Supply Chain - Treatment Process Technologies - Submerged Aerated Filter

Yorkshire Water’s Pocklington Sewage Treatment Works is located in the East Riding of Yorkshire. The site processes wastewater from the local catchment to safely return it to the environment, discharging treated effluent into the nearby Pocklington Beck. Yorkshire Water has delivered a £7.3m project to reduce the levels of phosphorus present in the treated wastewater returned to the environment and improve the water quality of more than 2km of the river downstream of the treatment works. Project drivers

The AMP 7 WINEP drivers for Pocklington STW include a reduction in phosphorus and iron by December 2024 and a UIMP6 storm storage capacity increase by March 2025. The revised Environmental Agency Permits were:

Parameter Existing Value New Value Total P (annual average) 1 mg/l 0.25 mg/l Iron (95%ile) N/A 4 mg/l Iron (upper tier) N/A 8 mg/l UIMP6 storm capacity 658m3 766m3 Existing works

The existing works comprise a screened inlet arrangement incorporating grit removal and screenings handling, with flows conveyed by gravity to a storm overflow weir chamber. Under normal operation, the main flow passes to the primary settlement tank (PST) distribution chamber and is treated across three primary settlement tanks. Subsequent treatment proceeds through four trickling filters before discharge to the humus sludge handling system via a screw feed, and onward to dual humus tanks for secondary clarification. From here, clarified effluent is directed to a high-lift pumping station, which transfers flows to the tertiary nitrifying sand filter for final polishing. The treated effluent then passes through a sampling chamber prior to discharge to the receiving watercourse.

[caption id="attachment_31381" align="alignnone" width="1200"] Inlet works - Courtesy of Enpure Ltd[/caption] Scope of works

The objective of the project was to achieve compliance with tightened phosphorus discharge consent in the final effluent, without breaching the revised total iron limits.

To meet these requirements, a comprehensive programme of process, mechanical, electrical, and civil upgrades was undertaken across the site, including the following key elements:

Chemical dosing

The existing chemical dosing kiosk was replaced with a new primary and secondary stage chemical storage and dosing system. This comprised twin internal storage tanks with a combined capacity of 20m³, together with duty/standby dosing pumps configured for automatic changeover. The installation included primary and secondary dosing lines with defined points of application, as well as associated safety infrastructure, including a safety shower.

Nitrifying sand filters

Refurbishment of the tertiary nitrifying sand filter (TNSF) system was carried out, including replacement of the process air compressors and decommissioning of the redundant process air blowers. The works also incorporated a new backwash pipeline and drainage chamber arrangement, complete with flow measurement, together with the provision of an additional washwater connection and hydrant.

High lift pumping station

Upgrades to the high-lift pumping station included the installation of new pumps and associated pipework, along with servicing and refurbishment of the existing bollfilter to ensure reliable downstream flow transfer to the tertiary treatment stage.

[caption id="attachment_31383" align="alignnone" width="1200"] Overview of storm tanks and chemical dosing plant - Courtesy of Enpure Ltd[/caption]

Storm capacity

The site’s storm storage capacity was increased from 658m³ to 766m³ through raising the coping levels of the existing tank walls and overflow weirs. In addition, structural modifications were undertaken to facilitate the replacement of the existing half-bridge scraper within the radial blind storm tank.

Electrical & control systems

Significant electrical and control system upgrades were also delivered. These included modification of the inlet works motor control centre (MCC) to accommodate the new dosing installation and scraper replacement, and upgrades to the sand filter kiosk MCCs to integrate the new TNSF equipment and allow for decommissioning of redundant assets.

Further works included modifications to all the MCCs by CEMA Ltd to enable integration into a new ethernet-based control network, installation of additional instrumentation and asset monitoring signals, and the provision of a new telemetry interface programmable logic controller (PLC) within the storm returns pumping station kiosk.

Ancillary works included the installation of site lighting to support new plant, process areas, and access routes, together with the associated electrical, control and instrumentation (EICA) systems necessary to support the upgraded infrastructure.

[caption id="attachment_31377" align="alignnone" width="1200"] Primary settlement tank distribution chamber - Courtesy of Enpure Ltd[/caption] Pocklington STW: Supply chain - key participants Main designer & contractor: BEJV Civils: Barhale Process & M&E: Enpure Ltd Electrical installation: Circle Control Mechanical installation: JBF Group Mechanical installation: Tushingham Steel Fabricators Ltd MCCs, PLCs & SCADA: CEMA Ltd Ferric dosing: IIES (Northern) Ltd Kiosks: Morgan Marine Ltd Safety showers/eyebaths: Aqua Safety Showers International Ltd Tertiary nitrifying sand filters: Hydro International Ltd Scraper bridge refurbishment: WGM Engineering Ltd Pumps: Xylem Water Solutions Valves: Cotswold Valves Ltd Trace heating & lagging: Jade Insulation Flow meters & level transmitters: ABB Hose reels: ARCO Ltd Inlet works

The existing works inlet consists of two Haigh Engineering screens complete with screenings handling and a grit removal system on the back end, which leads into the storm chamber.

Chemical dosing

To achieve compliance with the revised phosphorus discharge consent, implementation of both primary and secondary stage coagulant dosing was required. This was delivered via a purpose-built ferric dosing kiosk complete with integral chemical storage and a service water booster system. Given the nature of the chemical handling operations, a dedicated off-loading facility was also provided, comprising a bunded tanker delivery apron, an interlocked delivery point, and an emergency drench shower to meet safety and environmental requirements.

