 of which only 180m2 was usable for the construction activities.

[caption id="attachment_12435" align="alignnone" width="1200"] (left) Piling rig set up, (middle) piling reinforcement, and (right) piles cropped - Courtesy of Galliford Try[/caption] The stormwater storage tank

Prior to construction it was identified that there was contaminated water within the ground. After the initial sampling, Galliford Try requested further sampling to take place to identify if this was a one-off fuel spill or not. After the second survey, it was identified that contaminated water was still present and was an issue that required managing.

Galliford Try’s environmental team looked into the best practice options to manage this, and then engaged AGS Ground Solutions Ltd to undertake a Tier 2 survey of the site, as it was considered possible that a new fissure could be created during the piling stage which could expose the contaminated water to the environment.

Through further studies and multiple discussions around this topic, to mitigate the risk, Galliford Try utililised contaminated water handling plant and pumps from Siltbuster Ltd to manage flows. Along with this, Reconomy was engaged for the removal of any contaminated arisings.

The new storm tank was built upon twelve piles due to the strata within this area a mixture of Charmouth mudstone formed some 190 million years ago and poorly stratified angular rock with clayey hillwash. To undertake the piling, a piling mat and temporary works were required, which allowed Aarsleff Ground Engineeing to mobilise to site and install the twelve CFA piles at 450mm nominal diameter.

Throughout the piling exercise, contaminated water was managed through the Siltbuster Ltd plant, and the piling activity was successfully completed with zero impact to the local water courses.

With the piling compete, steel for the base was installed and tied into the piling reinforcement, shuttered and poured in two sections due to the need for a sump to install the return pumps. Wall steelwork was then installed up to 3m above ground and shutter pans used for the concrete pour.

Overflows from the new tank will spill into an existing chamber on the site and to screen these flows further, Jacopa Ltd fitted a new 2D wave screen to screen all flows to 6mm within the storm tank.

[caption id="attachment_12436" align="alignnone" width="1200"] (left) Base shuttered and wall starters, and (right) steelwork for base slab - Courtesy of Galliford Try[/caption] Inlet works screening

One of South West Water’s aims is for everyone to feel confident about the water at their favourite beach, river, or lake. Galliford Try have installed a number of inlet works enhancement screens on multiple sites throughout Devon as part of SWW’s WaterFit Programme, and through this have gained useful experience in installing screens whilst managing flows through to the works.

Following discussions on how to manage flows at Hawkchurch STW, a new 590 Series screen from Haigh Engineering Ltd was installed into the inlet channel. Flows are screened to 6mm, with bypass flows screened to 10mm.

Hawkchurch Storm Tank: Supply chain - key participants Project delivery, civils & MEICA: Galliford Try Ground surveys: AGS Ground Solutions Ltd Civil design: Eastwood & Partners Contaminated water handling: Siltbuster Ltd Removal of contaminated arisings: Reconomy Piling: Aarsleff Ground Engineering Tank construction: D Wall Construction Services Steelwork: GT Fabrications Wave screen: Jacopa Inlet screens: Haigh Engineering Ltd Pumps: Xylem Water Solutions Pipework: Saint Gobain PAM UK Flow meter: Siemens Instrumentation: Pulsar Measurement Kiosk: GR PRO Precision Manufacturing [caption id="attachment_12431" align="alignnone" width="1200"] (left) Jacopa wave screen in the storm tank, (top right) Inlet screen installation in the channel, and (bottom right) inlet screen in action - Courtesy of Galliford Try[/caption] Carbon savings & in-house capability

Local resources and materials were used where possible including subcontractors, which as a result provided the local economy with a financial boost during the construction phase. Where local suppliers were not available, Galliford Try strived to use off-site build solutions where possible to minimise commuting.

In-house resources that were utilised included project management, electrical design, LCP design/build, process control, and commissioning. The in-house workforce undertook  the site establishment, civil engineering, landscaping, MEICA works, and finally the demobilising the site.

Stakeholder management

At pre-construction phase, all third-party stakeholders were identified and entered onto a management plan. Galliford Try’s Customer Liaison Officer contacted all stakeholders prior to commencement to provide them with the appropriate project contacts should they have questions, queries, or complaints and to establish their requirements and desires throughout the construction phase of the works. As part of the management plan all communications where complaints or agreements are made are formally recorded, resolved, and closed out.

Conclusion

Initial progress on site was good with setting up site and setting the project up for an efficient delivery until delays were encompassed by switching the piling rig out due to the environmental considerations. Once this was managed and piling underway, the remainder of the project ran through a smooth transition and was delivered by the regulation date of 31 March 2024.

Tamlaght is a small village in County Fermanagh, strategically located just off the Belfast Road between Enniskillen and a growing cluster of expanding settlements including Lisbellaw (3 miles), Maguiresbridge (8 miles), Brookeborough (10 miles), and Lisnaskea (13 miles). This settlement pattern underlines the strategic importance of Tamlaght Wastewater Treatment Works (WwTW), making it a key asset in supporting both existing demand and future development in the region. As part of their six-year business plan (Price Control Period 2021-2027) and infrastructure programme, NI Water invested £3.7m to upgrade Tamlaght WwTW with modern new infrastructure and cutting-edge technology. The project introduced state-of-the-art treatment tanks, along with advanced electrical and mechanical systems to provide a robust future proof wastewater treatment solution all delivered within the existing site footprint. Existing treatment process

The original Tamlaght WwTW was designed for a population equivalent (PE) of 790, treating a current PE of 481 in 2019 with growth projections to 527. Despite having apparent headroom capacity, the works consistently failed to meet planning and discharge consent conditions, preventing further catchment development. The water order consent standard for the existing works was 40:60:10 mg/l (BOD:SS:Ammonia), however this was later relaxed by Northern Ireland Environment Agency (NIEA) to 40:60 mg/l for the future PE.

The existing works comprised an automatically raked inlet screen, compact activated sludge plant with oxidation tank and final settlement tank, control kiosk, and final effluent measurement flume.

[caption id="attachment_25920" align="alignnone" width="1200"] The existing wastewater treatment facility at Tamlaght: (top left) Overview of site, (top right) the existing compact activated sludge plant, (bottom left) the existing works entrance and (bottom right) the existing inlet works - Courtesy of DLJ Water Ltd[/caption] Project drivers

The wastewater treatment works at Tamlaght had been in operation for nearly 40 years, with NI Water investing continually in maintenance to sustain discharge compliance.

Over time, rising population demands placed additional pressure on the site, while ageing assets neared the end of their design life and parts of the site became increasingly vulnerable to flooding.

Although the works retained sufficient hydraulic headroom, it frequently breached consent conditions, restricting further catchment development. In addition, the condition of the site, the increased population equivalent, and evolving regulatory requirements all became significant drivers for investment.

The key project drivers can be summarised as follows:

Future growth: Support the anticipated growth of the local population in the Tamlaght catchment area, ensuring infrastructure meets requirements for a 25-year design horizon. Future-proof design: Deliver a flexible design that can accommodate future extensions, modifications in flows, loads, or regulatory consents with minimal disruption. Regulatory compliance: Achieve compliance with the new NIEA discharge consent standard of 40:60 mg/l (BOD:SS) and deliver environmental improvements through enhanced water quality discharge to Lough Erne in accordance with the Water Order Consent standard and Urban Wastewater Treatment Regulations (NI) 2007. Environmental protection: The treated final effluent is discharged into a tributary of Upper Lough Erne, a sensitive waterbody of high ecological value and recreational importance. Maintaining consistently high effluent quality was critical to protecting local watercourses and the wider rural ecosystem, supported by an environmental management pump station to ensure long-term protection. Operational efficiencies: Drive reductions in operational interventions and maximise overall efficiency, while supporting sustainability through: Blower energy consumption. Minimised visual impact. Reduced waste and disruption. Enhanced noise and odour control. Improved air quality. Positive socioeconomic outcomes. Flood resilience: Ensure that all new structures and equipment are constructed above the Q100 flood level, mitigating the risk of future flooding at the Tamlaght WwTW site. Existing process: Phased construction of the new treatment works on a constrained site, while maintaining full operation of the existing process to ensure all discharge consent standards are consistently met throughout the works. [caption id="attachment_25935" align="alignnone" width="1200"] Construction of the storm tank - Courtesy of DLJ Water Ltd[/caption] Project delivery team

DLJ Water Ltd, a highly experienced collaborative joint venture between Deane Public Works Ltd, Lowry Building & Civil Engineering Ltd, and Avove Ireland (formerly Jacopa Ltd), was appointed as the Principal Contractor and Principal Designer.

The multi-disciplinary joint venture specialises in civil, process, and MEICA design and engineering services for water and wastewater treatment plants and associated infrastructure assets, with full responsibility for delivering a turnkey MEICA and process design-and-build solution for the new Tamlaght works on time and within budget.

Tetra Tech RPS was appointed by NI Water as Project Managers and worked collaboratively with DLJ Water to ensure the successful delivery of the scheme. For the Tamlaght works, the process and MEICA designs were developed by treatment process specialist and joint venture partner Avove Ireland. Deane Public Works led the JV design alignment process and, together with the expert supply chain, oversaw the civil design and construction requirements.

Early contractor involvement

DLJ Water was awarded an NEC4 (Option A) Early Contractor Involvement (ECI) contract by NI Water in June 2022 for the multi-disciplinary design, construction, commissioning, and testing for a replacement treatment works at the existing Tamlaght WwTW site.

The extensive ECI phase allowed DLJ Water to align resources, integrate objectives, and gain an early understanding of the key project drivers in collaboration with NI Water, their project management team, and other key stakeholders. This proactive approach facilitated enhanced collaboration, innovation, and value, while improving operational efficiency and reducing whole-life costs for the project.

[caption id="attachment_25931" align="alignnone" width="1200"] (left) Storm tank installation and (right) MCERT installation - Courtesy of NI Water[/caption]

Regular design review and HAZOP (Hazard and Operability) meetings were critical throughout the ECI and construction phases to develop sequencing, review progress, identify potential risks, and ensure that design decisions met safety, operational, and regulatory requirements. These workshops provided the Integrated Project Team with the opportunity to review the proposed completed works, support clash detection, and advise on design changes or pinch points.

The collaborative working relationship developed between DLJ Water, NI Water, Tetra Tech RPS, and the wider supply chain through the ECI process and subsequent construction phase, facilitated greater innovation and the successful delivery of a robust, sustainable, modern wastewater treatment solution. The facility is capable of meeting stringent consent standards, protecting the environment and addressing future catchment needs over a 25-year projection horizon, meeting NI Water’s targets.

Tamlaght WwTW - Supply chain - key participants Client: NI Water Principal contractor & designer: DLJ Water Ltd Deane Public Works Ltd Lowry Building & Civil Engineering Ltd Avove Ireland Project managers: Tetra Tech RPS MEICA/process designer & contractor: Avove Ireland Civil/geotech/structural/temporary works design & construct: Deane Public Works Ltd Piling: Larsen Piling Steelwork: LA Steel Fabrications Ltd Formwork & concrete: TK Concrete Precast concrete/concrete: Tracey Concrete Rotating biological contactors: KEE Process Ltd Electrical/ICA/MCC: Pronto Automation Systems Ltd Inlet screen: Hydro International Ltd (M and N Electrical and Mechanical Services) Pipework: APP Fusion Group Water booster set: Dutypoint Ltd Fencing: O’Neill Fencing [caption id="attachment_25918" align="alignnone" width="1200"] Inlet screens installation - Courtesy of DLJ Water Ltd[/caption] MEICA/process design

Avove Ireland designed a full turnkey MEICA and process replacement plant for Tamlaght Wastewater Treatment Works, utilising best technologies and techniques to minimise operational expenditure while accommodating a projected population equivalent (PE) of 527.

The limited site footprint for the replacement works, combined with the requirement to maintain treatment capabilities in line with current discharge consent standards during construction, presented a significant challenge. These space constraints were addressed by optimising the layout within the available footprint and incorporating compact treatment technologies, including rotating biological contactors (RBCs) and package process units.

Additionally, the inlet works were non-compliant with NI Water Asset Standards, lacked flow measurement and control, and routed all flows to the CASP via supplementary interstage pumping.

Inlet works

The MEICA and process design for the new Tamlaght works encompassed the supply, installation, and commissioning of a new inlet works channel, featuring a 6mm perforated screening unit, with operation controlled via differential level measurement. Screenings are discharged to wheelie bins through a dedicated chute. The screening unit is equipped with frost protection cycles and a potable water supplied screening wash system from the site booster set, ensuring reliable operation under all seasonal conditions.

[caption id="attachment_25929" align="alignnone" width="1200"] Completed inlet works - Courtesy of NI Water[/caption]

The inlet channel is equipped with an emergency 10mm manual rake bypass screen and level probe detection, with influent diverted back to the flow control chamber for treatment. The bypass channel also incorporates an emergency overtop facility and a screenings launder, ensuring continued operation and safeguarding the downstream process under exceptional conditions.

A flow control channel has been incorporated into the inlet works to accommodate flows exceeding Formula A, with measurement provided via a level transducer, before onward passage to the 6mm screening unit and discharge to the nearby watercourse.

Storm tank

The system also includes full flow to treatment (FFT) overflow control, with flow measurement via level transducer, directing any excess FFT to the storm tank to maintain process stability and protect downstream infrastructure.

The storm tank provides storm influent retention and additional 6mm overflow screening, with level transducer monitoring for Event Duration Monitoring (EDM) and protection. Additional safeguard is provided by backup float switch activation. A storm water return pumping station, complete with associated pipework and valves, utilises two VSD-controlled storm water pumps operating in duty/standby mode, with flow measurement installed on the return main to ensure controlled and reliable return of storm flows to the treatment process.

Rotating biological contactors (RBCs)

 Flows up to full flow to treatment (FFT) are treated via two package rotating biological contactors, each complete with drive systems, media banks, and protective covers. Integral to each RBC is a primary settlement tank located upstream of the biological contactors and a final settlement tank positioned downstream of the biological treatment zone. Each RBC is designed to process up to 50% of the maximum FFT, ensuring redundancy and operational flexibility.

[caption id="attachment_25930" align="alignnone" width="1200"] The new rotating biological contactors - Courtesy of NI Water[/caption]

Each RBC is equipped with a dedicated sludge management system, comprising sludge draw-off hydrostatic pressure pipes positioned at intervals along the RBC length and terminating in a common manifold fitted with Bauer couplings and caps for removal by sludge tanker. A designated road tanker loading point with Bauer connection and spill containment apron is provided to facilitate safe and efficient sludge handling.

EMS Pumping Station

The site incorporates an Environmental Management System (EMS) pumping station, comprising a single submersible pump operating on duty-only mode. The pumping main conveys captured influent from the designated EMS area back to the treatment process at the flow splitter chamber, ensuring controlled return and integration with the overall wastewater treatment system.

Outfall

Process flows from each RBC are directed to a common discharge chamber and onward to an MCERT-compliant measurement chamber, which incorporates a thin-plate weir for regulatory flow monitoring of the final effluent prior to discharge to the undesignated watercourse. The MCERT chamber is also equipped with a turbidity probe for solids monitoring, a temperature probe, and a level probe to support comprehensive effluent data analysis and regulatory compliance reporting.

All flows from the process treatment, excess Formula A (F’A’), and storm water retention are combined in a common discharge chamber and released to the nearby watercourse, ensuring controlled and compliant effluent conveyance.

[caption id="attachment_25922" align="alignnone" width="1200"] MCERT installation - Courtesy of NI Water[/caption]

Incoming water supply

The upgrade includes a new incoming mains water supply with metering equipment, bypass facility, and location marker. A double check valve with inspection chamber is provided upstream of the meter for backflow prevention. A site potable washwater booster package plant was installed to service all wash-down points, comprising a duty/standby booster set housed within a compartmentalised GRP kiosk. Hosing and flushing facilities are provided within operational range of all process units and pumping stations to ensure effective cleaning and maintenance access.

Control system & power supply

A new intelligent MCC, including generator connection and automatic changeover facilities, has been provided, supplied by a new NIE power connection in accordance with NIE design specifications and direction.

The site is equipped with comprehensive telemetry, control, and instrumentation systems, including PLC and HMI functionality to enable real-time monitoring, operational control, and data management across all process units and pumping stations.

Civil/structural design & construction

Joint Venture partner Deane Public Works led the civil, structural, and geotechnical design and construction process for the Tamlaght works.

The scope included initial enabling and investigatory works during the ECI stage, followed by the detailed design for construction.

The civil and structural design comprised the overall site layout, including process pipework, ducting, site drainage, and hydraulic design. It also encompassed new inlet works with screening plant, Formula A and FFT flow controls, a new RBC unit layout with flow split chamber, a storm pumping station, MCC trench, grit chamber, and final effluent and flow measurement chambers. Additional civil design requirements included the structural design of reinforced concrete structures, such as pile slabs.

[caption id="attachment_25931" align="alignnone" width="1200"] (left) Storm tank installation and (right) MCERT installation - Courtesy of NI Water[/caption]

The existing Tamlaght WwTW site was constrained by its small footprint, containing a compact activated sludge plant (CASP) and inlet works with an above-ground gravity sewer. Limited space and the single-structure CASP required the proposed assets to be constructed fully offline while maintaining CASP operation. Furthermore, the above-ground alignment of the incoming sewer prevented it from crossing the existing site access, resulting in the inlet works being located along the southern boundary of the site, which in turn dictated the positioning of all other proposed assets.

A key civil consideration was ensuring the design of the new structures focused on elevating them relative to the existing site to reduce flood risk while ensuring gravity inflows to the WwTW were maintained. Formation levels were carefully set to preserve the correct hydraulic profile throughout the site. The presence of an existing floodplain, with Q100 flood levels approximately 1m above the common ground, presented additional hydraulic and level constraints. The proposed design addressed these challenges by protecting the assets from flooding while maintaining a fully gravitational hydraulic system for process flows.

Site investigations identified the presence of extensive peat within the substrata. Following a detailed review of the ground conditions, it was determined that deeper site structures would be supported using a mini-pile and pile slab arrangement. Temporary works cofferdams with hydraulic bracing were designed and installed to allow the deep storm tank construction in the challenging soil conditions of extensive peat (SPT N-value =0) extending to 16.6m below the surface.

For the site road and hardstanding, a geogrid solution was implemented using a floating road design. This approach allowed finished ground levels to be raised to the Q100 flood level while minimising backfilling, thereby providing effective flood protection for both the site roads and the process assets.

Adequate flexibility was incorporated into all interconnecting pipework to minimise the impact of any differential settlement between pile-supported structures.

[caption id="attachment_25919" align="alignnone" width="1200"] Completed flume - Courtesy of DLJ Water Ltd[/caption] Public/stakeholder engagement

Collaboration was integral to the planning, design, and construction of the new Tamlaght WwTW. NI Water, the DLJ Water Team, and Tetra Tech RPS worked together to develop a proactive communications and public relations strategy, ensuring that residents and the wider public were kept fully informed about the installation and project progress.

Continued regular stakeholder engagement throughout the project helped to prevent delays, with early and effective liaison ensuring that no issues arose from stakeholder concerns.

Challenges/constraints

DLJ’s Integrated Project Team overcame significant constraints and challenges through a collaborative approach, delivering an operationally efficient facility, including:

The project faced challenges in securing suitable land for the new site. By leveraging local knowledge, DLJ successfully identified and acquired adjacent land, allowing the project to progress as planned. Phased demolition of existing structures, combined with the staged construction of the new treatment works, further restricted the already confined site. Maintaining the existing process in full operation throughout the works to ensure compliance with all discharge consent standards. A delicate and prolonged ‘seeding’ period was required for biomass growth in the bio-contactor zone of the RBC, a process that was highly dependent on weather conditions. A strategic ‘seeding’ process was implemented using both existing infrastructure and new assets, ensuring compliance while effectively synchronising biomass development. Periods of hyper-inflation in material and labour costs during the design phase. Supply chain delays during a period of significant uncertainty, driven by Brexit and volatile market conditions. [caption id="attachment_25936" align="alignnone" width="1200"] Demolition of the existing CASP - Courtesy of DLJ Water Ltd[/caption]

The treated final effluent discharges to a tributary of Upper Lough Erne, a water body of high ecological sensitivity and recreational value, designated as a Ramsar site, Special Area of Conservation (SAC), and Special Protection Area (SPA).