[caption id="attachment_31373" align="alignnone" width="1200"] Chemical dosing kiosk and safety shower - Courtesy of Enpure Ltd[/caption]

The new ferric storage and dosing installation was designed to provide sufficient capacity and dosing control to consistently achieve the required phosphorus removal performance. The system incorporates approximately 10 days of on-site chemical storage and was factory-tested prior to delivery to minimise site commissioning risk. The site layout and bunded delivery arrangement were configured to allow a ‘drive-in, drive-out’ tanker operation, improving both safety and operational efficiency.

The primary dosing system was initially configured to deliver coagulant into the primary settlement tank (PST) distribution chamber. However, following site-based process optimisation trials, the dosing point was relocated to the inlet works outlet chamber to improve mixing conditions and enhance phosphorus removal efficiency.

Secondary stage dosing locations were similarly subject to on-site trials to determine the most effective point of application. The preferred primary secondary dosing location was established at the base of the humus tank screw feed, with a secondary contingency dosing point provided at the existing HST distribution chamber. Both points of application were configured with duty/standby dosing arrangements and automatic changeover to ensure operational resilience and continuity of treatment performance.

Tertiary Nitrifying Sand Filter (TNSF)

The tertiary nitrifying sand filter operates on a counter-current flow principle. Influent water enters via a distribution system located at the base of the unit and is treated as it flows upward through the granular media bed, in this case sand, prior to discharge through the filtrate outlet at the top of the reactor.

Biological nitrification is achieved by autotrophic nitrifying bacteria colonising the media. To sustain this process, adequate oxygen transfer and carbon dioxide availability are essential. This is facilitated by aeration hoods positioned within the upper region of the media bed, supplied with process air to maintain optimal dissolved oxygen concentrations and promote effective ammonia oxidation to nitrate. The resulting nitrates remain in solution within the treated effluent.

[caption id="attachment_31380" align="alignnone" width="1200"] Tertiary nitrifying sand filter - Courtesy of Enpure Ltd[/caption]

The media bed simultaneously functions as both a biological reactor and a physical filtration system, capturing suspended solids and biomass. To maintain treatment efficiency, the media undergoes continuous regeneration. Solids-laden media is drawn from the base of the unit via an airlift pump and conveyed to an integral media washing system located at the top of the filter.

Initial separation of impurities occurs within the airlift riser due to turbulent mixing. The media then discharges into a washing chamber (labyrinth), where it is subjected to a controlled counter-current flow of clean water. This process removes retained solids and sloughed biological growth.

The waste stream is discharged via the wash water outlet, while the denser, cleaned media is returned to the bed. This mechanism induces a slow, continuous downward movement of the media through the filter. Compressed air for the airlift system is supplied via a dedicated air distribution panel.

This continuous cycle of filtration and in situ media cleaning enables uninterrupted operation, eliminating the need for periodic backwashing and ensuring consistent treatment performance.

This element of the contract was awarded at an early stage whilst developing the remaining project scope. This approach allowed focused attention on this key component of the project, which involved confined space entry, along with a comprehensive condition assessment and overhaul of an existing, previously disused asset. This strategy also supported carbon savings and contributed to the circular economy.

The existing TNSF units were refurbished as part of the works. BEJV engaged Hydro International to deliver key process upgrades, including the supply and installation of two new compressors with acoustic enclosures, replacement filter media, full renewal of internal pipework, and system commissioning to restore operational performance and reliability.

[caption id="attachment_31379" align="alignnone" width="1200"] TNSF compressors - Courtesy of Enpure Ltd[/caption] Storm tanks

The original project scope proposed refurbishment of the existing storm tank, alongside the provision of additional capacity by increasing the coping level of the adjacent square storm tank.

However, during inspection under dry weather flow conditions, it became evident that the existing storm tank had deteriorated beyond economical repair due to its age and original construction. Consequently, the agreed solution was to demolish the existing structure and construct a new tank within the same footprint.

To maintain compliance with the site’s storm storage permit throughout the construction period, a temporary strategy was implemented. This comprised both temporary over-pumping arrangements and interim storm storage provision.

These works introduced additional logistical and operational constraints, including the requirement to secure temporary access to adjacent third-party land to accommodate temporary storm tanks while demolition and reconstruction activities were undertaken.

In addition, a separate ‘blind’ storm tank was incorporated into the overall strategy to supplement storm storage capacity. The initial scope included replacement of the existing scraper bridge and removal of the launder troughs, however, following a detailed condition assessment, the existing assets were found to be structurally sound and suitable for refurbishment.

The adopted solution involved raising the scraper bridge by approximately 300mm and applying a protective re-coating system. This approach delivered a cost saving of approximately £50,000 to the client while maintaining operational performance and extending asset life.

[caption id="attachment_31375" align="alignnone" width="1200"] Storm tanks - Courtesy of Enpure Ltd[/caption] Status

The upgraded works at Pocklington STW successfully met the regulatory compliance date, with all process-critical improvements completed by 31 March 2025. The overall project was subsequently finalised in March 2026 following the completion of additional works.

This scheme has significantly enhanced the treatment capability for incoming raw water, while stabilising throughput and increasing operational resilience. As a result, it delivers a robust and sustainable improvement to the local Yorkshire Water network, providing long-term benefits for the communities it serves.

Oakham is a market town at the centre of Rutland, surrounded by a largely rural catchment and closely connected to Rutland Water, one of the largest artificial reservoirs in Europe and a nationally protected Site of Special Scientific Interest (SSSI). Given the ecological importance of this waterbody, maintaining high water quality is critical to protecting local biodiversity, recreation and the long-term environmental health of the region. Increasing pressure on sensitive receiving waters has driven a renewed regulatory focus on nutrient control. In response, the Environment Agency has called for enhanced nitrogen removal and the generation of robust, real-world performance data to inform AMP9 planning and future regulatory standards. Due to its direct discharge to Rutland Water, Oakham Water Recycling Centre (WRC) was identified as a strategically important trial location. Background

Anglian Water appointed the @one Alliance to deliver a full‑scale nitrogen removal trial at Oakham, designed to generate the robust evidence needed to shape future nutrient management strategies across the sector. This trial represents one of the most significant nitrogen removal studies undertaken in the region in recent years.