Maintaining consistently high effluent quality is critical for compliance with statutory water quality objectives, the protection of local watercourses, and the safeguarding of the wider Upper Lough Erne catchment, an ecosystem of international significance.

This challenge was addressed through the implementation of advanced treatment processes, robust compliance monitoring, and resilient supporting infrastructure. Process optimisation secured adherence to stringent discharge standards, while the integration of an environmental management pumping station provided additional operational control and contingency against water quality risks. Continuous monitoring, proactive maintenance, and best-practice operational management further enhanced system reliability, ensuring the long-term protection of both local watercourses and the wider catchment.

Although compact, space-saving RBCs were incorporated into the design, the additional treatment capacity necessitated a substantial footprint within the existing NI Water site, where space for spoil storage or construction materials was limited. To address this constraint, a ‘just-in-time’ delivery approach was implemented, minimising on-site storage requirements and optimising construction logistics.

The new infrastructure was designed and elevated to ensure that all structures and equipment are positioned above the Q100 flood level, providing protection of critical assets during potential flooding events at the Tamlaght site.

[caption id="attachment_25923" align="alignnone" width="1200"] Completed storm tank - Courtesy of NI Water[/caption] Completion

Despite the challenges encountered, the new Tamlaght WwTW was completed with full site-wide testing and commissioning successfully undertaken ahead of handover to NI Water in February 2025, on time and within budget.

The new works was rigorously tested and commissioned before handover and is now producing excellent results, comfortably meeting the NIEA final effluent quality standards of 40 mg/l BOD, 60 mg/l suspended solids respectively.

This innovative wastewater treatment solution, designed, constructed, and commissioned by DLJ Water, offers the capability, flexibility, and reliability to meet future catchment needs over a 25-year projection horizon. It will support sustainable development in the Tamlaght area while providing increased environmental protection through enhanced water quality for the adjacent Upper Lough Erne.

The upgrade of Tamlaght WwTW provided a valuable opportunity to modernise a small rural wastewater asset, safeguard environmental integrity, and ensure compliance with evolving regulatory standards. By leveraging lessons learned from comparable projects, ultimately this project sets a precedent for how rural treatment works can be revitalised to deliver long-term benefits for both the environment and the local community.

NI Water Senior Project Manager, Michael Donnelly, commented on the benefits of the project for the local community and environment:

“The £3.7m investment in the new Wastewater Treatment Works at Tamlaght has delivered the latest safe and efficient technology in wastewater treatment that will protect the local environment and surrounding countryside, providing headroom within the works that will cater for growth in the community.”

Bidford-on-Avon Sewage Treatment Works, located in southwest Warwickshire, is operated by Severn Trent. The site treats wastewater from a population equivalent of approximately 8,300 and ensures that the effluent is suitable for discharge into the River Avon. The AMP8 investment scheme is driven by both projected population growth within the catchment and the tightening of environmental permits. By 2038, Severn Trent Water projections indicate that the population equivalent figure will rise by roughly 20%, to around 10,140, and consequently, this has resulted in the introduction of several new effluent quality permits. New permits

The new permits aim to safeguard the future operational capacity of the treatment works and enhance the quality of effluent discharged into the River Avon, thereby protecting sensitive habitats and preventing pollution of nearby designated wildlife sites.

Permitted full flow to treatment (FFT) to the site will be increased from 60.2 l/s to 87.0 l/s by December 2026, along with a new ammonia permit of 15 mg/l. Additionally, Total Phosphorus will be limited to 0.22 mg/l, and Iron to 4 (8UT) mg/l in December 2027. Biological oxygen demand (BOD) and suspended solids (SS) permits will remain the same at 25 mg/l and 45 mg/l, respectively.

[caption id="attachment_25888" align="alignnone" width="1200"] Google Maps image of existing Bidford site - Courtesy of MMB[/caption] Existing works

The current treatment works employs a biological treatment process. Flow enters the site and passes through the inlet works before proceeding to two 235m3 Dortmund-style primary settlement tanks (PSTs).

Here, sludge is settled out and directed to a dedicated 113m3 sludge storage tank, where it undergoes further thickening before being transported off-site for additional treatment. Partially treated effluent from the PSTs is then distributed evenly between three 28m diameter biological filters. Finally, three 235m3 Dortmund-style humus settlement tanks facilitate further sludge removal before the treated effluent is discharged into the River Avon.

Early engagement: Evaluating the received outline design

In 2023, Mott MacDonald Bentley (MMB) was appointed by Severn Trent, under an Early Contractor Involvement (ECI) agreement, to review the outline design for upgrading biological treatment at Bidford-on-Avon STW. The proposed scope included replacing the inlet works, constructing new primary and humus settlement tanks, enhancing sludge processing and storage, installing two biofilters, and integrating tertiary solids removal capabilities.

Initial site investigations highlighted major constraints, including topographical, ecological and spatial challenges within the site boundary, as well as potential difficulties in achieving regulatory permit dates. The scale and cost of temporary works were substantial, and there were significant health and safety risks associated with some elements of the scope.

Following a detailed review, MMB concluded that the original scheme presented excessive buildability and programme challenges, which could potentially result in failure to meet the regulatory date for the new consent.

To maintain project momentum, the design team considered alternative options. To support this, MMB undertook enabling works, including vegetation clearance, trial holes, and topographical and utility surveys. These actions ensured early service identification, allowed for safer construction methodologies to be considered, and helped mitigate programme risk.

[caption id="attachment_25891" align="alignnone" width="1200"] Revit model showing the proposed design whilst using a CDM area in the northern field - Courtesy of MMB[/caption] Optioneering & strategic re-assessment

A renewed optioneering phase was initiated to explore alternative solutions aimed at improving constructability whilst ensuring compliance with environmental and safety standards.

One key proposal involved constructing an offline solution in the northern field, replicating the assets outlined in the original design and connecting into the existing inlet works. Although this option would have mitigated many risks associated with the original design, it introduced new ones, such as delay in securing land ownership and planning permission.

Due to its complexity and the resulting uncertainty in the programme, this approach was ultimately deemed unfeasible.

However, the northern field remained in consideration as a potential location for the temporary working area. With the existing site too constrained to safely accommodate construction welfare alongside construction activities, this alternative offered a more practical solution. Yet, after several months of planning and evaluation, the proposal was ruled unviable, due to the inability to agree temporary access to the land.

Faced with land ownership constraints in the northern field, MMB and Severn Trent considered the option of a temporary working area in the field to the east of the site. Even though this initially appeared to be a workable alternative, the complex access strategy required, using the existing access road and new routes across the eastern field, came with its own ecological and archaeological hurdles. Mitigation efforts were expected to increase costs substantially and jeopardise the first regulatory permit deadline in December 2026.

[caption id="attachment_25890" align="alignnone" width="1200"] Revit model showing MMB’s latest oxidation ditch solution - Courtesy of MMB[/caption] Enabling success: Proposed scope change

In order to address the above challenges, MMB proposed a strategic shift in scope to Severn Trent, replacing the originally proposed biological filtration (fixed film) approach with an activated sludge (suspended growth) system.

This recommendation stemmed from a robust desk study, highlighting gains in programme efficiency, affordability, and process performance. To meet the increased flow from population growth and tightening environmental permits, the revised design comprises of a new prefabricated inlet works, a racetrack-style double oxidation ditch, steel final settlement tanks, chemical dosing, and tertiary solids removal capabilities, supported by containerised sludge thickening plant and a sludge holding tank.

Following detailed collaboration and review with Severn Trent, the scope change was approved, with MMB instrumental in driving the transition. The solution exemplifies how Severn Trent, as part of AMP8, is championing small-to-medium sized oxidation ditches for their operational benefits and how MMB is at the forefront of their delivery, setting a new benchmark for process excellence.

The revised solution is now positioned to meet the regulatory date whilst also providing a safer construction environment. This is to be achieved by maximising the available working area within the existing site, by minimising the footprint of the proposed assets.

Crucially, it does so whilst eliminating the need to build over existing assets, significantly reducing risk during construction. This approach also enables the establishment of a compliant CDM setup on-site, delivering substantial health and safety benefits and supporting efficient project delivery.

[caption id="attachment_25884" align="alignnone" width="1200"] Revit model showing the inlet works, oxidation ditch and FSTs, looking north - Courtesy of MMB[/caption] Bidford-on-Avon: Supply chain - key participants Principal designer: Mott MacDonald Bentley Principal contractor: JN Bentley Specialist consultancy: Mott MacDonald Ecological consultancy: RammSanderson Ecology Archaeological fieldwork: West Yorkshire Archaeological Services Inlet works designers & contractors: SPIRAC Ltd Oxidation ditch precast concrete panel designers & suppliers: FLI Precast Solutions Tertiary treatment cloth filters: Eliquo Hydrok Ltd Landscaping: Holts Tree Care Inlet works area: Design for manufacture & assembly

The site layout has been strategically engineered to optimise gravity flow, delivering long-term savings in operational expenditure. By eliminating the need for large pumping stations, the design significantly reduces energy demand and enhances sustainability, starting with flow management at the new inlet works.

This inlet works, to be supplied as a complete prefabricated package by SPIRAC Ltd, represents another proposed installation of the SPIRAC package in the Severn Trent framework. Designed as a raised inlet works, it incorporates screening and grit removal at the initial treatment stage. Utilising a solution manufactured off-site will streamline the construction and commissioning process, leading to significant programme savings.

[caption id="attachment_25883" align="alignnone" width="1200"] Revit model showing prefabricated inlet works from SPIRAC LTD - Courtesy of MMB[/caption]

The solution also includes a suite of other critical assets in the vicinity of the inlet works. Using pre-assembled, containerised assets where appropriate enables rapid installation and health and safety benefits during construction.

The proposed containerised sludge thickening plant exemplifies a streamlined installation process that reduces labour requirements and minimises disruption to other construction activities.

Efficient design & the oxidation ditch

The oxidation ditch, measuring 32m in length, 28m in width, and with a capacity of 3,800m3 has been designed in a double-ditch ‘racetrack’ configuration. This layout enables efficient air distribution through an aeration grid, which is integral to the activated sludge treatment process. Following the scope change, MMB acted swiftly to engage subcontractors early, accelerating programme delivery through smart, efficient structural design.

FLI Precast Solutions, with support from MMB, has designed the precast wall units by using finite element analysis. This has enabled optimised structural design that allows the bending moments and shear forces to be calculated accurately. This approach has also allowed for the reduction of embodied carbon by reducing the amount of concrete used within the structure.

The position of the oxidation ditch has also capitalised on the natural topography that was once considered a constraint. Now, it acts as a strategic advantage to enhance flow dynamics by gravitating through the process and enhances construction efficiency by reducing the amount of excavation required.

[caption id="attachment_25887" align="alignnone" width="1200"] Revit model showing the inlet works, oxidation ditch and FSTs, looking south - Courtesy of MMB[/caption] Secondary & tertiary treatment

The two 15m diameter final settlement tanks form a key stage in the treatment process, preparing flows for final polishing via tertiary solids removal. Having challenged conventional design standards, it is proposed to fabricate the final settlement tanks from stainless steel. This significantly reduces both the duration of construction and the carbon footprint.

A tertiary solids removal (TSR) stage will be delivered through Eliquo Hydrok TSR units; advanced cloth filters designed to remove suspended solids and ensure effluent quality. Once treated, the final effluent will be discharged into the River Avon.

As the site currently lacks chemical dosing infrastructure, a dedicated dosing area will be constructed as part of the upgrade. This will introduce controlled ferric dosing to promote particle coagulation, enhancing effectiveness of settlement and supporting overall process performance.

[caption id="attachment_25889" align="alignnone" width="1200"] Revit model showing the tertiary solids removal and associated assets - Courtesy of MMB[/caption] Sustainable drainage & biodiversity enhancement

The site will benefit from a complete drainage upgrade, aligning with modern drainage standards. Potentially contaminated rainfall will be directed back to the inlet works, while clean runoff will flow into a sustainable drainage pond. Suspended solids will be captured through a cascade system at the outfall, before flows enter the pond.

The pond improves environmental resilience and presents an opportunity for Biodiversity Net Gain to be embedded into the design. It could potentially offer a new wetland habitat and provide an area for the planting of native trees and wildflowers. These areas will enhance the ecological value of the area, support local wildlife and promote long-term environmental sustainability.

Conclusions: delivering value

The design for the Bidford-on-Avon scheme demonstrates engineering excellence through robust optioneering processes. These have resulted in bold scope change that aligns the solution with Severn Trent’s operational, financial, programme and environmental objectives, without sacrificing engineering quality.

[caption id="attachment_25885" align="alignnone" width="1200"] (left) Revit model showing the sustainable drainage pond, looking south and (right) looking north - Courtesy of MMB - Courtesy of MMB[/caption]

The adoption of an activated sludge process, gravity-led flow and design for manufacture and assembly has transformed the scheme from a project at risk of missing regulatory deadlines into one on track to meet all key milestones. This turnaround has been driven by procurement-led design, early supplier engagement and a strong focus on construction efficiency. Financially, the revised design is set to deliver £multi-million savings without compromising quality or compliance.

Additionally, environmental stewardship has remained central to the design philosophy, with carbon reduction embedded across design elements and a strong emphasis being placed on Biodiversity Net Gain and sustainable drainage.

The design ensures that Bidford-on-Avon treatment works can accommodate future population growth and deliver high-quality final effluent to the River Avon.

Located in North Lincolnshire, between Scunthorpe and Doncaster, Haxey-Graizelound STW is an existing medium-sized biofilter works serving the town of Haxey and Westwoodside Village. It has a permitted flow to full treatment (FFT) of 27.7 l/s and serves a population equivalent of 5,169 (rising to 5,464 in 2033). To achieve the new Total Phosphorus (TP) and ammonia consents that came into force in December 2024, a new activated sludge plant with enhanced biological phosphorus removal was constructed on the existing site, which had to remain fully operational during construction and commissioning. Existing works

The existing works comprised an inlet works (single screen and grit vortex), a primary settlement tank, four biofilters, one final settlement tank, final effluent monitoring, a storm tank and returns, and two sludge holding tanks.

The driver for the new works is a tightening in the Total Phosphorus (TP) and ammonia consent that came into force December 2024.

Existing consent New consent BOD 25 BOD 25 SS 45 SS 45 NH3 15 NH3 3 TP - TP 0.2 FE - FE 4 AL - AL 8 FFT 27.7 l/s FFT 27.7 l/s The new treatment works

The existing works is a fully pumped works with two catchment pumping stations (from Akeferry and Westwoodside) pumping to the inlet. The process of the new works starts off with primary treatment, where two screens from Huber Technology and a grit vortex from SPIRAC Ltd capture and remove inorganic materials (e.g. wet wipes and rocks) to be taken to landfill. After preliminary treatment, the flow enters a balancing tank to maintain flow to full treatment (FFT) during higher flows, preventing premature storm spills.

The secondary treatment consists of a pocket UCT ASP (University of Cape Town activated sludge process), 37.5m (length) x 11m (width) x 6m (height), two 8.95m internal diameter final settlement tanks (286.6m3 total volume) and a RAS return pump station, with integrated SAS thickening facility that leads to the sludge storage tank.

[caption id="attachment_25424" align="alignnone" width="1200"] Construction progress (March 2024) - Courtesy of MMB[/caption]

The ASP consists of two anaerobic pockets (total volume 115m3) to allow the site to utilise biological phosphorus removal, where the phosphorus removing organisms have a competitive advantage, due to there being no free oxygen for other organisms to use.

These pockets then flow into two anoxic zones (total volume 115m3) in which free oxygen is available for denitrification purposes. The flow then enters three aerated pockets (total volume 1,513m3) with tapered airflow, reducing in the percentage of supplied oxygen in each subsequent pocket - this is to reduce the amount of dissolved oxygen and nitrates recycled back to the anoxic zone in the form of RAS.

As this is a UCT configurated ASP, there is also a fixed speed denitrified mixed liquor pump, recycling anoxic effluent back to the anaerobic feed, this is to maintain anaerobic conditions within the anaerobic pockets.

Ferric sulphate is dosed into the final settlement tank distribution chamber (to act as a top-up dose in case EBPR is not consistently meeting the 1 mg/l target of total phosphorus off the ASP). The flow then splits equally to the two final settlement tanks which have half-bridge scrapers. The sludge is drawn off by the return activated sludge (RAS) return pump station that feeds into the start of the ASP to maintain the cyclical process.

[caption id="attachment_25431" align="alignnone" width="1200"] New ASP taken from top of new inlet works - Courtesy of MMB[/caption]

A secondary dose of ferric is supplied to the Mecana pile cloth filter (pre-TSR dose) from Eliquo Hydrok Ltd. This allows precipitation of soluble phosphorus, to further polish both the suspended solids and total phosphorus to meet the low 0.2 mg/l consent. The flow is sampled and monitored at the final effluent kiosk, before discharging to the outfall.

The surplus activated sludge (SAS) is directed towards sludge handling facilities which include a Huber S-DISC sludge thickener and polymer dosing equipment. The thickened sludge will then be held in a new sludge holding tank to be taken from site for use at other Severn Trent treatment works.

New scope of works

The full scope of the works is detailed below:

New raised inlet works comprising two screens and wash compactor with grit vortex and screw classifier. New UCT activated sludge plant with EBPR, consisting of two anaerobic zones, two anoxic zones and three tapered aeration pockets. Two new final settlement tanks. New RAS SAS pump station. New tertiary solids removal plant (Mecana pile cloth filters from Eliquo Hydrok Ltd). New chemical dosing unit. New sludge holding tank. New SAS thickening equipment. New main MCC and SAS thickener MCC. New laboratory. New pump stations and drainage. New road layout. [caption id="attachment_25429" align="alignnone" width="1200"] New TSR and FE - Courtesy of MMB[/caption] Haxey Graizelound STW: Supply chain - key participants Client: Severn Trent Principal designer & contractor: Mott MacDonald Bentley Electrical subcontractor: Main Electrical Ltd Mechanical subcontractor: STAL (UK) Ltd Inlet screens & compactor: Huber Technology Grit removal plant: SPIRAC Ltd Stainless steel tanks: Fluid Sealing & Engineering (FSE) Aeration diffusers for ASP: Suprafilt Ltd FST scraper bridges: Jacopa Ltd Weholite prefabricated chambers: SDS Limited FRC: Overhall Contractors Ltd Mecana tertiary solids removal: Eliquo Hydrok Ltd Glass-coated steel tanks: Goodwin Tanks Ltd MCCs: CEMA Ltd Kiosks: Morgan Marine Huber S-DISC sludge thickener: Huber Technology Ferric dosing: Colloide Mixers & submersible pumps: Xylem Water Solutions RAS pumps: Sulzer Pumps Wastewater Ltd SAS pumps: NOV Process & Flow Technologies UK Ltd Plug and Play VT2 & VT3 Booster Sets: Dutypoint Ltd DI pipe: Saint Gobain PAM UK Valves: AVK UK Ltd Penstocks: Waterfront Fluid Controls Lifting equipment: T Allen Engineering Services Ltd Access steelwork: Mectec Engineering [caption id="attachment_25425" align="alignnone" width="1200"] New sludge holding tank - Courtesy of MMB[/caption] Innovations, cost savings & carbon reduction

Following a cost benefit analysis carried out between Severn Trent and MMB in 2022, the preferred solution was to construct a crude activated sludge plant (ASP) with enhanced biological phosphorus removal (EBPR).

There were several challenges that the MMB design team and site team were able to overcome by working closely together.

Sub-artesian water pressure

During ground investigation it was identified that the site had high groundwater level with sub-artesian water pressure. Since the process is gravitated after the inlet works, the depths of the structures in the outline design would have been significantly impacted by sub-artesian water, requiring significant temporary works including groundwater abstraction. The design team was able to overcome this issue by interrogating the hydraulic calculations and highlighting the opportunity with Severn Trent to raise the inlet works and the ASP structure up, with the bases of the two FSTs rising to ground level.

Because of this, the team were able to avoid the sub-artesian water pressure and reduce the groundwater impact during excavation and construction, significantly reducing construction health and safety risks, and realising environmental and commercial benefits.

[caption id="attachment_25426" align="alignnone" width="1200"] New chemical dosing area - Courtesy of MMB[/caption]

Simplifying the TSR design

The original TSR design had a large bunded area that required a deep excavation and the use of more materials. Early on, the design team was able to discuss options with the supplier and other sites that had installed the same technology.