With new tertiary treatment processes, carbon dosing systems, infrastructure upgrades and enhanced analytical capability now fully installed, Oakham WRC is ready to begin delivering the insights required to inform future Total Nitrogen Technology Allowable Limits (TALs) and long‑term investment decisions.

By February 2026, the scheme had progressed into its final stages, following almost two years of design, construction, commissioning and close collaboration between Anglian Water, the @one Alliance and key supply‑chain partners. Once fully commissioned, the site will enter a year‑long monitoring programme designed to generate the critical performance data needed to support national decision‑making for the next asset management period.

[caption id="attachment_28639" align="alignnone" width="1200"] 3D model of Oakham WRC - Courtesy of @one Alliance[/caption] The drivers behind the Oakham WRC nitrogen trials

Following the sector-wide focus on phosphorus removal during AMP6/7, nitrogen has emerged as the next major regulatory priority. As environmental standards tighten and pressures on sensitive waterbodies increase, the water industry requires the same level of evidence, clarity and proven solutions for nitrogen removal.

The Environment Agency selected Oakham WRC as a strategic trial site due to its direct influence on Rutland Water, a highly sensitive SSSI where reductions in nutrient loading can deliver immediate and long-term ecological benefits. Any improvement in nitrogen performance at Oakham directly supports the protection of this nationally important asset and its wider catchment.

The scheme therefore addresses both immediate environmental protection requirements and the longer-term need to develop an evidence base that will inform regulatory and investment decisions across the UK water sector.

The solution

The Oakham WRC Nitrogen Removal Trial is centred on the installation and operation of a full-scale tertiary de-nitrifying sand filter system with carbon dosing, designed to remove total nitrogen from final effluent prior to discharge to Rutland Water.

This configuration enables biological denitrification to be trialled under real operating conditions, generating robust and transferable performance data to support future regulatory and investment decisions.

To minimise safety and regulatory risk, acetic acid was selected as the carbon source in place of methanol, avoiding the creation of a DSEAR-rated zone while maintaining effective denitrification performance. This approach, already proven elsewhere in the Anglian Water network, provides the industry with a practical and lower-risk carbon dosing solution that can be readily adopted at other sites.

The scheme includes the construction of concrete foundations for dosing systems and treatment kiosks, installation of a 30m3 dosing package from Lintott Control Systems Ltd, multiple control and monitoring kiosks, and new potable water infrastructure across the site.

[caption id="attachment_28642" align="alignnone" width="1200"] Preparing the concrete foundations - Courtesy of @one Alliance[/caption]

A new wet well and pumping station, DN250 auto-infeed strainer, static in-line mixer and carbon dosing arrangement have been installed to support consistent and controlled treatment performance.

Four DynaSand tertiary sand filters from Nordic Water (via Jacopa), housed within a dedicated kiosk, form the core of the nitrogen removal process.

Additional works include access road modifications, cross-site electrical ducting and new power connections, surface water drainage upgrades, and the installation of emergency safety facilities such as washdown points, showers and eyewash stations.

Enhanced sampling points and continuous Hach analysers for ammonia, nitrate and total nitrogen provide real-time performance monitoring, enabling detailed analysis throughout the trial period.

Oakham Nitrogen Removal Trials: Supply chain - key participants

The successful delivery of the Oakham WRC Nitrogen Removal Trial has relied on close collaboration across a wide range of technical and supply-chain partners.

Client: Anglian Water Project delivery: @one Alliance Principal contractor: MWH Treatment Civil works: DLO (@one Alliance Direct Labour) Dosing package & associated infrastructure: Lintott Control Systems Ltd Nordic Water DynaSand tertiary sand filters: Jacopa Ltd Mechanical & electrical installations: AVRS Systems Ltd Gorman-Rupp pump supply: Hydromarque Ltd Static mixers: Statiflo International Ltd Control systems: TES Group Continuous nitrate, ammonia & total nitrogen instrumentation: Hach Emergency shower facilities: Hughes Safety Showers Ltd Generators: Stuart Power Ltd Chemical storage tanks: Forbes Technologies Ltd Site security & construction timelapse: Wireless CCTV Ltd Crane hire: Ainscough Crane Hire [caption id="attachment_28643" align="alignnone" width="1200"] (left) DynaSand filters arriving at Oakham WRC and (right) installation of the first DynaSand filter - Courtesy of @one Alliance[/caption] Commissioning & trials

Commissioning is scheduled for completion by March 2026, with the trial running from April 2026 to March 2027. Interim reporting will be aligned to the N-TAL Technical Specification, with a final report due in May 2027.

During this period, Anglian Water operational teams will oversee performance monitoring, data analysis and reporting, ensuring that findings are robust, transparent and suitable for national application.

While delivered as a trial, the scheme provides immediate and long-term benefits. The treatment assets will reduce nitrogen loading to Rutland Water, one of the UK’s most sensitive and valued freshwater environments, supporting its ecological health both during and beyond the trial period where performance improvements are demonstrated.

Lessons learned

The project mirrors the approach taken during the AMP6 National Phosphorus Trials, generating high-quality evidence under seasonal and hydraulic variability.

The data collected will benchmark acetic acid dosing, assess operational complexity, energy use and resilience, and directly inform Total Nitrogen Technology Allowable Limits and AMP9 planning across the sector.