The option to part-bury the tanks enabled the removal of the large, below-ground bunded design, simplifying it to a single rectangular slab that the tanks would sit on and be backfilled around. This did not affect the hydraulics or the process and reduced the total excavation required and concrete usage which in turn, reduced the embodied carbon of the solution.

Inlet works location

A review of the construction programme and site layout highlighted an opportunity to construct the inlet works earlier whilst keeping access to the ASP and MCC area. The outline design had the new inlet works to the north of the existing inlet works. This would have prevented the MCC from being constructed as the crane would be located on top of it to service the original position.

However, during a design sprint with Severn Trent, the new inlet works was moved to the south of the existing inlet works. Whilst this meant it was located over an area with several services - since the level had been raised - the slab now sat above all the services in the area and would not clash. The site team was able to locate and prove the existing services, then excavate and construct the new slab and pipework.

[caption id="attachment_25430" align="alignnone" width="1200"] New inlet works screens and grit removal plant - Courtesy of MMB[/caption]

Site-drainage pumping station

A review by the MMB design team of the requirements for the new site-drainage pumping station found that the existing pumping station had sufficient space, volume and was in suitable condition to take the new flows and pumps that were required for the new works. This saved programme, time, cost and risk in having to construct a new site returns pumping station in an area heavily congested with live services including the main incomer to site, as well as remove any interface with the sub-artesian water.

Design efficiencies

There were several design efficiencies that were realised during the detail design phase including:

Changing the bypass channel sections on the raised inlet works into a piped bypass, which improved constructability and programme. Changing the ASP blister and FST distribution tanks from large concrete structures into prefabricated stainless-steel tanks resulted in carbon savings, programme savings and ease of constructability. Three prefabricated Weholite above-ground chambers from SDS Limited helped save on programme and concrete usage.

BIM360

Several benefits were gained during the project with the close communication between the site and design teams through regular site visits, weekly meetings and the use of Issues on BIM360, which helped to streamline the production of drawings.

Reviews by the relevant design disciplines and the site team could be tracked, and buildability checks could be raised in a timely manner. This also helped to improve design decisions having the early site involvement and helped to reduce redesign. The great construction and design collaboration helped to identify opportunities to enable services to either have a reduced dig depth or be constructed out of the ground, further reducing the ground water interface. One example being the FST outlet pipework being kept above ground to the collection chamber, which removed all excavation requirements.

[caption id="attachment_25427" align="alignnone" width="1200"] New S-DISC SAS thickening equipment - Courtesy of MMB[/caption]

ASP maturation

Significant programme gain came from challenging the ASP maturation period. The initial programme had 28-weeks for maturation, however, regular meetings between process engineers from both MMB and Severn Trent were held. This led to the development of a joint commissioning plan whereby hold points and process reviews could be used to trigger the next stage of the commissioning works.

Instead of waiting for the Severn Trent standard commissioning duration, if the target was achieved sooner, a joint review would be carried out and the next stage could start. This led to the maturation period of the ASP to be reduced to 12-weeks.

Water voles

Water voles impacted works on the installation of a new culvert for crossing the drainage ditch to which the site discharged.

MMB ecologists were able to carry out a survey of the occupational drainage ditch and highlight the areas where water vole habitats were located. A review carried out by both the design team and site team, found that by moving the culvert approximately 20m further north, it would still provide a suitable crossing point to site, whilst having no impact on the water voles or habitats.

Concrete sensors

An innovation that was used at Haxey STW during the construction of the ASP were converge concrete sensors. When constructing the concrete activated sludge plant, the team identified an opportunity to trial sensors to measure the concrete strength. The structure consisted of 6m tall in situ concrete walls; the perfect set up to trial the sensors.

[caption id="attachment_25474" align="alignnone" width="1200"] (left) Concrete sensor being cast into the wall and (right) analysis of data collected - Courtesy of MMB[/caption]

Initially the team were using a PERI shutter system and part of the temporary works states that the shutters cannot be struck until the concrete has reached 5N/mm2 compressive cube strength. With the ASP on the critical path of the programme, it was imperative that the walls were poured as efficiently as possible, striking the shutters as soon as possible, then moving onto the next pour.

The concrete sensors were cast into the walls and proved extremely effective as they were able to read the temperature of the concrete, convert it to compressive strength and notify the team when the shutters could be stripped. This resulted in an efficient process between each pour, streamlining the pour schedule and reducing the reliance on concrete cubes.

Using the sensors, the team were able to save one day per section of wall poured, removing 11 days from the programme. Both time and costs were reduced due to not having to prepare 45 cubes for early strength testing, saving over £700 in engineer time and cube crushing.

The key benefits of the sensors are:

Gain on programme. Quick turnaround. Lower carbon footprint. Instant strength monitoring. Quality assurance. [caption id="attachment_25434" align="alignnone" width="1200"] Completed works (January 2025) - Courtesy of MMB[/caption] Conclusion/summary

The main construction phase was completed by December 2024 with the commissioning phase subsequently starting after.

The project has been successful by the close communication between the client, site team, design team and operations. By having regular meetings throughout the week enabled both sides to raise and questions/concerns, ideas to be discussed and decisions made in a timely manner.

With flows switched to the new works, the existing works is to be decommissioned and abandoned.

Queensferry Wastewater Treatment Works (WwTW) is situated on the banks of the River Dee in North Wales serving a population equivalent (PE) of 55,100 (split 60% domestic/40% trade), with catchment growth expected to increase to 62,830 PE by 2040. Currently, all flows arriving at the works discharge through a series of bellmouths into a single covered reception chamber. There are 12 bellmouths discharging a mixture of gravity and pumped rising main sewage. In addition to domestic sewage, the works received high trade concentration and tanker imports. The combination of gravity and pumped flow has been detrimental to the inlet works structure and plant including; 6mm escalator screens, macerator, grit traps and associated grit classifiers with corrosion present from hydrogen sulphide (H2S) attack. The harsh environment, along with the projected growth has led to the inlet works being identified as at end of its working life. Background

The reinforced concrete reception tank and inlet channels were constructed in the late 1970s and were originally covered with open mesh galvanised steel flooring. To resolve odour concerns, the covers were replaced with solid covers in the late 1990s, in addition to the installation of odour extraction equipment and a ferric chemical dosing system.

[caption id="attachment_18217" align="alignnone" width="1200"] Hydrogen sulphide attacks: (left) to the existing isolation penstocks, and (right) to the existing inlet channel walls - Courtesy of Morgan Sindall Infrastructure[/caption]

The covering of the inlet channels, together with poor odour control arrangements, sped up the chemical corrosion to the internal surfaces of the channel caused by hydrogen sulphide (H2S), with particular effect on the concrete wall surfaces located above the water level. H2S has also corroded the plant and equipment located below the covers. To summarise:

The internal walls of the channel showed signs of degradation and loss of aggregate materials allowing exposure of the original reinforcement steel mesh and beyond in a number of places. Channel covers, particularly their supporting frame fixings into the concrete channel have become loose - the worst affected located nearest the inlet rising main bellmouths. Corrosion of all channel isolation penstocks making them inoperable. Surface corrosion of the original handrailing system which surrounds the edges of the inlet channel. All associated grit trap plant and equipment are disused. Solution

The project has been released by Welsh Water to Morgan Sindall to provide a resilient and safe inlet works able to treat both gravity and pumped flows from the existing incoming pipelines as well as making provision for three additional incoming rising mains from known future developments.

[caption id="attachment_18211" align="alignnone" width="1200"] 3D model of the existing and new structures – Courtesy of Arcadis[/caption]

The scope of the project is to provide a new inlet works comprising:

Diversion of the 12 incoming pipelines to connect into a new reception chamber. Provide a replacement inlet reception tank with associated odour control unit and tanker import connection. Provide duty/standby 6mm - 2D screening arrangement complete with duty/standby screen handling units suitable for both current and predicted incoming flows to 2040 growth. Refurbishment of the original grit settlement traps and associated grit removal plant and equipment. New MCC and kiosk to service the new inlet works plant and equipment. Decommissioning of the existing inlet plant. Solution overview

The system was required to be safe, energy efficient, and conform to legislative requirements, Welsh Water internal specifications, and current best practice.

Due to the condition of the existing reinforced concrete reception tank and inlet screen channels, the Arcadis design team identified the need to build the new reception tank of a resilient material. Stainless steel was selected as a proven, resilient material to deal with H2S attack.

Queensferry Inlet Works: Supply chain - key participants Principal designer & contractor: Morgan Sindall Infrastructure Designer: Arcadis Civil groundworks: William Hughes Civil Engineering Ltd Piling: Universal Piling Grit trap & channel de-silting/cleaning: Celvac Ltd Overpumping: Pump Supplies Ltd Overpumping: Selwood Mechanical installation: Whitland Engineering Ltd MCC, ICA controls & electrical installation: Lloyd Morris Electrical Ltd Systems integration: Merlin Systems Ltd Inlet screening: Huber Technology Odour control: Air-Water Treatments Ltd Grit plant: Tuke & Bell Pumps: Xylem Water Solutions Flow controls: AFFCO Flow Control (UK) Ltd Drawpit manufacturer: Cubis Systems Combined booster set kiosk & tank: Dutypoint Ltd Bollfilter manufacturer: Bollfilter UK Ltd Pipework manufacturer: Wavin Osma Drainage solution: ACO Water Management GGBS (admixture) supplier: Civil & Marine Ltd Cement supplier: Castle Cement Ltd Concrete supplier: Hanson UK [caption id="attachment_18212" align="alignnone" width="1200"] 3-D model showing all pipelines rising from ground and entering reception tank – Courtesy of Arcadis[/caption] Hydraulic & connectivity assessment

An initial hydraulic assessment was carried out to determine the impact of the top water level (TWL) for the proposed inlet arrangement over the existing inlet bellmouths for the future maximum design flow. It was found that under normal operation, the TWL in the new reception chamber would be approximately 500mm above the existing bellmouth levels, leading to reverse flow and hydraulic restrictions.

With the increase in levels, a connectivity study was undertaken to determine impact on the incoming gravity and pumped inflows. This highlighted a number of connections to be higher risk with the works being undertaken, in particular the site returns and gravity/siphon sewer from the adjacent catchment. Investigation was undertaken to determine the impact of high level of water in the reception tank on the incoming gravity/siphon sewer.

The modelling results indicated that the last-in-line catchment CSO consents were still met.

Replacement of reception chamber

The placement of the replacement reception tank proved challenging. Two options were considered, both of which came with their different hazards and risks.

Take the existing chamber offline and replace in situ: This would require the diversion of all the incoming below-ground incoming mains and sewers into a temporary reception tank, through temporary screens before connecting back into the inlet channel. Construct a new tank offline, adjacent the existing structure (to the left, or right): This option would require either extending the incoming pipelines through the existing reception channel, or building over the existing incoming pipelines, dependent on which side of the existing reception tank the new structure was constructed.

Early in the design stage it was decided that rather than constructing a temporary reception tank, making the tank permanent would provide longevity and reduce whole life cost. The tank was to be located on the side where the existing sewers and rising mains enter the treatment works. This allowed the new screens to be constructed off-line and then connect back into the existing inlet channel upstream of the grit trap.

[caption id="attachment_18215" align="alignnone" width="1200"] Installed reception chamber and rising mains - Courtesy of Morgan Sindall Infrastructure[/caption] Incoming pipeline constraints

The reception tank was to be located over the existing incoming rising mains and gravity sewer siphons. These pipelines have been in the ground since the construction of the existing reception chamber construction and the conditions were unknown. To minimise additional stress whilst the tank was being constructed, Arcadis designed a bridging slab to span across the pipelines.

Morgan Sindall undertook numerous surveys - initially ground penetrating radar (GPR) - before carrying out a vacuum excavation (VacEx) to accurately pinpoint the location of each pipeline.

Once each pipeline was located, its exact location was mapped, to allow a 3D model to be generated detailing the connections of each pipeline into the pre-fabricated steel reception tank.

Reception tank & screen channels

The surveys and 3D model allowed the mechanical installation contractor, Whitland Engineering Ltd, to design and construct a DfMA reception tank (11m long x 3m wide and 2.5m high), which incorporated all of the incoming pipelines, including internal rising bellmouths and three blanked-off connections for future use as part of the River Dee rising main diversion scheme being undertaken by Welsh Water.

Stainless steel was selected to provide additional resistance to H2S and increase longevity. This material also reduced the additional overburden the existing rising mains would be subjected to during construction.

Due to existing ground conditions, it was confirmed that to minimise further the additional burden on the existing rising mains, the bridging slab required to be piled. A 15m long bridging slab was then constructed in situ to span the existing incoming pipelines.

The DfMA continued with the off-line installation of the new inlet screens and screen chamber. The reception tank and inlet screen chamber (10m long x 2m wide x 2.5m high) were linked by a 1,200mm stainless steel pipe. Two 6mm-2D escalator screens from Huber Technologies were installed within the new tanks. The screens will operate duty/standby, sized for the future maximum flow of 784 l/s. Screenings drop into a common launder trough before discharging into two duty/standby screening handling units.

[caption id="attachment_18222" align="alignnone" width="1200"] (left) DfMA installation of new inlet screens and chambers, (top right) the screenings skip canopy, and, (bottom right) internal photograph of bellmouth discharge points in reception tank - Courtesy of Morgan Sindall Infrastructure[/caption] MCC

The Morgan Sindall/Arcadis team which delivered the Leominster WwTW phosphorus removal scheme was instrumental in working with Welsh Water to create a standard product in the form of a new low voltage distribution board kiosk and a new tertiary filter MCC kiosk.

The DfMA GRP kiosks are mounted on a raised steel frame floor to support the MCC and the access covers while giving ample space beneath the structure for cable connections and testing.

This kiosk design reduced H&S risks associated with installation and commissioning and led to considerable reduction in installation time on site, as the kiosks were delivered to site, off loaded, and fixed down, all within a few hours. The standard product was utilised for the Queensferry project, with a 7.5m long x 3m wide x 3m high installation adjacent the new inlet works.

Odour control unit

Due to the high level of hydrogen sulphide arriving at the reception tank and the risk of aerosols from the bellmouth discharge, the reception tank and screenings chamber have been designed to be covered.

To mitigate odorous gas build-up, a new odour control unit has been installed replacing the end-of-life existing unit. An Air-Water Treatments Ltd Peacemaker™ P2000 duty/standby unit has was selected.

Grit detritors

The final scope element for the project is the refurbishment of the existing two grit detritors, grit rakes and organic return pumps. To allow the grit detritors to be taken off-line, the new reception tank and inlet screens required to be operating in full and bypassing the grit trap (see commissioning sequencing below).

To enable this to happen, an additional chamber was constructed downstream of the inlet screens, which allowed all flows to run through a number of temporary above ground pipes, before discharging into the existing continuation channel downstream of the grit trap.

Once isolated, the inlet channel and grit detritors were cleaned out. Approximately 53,300kg of grit was removed. The existing grit plant; detritors, grit rakes, organic return pumps and inlet baffles were removed, as well as the existing GRP covers, which provided odour suppression. Tuke & Bell then installed replacement grit detritors, rakes, pumps and inlet baffles.

To allow future isolation for maintenance, four new isolation penstocks were installed at the inlet and outlet of each detritor.

The permanent connection from the new inlet screens into the existing inlet channel was carried out through hydro-demolition of the existing wall at the same time as the works to the grit trap.

[caption id="attachment_18216" align="alignnone" width="1200"] Overpumping manifold to isolate existing inlet works and grit plant - Courtesy of Morgan Sindall Infrastructure[/caption] Commissioning sequencing

Once dry commissioning was complete, the inlet screens required flow to carry out wet commissioning. To minimise the impact of untoward/non-operational screening, the flows from each main were switched sequentially with support from Welsh Water Operations controlling the flows from the network pump stations.

This allowed partial flow from the old reception chamber to the new to prove the operation of the new screens before all the rising mains were transferred.

Once the screens were proven operational, the remaining rising mains and gravity siphons were switched between the old and new reception tanks, allowing the grit trap to be isolated.

Conclusion/summary

Works began on site on 22 September 2022, with the major civils components completed in September 2023 and the M&E completion of the inlet works at the end of March 2024. All incoming flows were fully transferred from the old reception tank to the new reception tank by the end of May 2024, allowing the grit chamber to be isolated.

At the time of writing (July 2024) activities on site include the installation of the grit/silt washpactor and skip canopy. The project is forecast to be completed on site by the end of August 2024, with handover to Welsh Water by October 2024.

Guildford, the county town of Surrey, sits a commutable 30 miles south west of London and 70 miles from the south coast. Boasting a castle, a cathedral, a picturesque town centre and a university, it is surrounded by Green Belt countryside. The River Wey flows through the town centre and then northwards through water meadows where it provides the outfall for the STW. The Wey eventually discharges into the Thames. The current STW serves a population equivalent (PE) of around 107,000, but the town has a growing population which is expected to grow to circa 125,000 PE by 2041. Background

The town and immediate area are currently served by a sewage treatment works established at the turn of the last century and upgraded over the years. It is located beside the River Wey, to the north of the A3 trunk road and north of Guildford town centre. It lies just south of Slyfield Industrial Estate. The current STW has a capacity to cater for a population equivalent of around 120,000.

Guildford Borough Council’s Local Plan adopted in 2019 allocates a site to the west of the River Wey wrapping around the eastern side of Slyfield Industrial Estate for mixed use development. Part of the 40 Ha allocated site is currently occupied by the existing sewage treatment works.

Weyside Urban Village is a mixed-use regeneration project which will provide some 1,500 new homes, new community facilities, Gypsy and traveller pitches and 6,500m2 of additional light industrial and trade space. 11Ha of the site are allocated for waste management purposes. The plans include a new council depot, a public recycling centre and a new, relocated sewage treatment works.

In order to bring the development site forward, within the plan period to 2034, Guildford Borough Council (GBC) have entered into partnership with Thames Water Utilities Ltd (TWUL) to build the new STW as the first phase of the redevelopment. The new location is slightly further north on the eastern edge of the Industrial site and is a brownfield site, formerly a gravel quarry and subsequently a landfill tip.

[caption id="attachment_26867" align="alignnone" width="1200"] Figure 2: Site overview: BIM model of new Guildford STW - Courtesy of BAM Enpure JV[/caption]

The new sewage treatment works allows for an increase in capacity to serve a population of 125,000 allowing for predicted population growth in the town and surrounding area as well as more stringent effluent discharge standards.

The new site also includes areas within the new works for future expansion and increased treatment capacity as need arises.

Previously in Water Projects

The scheme to build a new sewage treatment works (STW) in Guildford is now mid-way through construction. This article provides an update to the project following on from previous articles published in Water Projects. In 2023, Enpure Ltd’s Project Delivery Director Shaun Christopher described in detail the process and assets being provided in the new works and in 2024, Dan Russell, BAM’s Operational Lead, gave an update on the progress of the project one year into the construction.

This article also covers some of the planning considerations and requirements for the scheme.

Contract

In 2021 TWUL awarded a contract to a BAM-Enpure Joint Venture to design, build and commission a new STW for Guildford, and once operational, to de-commission the existing works. BAM-Enpure Joint Venture (JV) is a non-integrated Joint Venture, formed specifically to combine experienced civil engineering contractor BAM with the process engineering MEICA specialism of Enpure, to deliver a turnkey solution for TWUL.

Construction began in the spring/summer of 2023 with BAM undertaking design and construction of the civils works and Enpure providing process and MEICA design and installation. BAM have employed Arcadis as their main civils designer and the JV has let a number of specialist sub-contractor design packages alongside.

[caption id="attachment_26869" align="alignnone" width="1200"] Figure 3: 3D design using a model hosted by Arcadis, image from Autodesk’s Navisworks viewer - BAM Enpure JV & Arcadis[/caption] The project

The project consists of the following:

A transfer tunnel. An inlet pumping station. Inlet works screening. Primary settlement. Activated sludge treatment. Final settlement. Tertiary treatment of final effluent. Chemical dosing facilities. Storm storage tanks. Import cess and sludge facilities. A new control centre. New welfare building. Outfall into the River Wey.

A detailed description of the process and assets being installed is set out in the previous Water Projects article published in 2023.