In parallel, the scheme enhances understanding of integrated nutrient management by exploring how nitrogen and phosphorus treatment processes interact. With future phosphorus obligations already anticipated, this insight supports more efficient long-term planning and coordinated investment strategies.

The installation of new pumps, kiosks, mixers, analysers and control systems improves site resilience and operational flexibility, delivering lasting value regardless of future nitrogen compliance requirements.

Collectively, the project strengthens collaboration between Anglian Water, the Environment Agency, operational teams, suppliers and the @one Alliance, ensuring that future nitrogen standards are underpinned by verified, shared and evidence-based learning.

[caption id="attachment_28646" align="alignnone" width="1200"] DynaSand filter installation nearing completion - access stairs being lowered into place - Courtesy of @one Alliance[/caption] Conclusion

As Oakham WRC Nitrogen Removal Trial enters the final stages of commissioning, the site is now positioned to support one of the most influential nitrogen removal trials in the UK water industry.

The integration of advanced tertiary treatment, acetic acid carbon dosing, enhanced monitoring and robust process control provides a strong platform for generating the evidence required to inform future regulation and investment.

Oakham WRC has become a demonstrator for innovation, collaboration and evidence-led environmental improvement, helping to shape a cleaner, more resilient future for both the region and the wider water sector.

Located in Lincolnshire east of Doncaster, Severn Trent’s Haxey Graizelound Sewage Treatment Works (STW) serves a residential population equivalent of 5,169 with no trade loads within the catchment. The works receives pumped flows from two pumping stations located in the catchment. The present permit is BOD 25mg/l, suspended solids 45mg/l, ammonia 15mg/l with a dry weather flow (DWF) of 1,100m3/day and a flow to full treatment (FFT) of 37.7l/s. Due to the Water Framework Directive the site will receive a 3mg/l ammonia and 0.2mg/l phosphorous discharge consent, and should chemical dosing be required to achieve the phosphorus removal, a corresponding 4mg/l iron discharge permit will be introduced. Existing works The present works consists of a high-level balancing tank that collects the pumped flows from the catchment before transferring the flows to an all-flows screen, grit removal and a flume controlling FFT and storm separation. Assets include: 1 (No.) radial primary settlement tank (PST). 4 (No.) biological filters. 1 (No.) radial humus settlement tank (HST). 1 (No.) storm storage tank. 2 (No.) co-settled sludge holding tanks 1 (No.) works return pumping station. Technical solution Due to the tightening of the ammonia permit to 3.0mg/l, any expansion to the existing fixed film biological filtration process was deemed to have a high process risk and was discounted early on. The remaining options considered for the scheme were: Retain the existing works with tertiary ammonia removal. Retain the existing works with MBBR and reed beds. Crude oxidation ditch/activated sludge plant with chemical phosphorus removal. Crude oxidation ditch/activated sludge plant with enhanced biological phosphorus removal (EBPR). Settled oxidation ditch/activated sludge plant with chemical phosphorus removal. Settled oxidation ditch/activated sludge plant with enhanced biological phosphorus removal. Activated granular sludge plant. Following a costs benefit analysis (CBA), a crude pocket ASP with EBPR was selected as the preferred solution. [caption id="" align="alignnone" width="1200"] 3D model of the existing site - Courtesy of Cloud Conversion Ltd[/caption] Design phase Severn Trent took the strategic decision to bring design back in-house for AMP7 and become an intelligent and informed client. As with all transformations this became a journey and not an overnight change. Modern-day up to date policies and procedures were implemented to support a design organisation, new designers were recruited, and existing staff members were upskilled in the current world of design. Alongside the development of the design team, the commercial team established new support contracts to allow survey work, ground investigation and environmental data to be collated to feed into the design process. The internal design team started to cut their teeth on repeatable WFD projects however the skills developed at a rapid rate leading to the designer’s desire to undertake projects which are larger in size, cost and complexity. This led to the team taking on the outline design for the works replacement at Haxey Graizelound STW. The existing site was surveyed by Cloud Conversion Ltd to produce a 3D building information model (BIM) in software Autodesk Revit, by undertaking a point cloud scan, topographical survey, and underground/utilities survey. This enabled the design team to have a detailed up to date digital twin of the existing site to base the future design on. Intrusive site investigation (SI) was undertaken to determine the extent and the details of the existing decommissioned underground structures on site. In addition, ground investigation (GI) was undertaken to determine the existing ground makeup and to establish the water table in the area. [caption id="" align="alignnone" width="1200"] Cropwell Bishop STW FST: Visiting recent installation to learn lessons and replicate good designs - Courtesy of Severn Trent[/caption] The discipline-specific design engineers produced their designs which were fed into the Autodesk Revit 3D model by the Severn Trent internal digital design team, prior to been used for design reviews, Hazard & Operability (HazOp) study and stakeholder engagement. Following design acceptance, 2D sections and details were produced in Revit which were submitted to the Severn Trent cost and estimating team to set a target price (TP) for the project. The 2D sheets communicate clear designs to allow a robust TP to be set. The design pack was then submitted to the supply chain for tender where risk has been reduced due to the level of design detail provided. This in turn leads to reduced cost risk for Severn Trent and increased confidence from the supply chain in the work they have been asked to undertake. Haxey Graizelound STW: Supply chain - key participants Client: Severn Trent Detailed design & construction: MMB 3D scans, topographical surveys: Cloud Conversion Ltd Ground investigation: Ian Farmer Associates Environmental Consultants: Penny Anderson Associates Geo-Environmental Consultants: Sirius Geotechnical [caption id="" align="alignnone" width="1200"] 3D model of the proposed works improvement - Courtesy of Severn Trent Water Digital Design Team[/caption] Sustainability considerations The internal design team were able to undertake the design process with sustainability at the forefront of their minds. Following the GI, the team were able to reuse an existing area of the site where disused assets were installed, eliminating the need to build on green areas and allowing us to develop these areas to enhance the biodiversity on site. Working with the framework ecologists a biodiversity baseline assessment and a biodiversity enhancement plan were produced, which has led to a design providing a biodiversity net gain of 16% habitat units and 254% hedgerow units. To support Severn Trent’s journey to net Carbon Zero the team were able to use the newly developed carbon tool to review options to select lower carbon alternatives. This included a stainless steel prefabricated high-level inlet works structure, fabricated off-site and delivered to site, rather than a traditional concrete structure cast in situ. The internal design team were able to assess the network pumping stations feeding the site to determine the maximum head they could deliver to. This allowed the hydraulic designer to set the inlet level, and when considered with the fixed outlet river level the works was designed to gravitate all the flows through the process. This eliminated the need to install any interstage pumping stations which reduce assets installed, energy usage and provides a more robust process solution. [caption id="" align="alignnone" width="1200"] Winchcombe STW sludge thickener: Visiting recent installation to learn lessons and replicate good designs - Courtesy of Severn Trent[/caption] Conclusion The transformation strategy for AMP7 has achieved its goal of bringing design back in-house with Haxey Graizelound as a great example of what the team can produce. The project has been contracted to Mott MacDonald Bentley (MMB) who, with the support of the Severn Trent Design team, will be undertaking detailed design and turning our design into reality.