Timeline Phase 1: Ground improvement: Started summer 2023 and completed February 2025 Phase 2: Civil engineering: Started summer 2023 with completion due in late 2025. Phase 3: Mechanical & electrical engineering: Started autumn 2024 and is due to complete summer 2026. Phase 4: Commissioning: Starts winter 2025 and is due to complete in spring 2027. [caption id="attachment_26883" align="alignnone" width="1200"] Figure 4: 3D model of the sludge processing area - Courtesy of BAM Enpure JV & Arcadis[/caption] Developing the site

The new site comes with additional challenges in that it is brownfield site formerly used for gravel extraction and then landfilled through the 1960s, 70s and 80s, with mainly domestic and some commercial waste. The site is classified as a waste development such that the local planning authority is Surrey County Council (SCC).

The planning permission granted was subject to a number of conditions and commitments, not only relating to the siting and development of the STW itself such as visual impact, odour, noise and traffic generation, but also to the remediation and reuse of the landfill site. Plans and construction methods needed to ensure that there was no temporary or permanent environmental damage to the surrounding area as a result of the impact on or disturbance of the buried waste material and that operatives working on the new STW were protected from any ill effects of the landfill during operation of the site. The landfill also poses particular constraints and hazards during the construction phase.

The strategy for the site was to leave as much of the landfill waste in situ and build above and through the waste. A detailed remediation strategy formed part of the planning requirements. The plan set out how the construction and operation phases of the project would manage issues of ground water and ground gas, potential ground water contamination and leachates, contaminated solid material including asbestos, and short- and longer-term settlement of the landfill.

Dan Russell’s case study in Water Projects 2023 provided a detailed description of the use of a combination of ground improvement and foundation techniques, which consisted of:

Rapid Impact Compaction (RIC) to improve ground strength and reduce long-term settlement of the landfill. Vertical Rigid Inclusions (VRI), a displacement concrete pile technique which provided support for roads, lighter structures pipes and ducts. Driven concrete piles bedded in the London Clay below the land fill to support large structures, tanks and pipelines.

Figures 5 (below) show the historic gravel extraction map and depth of landfill determined by ground investigation - both images were extracted from the project’s Detailed Remediation Strategy.

[caption id="attachment_26880" align="alignnone" width="1200"] Figures 5: (left) Spatial variation in landfill thickness 2023 and (right) historic site layout (1976) with present day boreholes overlaid - Courtesy of Arcadis[/caption]

However, the impact of the waste material goes beyond its bearing capacity. The site was already being subject to long term monitoring for ground gas and groundwater quality by Thames Water to provide a baseline for the project. Additional boreholes were sunk and a Groundwater & Ground Gas Monitoring Plan was approved by the local authority. Daily and continuous automatic remote monitoring was undertaken during the ground improvement and excavation phases with trigger levels set and exceedances reported back to SCC and a requirement for quarterly summary reporting. Monitoring will continue during commissioning of the site at less frequent intervals.

Asbestos: Asbestos had been discovered in a third of samples taken during the ground investigation and so a monitoring regime was established. Air sampling around the perimeter of the site ensured any airborne particles were detected and works could be stopped if necessary. Proximity asbestos monitoring and identification of asbestos material in excavation has also been used extensively during excavation across the site. The project used Socotec to undertake asbestos monitoring and testing.

Ground gas: A ground gas protection design has been necessary to reduce risk of ground gas entering occupied buildings, kiosks, tanks and chambers where operational or maintenance access is undertaken. A ground gas design protection strategy was set out by Arcadis with PAGeo Contracting Ltd providing expert advice and a detailed ground gas design, PAGeo then supplied gas dispersal matting, venting components and gas membranes. Both the strategy and the detailed design for ground gas protection have been submitted to and approved by SCC.

Independent verification of the gas protection installation has been provided by MTS Ltd as verification of the installation and subsequent reporting to SCC is a planning condition.

[caption id="attachment_26872" align="alignnone" width="1200"] Figure 6: Gas protection void former being laid on stone blanket prior to tank base blinding, Connections to vents at tank perimeter - Courtesy of BAM[/caption]

Surface drainage: On-site surface drainage has been carefully designed such that new impermeable areas are positively drained to the site drainage system to remove the risk of a spill causing environmental pollution. This surface water is then fed into the inlet pumping station for processing through the works. As the permeable area of the site has been greatly reduced this also significantly reduces leachate mobilisation.

Biodiversity: Another planning condition is the provision of Biodiversity Net Gain (BNG). In conjunction with GBC, the project provides 10% net biodiversity gain by use of on-site planting and off-site enhancement of the land directly to the north of the new STW. A Site of Natural Green Space, biodiversity enhancements to an area of farmland, and a marshy meadow along the River Wey are being provided.

The Environment Agency have also constructed a new fish pass in this area allowing fish to migrate around Old Bucks Weir.

Guildford STW: Civils works supply chain - key participants

Main contractor: Bam Nuttall Ltd Planning consultant: Adams Hendry Consulting Ltd Civil engineering design: Arcadis Group Ltd Boreholes & testing: Geo-Environmental Services Ltd Asbestos monitoring: Socotec Ltd Rapid impact compaction: Cofra Ltd (Boskalis Group) Vertical rigid inclusions: Foundation Piling Ltd Concrete piling: Aarsleff Ground Engineering Ltd Temporary works specialist: Mabey Hire Ltd Temporary works specialist: MGF Ltd Tunnels & shafts: Joseph Gallagher Ltd In situ concrete works: Kelly Formwork Ltd In situ concrete works: DJ Civils Ltd Precast concrete manufacturer: FLI Precast Solutions Precast concrete manufacturer: A-Consult Ltd Pipe supplier: Electrosteel Castings (UK) Ltd Pipe supplier: Saint Gobain PAM UK Soil processing: Remediation Waste Management Services Concrete supplier: Heidelberg Materials Gas protection: PAGeo Contracting Ltd Gas protection system installation verification: MTS Ltd [caption id="attachment_26876" align="alignnone" width="1200"] Figure 7: Sludge processing area: MCC kiosk (grey in foreground), sludge blending tanks (top left), poly dosing kiosks (top right) - Courtesy of BAM[/caption] Overview of project progress

As of summer 2025, civils works are nearing completion and MEICA fit out has started.

The installation of piled supports has been undertaken, and all major structures are complete. Installation of the below-ground pipework and buried ducting is in progress and the welfare building is watertight and available for equipment installation. Moving towards installation of MEICA equipment, the water testing of structures started in the February of 2025.

Steel staircases and high-level walkways are mostly complete. The inlet screens and grit removal system are in place. GRP tanks for sludge processing are being installed and many control kiosks are in place. Electrical supply buildings are near completion.

MEICA work commenced in February 2025, overlapping with completion of civils to maximise programme efficiencies. Designed alongside the civils elements of the site, the MEICA installation has taken place apace with the first bridges on the final settlement tanks attached, the larger glass coated steel tanks for the sludge area in place, and generators and some kiosks have been installed.

BAM has started the installation of the above-ground pipework and cable pulling in buried ducts, and the fit out of control rooms will commence shortly. Construction of MCC basements has been completed and two of the three MCC kiosk, and power supply and distribution works are nearing completion.

[caption id="attachment_26878" align="alignnone" width="1200"] Figure 8: Sludge processing area: (left) the bases for elevated cake silos, (middle), sludge belt presses, and (right) the poly prep & dosing kiosks - Courtesy of BAM[/caption] Guildford STW: MEICA works supply chain - key participants Main designer/contractor: Enpure Ltd CFD analysis: The Fluid Group Cake silo: Saxlund International PST scrapers & ferric dosing plant: Colloide Inlet works & PST odour covers: Power Plastics Ltd Grit remover plant: Jacopa Escalator screens: Longwood Engineering Imported sludge Strainpress: Huber Technology Sludge thickening & dewatering: Kent Stainless Ltd Odour control plant: Odour Services International Ltd FBDA grids & blowers: Xylem Water Solutions Cloth pile filters: Eliquo Hydrok Ltd Storm tank cleaning system: Sulzer Pumps Wastewater Ltd Tank logging system (WASP): JR Pridham Services Ltd Glass lined steel tanks: Balmoral Tanks Ltd Sludge tank mixing: Landia UK Ltd Tunnel

A 1.5m diameter gravity tunnel, 1.5km long, transfers flows from the existing works and intercepts minor sewers en route. There are six shafts along the tunnel route, some of which act as junctions between the new tunnel and the existing sewers. Shafts were sunk by Joseph Gallagher using the caisson method and the tunnel was driven between them using a full-face tunnel boring machine, (named Daphne by a local school). The tunnel and shafts were completed in 2024 and the final work remaining are the completion of the large inlet pumping station (IPS), shaft (E2) at the new works and connection of Guildford’s main sewer to the head of the tunnel, which will allow all flows to be diverted to the new tunnel.

[caption id="attachment_26873" align="alignnone" width="1200"] Figure 9: (top left) 3D model of the Inlet Pumping Station (IPS) - Courtesy of Arcadis, (bottom left): steel fixing to IPS internal walls - Courtesy of BAM Enpure JV, and (right): IPS shaft construction - Courtesy of BAM[/caption] Inlet pumping station

The new inlet pumping station (IPS) is a 12.5m diameter shaft with a depth of 17m, which houses six pumps with the capacity to lift flows of around 2,500 l/s from the tunnel entry, at the base of the shaft, to the inlet works where all flows are screened. The shaft is complete except for the internal walls and installation of penstocks which allow isolation of half the well at any time for maintenance of the pumps. This will be completed in the autumn of this year.

Storm tanks & inlet works

Two storm tanks provide a combined capacity of approximately 8 million litres to which flow can be diverted to temporarily hold sewage arriving at the new works should flows exceed the capacity of the works. Constructed onto in situ bases, the walls of the storm tanks were prefabricated, placed and post-tensioned by A Consult Ltd.

The inlet works and larger chambers were entirely cast in situ due to lack of repeatable sections and logistics. In situ concrete work for these was undertaken by Kelly Formwork. The inlet screens have been installed and walkways are in place.

[caption id="attachment_26874" align="alignnone" width="1200"] Figure 10: Circular precast storm tanks and Inlet works (August 2025) - Courtesy of BAM[/caption] Primary settlement, activated sludge plant & final settlement tanks

Screened flows from the inlet works will then pass through primary and secondary treatment tanks comprising rectangular primary settlement tanks (PSTs) and activated sludge plant (ASP) tanks. The walls for these tanks were designed and supplied by FLI Precast Solutions Ltd and installed by BAM and DJ Civils Ltd on in situ bases prepared by Kelly Formwork Ltd. These tanks are complete with pipework being fitted and the ASP has commenced water testing.

To ensure watertightness of the larger rectangular tanks, Heidelberg Materials and Sika’s concrete technology were used.

Concrete containing Sika WT-200 P was utilised for the PSTs and the ASP. Sika WT-200 P is a combined water-resisting and crystalline waterproofing admixture used to reduce the permeability of concrete, making it suitable for water retaining structures.

Gas protection has been laid under all large tanks. Materials were supplied by PAGeotechnial Ltd and verified by MSL Ltd. Void former mating laid on a bed of single grade 40mm stone provides a preferential escape path for ground gases and is connected to vents at the tanks periphery allowing ground gases to vent to atmosphere.

These tanks are not habitable spaces and only require a dispersal system to discourage any build-up of gas below the large tank bases.

[caption id="attachment_26875" align="alignnone" width="1200"] Figure 11: From top: Activated sludge plant, primary settlement tank, and two of the four final settlement tanks - Courtesy of BAM[/caption] Final settlement tanks

The four final settlement tanks were also precast, supplied, installed and post-tensioned by A-Consult Ltd onto in situ bases prepared by Kelly Formwork Ltd. The FSTs are complete with bridges and scrapers installed and are currently being water tested.

Tertiary treatment plant & outfall

Following final settlement, flows will pass through final filtration in the tertiary treatment plant before being discharged to the River Wey via new, twin outfall pipes. Civil construction is complete and MEICA installation of cloth pile filters and drums from Eliquo Hydrok Ltd is underway.

The outfall pipework has been fully installed across the water meadow and the headwall has been constructed at the discharge point into the River Wey.

[caption id="attachment_26877" align="alignnone" width="1200"] Figure 12: Tertiary treatment plant construction (August 2025) - Courtesy of BAM[/caption] Sludge processing

The project also provides a dewatering facility for imported sludge from other small treatment works. This area is nearing completion with the larger coated glass sludge blending tanks in place and the smaller buffer tanks being installed. Gas vent pipes have been installed below the extensive concrete slabs to allow venting of ground gases to the atmosphere.

The sludge belt presses from Kent Stainless Ltd for sludge dewatering and thickening have been installed adjacent to the bases for the elevated sludge cake silos. The silos from Saxlund International have been sized to provide storage of seven days’ worth of processed sludge, which can be discharged to trucks for export from site.

Power & control

Power supply and distribution infrastructure is now in place. The three MCCs have been constructed in sequence and the first two are being fitted out.

Welfare building

A new welfare building houses the automated systems for running the new plant and controlling effluent quality as well as office and mess space for Thames Water staff and operatives. The building is watertight with cladding being installed and the fit out of building fixtures and plant control equipment is in progress.

[caption id="attachment_26871" align="alignnone" width="1200"] Figure 13: Welfare building housing plant control systems - Courtesy of BAM[/caption] 3D modelling

Design has utilised a 3D model hosted by Arcadis with each designer adding in modelling information as their design capabilities have allowed. This has enabled precise integration of designers individual input and interrogation of the integrated design

The model is used extensively by engineers on site. 3D modelling has, for example, allowed duct chambers to be precast with precision positioning of cable openings, saving on in situ working and substantially reducing programme on these installations.

Piling & ground improvement

To enable the STW to be constructed on the site without the waste being removed a combination of ground improvement techniques have been employed including driven concrete piles, Rapid Impact Compaction, and Vertical Rigid Inclusions.

The Rapid Impact Compaction work undertaken by Cofra was completed in late summer of 2023. From July 2023 to the spring of 2024, to support the larger structures, tanks and main process critical pipelines, 3500 concrete piles were driven through the landfill into the clay. The design and installation of this piling operation was undertaken by Aarsleff Ground Engineering.

[caption id="attachment_16135" align="alignnone" width="1200"] (left) Driving precast concrete piles and (right)Vertical Rigid Inclusion installation - Courtesy of Bam Nuttall Ltd[/caption]

In areas where settlement criteria were less critical, but needed controlling (for example roadways and minor pipework), a Vertical Ridged Inclusion (VRI) piling technique was used. The system involves displacement drilling a column in the landfill and filling the void with concrete. This works by consolidating the soil around the pile, transferring load to lower layers, thus increasing bearing capacity and reducing settlement over time.

Since 2024 the installation of VRIs by Foundation Piling has been completed with 7500 inclusions installed across the site. During detailed design, the project was able to remove the need for a load transfer platform above the VRIs across much of the site. This was done by detailed analysis of the 3D model to target differing requirements for support and by reducing inclusion spacings, thereby reducing the expected landfill removal by 37,500m3.

The load transfer platform remains below roads, but pipework sits within the grid of VRIs.

The year ahead

Completion of the mechanical works is expected in the first part of 2026 with installation of electrical and control systems expected to complete in the second part of 2026. Dry and wet commissioning will be undertaken sequentially across the site throughout the coming year, ensuring the new works is ready to commence process commissioning.

The final, and arguably most challenging activity, will be to connect the existing sewer network to the new tunnel, diverting flows from the existing STW to the new STW. A series of interventions will be required to intercept the various sewers, along the route of the tunnel, all the whilst ensuring the new STW is performing within strict limits and the existing STW is able to maintain its performance during the ramp down of flows.

Ballyronan is a small village situated in County Londonderry, within the Mid-Ulster District Council area located on the western shore of Lough Neagh. The towns of Magherafelt and Cookstown are both approximately 4 miles to the north-west, and 11 miles to the south-west respectively. The existing Ballyronan Wastewater Treatment Works (WwTW) was constructed to cater for a design population equivalent (PE) of 571, but in 2021, it was calculated that the existing works was dealing with a PE of 1,020 and that a future PE of 1,520 was anticipated. Existing works

The existing works comprised of an inlet chamber, a rectangular hopper-bottomed primary settlement tank, two percolating filters, a hopper-bottomed humus tank and a sludge holding tank. There was also a brick building which housed the control panel and NIE supply for the WwTW. Interstage pumping was also required to lift the primary settled flows to the biological filters.

The existing works was required to comply with a discharge consent of 40 mg/l BOD, 60 mg/l total suspended solids, and 7.5 mg/l ammonia.

[caption id="attachment_16703" align="alignnone" width="1200"] (left) Existing site on western shores of Lough Neagh, (top right) existing PSTs, and (bottom right) existing percolating filters - Courtesy of NI Water[/caption] Project drivers

Though the treatment process was generally in compliance with the current standard, the Northern Ireland Environment Agency (NIEA) had indicated that a new, more stringent consent would be imposed for future flows discharging to Lough Neagh. In addition, the existing works was operating beyond its capacity, many of the structures were nearing the end of their design life, and regular operator intervention was required to maintain compliance.

Since the existing works was not capable of fulfilling the requirements of NI Water’s long-term strategy to enhance wastewater services, and was expensive to operate and maintain, a new treatment works was deemed essential to ensure compliance with the stricter consents throughout the design horizon.

The provision of a new fully automated rotating biological contactor (RBC) WwTW would provide effective and robust wastewater treatment services for the future catchment area, catering for economic growth (having a design population equivalent of 1,520), and improving the local environment by adhering to a tighter discharge consent of 20 mg/l BOD, 30 mg/l total suspended solids, and 7.5 mg/l ammonia.

Project team

As principal contractor, GEDA Construction had overall responsibility to deliver the project on time and within budget. Water Solutions Ireland were responsible for designing and delivering a full turnkey MEICA, process design and build solution for the new works.

McAdam provided civil, structural, and geotechnical design services, including the initial enabling and investigatory works carried out at the Early Contractor Involvement (ECI) stage, as well as the detailed design for construction.

[caption id="attachment_16706" align="alignnone" width="1200"] Early excavation works with compound set up - Courtesy of NI Water[/caption] The contract delivery team worked in a collaborative manner with NI Water, project managers RPS, and key suppliers and subcontractors to deliver a robust, effective and modern treatment solution which allows for future growth in the catchment area and protects the environment by adhering to a tighter discharge consent. Ballyronan WwTW: Supply chain - key participants Project managers: RPS Civil contractor: GEDA Construction MEICA & process designer/contractor: Water Solutions Ireland Civil, structural & geotechnical design: McAdam Electrical design: SBE Design PLC software & commissioning: Ashdale Engineering MCC: R&R Engineering Mechanical storm screen: Jacopa Ltd Static storm screen: Eliquo Hydrok Ltd 6mm inlet screening: M&N Electrical & Mechanical (Hydro International Ltd's UK Wastewater Services Division) Rotating biological contactors & primary/final settlement tanks: KEE Process Ltd Pumps & mixers: Xylem Water Solutions Instrumentation: Park Electrical Systems Flow measurement: Siris Environmental Ltd Flow measurement: AMPM Flow & Energy Services Ltd Penstocks, valves & actuators: Flow Technology Services Storm tank cleaning tipping bucket: CSO Group Ltd GRP kiosks & site-wide metalwork: Victoria Engineering 10mm bar screen, skip rails & trolleys: Graham Steelwork Engineering Potable & FE service water boosters: Dutypoint Ltd Lifting equipment: Columbus McKinnon Co Ltd Access covers: JP Corry Site security fencing & gates: NK Fencing Concrete & precast products: FP McCann Pipes & fittings: APP Welfare unit: Sean Jordan Engineering [caption id="attachment_16704" align="alignnone" width="1200"] Excavation of FSTs to depth of 5m - Courtesy of NI Water[/caption] Project description & scope

The RBC treatment process at Ballyronan WwTW was to be constructed within the same footprint of the existing site. The new treatment works was designed and built to include the following individual process stages for robust and effective treatment of incoming flows:

A preliminary treatment process stage comprising of 6mm mechanical inlet screening and forward flow control equivalent to Formula ‘A’. Any flows greater than Formula ‘A’ are treated via a mechanical storm screen. A new interstage pumping station for passing forward flows equivalent to FFT to the downstream treatment processes. A new storm storage and management facility, providing a total storage capacity of 81m3 for both storm and emergency flows. The storm tank is also equipped with a tipping bucket system for efficient cleaning of the storm tank floor from CSO Group Ltd. The interstage pumps transfer FFT to two primary settlement tanks each of 6m diameter. The primary sludge from the primary settlement tanks is drawn off by the primary sludge pumping station for transferring to the new concrete sludge holding tank. Primary settled flows then gravitate to the biological treatment process; three RBCs from KEE Process Ltd. Following treatment in the three RBCs, the treated effluent gravitates to the two final settlement tanks each of 6m diameter. The sludge from the final settlement tanks is drawn off by the humus sludge pumping station, which can either be transferred directly to the new concrete sludge holding tank or to the primary tanks for co-settling with the primary sludge, before being stored in the new concrete sludge holding tank prior to transporting off-site. Following final settlement, the treated effluent gravitates through a final effluent washwater transfer pumping station, prior to discharge at the final effluent outfall location. [caption id="attachment_16698" align="alignnone" width="1200"] Bottom section of FSTs installed - Courtesy of GEDA Construction[/caption]

The new Ballyronan WwTW includes a new concrete sludge storage tank sufficiently sized for 10 days’ storage prior to being tankered off site.