Situated adjacent to the M1 motorway, approximately 6km north-east of Sheffield, Blackburn Meadows Wastewater Treatment Works is one of Yorkshire Water’s critical assets, treating up to 4,000 l/s. The existing works comprised a raised inlet works including screens and grit removal, primary treatment via primary settlement tanks, activated sludge processes for biological treatment, and secondary treatment via final settlement tanks. Following notice of the introduction of tighter phosphorus and iron discharge consents by the Environment Agency, Yorkshire Water commissioned Stantec UK to carry out investigation, optioneering and the outline design of the most appropriate long-term solution. Project summary

In 2022, Glanua Group was awarded a contract under the AMP7 WINEP Programme to design and construct a tertiary solids removal (TSR) plant incorporating Evoqua’s CoMag® technology from Xylem Water Solutions.

At £36.5m, the project represents a significant CAPEX investment and a key advancement in wastewater treatment performance, delivering enhanced solids and phosphorus removal efficiency.

[caption id="attachment_26835" align="alignnone" width="1200"] Overview of Blackburn Meadows STW - Google Maps[/caption]

By integrating innovative and sustainable treatment processes, the scheme will comply with stringent environmental standards and contribute to improved effluent quality and environmental protection.

The construction and MEICA installation of the TSR plant have been completed, and the project commissioning team is now operating the system in preparation for reliability testing and handover. The CoMag® TSR process is consistently achieving phosphorus concentrations well below the consent limit of 0.3 mg/l, demonstrating robust process performance and operational reliability.

Scope of works

The upgrade works includes five Flygt channel impeller pumps from Xylem Water Solutions to lift current final effluent to the TSR plant, via a distribution chamber, where flow from five inlets splits evenly into two streams.

Ferric sulphate is dosed upstream of the CoMag® reactor and continuously mixed to encourage the formation of flocs. A magnetite slurry and a poly-acrylamide solution are also dosed and mixed to add weight to the flocs, enhancing their settlement in the two 23m diameter clarifiers.

The scheme also includes the provision of an upstream ‘primary’ ferric sulphate dosing system, which is integrated into the existing treatment process. This adjusts the pH and phosphorous levels upstream of the TSR plant, allowing optimisation of the CoMag® system.

[caption id="attachment_26838" align="alignnone" width="1200"] One of the completed clarifiers - Courtesy of Glanua[/caption] Blackburn Meadows STW: Supply chain - key participants (part 1) Client: Yorkshire Water Principal designer/contractor: Glanua Group Outline design: Stantec UK Civils design: AtkinsRéalis Design assistance & hazard studies: MEP Projects (UK) Ltd DfMA solutions: Glanua Industrial Evoqua CoMag® technology: Xylem Water Solutions Over pumping temporary works: Selwood Piling: Aarsleff Ground Engineering Civils contractor: Indepth Civil Engineering Services Ltd Civils contractor, temporary works & shoring: Hernons ME Temporary works, manholes & trench boxes: MGF Ltd Mechanical installation: Powerrun Pipe-Mech Ltd Mechanical installation: Fluid Sealing & Engineering (FSE) Electrical installation: MEICA Technical Services (MTS) Electrical installation: PLR Building Services Ltd Precast concrete tanks: FLI Precast Solutions MCCs & systems integration: CEMA Group

Blackburn Meadows TSR Plant - Courtesy of Glanua

Blackburn Meadows STW: Supply chain - key participants (part 2) Transformers & HV works: Integrated Utility Services MCC kiosks: Quinshield Ltd Heating & ventilation: Air Technology Systems (ATS Climate) Pipework: Scott Parnell Ltd Pipework: Electrosteel Castings (UK) Ltd Pipework: Freeflow Pipesystems Pipework: Franklyn Yates Engineering Ltd Chemical dosing: NPS Engineering Group Pumps: Xylem Water Solutions GRP access: Relinea Valves: Cotswold Valves Ltd Penstocks: Glenfield Invicta Static mixers: Statiflo International Flow meters & instrumentation: ABB Group Instrumentation: Endress+Hauser Instrumentation: Hach Lange Instrumentation: Siemens Tertiary solids removal (TSR) process

The CoMag® system is a ballasted separation and recovery process. It utilises magnetite alongside coagulants to create a ballasted flocculation system, thus enhancing settling rates and increasing the performance of the wastewater treatment plant. The high-density, magnetite ballasted floc flows into a compact high-rate clarifier. The clarifier includes baffle plates to dissipate the velocity of the inflow, encouraging optimal settling, and a rotating rake directs sludge into the hopper.