The site-wide drainage system is segregated between storm and dirty drainage, with any dirty drainage directed to the new return liquors pumping station which transfers additional flows back to the head of the works for treatment.

The old brick building was demolished, and the new works was provided with a new GRP kiosk housing a dedicated main works MCC which controls all mechanical and electrical plant equipment and instrumentation.

As the new works had to be built within the confines of the existing site boundary, a complex construction phasing plan was developed to bring the new treatment works online in four separate stages. GEDA Construction, Water Solutions Ireland and McAdam worked closely with NI Water Operations to ensure effluent compliance was maintained throughout the individual construction phases.

Early contractor involvement

GEDA Construction was awarded an NEC 4 (Option A) Early Contractor Involvement (ECI) contract in February 2021 for a replacement treatment works at Ballyronan WwTW. To assist with the development of a turnkey design and build solution for a replacement treatment works, GEDA appointed Water Solutions Ireland as the MEICA & Process Contractor and McAdam Design as the Civil Designer to deliver both the ECI contract and construction contract.

An extensive ECI process was undertaken for the replacement treatment works at Ballyronan WwTW, which included ongoing collaboration with NI Water for design outputs and workshops such as HAZOP and Value Management. The ECI phase allowed GEDA Construction, Water Solutions Ireland and McAdam to gain an early understanding of the key drivers for the project and achieve buy-in from all stakeholders within NI Water and their project management team from RPS to benefit delivery.

The collaborative approach between the Contractor and NI Water in the ECI contract was an exemplary reflection of NI Water values, purpose and vision. As a result, the ECI led to enhanced value, robustness and operational efficiency for the overall construction project.

[caption id="attachment_16697" align="alignnone" width="1200"] Make up of the FSTs from KEE Process - Courtesy of GEDA Construction[/caption] MEICA & process design

GEDA Construction, in conjunction with Water Solutions Ireland and McAdam, undertook an optioneering exercise to investigate the ideal treatment solution for Ballyronan WwTW under a back-to-back NEC 4 (Option A) ECI contract. This optioneering exercise included the process design requirements of a new treatment works and the potential option of employing temporary treatment facilities to replace the existing works during construction. A full turnkey MEICA design was provided, including steelwork structural drawings and ICA documentation such as PLC architecture and Functional Design Specification for the new process.

Civil design

McAdam was appointed under a bespoke Professional Services Contract to GEDA Construction for all civil engineering design requirements for the ECI and was also engaged by GEDA for the construction contract.  The ECI contract allowed McAdam to develop a turnkey civil design including a detailed construction sequencing plan which included the use of both temporary pipework and permanent pipework for the new structures to enable phasing.

An offline build solution was presented to NI Water as an option during the ECI phase for ease of construction and ongoing process management during construction. However, in agreement with all stakeholders, the preferred design for the replacement WwTW was constructing the new treatment works in a phased manner within the existing site footprint whilst the existing works remained operational. This approach satisfied the long-term operation and maintenance requirements for the new works and negated the need for NI Water to purchase additional land.

Main challenges for design/construction

Existing site: The key challenge around the design and construction of the new Ballyronan WwTW was building a new treatment works in its entirety within the same site boundary as the existing WwTW.

[caption id="attachment_16699" align="alignnone" width="1200"] Installation of RBCs - Courtesy of GEDA Construction[/caption]

Interface between new and old works during construction: The construction of the new treatment works at Ballyronan required a continuous interface between the new and old works during construction. The new WwTW was constructed and commissioned in four individual phases.

Phase 1: Relocation of existing MCC and temporary diversion of NIE connection. The existing brick building housing the MCC was then demolished which provided the required footprint to construct two new final settlement tanks and humus sludge pumping station.

Once the new final settlement process was constructed and commissioned, a temporary diversion of flows from the outlet of the existing percolating filter beds was put in place via a temporary pumping station. This made the existing humus tank redundant and available for demolition.

Phase 2: The new interstage PS and storm tank was constructed. The existing humus tank was demolished which created space on site for constructing the three RBCs. Following construction and commissioning of the new interstage PS, storm tank and RBC process, primary settled flows were diverted to the new RBC flow splitting chamber for seeding.

At the initial stages of turning flows between the two biological treatment processes, any effluent from the RBCs was re-diverted for re-treatment through the existing filter beds to ensure effluent compliance. The effluent from the filter beds was then pumped via a temporary pumping station to the new final settlement tanks before gravitating to the effluent discharge location.

Both the effluent from the new RBCs and the existing filter beds was rigorously tested, and once the RBCs were fully seeded and proved to be treating incoming flows to the required standard, NI Water granted approval to demolish the two existing filter beds. The construction of a section of the site-wide dirty drainage and the new return liquors pumping station also took place in this phase.

Phase 3: The existing two filter beds were demolished in Phase 3 which then created sufficient space on site for constructing the two PSTs. The new inlet works comprising Formula ‘A’ flow control was constructed in the final phase, as was the new concrete sludge holding tank.

[caption id="attachment_16700" align="alignnone" width="1200"] Construction of inlet works, sludge tank & storm tank - Courtesy of NI Water[/caption]

Phase 4: The final phase involved the construction of the two new primary settlement tanks (PSTs) and completing a successful turn of flows from the interstage PS to the new PSTs. Once this was completed, Water Solutions Ireland and GEDA Construction were granted approval to respectively decommission and demolish the existing primary settlement tanks.

The new MCC panel and kiosk were also installed in this final stage, with the entire site transferred across and commissioned as a whole. Other works included:

The construction of the new final effluent outfall configuration which included a new outfall pipe and headwall. FE washwater transfer PS FCOM flow measurement chamber FE washwater booster and potable washwater booster.

At the end of Phase 4, the incoming flows were fully treated by the new RBC works at Ballyronan WwTW.

Turn of flows

As the new works was brought online in four individual phases, a complex turn of flows plan was carefully developed to ensure effluent compliance for NI Water.

GEDA Construction and Water Solutions Ireland managed the individual turn of flow processes between the existing works and new treatment works. A rigorous on-site and external sampling regime was undertaken to regularly monitor the performance of the existing and new works. This sampling regime proved critical in allowing the site team to advise NI Water when the new RBC treatment process was fully functional and treating effluent to the required standard.

[caption id="attachment_16701" align="alignnone" width="1200"] Completed Ballyronan WwTW - Courtesy of GEDA[/caption]

As a result, NI Water granted approval for the decommissioning of the existing filter beds. From this, the existing biological filter beds could be demolished to allow further construction to progress.

The turn of flows process, particularly from the old filter beds to the new RBCs, had to be carefully managed both hydraulically and biologically to ensure the treatment process was optimised and effluent compliance was maintained at all times.

The various turn of flow processes required both temporary gravity-fed lines and temporary over pumping lines to demolish existing structures. For example, GEDA Construction had to lay a temporary sewer to divert flows from the existing primary tanks to the new interstage pumping station in Phase 2.

Both GEDA and Water Solutions Ireland had to construct and fit-out a temporary pumping station to direct flows from the outlet of the existing percolating filter beds to the new final settlement tanks.

Commissioning

Construction work on the new Ballyronan WwTW was completed early September 2024 with site-wide testing and commissioning of the plant successfully undertaken for handover to NI Water in October 2024.

Speaking about the economic and environmental benefits of the project, Senior Project Manager, Sean Milligan commented:

“NI Water’s substantial investment of around £5m has provided a robust wastewater treatment solution for the Ballyronan area that will support local development and help improve water quality in Lough Neagh.”

Beckton Sewage Treatment Works (STW) is the United Kingdom’s largest STW serving a population equivalent of over four million. The AMP7 project is a major £185m investment to increase the site’s treatment capacity for growth, by a population equivalent of 200,000, by extending the existing activated sludge plant (ASP). Beckton STW will receive stormwater from the Thames Tideway Tunnel ‘Super Sewer’ when it is commissioned in 2024. The project will improve resilience of the inlet works by providing more screening and grit removal plant to increase redundancy, the improvements will deliver on a Regulatory Performance Commitment. The project also includes elements of capital maintenance; mainly on electrical infrastructure and sludge treatment, to ensure resilience and effluent quality is maintained. The existing plant The first works at Beckton was built in 1864 by Sir Joseph Bazalgette as part of the revolutionary Victorian sewer network, which drastically improved water quality in the River Thames. The plant has since been extended numerous times and covers over 100 hectares (250 acres). Sewage is received from a large collection of sewers and pumping stations, which all connect to the Northern Outfall Sewer (NOS) that comprises five large brick barrels. Beckton’s flow to full treatment is 27m3/s, with peak storm flow of 32m3/s. The preliminary treatment is by coarse and fine screens, with grit removal located between the screens. Primary treatment is by two banks of rectangular primary settlement tanks (PSTs), each consisting of eight PSTs. The secondary treatment is by a conventional activated sludge process with three separate streams ranging in age, numbered ASP2, ASP3 and ASP4. Each of the ASPs include a set of final settlement tanks (FSTs). Final effluent is discharged to a common channel that leads to the main outfall to the River Thames, upstream of the Barking Creek Barrier. Sludge is treated through a process of anaerobic digestion and thermal hydrolysis. Biogas is captured from the digestion process and generates electricity and heat through combined heat and power engines (CHP). Beckton can produce half of the required electricity to run the treatment process from the CHP engines, and an on-site wind turbine. Digested cake is exported from the site to agriculture and there is an option to process the sludge in the sludge powered generator that also provides electricity for the site. [caption id="" align="alignnone" width="1200"] ASP4 South Tank twin wall under construction - Courtesy of Laing O’Rourke[/caption] What’s being provided? Thames Water has appointed Laing O’Rourke to deliver the project, with multidisciplinary design services being provided by Atkins (SNC Lavalin). The contract was awarded in July 2020, with construction works starting in April 2021 and the works will be completed and handed over in phases throughout 2024. New and existing inlet works A new inlet works will be constructed comprising three lanes that contain coarse (50mm) and medium screens (20mm) provided by Huber Technology, and grit removal plant. One of the existing inlet works lanes will be sacrificed to provide the feed to the new lanes, hence the provision of two additional lanes in terms of redundancy. The constant velocity grit channels have a capacity up to 15m3/s with SAVECO Environmental Ltd supplying traditional grit bridges with an alternative method of grit suction. The associated instrumentation is from Vega Controls Ltd and the automation and control panels for the grit bridges has been designed and built by Te-Tech Process Solutions. Grit classifiers with combined output of up to 88 tonnes/hour and launder channels in this process stream are being supplied by FLSmidth, and Fluid Sealing & Engineering (FSE) Ltd respectively. The process streams for screening and grit removal along with the associated handling plant for the new inlet works follow a similar arrangement to the existing inlet works. The existing inlet works will be supplemented with medium screens, supplied by Huber Technology, in the remaining five lanes to reduce the load passed forward to the fine screens and to improve the reliability of the existing grit removal plant. A significant upgrade to the electrical infrastructure is required with a large glass reinforced plastic switchroom supplied by Morgan Marine. Winder Power Group are supplying the transformer and electrical installation has been subcontracted to AVRS Systems. The new switchroom houses the new high voltage (HV) and low voltage (LV) electrical panels, provided by Siemens and Total Automation & Power (TAP) respectively, supplemented by a new diesel operated generator to improve resilience. [caption id="" align="alignnone" width="1200"] New inlet works under construction - Courtesy of Laing O’Rourke[/caption] ASP4 extension and sludge improvements ASP4 was installed under the last major upgrade at Beckton (by Laing O’Rourke), which completed in 2014 and currently treats up to 8m3/s. This project will provide two new aeration lates in separate tanks, referred to as the North and South Tank. Each are 85m long, 41m wide and 8.5m deep. Four new FSTs will be provided; each being 45m diameter and 5m deep. A new aeration building is required to house blowers for the new aeration lanes with the aluminium clad structural steel building envelope installed by Galloway Construction Ltd. The aeration blowers are supplied by Howden, diffusers by Xylem Water Solutions and new transformers by Winder Power Group as part of a substantial upgrade to the existing electrical infrastructure for the new ASP. The sludge improvements include new Huber Technology raw sludge screens to remove rags and improve resilience in the sludge treatment stream. Sludge treatment capacity improvements, surplus activated sludge (SAS) thickening, is by new gravity belt thickeners (GBTs), supplied by Kent Stainless Ltd in a new building. An extension to the existing sludge cake barn building to increase sludge cake storage capacity is required. The sludge steam has further resilience work by the provision of a polymer dosing facility, new electrical infrastructure, new sludge holding tanks from Stortec Engineering Ltd, and an upgrade to existing tanks. [caption id="" align="alignnone" width="1200"] ASP4 North Tank completed and new blower building cladding underway - Courtesy of Laing O’Rourke[/caption] Capital maintenance There are a number of improvements to the existing site wide electrical infrastructure such as the refurbishment of existing LV panels. The other key element is replacing the outfall channel flap valves to prevent site flooding. Fibre optic network upgrade The site-wide fibre optic network will be replaced as it has reached its design limit and has no capacity to be extended to accommodate the growing operational and performance requirements. Laing O’Rourke and Atkins are working with Thames Water to develop a new network architecture based upon the utilisation of a ‘Layer 3’ backbone network. The design will incorporate four ‘Layer 2’ process networks with firewalls between each Layer 2 network and the backbone Layer 3 network. The updated network architecture will improve resilience and security of the network. Design Around 40% of the project’s civil works have been designed using DfMA (design for manufacture and assembly). The lessons learnt from using DfMA method of construction completed in the previous Beckton upgrade project were implemented in this project. The lessons included manufacturing methods, reinforcement design and detailing, and the use of leaner temporary works required for reinforced concrete structures. Digital Build models produced by Laing O’Rourke have been used to understand the steps involved in the precast construction and identify hazards during pre-construction reviews. [caption id="" align="alignnone" width="1200"] (left) 3D BIM model of new inlet works and (right) new inlet works under construction - Courtesy of Laing O’Rourke[/caption] Another lesson learnt applied was to implement solutions with Engineered Safety in mind, both for temporary and permanent works. Engineered Safety is Laing O’Rourke’s approach, which aims to improve health and safety outcomes for those who design, construct, use, maintain and dismantle the assets (examples outlined later). This approach has helped to identify key hazards further to which simple but effective solutions have been implemented to eliminate or mitigate risks. Notwithstanding the above implemented lessons, one of the key ethos of this project is capture and disseminate new lessons learnt during the design, construction, commissioning, and handover stages of the Beckton STW upgrade and future projects. Digital tools Federated model for coordination and collaboration With the three main organisations (Thames Water, Laing O’Rourke and Atkins) exchanging information, it was necessary to use a common platform to record and share design progress on a regular basis. As such a project 3D federated model has been published on a regular basis and shared via BIM360 and Asite. The model has also been used as a collaborative tool to identify and resolve clashes and for use in workshops and presentations. The model has been produced to BIM Level 2, with Level of Detail 3 (LOD3) for the mechanical and electrical elements of the design, and LOD4 for civil and structural design where third party designs are not required. Whilst Laing O'Rourke's Asite and Thames Water’s TWEXnet Business Collaborator has been used to record outcome of technical assurance and approvals, BIM Collab has been used to monitor resolution of clashes and record actions from pre-construction model reviews. Although traditional spreadsheets were originally developed for reporting design progress, this has gradually been migrated to a Power BI based system. The lessons learnt from this process is now being implemented to monitor and close out HAZOP/OPMAN actions and to plan and monitor progress for handover documentation. [caption id="" align="alignnone" width="1200"] (left) Extract from 3D BIM model: raw sludge screens and (right) raw sludge screen civil works - Courtesy of Laing O’Rourke[/caption] Digital build Laing O'Rourke’s construction assurance procedure requires the use of digital build models prior to construction. Whilst the federated model aims to show the permanent works, the digital build process aims to incorporate both permanent and temporary works requirements by reconstructing the model using 2D outputs from detail design. This has allowed Laing O'Rourke to minimise health and safety risks by planning the build with better accuracy. Drone deploy To monitor progress in construction, drone technology has been used to capture photos and videos. Drone Deploy platform which utilises the rich data captured also allows superimposition of detail design drawings showing outline of permanent works. This tool has been used effectively in collaboration meetings to demonstrate progress or to resolve complex engineering problems, and to plan construction activities. Point Cloud surveys Point Cloud surveys have been used to inform the detail design. This method of survey that capture fine details of location of civil assets and MEICA plant and equipment in 3D format. Although, it requires careful treatment before incorporating into the 3D model. In particular, areas with high density of MEICA plant and equipment such as the sludge tanks, existing grit channel at the inlet works, and existing cake barn ventilation were surveyed using Point Cloud surveys. Design challenges due to scale - constant velocity channel and grit bridges design The scale of the works at Beckton STW created several design challenges around plant sizing, meeting performance requirements and space constraints. One example of this being the grit removal solution on the new inlet works. Conventional design methods for calculating grit channel lengths have been challenged. CFD modelling has been used to size the constant velocity grit channels and to demonstrate the proposed location of flow measurement devices are acceptable. This has reduced the length of the channel by 23m and hence the cost of civil infrastructure. The pumps in the grit bridges are specified to remove up to 3.5kg/s and calls for an automatic system with level instrumentation to detect grit. This would make the classifiers ones of the largest in Europe. Borger Pumps and SAVECO Environmental Ltd are providing rotary lobe type pumps to achieve the specified rate. This design rate of removal is exceptionally high, taking into consideration the incoming grit from the Tideway Tunnel. As detection systems in this scenario are not usually required in the UK, market research had to be undertaken to select the detection system in discussion with the supply chain with their experience from other industries to reach to a solution. [caption id="" align="alignnone" width="1200"] (left) 3D BIM model of new inlet works screens and (right) new inlet works forebay with coarse and medium screens upstream of the constant velocity grit channels - Courtesy of Laing O’Rourke[/caption] Beckton STW: Supply chain - key participants Main contractor: Laing O’Rourke Designer: Atkins UXO pile probing: Safelane Global Limited Piling & earthworks: Expanded Piling Sheet piling: Sheet Piling (UK) Ltd Mini piling: Keller Limited Tunnelling works: Joseph Gallagher Ltd Diving support: DiveCo Marine Limited Structural steelwork & cladding: Gallaway Construction Pipelaying: J Murphy & Sons Limited Structural steel: Reidsteel Precast walls to the FST tanks: A-Consult Ltd Blockwork: Pyramid Builders Limited Precast tank walls: Explore Manufacturing Access steelwork (ASP4): Steelway Fensescure Limited Specialist cable installation: Elsym Installations Limited Electrical installation inlet & ASP4: AVRS Systems Fibre optic installation: VVB Low voltage assembly (inlet): Total Automation & Power Transformers: Winder Power Group Mechanical installation: Fluid Sealing & Engineering Ltd Desalination pipeline diversion: Franklyn Yates Engineering HV switchboard & switchgear: Baldwin & Francis Power management: Regulateurs Europa Ltd HV switchboard & installation: Siemens PLC Inlet works & raw sludge screens: Huber Technology Grit bridges: SAVECO Environmental Ltd Grit bridges control panel design/build: Te-Tech Process Solutions Grit bridges instrumentation: VEGA Controls Ltd Rotary lobe pumps: Borger Pumps Grit classifiers: FLSmidth Blowers: Howden UK Limited Aeration diffusion grid: Xylem Water Solutions SAS gravity belt thickeners: Kent Stainless Ltd Glass coated steel tanks: Stortec Engineering Ltd Odour covers: MSD Design Limited Penstocks & stoplogs: Glenfield Invicta Ltd Scraper bridges: Jacopa Limited Valves: AVK UK Ltd Tank mixing: System Mix Limited Inlet washwater booster set: Crown House Technologies Odour control: Odour Services International Ltd CTM screenings belt conveyors: CTM Systems Ltd Diesel generator: DTGen GRP LVA inlet kiosk: Morgan Marine Limited Polymer plant: Richard Alan Engineering Company Limited Overhead cranes: Bramley Engineering (Lifting Gear) Ltd Skip compactors: Thetford International Compactors FE washwater break tank: Forbes Technologies Ltd Welfare & plant: Select Plant Hire Construction Collaboration The team have strived to maintain collaboration at all levels throughout the project to support health and safety focus, sustainability and dealing with site challenges. In line with the approach in design development and approvals, collaborative planning sessions and workshops have provided great insights in problem solving and the planning of complex tasks, for example the diversion of a 132kV cable, tie in details of the new inlet works to the existing inlet works channel and materials management plan (MMP) for dealing with excavation arisings. [caption id="" align="alignnone" width="1200"] ASP4 North Tank under construction - Courtesy of Laing O’Rourke[/caption] Sustainability The project aims to minimise off-site landfill disposal by re-using spoil for engineering works or redistributing it on site through landscaping activities and creating additional biodiverse habitats. This has been the strategy included in the MMP from the inception of the project. This has been reviewed and updated with new information rising during the construction activities. Any contaminated sections of the excavated materials were monitored with greater scrutiny, supported by chemical testing and analyses. Localised treatment has been implemented complying with environmental standards. For instance, the identification and safe method of disposal of soil contaminated with Japanese knotweed has been carefully selected with engagement from all stakeholders and planning requirements. The above measures have assisted in ensuring construction activities are conducted in a sustainable manner. Another area where sustainability has been considered is in concrete mix design. Due to the large volume of concrete required on site, the use of ground granulated blast furnace slag (GGBS) has been maximised in line within the parameters defined in the project specifications. This has assisted in reducing carbon footprint of the project. Overcoming challenges - Cadent gas main diversion An example how a complex engineering problem was solved in close collaboration with key stakeholders is the resolution of the crossing of the Cadent gas mains to enable the construction of the new inlet works channel. The new structure had to cross an intermediate pressure steel 600mm diameter gas main and a medium pressure 30” cast iron main which then split into two polyethylene (PE) mains. The mains then cross beneath the historical Victorian NOS brick barrels. Engagement with Cadent instigated extensive and detailed assessments of the existing gas mains, this identified the need for the MP cast iron main to be replaced due to excessive ground settlement driven by changes in ground levels. The medium pressure gas main was replaced with a new 750mm steel main, which included a section inserted into a microtunnelled concrete sleeve underneath the NOS. In addition, pipe protection measures using polystyrene blocks and lightweight fill were required to minimise the loadings on the intermediate pressure mains. [caption id="" align="alignnone" width="1200"] New 45m diameter FSTs under construction - Courtesy of Laing O’Rourke[/caption] Engineered safety - DfMA DfMA has effectively been driven by Laing O’Rourke as part of their design development. The level of detail and timing of coordination required between the manufacturing team and designer was clarified early in the programme to ensure an alignment of principles, opportunities, and understanding of the likely constraints. Following are some examples of the benefits that DfMA has given. Aeration tanks and FSTs Precast concrete water retaining solutions are common within the water industry. At Beckton STW, the project has benefitted from incremental innovation of the previous project solution for the construction of the aeration tanks. The twin wall solution has incorporated lessons that resulted in modifying the lateral support beam tie-in arrangement, simplifying the formwork for the pouring of concrete in between the twin wall, and minimising site effort by reducing the complexity at the concrete panel connection interface points. These provided benefit in requiring less working space, plant, and labour, thereby also improving productivity. Furthermore, regarding embedded carbon, the DfMA solution is carbon neutral compared to an in situ tank. Though the same materials are used in similar quantities there has been a 5% reduction in wastage. DfMA has also been used in the design and construction of the final settlement tanks, where post-tensioned precast walls have been utilised by A-Consult Ltd. [caption id="" align="alignnone" width="1200"] Engineered safety: (left) use of access hatch to internally access FST during precast wall installation  and (right) use of RMD soldiers for aeration tank construction - Courtesy of Laing O’Rourke[/caption] ASP4 tank walkway handrailing The installation of walkway handrailing from Steelway Fensecure Ltd has been developed for this project and proven to reduce the site installation period and improved safety by reducing the working at height requirements. The lifting operations have benefitted from the site already having large lift capacity craneage and the construction logistics have enabled access into the working areas to align with the civil engineering works. Systemising pipework and cable containment onto the walkways for future projects are the next generation opportunities to be investigated. Use of RMD soldiers for twin wall propping A simple solution to negate the use of inclined props to create more workspace and reduce hazards is to use RMD soldiers. This required careful planning from the design of twin wall during temporary phase and ensuring appropriate measures are in place within the panels to allow safe fixing of the RMD soldiers in place. Access hatch to FST walls Another example of a simple solution to reduce safety risk is the provision of an access hatch to enable access during the erection of the precast panels, which was developed with the precast wall supplier A-Consult Ltd. This negated the need for providing high level access through temporary staircases and reduced risk of working from height. The above examples emphasize the benefits of DfMA accrued at Beckton STW of an improved product, reduced installation period, and the on-going development opportunity that has made construction activity safer. The project has demonstrated how incremental innovation can be achieved on a relatively new and stable construction method using twin wall construction techniques. [caption id="" align="alignnone" width="1200"] Precast construction of 45m diameter FST - Courtesy of Laing O’Rourke[/caption] Use of non-piled solution As old structures have been historically filled with mass concrete to significant depth, the reuse of these mass fill structures as foundation for new structures was explored as a safer and more sustainable solution. This enabled the project team to avoid the need for mobilising piling rigs, reduce lifting requirements and need for heavy plant and equipment. High-risk service diversions of were also avoided. The SAS thickening system comprising the GBT building, polymer facility, potable water supply facility and the SAS storage tank all are founded on the existing mass concrete foundations. The choice of foundations was supported by structural analyses and further ground investigations. Designer tours To instill a culture of continuous improvement, designer tours encouraged the main designer and those from trade contractors to visit the site, inspect works being undertaken and provide feedback on how hazards are being mitigated on site. The aim being to capture feedback and consider them in future design work on Beckton STW and other projects. Commissioning and handover Preparation for commissioning started well in advance with different sequencing of activities and scenarios discussed with Thames Water and factored in the programme. Several factory acceptance tests (CFATs) have successfully been undertaken for the diffusers in the aeration tanks, inlet works screens, grit classifiers and transformers. The sequence of commissioning activities will lead to a ‘power on’ milestone, followed by dry and wet commissioning when flows are allowed to pass through the works. With a large pool of subcontractors and four main sections of work, Laing O’Rourke are setting up tools and systems to track and collate documentation which will in turn be required to be handed over to Thames Water and for Laing O’Rourke records. This ranges from records of testing, operation and maintenance manuals, training documents, to design assurance documents and quality records. The philosophy adopted is to aim for a continuous handover of documents as and when they are ready, instead of waiting up to the end of the project. [caption id="" align="alignnone" width="1200"] New FSTs with backfilling underway - Courtesy of Laing O’Rourke[/caption] Construction progress The construction of the new inlet work is progressing well with most of the channel structure completed. The upstream and downstream connections to the existing channel will be the last activity before wet commissioning. The new inlet works has transitioned into the mechanical and electrical phase with the installation of the plant items underway. Good progress has been made with the new aeration tanks that are fully constructed and water tested, with diffuser pipework and diffusers installed. The blower house and final settlement tanks have been constructed. The focus is on progressing the aeration blower installation and associated electrical works. The civil works for the sludge area is underway in preparation for the mechanical and electrical plant installation. Overall, the project is on track to complete various works elements throughout 2024 and will be handed over in a phased approach.

Newthorpe Sewage Treatment Works, in the Erewash Valley in Nottinghamshire, is undergoing a major expansion. The new works will duplicate its current capacity, from 324 l/s and 41,000 population equivalent (PE) to 649 l/s and 100,000 PE, to receive the flows of the Heanor Milnhay STW catchment area. A 2.5 km dual-rising main will connect both sites. Heanor Milnhay STW, a dual-stream site in Derbyshire currently treating 258 l/s (41,000 PE), has reached its maximum capacity and its geographical location makes it impossible to cope with the projected population growth. The process will be decommissioned, and the site will be re-purposed to hold a storm storage capacity that exceeds the current storm storage capacity by more than three times. The client, Severn Trent, and Mott MacDonald Bentley, principal designer and contractor, are the main stakeholders of this project. Project objectives The main project objectives align with the current social and economic environment. With the expansion of the works, Severn Trent is aiming to: Improve the effluent quality, especially phosphorus content. The new site will reduce the phosphorus concentration in the effluent from 2 mg/l to less than 0.2 mg/l. Reduce the running costs and maintenance costs of the plant by merging two sewage treatment works and using a less-intensive chemical usage treatment process. Reduce the non-treated sewage spillage by increasing the stormwater storage capacity at Heanor from 2,200m3 to 7,000m3. Additionally, all the storm flows will be preliminary treated by physical screening and settlement. [caption id="attachment_18498" align="alignnone" width="1200"] Newthorpe STW: (left) site compound and storage, (top) existing site, and (bottom) the new expansion (August 2024) - Courtesy of MMB[/caption] Process description: Preliminary & primary treatment

Once the expansion is completed, Newthorpe flows and Heanor flows will have separate preliminary and primary treatment streams, before combining in the secondary treatment stage.

Flows from the Newthorpe catchment will arrive at the existing inlet works. This area will stay as per the current arrangement and only the mechanical equipment will be upgraded. The flows are lifted using Archimedes screw pumps to a raised inlet works structure.

This structure holds the fine screens, which are designed to capture at least 80% of all the solids above 6mm. After the screens, a detritor will settle all grit and inorganics such as sand; removing them from the process stream to avoid damage to the mechanical equipment.

The wastewater from the catchment then flows to the primary treatment area, where the first physical separation of particles using gravity to settle the fines at the bottom of the two existing primary settlement tanks is carried out.

The effluent from the primary settlement tanks, that is currently connected to a secondary treatment consisting of trickling filters and hummus tanks, will now be diverted to the new works’ expansion.

Flows from the Heanor catchment area that arrive at Heanor will be pumped 2.5km to a newly build inlet works at Newthorpe. Similar to the existing inlet works, the new inlet works will feature 2D 6mm screens provided by Longwood Engineering Company Ltd and a 4.5m detritor provided by Tuke & Bell Ltd.

[caption id="attachment_18497" align="alignnone" width="1200"] Heanor flows inlet works (August 2024) - Courtesy of MMB[/caption]

After the detritor, the flows merge, without having been settled, with the Newthorpe flows. Keeping the Heanor flows unsettled is key to provide the right load for the process to work.

Process description: Secondary treatment

The main biological treatment happens in this secondary stage, where the aim is to reduce to the consented levels certain parameters such as Phosphorus, ammonia, iron and suspended solids. The process selected for Newthorpe is an enhanced bio phosphorus removal process in a modified University of Cape Town (UCT) configuration.

The first stage in the process is the anaerobic zone, where the polyphosphate-accumulating organisms (PAOs) thrive in an environment with no oxygen nor nitrogen introduced. In this stage, the PAOs accumulate volatile fat acids which will help them being biologically competitive in the aerobic phase of the treatment.

The next stage is the anoxic zone, where recirculated active sludge (RAS) from the secondary settlement process is introduced.

[caption id="attachment_18495" align="alignnone" width="1200"] Enhanced Bio Phosphorus Removal UCT configuration - Courtesy of MMB[/caption]

This RAS recirculates the bacteria through the system as well as introduces nitrogen oxides which have been created in the aerobic section by the oxidation of ammonia (NH4). In this anoxic zone, the nitrogen oxides are transformed into nitrogen gas which escapes to the atmosphere.

The third stage of the process is the aerobic zone in which air is introduced. Under these conditions, three main processes concur:

The nitrification process, where ammonia is transformed into nitrogen oxides which then are degraded to N2 in the anoxic zone as previously mentioned. To carry out this process, the bacteria need energy which they obtain from the organics load in the sewage. The PAOs previously mentioned consume the VFAs accumulated in the anaerobic zone to accumulate phosphorus. The phosphorus accumulated at this stage is larger than the phosphorus released in the anaerobic stage, hence producing enhanced bio-phosphorus removal.

The final stage of the secondary treatment is the secondary sedimentation on the final settlement tanks, where the rich-P sludge is removed from the system and either recirculated to the anoxic zone; or thickened and wasted to produce other products such as gas and cake on sludge digestion processes.

Process description: Tertiary treatment

The final stage of the process aims to further reduce the P levels in the effluent by capturing non-organic phosphorus.

Ferric sulphate is dosed upstream of the tertiary solids removal unit to cluster the particles into larger floccules that are then removed by a physical filtration system. The system selected in Newthorpe is FilterClear (mixed media filtration), designed and manufactured by Bluewater Bio Ltd. Once commissioned it will be the largest FilterClear system in wastewater treatment.

[caption id="attachment_18502" align="alignnone" width="1200"] Installation of the tertiary solids removal units (August 2024) - Courtesy of Mott MacDonald Bentley[/caption] Delivering innovation

MMB and Severn Trent will be working together during the commissioning of the plant to understand the emissions of greenhouse gases in sewage treatment works and how to optimise the plan to reduce them. Instrumentation to measure NO and N2O will be installed on the ASP.

Nitrous oxide is produced during the biological removal of ammonia in nitrifying ASPs. Monitoring nitrous oxide emissions (along with nitrite) during commissioning at Newthorpe will not only provide STW with a baseline process emissions factor (EF) for the site but also with valuable insights into the mechanisms resulting in nitrous oxide production.

Newthorpe STW: Supply chain - key participants Client: Severn Trent Principal designer & contractor: Mott MacDonald Bentley CFD analysis, planning, mining studies: Mott MacDonald CFA piling: Van Elle ASP FRC: Bell Formwork Services Ltd Inlet works FRC: TCL Structures UK Ltd Design/build of FRC final settlement tanks: Tank Consult Ltd Rising main HDD: Johnston Trenchless Solutions (JTS) Mechanical installation: Alpha Plus Ltd Electrical installation: Main Electrical Inlet screens: Longwood Engineering Company Ltd Grit removal plant: Tuke & Bell Ltd Scraper bridges: EPS Water Glass-coated steel tanks: Goodwin Tanks MCCs: CEMA Ltd Aeration diffusers for ASP: Xylem Water Solutions Polymer dosing: Richard Alan Engineering Alkalinity dosing: Lintott Control Systems Ferric dosing: Colloide Mixers, blowers & submersible pumps: Sulzer Pumps Wastewater Ltd Progressive cavity pumps: NOV Booster pumps: Grundfos Tertiary solids removal: Bluewater Bio Ltd Gravity belt thickeners: Alfa Laval Kiosks: Morgan Marine Steel buildings: LGSF Valves: AVK UK Ltd Penstocks: Waterfront Fluid Controls Ltd Lifting equipment: T Allen Engineering Services Ltd Steelwork & storm distribution chamber: GT Fabrications Steelwork: GWH Fabrications Ltd Steelwork & GRP platforms: APT Marine Engineering Ltd FE monitoring: Servitech International Fencing: Town & Country Fencing (Midlands) Ltd [caption id="attachment_18499" align="alignnone" width="1200"] Heanor site overview (September 2024) - Courtesy of MMB[/caption] Progress: Heanor STW

At Heanor, the main structure, which is the new transfer and storm pumping station structure, is currently in its final stages.

The design of the structure was a challenging process where the proximity of nearby structures and the groundwater were the main constraints. The final structure consists of a wall of secant piles by Van Elle, which has been incorporated into the permanent structure. This secant pile provided a cut-off for groundwater that was key to delivering the pumping station installation safely. The blind tank, which is a 1,700m3 glass-coated steel tank provided by Goodwin Tanks Ltd, has been completed in September 2024. The slab and all drainage pipework are now completed. A steel storm distribution chamber fabricated by GT Fabrications is being manufactured and will be installed in October 2024. Finally, the MCC has been installed and powered in September 2024.

The site will be operational in its final configuration by December 2024 to meet the regulatory requirements.

Progress: Rising main

The 2.5km 450mm dual rising main connecting Heanor STW to Newthorpe STW is now completed by with only the pressure testing and its final connection to Newthorpe STW pending. The rising main will be ready to transfer flows in October 2024, to aid with the EBPR maturation process ahead of the regulatory commitment.

The route of the rising main crossed several historical mine sites. MMB’s geotechnical team conducted an investigation to understand the status and position of the mine entries and any other mine-related features along the route. Additionally, a watching brief was in place to quickly identify any non-natural ground features.

Thanks to this effort all the risks were mitigated, and the rising main was safely constructed by Johnston Trenchless Solutions.

[caption id="attachment_18503" align="alignnone" width="1200"] Rising main site just outside Newthorpe (August 2024) - Courtesy of MMB[/caption] Progress: Newthorpe STW

At Newthorpe, all major civil structures are completed, and on the site, a major operation of backfilling, electrical and mechanical installation is currently ongoing.

Inlet works: The new Heanor flows inlet works structure was built by TCL Structures UK Ltd, with the new 2D 6mm screens being provided by Longwood Engineering Company Ltd and a 4.5m detritor being supplied by Tuke & Bell Ltd. Final settlement tanks: The three 33m FSTs built by Tank Consult Ltd with full scraper bridges provided by EPS Water are now complete. Activated sludge plant: The four-lane ASP built by Bell Formwork & Civil Engineering Services Ltd is also complete. The aeration grid and pipework supplied by Xylem Water Solutions, the blowers and the mixers from Sulzer Pumps Wastewater Ltd, and the tank steelwork from GT Fabrications has all been installed. Chemical dosing: The four tanks of the chemical dosing area are now installed. The ferric dosing system was provided by Colloide while the alkalinity dosing system is provided by Lintott Control Systems Ltd. Site buildings: The Newthorpe site is changing rapidly and at the end of September 2024, the building that will house the Alfa Laval gravity belt thickeners and the Richard Alan Engineering polymer dosing plant, has been erected by LGSF. Tertiary treatment plant: The four Bluewater Bio Ltd FilterClear tertiary solid removal vessels are now installed on site. All ancillaries such as pipework and service tanks are currently being installed and the TSR plant will be ready to start commissioning in November 2024. Motor control centre: The MCC that will be controlling the expanded works was provided by CEMA Group and is housed in a kiosk manufactured and installed by Morgan Marine. All the electrical installation on site is being carried out by Main Electrical. [caption id="attachment_18500" align="alignnone" width="1200"] Sodium hydroxide (left) and ferric sulphate (right) dosing systems(August 2024) - Courtesy of MMB[/caption] An award-winning project

In 2024, the Newthorpe STW expansion project has been awarded two Green Apple Awards in the categories of Building & Construction and Sustainable Water Management. The project also won the first Ground Engineering Awards for MMB for the UK Project with a Geotechnical Value of between £500k and £1m.

Conclusion

Newthorpe STW and Heanor Milnhay STW have been merged in one of the major AMP7 Severn Trent projects, with Mott MacDonald Bentley as principal designer and contractor. The expansion to Newthorpe STW will be one of the largest enhanced bio-phosphorus treatment sites in the region covering a population equivalent of 100,000 and will achieve a tightened permit of 0.2 mg/l, whilst minimising the use of chemicals to remove phosphorus.

The project is currently on track to achieve the biological maturation of the EBPR by its regulatory date in December 2024.