[caption id="attachment_26840" align="alignnone" width="1200"] The completed clarifiers - Courtesy of Glanua[/caption] The CoMag® system employs both a sludge and magnetite recycle function, to increase the system performance and the clarity of its effluent. Approximately 70% of the clarifier’s settled sludge is recirculated back into the system’s reactor tanks.

The remaining 30% of the sludge is processed through magnetite recovery system, which includes an inline, high-speed shear mixer where the magnetite is separated from the floc. The resulting two-part slurry is then passed through a magnetite recovery drum.

The permanent and stationary magnets inside the drum help to capture and reuse more than 99% of the magnetite, meaning that once primed, the CoMag® operates with very low magnetite consumption and low OPEX.

The sheared sludge, minus the magnetite, flows into the wastewater pumping station, where it is returned to the main WwTW via a new rising main, discharging immediately upstream of the primary settlement tanks.

TSR feed pumping station: Construction & temporary works

Originally, the WwTW’s final effluent discharged to the River Don via twin 1400mm brick-built culverts, buried at 6m cover to crown, which are believed to have been constructed in the Victorian era. A crucial and complex part of the scope was to excavate around and break into the culverts to enable flow diversion to the TSR. This required significant temporary works in the form of over pumping the final effluent and allow the culverts to be drained and isolated.

[caption id="attachment_26841" align="alignnone" width="1200"] TSR pumping station rebar structure and flume pipe tie-in - Courtesy of Glanua[/caption]

The number of shutdowns and over-pumping operations were minimised due to refinement of the construction sequencing and programme, reducing environmental risk exposure associated with temporary over-pumping installations. This accomplishment followed a huge effort by Glanua Group, Selwood and Yorkshire Water, and was completed under the guidance of, and in liaison with, the Environment Agency.

The condition of the culverts was largely unknown prior to excavation, with limited information available from trial holes. There were concerns about how the vibration from the sheet piling works would affect the culverts, during the installation of the cofferdam. As such, the temporary works design specified the use of silent piling technology with pre-augering to loosen the dense granular strata identified in the ground investigation.

Once excavated and broken out, temporary steel supports were affixed to the structural blinding, and mild steel pipework was installed to reintroduce flows, and decommission the over-pumping.

The TSR feed pumping station, utilising a cast in situ design, was constructed by Hernon ME around the temporary pipework, reducing the reliance on over-pumping from approximately six months to six weeks.

[caption id="attachment_26833" align="alignnone" width="1200"] TSR feed pumping station - Courtesy of Glanua[/caption] Digital delivery & common data environment

The Blackburn Meadows project was delivered through BIM 360, was Glanua Group’s Common Data Environment (CDE) and Information Delivery platform. This ensured that all project information was structured, reviewed, and approved within a controlled digital environment aligned with Glanua’s ISO 9001 Quality Management System and industry best practice for Digital Project Delivery.

Effective digital processes were central to how the project was delivered. By using the CDE, the flow of information was structured, auditable, and transparent across all design and delivery teams. This enabled consistent adherence to Glanua’s BIM and information management principles, ensuring the right information reached the right people at the right time.

Autodesk Revit was used for 3D modelling and drawing production across all disciplines (civil, structural, mechanical and electrical), which enabled integrated and coordinated design deliverables. The built-in review and approval workflows within Autodesk BIM 360 supported rigorous checking, digital mark-ups, and traceable approvals throughout design and construction.

The model coordination module was used by the entire project team and central at key design and construction milestones. Digital coordination reviews, HAZOPs, and ALM reviews were all conducted within the model environment to provide clear visual context. This approach improved decision-making, enhanced safety in design, and identified construction efficiencies, directly supporting programme delivery and quality outcomes.

[caption id="attachment_26836" align="alignnone" width="1200"] One of the clarifiers - Courtesy of Glanua[/caption]

Through the asset module in BIM 360, critical asset information was digitally captured and managed to support data-driven decision-making throughout the project. Each asset’s installation, commissioning and testing status was tracked and updated with specific information required to meet the client’s asset data handover.

By analysing this data, the project team was able to identify the most efficient point in the delivery process to input the information required on the client’s platform, ensuring accuracy and consistency were married with efficiency.

By beginning with the end in mind, operation, maintenance, and handover information was accurately collated throughout delivery.

Relevant commissioning checklists were also linked to these assets, allowing the commissioning team to directly access and complete commissioning data within Glanua Group’s Common Data Environment.

Designing for sustainability: Concrete & materials reuse

A total of 187 precast panels were manufactured, shipped and placed during construction of four of the five main structures which has shown a significant carbon saving, compared to the use of an in situ concrete solution.

A calculation from FLI Precast Solutions demonstrated that the cement content, reduced by 50% and replaced with ground granulated blast furnace slag (GGBS) in the design mix for the precast panels, would provide a total CO2e saving of 137.2 tonnes. By comparison, this saving is shown as the equivalent of not driving for over 1.1 million kilometres, or the carbon absorbed by 3430 trees growing for 10 years.

[caption id="attachment_26834" align="alignnone" width="1200"] Clarifier and CoMag® tank precast installation - Courtesy of Glanua[/caption]

For the remaining in situ slabs and structures, the concrete volumes have been reviewed and rationalised where possible. For example, the proposed perimeter wall was changed from a design containing 0.80m3 of concrete per linear metre to an equally effective design containing just 0.16m3 per linear metre, an 80% saving of concrete on this item of scope, demonstrating that a critical review in a small area can yield a significant impact.