In recent years, the village of Boherbue in north-west Cork has undergone considerable expansion, resulting in increased demand for housing. This growth has presented challenges, particularly for the existing wastewater treatment facility, which has struggled to cope with the surge in population. Additionally, the plant has fallen short of the Environmental Protection Agency’s treatment standards, underscoring the pressing need for an upgrade. Of particular concern is the discharge of treated wastewater into the River Brogeen, a protected conservation area that serves as the habitat for the freshwater pearl mussel. In collaboration with Uisce Éireann (Irish Water) and Cork County Council, a comprehensive project has been undertaken to modernise and enhance the capacity of the treatment plant. This initiative not only addresses the immediate needs of Boherbue’s growing community but also ensures compliance with environmental regulations. Early Contractor Involvement

The project, delivered under the innovative Early Contractor Involvement (ECI) framework, aimed to address the overloaded and outdated infrastructure while ensuring compliance with regulatory standards and meeting the evolving needs of the community. The innovation in this project lies in its multifaceted approach to efficiently treat wastewater, reduce carbon emissions, and protect natural ecosystems.

Leveraging the ECI framework allowed for the integration of innovative solutions such as solar energy, natural sludge drying reed beds, and the preservation of existing constructed wetlands for stormwater overflow. This innovative approach not only sets a new standard for sustainable wastewater treatment but also ensures long-term environmental benefits for Boherbue and its natural surroundings.

[caption id="attachment_16527" align="alignnone" width="1200"] Google Earth image of Boherbue[/caption]

The scope of works for the upgraded facility included:

A new inlet works. A stormwater storage tank. Biological treatment processes. Tertiary solids removal cloth filtration system. Sludge drying reed beds.

A description of these key features follows.

New inlet works

An inlet works with fine screening to 6mm in 2D and a manual bypass screen to 19mm with a stone trap upstream of the screens were installed. The screens were designed to cater for the Phase 2 Formula A flows of 23.2 l/s screens are to be designed to cope with a minimum of 150% of the design capacity for works under 2,500 PE, i.e. a design capacity of 35 l/s based on the Design Formula A. The hydraulic design of the inlet works was also based on the fine screen(s) being blinded by a minimum factor of 70%. The screen selected by the ECI team was the Definitive Ecology SF/T3 in-tank screw screen, with SDACA (specially designed anti-clog auger) system to ensure compliance with the screening handling requirements.

[caption id="attachment_16526" align="alignnone" width="1200"] Inlet works preliminary treatment - Courtesy of Glanua[/caption] Stormwater tank

Flows exceeding the plant’s peak design flow, overflow by gravity (weir discharging via overflow screen) to the stormwater holding tank, which has been designed to provide a retention time of two hours for the difference between the Design Formula A and FFT flows plus 40 l/PE for SWO compliance as only 1:7.1 dilutions will be available for the WwTP effluent in the Brogeen River (based on DWF and 95th percentile river flow).

The stormwater holding tank is provided with a Eliquo Hydrok CWF flushing bell in order to automatically clean the tank once the storm flows have abated and the tank has been emptied; which is an innovative approach to this, requiring no energy input.

The CWF Storm Flush system is a highly effective non-powered cleaning system for all stormwater retention tanks, utilising the sewage stormwater for the flushing process thus requiring no additional fresh water. Storm return pumps located in a sump within the storm tank, which will reduce retention of larger volumes of waste and reduce the risk of odour.

Biological treatment processes

The secondary treatment stage for Boherbue includes the following:

Two anaerobic selector tanks with three separate selector cell volumes. Two 624m3 aeration tanks with 109m3 of anoxic volume each for denitrification. Settlement provided by two 5m diameter/3.5m side wall depth secondary settlement tanks. [caption id="attachment_16524" align="alignnone" width="1200"] Secondary aeration treatment - Courtesy of Glanua[/caption]

Each aeration tank is 15.6m length x 5m width x 4m working depth. Aeration is provided to the tanks using a fine bubble diffused aeration system designed to achieve an overall peak standard oxygen transfer rate of 66.15 kgO2/h (i.e. 33kg O2/h per cell).

The aeration system comprised three screw blowers from Kaeser Kompressoren operating on a duty/duty/standby basis, with automatic changeover of the standby blower on a time-basis; ensuring equal use of the equipment. Air from the blowers is forwarded to each aeration cell by an air header, which feeds individual branches into the aerobic cells. The diffusers are disc membrane units from Xylem Water Solutions.

Tertiary solids removal systems

Following settlement, secondary treated effluent is passed onto a tertiary solids removal treatment stage for final effluent polishing prior to discharge to the Brogeen River. The TSR process was required in order to ensure compliance with the WwDL ELVs, and in particular with the phosphorus ELV of 0.25mg/l, through coagulation/flocculation and filtration treatment.

[caption id="attachment_16528" align="alignnone" width="1200"] Cloth filter tertiary treatment - Courtesy of Glanua[/caption]

During the design stage and evaluation of the ECI team, the supplier Eliquo Hydrok was found to have the most reliable, energy and cost-efficient equipment that includes both flocculation and filtering stage. The package unit includes a flocculation stage comprised of one stream with two chambers that split into the cloth filters.

Sludge drying reed beds

The implementation of sludge drying reed beds (SDRB), which significantly increases sludge concentration to up to 40% dry solids (DS) after 10 years of operation is a key innovation. This revolutionary approach reduces sludge export volumes by more than tenfold compared to conventional methods, thereby minimising transportation and dewatering costs while substantially reducing the carbon footprint of the Boherbue WwTP. SDRB sludge can also be directly land spread without the need for additional chemical conditioning, further enhancing its environmental benefits.

There are numerous benefits in the inclusion of the sludge drying reed beds vs traditional sludge management practices. These include but are not limited to the following:

Reduction of carbon footprint of the plant by approximately 45 T over a 10-year period. Carbon capture via natural plant growth. Up to 25% organic matter removal due to mineralisation. Dewatering process completed with zero energy consumption. At full design loads, the SDRBs will remove over 49 (No.) 20,000 litre tankers from the road per annum. [caption id="attachment_16533" align="alignnone" width="1200"] Sludge drying reed beds to process wastewater sludge naturally - Courtesy of Glanua[/caption]

The construction of the sludge drying reed beds (SDRBs) commenced in early February 2023, incorporating earth embankments and precast concrete wall sections for formation. Each cell was meticulously lined to ensure water-tightness, with feed and drainage pipework installed for optimal functionality. Reeds were planted in late April to establish and grow during the summer months, aided by the importation of sludge to promote growth. This comprehensive approach ensures the effectiveness and sustainability of the SDRBs in treating wastewater and reducing the carbon footprint of the Boherbue WwTP.

Solar technology

The use of solar technology underscores the project’s commitment to renewable energy sources, contributing to further reductions in carbon emissions. By leveraging these innovative technologies and practices, the initiative sets a new standard for sustainable wastewater treatment, offering a replicable model for other treatment plants to follow. This holistic approach not only improves operational efficiency but also promotes environmental stewardship, paving the way for a cleaner and more sustainable future in the wastewater sector.

50Kw solar panels from The Low Carbon Energy Company Ltd have been installed which will produce 42,500Kwh of electricity per year. This alone will introduce a carbon saving of 13.7T/CO2 per year which shows significant savings versus a traditionally built wastewater treatment plant of this kind.

[caption id="attachment_16532" align="alignnone" width="1200"] Solar panels for clean, renewable energy - Courtesy of Glanua[/caption] Reuse of constructed wetlands

The integration of the existing constructed wetlands into the wastewater treatment facility which was core to the design development brought a multitude of benefits, ranging from low operational costs, support for diverse ecosystems as well as sustainable water management. The wetlands improve water quality of streams and rivers in surrounding area creating conditions for aquatic life to thrive, and also create a scenic area in the village, promoting biodiversity and providing a habitat for small animals.

Boherbue WwTP: Supply chain - key participants Precast concrete: Glanua Group Designers: Jennings O’Donovan & Partners Designers: Construct Engineering Precast concrete: Shay Murtagh Precast Precast concrete: Carlow Tanks Precast concrete: FLI Precast Solutions Precast concrete: Tracey Concrete PLCs & automation: UMAC Systems Inlet screens: Definitive Ecology Tertiary solids removal cloth filters: Eliquo Hydrok Ltd Aeration blowers: Kaeser Kompressoren Aeration diffusers: Xylem Water Solutions Solar panels: The Low Carbon Energy Company Ltd CWF Storm Flush system: Eliquo Hydrok Ltd Steel modular buildings: Shanette [caption id="attachment_16530" align="alignnone" width="1200"] (left) Precast concrete aeration tanks reduced construction time and safety risks and (right) view of final clarifiers and cloth filters - Courtesy of Glanua[/caption] Innovative construction methods

Throughout the entire design process, Glanua Group and Uisce Éireann’s PMO team evaluated several project aspects such as energy efficiency (BEP), TOTEX costs, and environmental impact.

Energy efficiency of all motors and equipment (BEP). Process and equipment selected on TOTEX costs (including CAPEX, OPEX and capital replacement at end of life). The impact to the local environment was carefully assessed for all design options considered during the planning phase. Modular and off-site construction

Modular/off-site construction was used to reduce the carbon footprint and on-site safety risks, with precast panels and BCAR-compliant steel modular buildings used to promote efficient delivery and enhance safety.

Precast panels were instrumental in constructing the main aeration tank, reducing construction time and mitigating safety risks compared to traditional in situ methods. Precast wall sections were used to separate the sludge drying reed beds sections to reduce the footprint size and again to reduce construction time and safety risks. Throughout the project, precast process tanks were used extensively contributing to streamlined construction processes and improved safety measures.

A BCAR-compliant steel modular building from Shanette was used for the control room, laboratory, and caretaker’s office facilities. This has a significantly lower carbon footprint than that of a conventional block-built structure and in turn reduced health and safety risks significantly during construction due to fabrication being completed before assembly on site.

[caption id="attachment_16529" align="alignnone" width="1200"] Off-site fabrication of steel building, fully assembled as works have been completed (April 2024) - Courtesy of Glanua[/caption] Sustainability

The construction of the Boherbue Wastewater Treatment Plant is an example of Uisce Éireann and Glanua Group’s commitment to sustainability across various dimensions, including environmental, social, and economic considerations.

The inclusion of sludge drying reed beds demonstrates dedication to environmental sustainability. These beds offer an innovative solution for sludge management, reducing the environmental impact of waste disposal while also providing opportunities for ecological conservation.

By using nature-based solutions to treat and manage sludge, the carbon footprint associated with traditional disposal methods is minimised; thereby mitigating environmental harm. The SDRBs also significantly reduces operational costs, providing a long-term cost-effective solution.

The integration of solar technology underscores the commitment to renewable energy and carbon reduction. By harnessing solar power to supplement the energy needs of the wastewater treatment plant, reliance on fossil fuels is reduced, contributing to the transition towards a more sustainable energy future. This not only reduces operational costs but also mitigates greenhouse gas emissions, thereby supporting climate action efforts and environmental preservation.

Socially, the decision to reuse the existing wetlands demonstrates dedication to maintaining and sustaining biodiversity in the Boherbue community. By incorporating natural elements into the design, not only is disruption to local ecosystems minimised, but also to the overall health and vitality of the local environment.

Darran O’Leary, Programme Manager at Uisce Éireann said:

“We are delighted to have delivered this important project for the community of Boherbue. The modernisation and improvement of the wastewater infrastructure will accommodate further growth in the area and ensure that cleaner and safer treated wastewater is being discharged into the Brogeen River.

“It also adds biodiversity value to the area and remains sensitive to the surrounding landscape. This, coupled with the use of solar energy, demonstrates our commitment to putting sustainability at the heart of everything we do”.

Boherbue WwTP upgrade works is a flagship project for sustainable and carbon saving treatment processes and will serve as a reference project for future similar projects within the industry.

By demonstrating the feasibility and benefits of integrating renewable energy, advanced treatment technologies, and ecological conservation practices, this project sets a precedent for industry-wide innovation and best practices.

It complies with stringent Environmental Protection Agency (EPA) discharge consent standards, while minimising impact on the existing landscape, demonstrates a commitment to environmental sustainability, operational efficiency, and community well-being, making it a catalyst for positive change within the wastewater treatment sector and beyond.

Southern Water are investing £31m to upgrade Horsham New Wastewater Treatment Works (WwTW) in West Sussex, which will improve the site’s treatment processes and capacity, and boost the quality of the final effluent returning to the River Arun, thanks to a range of new hi-tech machinery, control and monitoring systems, as well as the replacement and refurbishment of existing equipment. The major upgrade started on site in September 2022 and is being delivered by CMDP JV, a joint venture between Costain and MWH Treatment. Completion of the works is expected in spring 2025. Drivers

The capital scheme at Southern Water’s Horsham New WwTW will deliver an upgrade to the treatment facilities at the site to cater for the significant growth forecast within the Horsham catchment and surrounding areas over the next ten years, together with an improvement in the Total Phosphate final effluent emission standard, tightening from 1 mg/l to 0.25 mg/l.

These improvements to the site’s treatment processes have been designed for a 2035 population equivalent of 93,345, representing a 15% increase since 2020. There are no proposed increases to the permitted dry weather flow or permitted flow to full treatment as part of the scheme.

As well as the WFD quality driver, the project also encompasses an element of capital maintenance to be delivered by 31 March 2025, as follows:

Replacement of two existing band screens with two new fine screens, located within the existing inlet chamber and configured as duty/assist. Each screen is rated at 1,700 l/s. Provide duty/standby screenings handling equipment (SHE) and a common launder channel. Provide a new centrifugal pump with a duty of 640 l/s to assist the two existing storm screw pumps. Replace the screw pumps within the existing works, with two new screw pumps, each rated at 640 l/s. Replace the two diesel engines and gearboxes with electric motors.

The third and final project driver, also to be delivered by 31 March 2025, is the need to ensure the upgraded Horsham New WwTW has sufficient hydraulic and process treatment capacity to allow for the 15.5% increase in expected growth in the local population up to 2035.

[caption id="attachment_14167" align="alignnone" width="1200"] New inlet screens supplied by Hydro International UK Wastewater Services division - Courtesy of CMDP JV[/caption] Project scope for the Quality Driver

Ferric dosing

80m3 bulk storage facility comprising two 40m3 tanks in common bund. 3-point dosing facility. POA1Fe downstream of inlet flume. POA2Fe at two humus tank distribution chambers. POA3Fe at sand filter feed pumping station.

Alkalinity dosing

80m3 bulk storage facility comprising two 40m3 tanks in common bund. 2-point dosing facility. POA1alk filter distribution chamber. POA2alk humus tank outlet.

Tertiary Treatment

Extend deep-bed sand filters by provision of additional three cells. Media top up of existing five cells. [caption id="attachment_14157" align="alignnone" width="1200"] The existing deep bed sand filter is being extended with three additional cells to enhance the tertiary treatment process - Courtesy of CMDP JV[/caption] Project scope for the Capital Maintenance Driver

Inlet screens

Replace inlet screens and screenings handling plant with larger capacity plant. Remove need for screenings conveyors by discharging directly to launder channel to feed screenings handling plant.

Storm pumping

Replace two storm screw pumps (duty/assist). Convert pumps from diesel drives to electric drives. Provide an additional centrifugal storm pump to supplement screw pumps. Pumps to be configured duty/assist/assist. Project scope for the Growth Driver

Re-configurate secondary treatment stage

Convert the 2-stage biological filter process to single pass carbonaceous process.

New Moving Bed Biofilm Reactor (MBBR) nitrification process stage

MBBR nitrification process stage comprising two GCS reactors, process media, process air system and associated infrastructure. Upgrade the ADF pumping station to intermediate/MBBR feed pumping station. [caption id="attachment_14154" align="alignnone" width="1200"] The two new Moving Bed Biofilm Reactors (MBBR) to remove ammonia from the final effluent returning to the River Arun - Courtesy of CMDP JV[/caption]

Upgrade site HV infrastructure

New DNO incoming supply including two RMUs. New high voltage assemblies (HVA1 & HVA2). New transformers (TX1 & TX2) from Wilson Power Solutions Ltd and replacement of HV cable from mains incomer to TX2.

Upgrade site standby power infrastructure

New 1250KVA standby generator to serve the inlet works and sludge treatment areas. New 500KVA standby generator to serve the MBBR and tertiary treatment areas.

Site SCADA & telemetry upgrade

Sludge treatment

New dry solids sludge centrifuges and associated infrastructure. New ‘big bag’ polymer storage, make-up and dosing plant to serve centrifuges. Partial demolition of cake-bay building. Retain existing cake pump and sealed container facilities. Replace the odour control unit’s (OCU) motor control centre (MCC) with new combined LVA to facilitate location of new centrifuges. Make existing dewatering plant with sludge building redundant and make safe. [caption id="attachment_14152" align="alignnone" width="1200"] DN900 outlet pipework installed on one of the newly constructed MBBRs - Courtesy of CMDP JV[/caption] Horsham New WwTW: Supply chain - key participants Client: Southern Water Design & main contractor: CMDP JV Costain MWH Treatment Confined space rescue services: Rescue 2 Utilities Division Deep excavation & trench work: Rochester Utilities Ltd Formwork, reinforcement & concreting: McHugh Concrete Demolition contractor: John F Hunt Group Drilling & linestopping: Swan Pipelines Electrical installation: Field Systems Design Ltd Mechanical installation: R&B Engineering Ltd Inlet screens & screenings handling plant: M&N Electrical & Mechanical (Hydro International Ltd's UK Wastewater Services Division) Moving bed biofilm reactors: Veolia Water Technologies MBBR blowers: Aerzen Machines Tertiary treatment plant: De Nora Water Technologies UK Chemical dosing plant: Bridges Electrical Engineers Ltd Polymer dosing plant: Richard Alan Engineering Centrifuges: GEA High voltage engineering works: Powersystems UK Ltd LV & HV switchgear services: Max Wright Ltd Transformer manufacturer: Wilson Power Solutions Ltd Critical power specialists: P&I Generators Ltd Progressive cavity pumps: NOV - Mono Pumps Submersible pumps: Xylem Water Solutions Flow controls: AFFCO Flow Control (UK) Ltd Below-ground DI pipework: Saint Gobain PAM UK Construction labour services: Hercules Site Services Construction labour services: NBC Group Replacement inlet screens

The replacement of the existing 40 year old inlet screens was always going to be a significant milestone for the project and a very challenging operation. Before the new screens could be installed, which are needed to remove a vast amount of solid matter from the treatment process, the existing inlet channels were widened in places using a wire saw to provide additional room for the inclined toe of the new screens. The existing screens were electronically isolated and disconnected, along with an existing spiral conveyor, before being mechanically disconnected and removed.

This complex activity required specialist support from supply chain partners John F Hunt, FSD and R&B Engineering, to ensure a safe and successful operation.

[caption id="attachment_14155" align="alignnone" width="1200"] (left) One of the two existing inlet screens being removed, (middle) one of the new 12.8m long Alpha Beta Escalator Screens being lifted carefully into place, and (right) the new inlet screens installed - Courtesy of CMDP JV[/caption]

Manufactured by FSM Frankenburger in Germany on behalf of M&N Electrical & Mechanical (Hydro International Ltd’s UK Wastewater Services division), the new state of the art inlet screens measure 12.8m in length and are among the largest Alpha Beta Escalator Screens not only in the UK, but in Europe. Accordingly, their installation required close collaboration between CMDP JV, Southern Water and all relevant supply chain partners.

With just over 10mm tolerance on either side, the new screens were successfully slotted into position within their concrete inlet channels. Pipework and cabling were installed before commissioning was completed.

Deep bed sand filter extension

As part of the project scope for the WFD quality driver, the tertiary treatment process has been enhanced by extending the existing deep bed sand filter. This has involved the construction of three extra cells, to complement the four cells already in situ.

Due to the ground conditions in this area of the site, piling was required to ensure the structural validity of the new cells, with a significant amount of temporary works required. At the time of writing (July 2024), the internal pipework has been completed and walkway platforms are in the process of being installed, with external pipework scheduled for completion at a later date.

Moving bed biofilm reactors (MBBR)

The addition of a new moving bed biofilm reactor (MBBR) nitrification process stage to the treatment process is a key element of the project, with the installation of two new reactors undertaken by Veolia Water Technologies. As part of the scope for the project’s growth driver, the new MBBR process introduces fixed film controllable biological treatment to the works’ capabilities.

Prior to the installation of the new MBBR reactors, a substantial amount of piling was required to ensure the stability of the ground in the area where they are now situated. Work is now underway to install the underground feed pipe that will serve the new reactors.

[caption id="attachment_14158" align="alignnone" width="1200"] Inside one of the new MBBRs as its installation approached completion - Courtesy of CMDP JV[/caption] Alkalinity dosing

The scope for the project’s quality driver includes an enhancement to the works’ alkalinity dosing capability, with a new 80m3 bulk storage facility comprising of two 40m3 tanks in a common bund and two-point dosing facility at the carbonaceous filter’s distribution chamber and the humus tanks effluent chamber. This element of the project was led by MEICA specialist Bridges Ltd.

When the new tanks were being installed at the bottom of a sloped area of the site, concerns emerged around the stability of this a bank in the immediate vicinity. As a result, a decision was taken to sheet pile the bank, thus ensuring its stability.

The base of the area housing the new dosing equipment was also piled, prior to a concrete slab being poured. The existing dosing capability will remain in operation until the upgrade goes live, at which point it will be decommissioned.

Self-delivery success

A ‘self-delivery’ approach to construction was adopted, with CMDP JV directly contracting the various specialist sub-contractors required to deliver the project.

Through careful management by the site team, this approach has resulted in significant cost savings, through a reduction in the amount of non-productive time spent on site by the supply chain. This has been particularly beneficial due to the number of unchartered services unearthed on site that would have otherwise resulted in time delays.

A self-delivery approach has also allowed further savings through the avoidance of mark-up of goods and services that would have been imposed had CMDP handed control of management of the wider supply chain to a third party. This has also allowed CMDP to prioritise the use of local suppliers wherever possible.

[caption id="attachment_14163" align="alignnone" width="1200"] Setting out for piling works in alkalinity dosing area with sheet piling in place for bank stability - Courtesy of CMDP JV[/caption] Health & Safety

A significant challenge throughout the lifespan of the project has been the excess of buried and unchartered services on site. To control the high risks of excavation works, since the start of construction CMDP JV has issued a total of 182 “permits to dig”, with no service strikes recorded at the time of writing.

Another significant health and safety challenge faced by the project has been the fact that Horsham New WwTW serves as a Sussex area hub for four other Southern Water “Tier One” suppliers, resulting in a large amount of vehicle traffic on a constrained site.

Recognising that, proactive communication with all internal stakeholders has paid dividends, reducing delays to the project and disruption to other users of the site.

Environment

The project involves a combination of environmental mitigation and improvement, with landscaping and habitat enhancements on-site ensuring an overall 9% gain in biodiversity within the boundaries of the works.

To minimise any detrimental noise impact resulting from the operation of the upgraded works, the three blowers from Aerzen Machines that form part of the new MBBRs will have acoustic barriers installed. These barriers will ensure that any noise from the blowers, which form part of the process air system, will not impact the residential properties located closest to the works.

An opportunity to further minimise the environmental impact of the project has been possible through the use of local suppliers, as detailed further in the ‘Social Value’ section below.

[caption id="attachment_14153" align="alignnone" width="1200"] The new MBBR blowers are fitted with acoustic barriers to minimise any possible impact on nearby residential properties - Courtesy of CMDP JV[/caption] Award-winning site team

In line with the commitment shared by both Southern Water and CMDP to ensure a positive impact upon the communities they operate within, the efforts of the site team at Horsham New WwTW were recognised with a national award.

The Considerate Constructors Scheme (CCS) National Site Awards are one of the most prestigious accolades in the sector, highlighting those sites that have made the greatest contribution towards improving the image of construction. At a ceremony held in London, CMDP JV Construction Manager Garry Burgess was presented with a Bronze Award to recognise the efforts of the Horsham New team in terms of creating value in the local community and being respectful to the public, the workforce and the environment.

A customer-centric approach and focus on protecting and improving the environment has proved very successful for this project, with the site team achieving a top score of 45/45 (ranked as excellent) for three consecutive assessment visits.

Social value

With very few homes or businesses in the immediate vicinity of the works, the construction phase of the project has had negligible impact on the local community.

However, with the importance of ‘Social Value’ growing rapidly within the water industry, and Southern Water aspiring with the help and support of CMDP JV to improve the communities in which it operates, the project team partnered with Horsham District Council’s voluntary sector support team.

This has led to project staff regularly taking time away from the scheme to support local organisations in need of volunteers to help worthy causes in and around the town; ensuring the project delivers a long-term positive impact on the local community and wider area.

This approach has helped to make the project an exemplar for both companies in terms of the creation of long-term social value and furthers Southern Water goal of being a local company that cares.

[caption id="attachment_14159" align="alignnone" width="1200"] (left) Garry Burgess, CMDP Construction Manager, receiving the award for the efforts of the Horsham New WwTW team and (right) CMDP JV and Southern Water staff pictured volunteering to support local charity, Ten Little Toes - Courtesy of CMDP JV[/caption]

As well as partnering, efforts have been prioritised in areas where a genuine need exists within the local community, and where the project team could employ their skills most effectively. The Social Value portal’s ‘Themes, Outcomes, Measures (TOM)’ system was used to measure and report the value of the wealth of social value activity undertaken by the project team, which includes:

£2.4m spent on equipment and services with businesses within a 20-mile radius of the site, including £100,000 spent with businesses located within five miles of the works. This has helped to reduce the project’s carbon footprint and sustain the local economy. Joint collection for a local charity supporting families and parents in crisis and/or facing difficult circumstances throughout West Sussex. 49 staff hours dedicated to local school and college visits. 65 weeks of apprenticeships spent on the project. Over 100 hours spent by project staff volunteering to support local community projects. In total, the project has made over £3,000 worth of donations and in-kind contributions to local community projects.

Use of the ‘Themes, Outcomes, Measures’ system allows the project team to track success and ensure momentum, which in term will help to set a benchmark for the social value element of future projects.

With strong relationships established with a wide range of local organisations and key stakeholders, the figures listed above will continue to grow as the project progresses towards its scheduled completion in 2025.

Conclusion

The complex upgrade of Horsham New WwTW involved the installation of a range of new hi-tech machinery; including two of the largest Alpha Beta Escalator Inlet Screens in Europe.

CMDP JV’s self-delivery approach has provided added flexibility and numerous benefits, and a keen focus on social value will ensure a long-lasting positive impact beyond the scope of the project itself.

Once complete, the upgraded works will be equipped to cater for the significant growth forecast within the Horsham catchment and surrounding areas over the next ten years. It will increase the quality of the treated water being returned to the River Arun and ensure Southern Water fulfils its regulatory requirements.

Ballygowan is a small village situated in County Down, within the Ards & North Down Borough Council area. The towns of Comber and Saintfield are both approximately 4 miles to the north-east, and to the south respectively, with the city of Belfast 7 miles north-west. The 2021 Census indicates that the population of Ballygowan is approximately 3,138. The existing WwTW was constructed in the village in the 1950s and comprised an inlet works, a CAS basin, a storm tank and a small sludge holding tank, as well as an MCC building to control the works and was designed to treat a population equivalent (PE) of 2,700. The existing works was therefore beyond capacity to treat the present day population, and the structures had exceeded their design life. An extensive upgrade was required to provide effective and robust wastewater treatment services for the future catchment area, allowing economic growth, while improving the local environment and adhering to a much tighter discharge consent of 7mg/l BOD, 10mg/l total suspended solids, and 1.5mg/l ammonia. The new fully automated works will serve a PE of 4,513. Primary drivers for the upgrade The existing wastewater treatment works (WwTW) was undersized for the current flows coming into the works. The existing works was not complaint with the Northern Ireland Environment Agency’s discharge consent standard for Ballygowan WwTW. Future planning applications for residential properties in the Ballygowan area had been put on hold due to the existing WwTW operating beyond its intended design capacity. The existing works was not capable of fulfilling the requirements of NI Water’s long-term strategy to enhance wastewater services and ensure environmental compliance and was expensive to operate and maintain. An even tighter NIEA standard was imminent. [caption id="" align="alignnone" width="1200"] (left) Existing Ballygowan WwTW - Courtesy of NI Water and (right) demolition in progress: (top) the existing storm tank and (bottom) the existing CAS basin tank - Courtesy of  GEDA Construction[/caption] Project description & scope Designed for a 2045 population equivalent of 4,500, the new Combined Activated Sludge Plant (CASP) at Ballygowan WwTW, was to be constructed east of Dickson Park in Ballygowan, in a green field site that bordered the southern boundary of the existing site: The preliminary treatment process comprising of 6mm inlet screening and forward flow-control equivalent to Formula ‘A’. A new storm storage management facility including a CSO storage tank, and two storm tanks providing a total capacity of 224m3. The CSO storage tank and two storm tanks are equipped with a tipping bucket system for effective cleaning of the storm tank floor. Flows equivalent to Full Flow to Treatment (FFT) are pumped forward via a new interstage pumping station. FFT is then split with equal flows going to two CAS basin tanks. The selector chamber was carefully designed to assist with controlling filamentous bulking in activated sludge systems which can be a common operational challenge issue in activated sludge plants. Downsteam of the flow split chamber, there are two CAS tanks complete with final settlement tanks (FSTs) accommodated centrally, each aeration stream comprising of an anoxic zone to aid denitrification, and three individual aeration zones equipped with tapered aeration diffuser grids. The design and construction of the biological treatment process on this site was critical and to ensure compliance with an extremely stringent discharge consent of 1 mg/l ammonia alkaline was dosed at this stage in the process, detailed below. Due to the restricted footprint available for the site, the CAS tanks were selected to accommodate the final settlement stage within the biological treatment footprint. Two FSTs were constructed, with the CAS (anoxic and aeration zones) wrapped around the FSTs. [caption id="" align="alignnone" width="1200"] CAS basins  - Courtesy of NI Water[/caption] Following final settlement, the treated effluent gravitates to a tertiary treatment plant for further solids removal prior to discharge at the final effluent outfall location. A new combined RAS/SAS pumping station was constructed adjacent to the selector/flow split chamber to aid best use of available footprint. This pumping station houses two RAS pumps to replenish the bacteria within the biological treatment system and maintain the required MLSS levels for effective treatment. A further two SAS pumps are also provided to pump away sludge to the new sludge storage facilities should the MLSS levels within the treatment process exceed the desired levels. The new Ballygowan WwTW includes two sludge storage tanks, one mechanical sludge thickener and a polymer chemical dosing plant for processing sludge prior to being tankered offsite. To ensure a robust solution was provided for the client to meet the 1 mg/l ammonia consent, a supplementary alkalinity chemical dosing plant was provided for dosing into the aeration lanes. The provision of this dosing plant which utilises sodium carbonate ensures there is sufficient alkalinity available within the biological treatment process for effective and complete nitrification under all flow and load conditions. The works also comprises a new MCC room which controls all mechanical and electrical plant equipment and instrumentation, a welfare unit, a standby backup generator, and associated access and drainage. As the treatment works was built in close proximity to a neighbouring residential area, the odour model highlighted areas of the treatment process that required covers with passive odour abatement being provided. The site was also landscaped to include a site bund to reduce the visual impact on the neighbouring residential area of Dickson Park. [caption id="" align="alignnone" width="1200"] New storm tank being utilised during construction - Courtesy of GEDA Construction[/caption] Main challenges for design/construction Discharge consent The key challenge around the design and construction of the new Ballygowan WwTW, was ensuring that the new WwTW would comply with a very tight water order consent (WOC) set by NIEA. The WOC is one of the tightest consents in Northern Ireland. The discharge consent was originally advised as 7:10:1.5 mg/L (BOD/TSS/ammonia), however the design and construction was further challenged when NIEA confirmed that the ammonia consent would be restricted to 1mg/l ammonia. GEDA Construction, in conjunction with their MEICA and process subcontractor Water Solutions Ireland Ltd, reviewed the design and construction proposal to provide a solution which incorporated minimal changes, minimising costs to NI Water, but still providing effluent treatment compliance. Site location The WwTW site is bordered by agricultural land to the north and east, and has a housing development to the west. To construct the new WwTW and keep the existing plant operational, NI Water purchased an area of land (formerly a football pitch) to the south of the site belonging to the local council. The existing WwTW access road is through Dickson Park housing estate and runs directly alongside a children’s playpark. In advance of construction the project team took the proactive decision to look at creating a temporary construction access to the south of the site through agricultural land so that all construction traffic would not have to travel near Dickson Park or the children’s playpark. Extensive consultation took place with local landowners, the residents’ association and roads authority and the temporary road was successfully constructed ahead of construction start. Due to the close proximity of the new WwTW to the housing development, consideration was also given to any potential visual and odour implications to the neighbouring housing development. It was decided at an early stage to design the structures in such a way that they would have minimal visual impact. This meant designing and constructing structures as low in the ground as possible to keep them out of view of the neighbouring properties. An earth bund was also constructed to the west boundary of the site and planted with trees/bushes and shrubs in order to further hide the treatment works as well as helping to combat any odours coming from the site. [caption id="" align="alignnone" width="1200"] Ballygowan WwTW under construction (December 2021) - Courtesy of NI Water[/caption] Interface between new and old works during construction The majority of the new WwTW works was to be built on a greenfield site which allowed GEDA Construction to build most of the new structures without having to work around existing infrastructure. However, in order to construct pipelines which would eventually take the flow into the new works, and to construct the new WwTW access road, it was necessary to demolish the existing storm tank in the old works prior to the new works becoming live. GEDA Construction carried these works out by utilising the newly-constructed storm tank and incorporating a carefully developed phasing plan. A temporary 300mm gravity fed sewer was laid from the existing inlet works to the new storm tank, which in turn rendered the existing storm tank surplus to requirements, as all storm flows had been diverted away from it. GEDA Construction also had to lay a temporary 200mm pumped sewer from the new storm tank complete with temporary pumps to send the storm flows back to the existing pumping station in order for the influent to then go through the treatment process. This in turn allowed us to demolish the existing storm tank and construct the new permanent inlet sewers to the new works ahead of turning flows. This process had to be carefully managed both hydraulically and biologically to ensure the treatment process was optimised and effluent compliance was maintained at all times. [caption id="" align="alignnone" width="1200"] New permanent high-level sewer under construction - Courtesy of GEDA Construction[/caption] Turn of flows Influent flows were successfully diverted into the new works in early May 2022. In order to bring the new biological treatment process online, several tanker loads of seeded sludge were brought to site from another treatment facility and were introduced into the new CAS basin tanks to promote bacteria growth. With flows diverted, and effective treatment established through a rigorous sampling regime, approval was received from NI Water to proceed with the demolition of the remainder of the existing treatment works. Once the existing works were decommissioned and demolished, the entire new WwTW site was able to be finished and access roads completed. Demolition Post turn of flows in early May 2022, the existing treatment works was decommissioned and then demolished. Reusable mechanical and electrical assets from the old treatment process were removed for future use by NI Water, while the effluent left in the old CAS basin and pumping station was removed from the site to allow demolition to commence. Effluent was filtered through the new treatment process to minimise unnecessary removal and disposal from site. Project team As principal contractor, GEDA Construction had overall responsibility to deliver the project on time and within budget, which they succeeded in doing by working collaboratively with NI Water, project managers Tetra Tech, key suppliers and subcontractors to identify and plan for key project milestones. McAdam provided civil, structural and geotechnical design services, including the initial enabling and investigatory works carried out at the Early Contractor Involvement (ECI) stage, as well as the detailed design for construction. Water Solutions Ireland (WSI) were responsible for designing and delivering a full turnkey MEICA, process design and build solution for the new works. Ballygowan WwTW: Supply chain - key participants Civil contractor: GEDA Construction Project managers: Tetra Tech MEICA contractor: Water Solutions Ireland Civil, structural & geotechnical design: McAdam Electrical design: SBE Design Mechanical design: McWall Drawing & Design PLC software & commissioning: Ashdale Engineering Odour control: Anua Clean Air UK Storm screens: Eliquo Hydrok Ltd Grit removal plant: Jacopa 6mm inlet screening: Hydro International (M and N Electrical and Mechanical Services) Aeration blowers: Aerzen Machines MCC: Greenville IDC Pumps, mixers, fine bubble diffusers: Xylem Water Solutions Tertiary treatment plant: WPL Chemical dosing: Richard Alan Engineering Instrumentation: Park Electrical Systems Flow measurement: Siris Environmental Ltd Flow measurement: AMPM Flow & Energy Services Ltd Penstocks, valves & actuators: Flow Technology Services Storm tank cleaning tipping bucket: CSO Group Ltd GRP kiosks, FST scrapers & site-wide metalwork: Victoria Engineering 6mm bar screen, skip rails & trolleys: Graham Steelwork Engineering Potable & FE service water boosters: Dutypoint Ltd Lifting equipment: Columbus McKinnon Co Ltd Solar panels & EV charger: Solmatix Renewables Ltd [caption id="" align="alignnone" width="1200"] CAS basins in operation - Courtesy of NI Water[/caption] Solar It was recognised that a large area of land within the footprint of the existing WwTW site would be available for use following demolition of old structures. As a result, NI Water asked GEDA Construction and Water Solutions Ireland to investigate the feasibility of installing solar energy within the space available. Following a successful outcome of the feasibility study, it recommended that a 62Kw solar PV array would be installed in the free space which would provide renewable energy to run some of the WwTW operations and boost the sustainability of the site. A 22KW dual EV charger unit was also installed which is used by NI Water’s growing fleet of electric vans. Solmatix Renewables Ltd installed a ground-mounted solar PV panel system consisting of 164 solar panels within the footprint of the old works. New electrical invertors and controls housed within the new MCC kiosk were installed and cabled directly onto the new MCC. The solar system has been set up as zero export, meaning everything that is being generated on site, is used on site through the plant and other electrical equipment. The estimated payback period on NI Water’s £70k investment is 6.5 years (savings of £11,000/year on electricity costs at Ballygowan WwTW). [caption id="" align="alignnone" width="1200"] Solmatix Renewables Ltd solar farm - Courtesy of NI Water[/caption] Alkalinity A challenging issue encountered during the design and construction of the new works at Ballygowan WwTW was the high acidic nature of the incoming influent. During review of the design and aided by a sampling regime of the influent under varying flow conditions, it was determined the site required alkalinity dosing to allow the wastewater treatment process to provide adequate nitrification (in other words ammonia reduction) within the biological treatment to meet the 1mg/l ammonia discharge consent. This problem required NI Water and GEDA Construction to design, supply, install and commission a supplementary packaged chemical dosing system to increase the alkalinity levels and achieve a stable pH within the wastewater to safeguard optimum treatment. NI Water shared some past negative experiences encountered with similar alkalinity dosing plants which was invaluable to ensure that a well thought out, comprehensive solution was selected, which would deliver the requirements of supplementary dosing but reduce the ongoing operation and maintenance requirements encountered on other schemes for NI Water. The agreed solution was to provide a new proprietary sodium carbonate (powder) make up and dosing system, all housed within its own GRP kiosk and standalone control panel. Odour control Due to the proximity of nearby residential housing, the design and execution of odour containment and treatment was a major consideration for this project. Early odour models and specialist supplier engagement was imperative to ascertain the potential effects of odours. GEDA Construction provided a cost-effective, proven solution through a carbon filter plant dedicated for the inlet screening and grit removal works, and a second Mónashell Biofilter plant from Anua Clean Air UK was provided solely for the sludge treatment and storage tanks. Both systems, along with covering large areas of the works with solid top flooring, safeguard against the negative effect odours can cause. [caption id="" align="alignnone" width="1200"] Ballygowan WwTW nearing completion - Courtesy of NI Water[/caption] Collaboration and PR Collaboration was instilled throughout every aspect of the planning, design and construction phases for the new Ballygowan WwTW. NI Water and its project management team developed a proactive communication and PR strategy for project which included erection of storyboards; circulation of project brochure; issuing of regular updates to residents; briefings for elected representatives; circulation of press releases and a number of events and initiatives with the local residents’ association. A collaboration initiated with the local council also saw the creation of a small orchard by local children on an area of disused council land adjacent to the WwTW, which GEDA prepared for planting out. Outcome By working in partnership with each other, as well as myriad stakeholders, NI Water, Tetra Tech, GEDA Construction and the wider supply chain were able to successfully overcome difficult challenges to deliver a sustainable, state-of-the-art wastewater treatment solution, capable of meeting its stringent consent standard and serving the community for many years to come.