Designing for sustainability: Energy

The five TSR feed pumps are controlled from large variable speed drives (VSDs), which are housed in individual sections of the main site MCC. Whenever a pump is running, an extractor fan pulls 3,760m3/hr of air though each VSD section, expelling it directly to the atmosphere external to the kiosk.

Replacement air is drawn into the kiosk through 30 vents in the kiosk wall. Whilst this is fine in summer, during winter months, the kiosk would require significant heating to avoid condensation forming inside the panels. It was calculated that 90kW of electric heaters were required in the kiosk to maintain an internal temperature of 10°C, when the ambient external temperature was -5°C.

It was considered too wasteful to provide so much heat, just for it to be exhausted to the atmosphere, in addition to the OPEX associated with this level of heating. In conjunction with supply chain partner, Air Technology Systems (ATS Climate), the VSD exhaust system was redesigned to include an air diversion and recirculation option, which automatically changes over based on temperature set points within the kiosk.

During a recirculation scenario, air is not extracted from the kiosk, meaning there is no low pressure causing cold air to be drawn in to the kiosk, eliminating the requirement for specialist heating of the kiosk beyond standard building services.

[caption id="attachment_26832" align="alignnone" width="1200"] The completed works - Courtesy of Glanua[/caption] Summary

The introduction of the TSR plant at Blackburn Meadows is a significant investment by Yorkshire Water in the environmental protection of the River Don and the surrounding area. By embracing the new CoMag® technology, Yorkshire Water have signalled their intent to support innovative solutions when complying with tighter water quality consents to protect the environment.

Glanua Group would like to thank Yorkshire Water and all delivery partners involved who have collaborated to bring project together through proactive and solution-orientated design and build engineering.

Located in south-east Staffordshire, Lichfield Sewage Treatment Works is a medium sized works operated by Severn Trent. The site treats wastewater from a population equivalent of approximately 40,200 and ensures that the effluent is suitable for discharge into the Full Brook. The investment into the sewage treatment works is driven by both the tightening of environmental permits, and projected population growth within the catchment. By 2038, Severn Trent’s forecasts that the population equivalent will rise to around 56,000 - an increase of roughly 30%. Existing works

The Existing Lichfield STW employs a biological treatment process. Flows entering the site pass through the inlet works before proceeding to three rectangular primary settlement tanks (PSTs). Here, sludge settles out before being pumped to four sludge tanks where it is thickened via decanting before being transported off-site.

Effluent from the PSTs is then distributed evenly between twelve biofilters, before passing through seven hummus settlement tanks (HSTs). The partially treated effluent then passes through a moving-bed biofilm reactor (MBBR), deep bed sand filter (DBSF) and four Mecana cloth filters before the treated effluent is discharged to the Full Brook.

[caption id="attachment_30529" align="alignnone" width="1200"] Google Earth image of the existing Lichfield STW[/caption] New consent permits

The following effluent quality permits of the River Trent will be enforced by end of December 2026:

Permitted Full Flow to Treatment (FFT) of the site will be increased from 263 l/s to 373 l/s. Permits for biological oxygen demand, ammonia, phosphorus and iron will be relaxed to 20 mg/l / 3.0 mg/l / 0.5 mg/l / 4.0 mg/l respectively. Additionally, the suspended solids permit will be limited to 30 mg/l.

These permits aim to protect the sensitive habitats of the River Trent as well as ensuring the future operational capacity of the treatment works.

Due to the significantly increased catchment and the tightening effluent quality permits of the local brook, Severn Trent proposed constructing a final effluent pumping station to discharge effluent 5km north at the River Trent. Comparatively, continuing to discharge to Full Brook was not economically viable and a higher risk to meeting the required permit.

[caption id="attachment_30517" align="alignnone" width="1200"] Revit model showing the site layout - Courtesy of MMB[/caption] Early Contractor Involvement 1

During 2024, Severn Trent appointed Mott MacDonald Bentley (MMB) under an Early Contractor Involvement (ECI) agreement to review the provided outline design for the upgrade to treatment at Lichfield Sewage Treatment Works.

The proposed scope included new combined storm overflow, new storm screens, replacing the primary settlement tanks (PSTs) with three new Dortmund-style PSTs, new gravity belt thickener sludge handling, new side stream activated sludge process (ASP) and two final settlement tanks (FSTs), new final effluent pumping station and pipeline (let as a standalone Infra Project), and converting the existing PSTs into storm storage tanks.

MMB conducted a detailed review of the outline design which concluded that the original scope held excessive programme and cost challenges, which would result in failure to meet the permits regulatory date. Upon issue of the initial target price from MMB, Severn Trent posed an affordability challenge with the initial price needing to be reduced by approximately 40%.

[caption id="attachment_30528" align="alignnone" width="1200"] (left) The three existing PSTs and (right) the two existing storm tanks - Courtesy of Severn Trent[/caption] Lichfield STW: Supply chain - key participants Client: Severn Trent Principal designer: Mott Macdonald Bentley Principal contractor: JN Bentley Specialist consultant: Mott Macdonald Final effluent pumping station & pipeline (infra scheme): GEDA Construction Ground investigation: Geotechnical Engineering Ltd Helical screw piles: UKHelix Co Ltd FRC works: Bell Formwork & Civil Engineering Services Ltd Electrical installation: Main Electrical Precast panels: Naylor Concrete Products Ltd Scraper bridges: EPS Water RAM pumps: EMS Industries Ltd Storm return pumps: Sulzer Pumps Wastewater Ltd Scum pumps: NOV Mono Pumps Mecana cloth filter TSR: Eliquo Hydrok Ltd Flushing gates: Jacopa Ltd Storm screens: Spirac Ltd MCCs: BGEN Ltd Kiosks: NPS Engineering Group Valves: AFFCO Flow Control (UK) Ltd Pipes: Saint Gobain PAM UK Pipes: Aquaspira Ltd Lifting equipment: T Allen Engineering Services Ltd Access steelwork: Utiliqo Ltd Backup generator: Central Power Services Sampling: Servitech International Ltd Landscaping: Holts Tree Care [caption id="attachment_30524" align="alignnone" width="1200"] PST earthworks completed early to bring programme forward - Courtesy of MMB[/caption] Optioneering

With the affordability challenge outlined in the ECI Phase, Severn Trent initiated a renewed Optioneering and Outline Design Phase in 2025 with MMB to ensure the December 2026 permit regulation date is met within Severn Trent’s budget.

Using the Outline Design as a starting point, Mott MacDonald Bentley reviewed the existing sites capacity to understand the limitations it had, and where MMB could propose further optimisation to the existing assets and reduce the original scope down collaboratively with Severn Trent. By challenging the ways of thinking, the client’s standards and pushing the boundaries of efficient delivery.

The original storm storage solution of re-purposing the existing PSTs to additional storm storage was challenged by MMB, with an opportunity for a significantly reduced programme to be unlocked by building a new storm tank, due to not requiring the commissioning of the new PSTs to enable the removal of the existing PSTs from service. This meant that the new storm tank could be built simultaneously as the new PSTs.

This also removed significant design, and health and safety risks, which required puncturing and underpinning the existing base of the tanks which are nearly 100 years old; and due to the original programme, working during on this tank in the winter months.

[caption id="attachment_30522" align="alignnone" width="1200"] Revit model of existing inlet works and new storm screens - Courtesy of MMB[/caption]

To save capital costs, MMB proposed constructing two larger PSTs instead of three, and relocated their position to optimise hydraulics and minimise pipework requirements. Each PST was designed to take the FFT until 2038, ensuring continued operation in the event a tank needs to be taken out of service for maintenance.

MMB discovered an opportunity to remove the filter feed pumping station from the scope by optimising the hydraulics. To prove this, MMB highlighted investigation work to be conducted in ECI 2, which would confirm the feasibility. To maintain design progress, MMB and Severn Trent agreed to assume that this opportunity could be realised, and to proceed with the design at risk.

With agreement from Severn Trent to take on increased tanker loads from site, the proposed sludge gravity belt thickening system was removed on a risk-based approach. With the existing sludge decanting system deemed serviceable for the immediate term.

With inputs from Process Engineering, MMB was able to question Severn Trent on the requirement for the ASP and FSTs by challenging the limits on hydraulics through existing secondary treatment, and process optimisation in the tertiary area.

This resulted in a side stream Mecana cloth filter and a mass blend at the final effluent collection chamber before sampling. New bypasses were also required to ensure the existing assets do not exceed their process or hydraulic limits.

[caption id="attachment_30520" align="alignnone" width="1200"] Revit model showing new CSO chamber - Courtesy of MMB[/caption] Early Contractor Involvement 2

In 2025, MMB was engaged again under an ECI Contract to complete a new outline design incorporating the affordability challenge changes outlined above. In addition to the cost challenge, MMB optimised the programme to facilitate designing and building the scheme within 18 months to meet the regulatory compliance date in December 2026.

The new MMB outline design consisted of the following:

New combined storm overflow. New storm screens. A new storm tank. Two new Dortmund-style PSTs. A new side-stream Mecana cloth filter and tertiary asset bypasses. A new final effluent pumping station and pipeline; let to GEDA Construction as part of the Infra Scheme.

To minimise future delays and enable effective planning, MMB conducted extensive site investigation works during this period to confirm existing site drawings due to the nature of the tight hydraulics through the site and route proving to mitigate potential clashes with our critical gravity underground pipes. Ecology surveys were completed early to highlight all risks which required monitoring and mitigating to protect our challenging programme prior to any of the main construction works commencing.

Due to location of assets in the outline design changing, as well as the proposal of new structures, geotechnical information was missing in key locations. To address this, MMB specified additional boreholes during ECI 2 while continuing the structural design using the best available data, with the designs verified once the new information was obtained.

[caption id="attachment_30518" align="alignnone" width="1200"] Revit model showing side-stream Mecana filter and AMP8 Infra scheme pump station – Courtesy of MMB and GEDA[/caption]

Trial holes and surveys were completed to assess restricted hydraulics and ascertain whether the scope was possible. These surveys also proved useful in chasing opportunities on scope reductions with agreement from Severn Trent to reinforce the affordability challenge on this project.

To maintain project momentum, the design team started detailed design early to help enable the early excavation works at the end of 2025, which were critical to achieving programme.

This was only possible due to the close collaboration with Severn Trent and the earned trust shared between both parties.

The detailed design was developed for efficiency in delivery, with a focus on Mott MacDonald Bentley’s right first-time attitude, and use of its in-house Production Hub, to integrate standard designs that are proven to gain early wins within the design development, and programme opportunities in the design and construction programme.

The site team exploited opportunities in the programme, identifying areas which could be completed ahead of time, which may have held slight cost inefficiencies, but had significant programme gains. This included full landscape clearing of the site and the intended working areas.

With the site setup completed, significant earthworks for the PST area began to ensure construction could begin as soon as the design information was issued. This resulted in immediately pulling the construction programme ahead of schedule by approximately a month.

[caption id="attachment_30519" align="alignnone" width="1200"] Revit model showing the PSTs and storm tank - Courtesy of MMB[/caption] Collaborative working

MMB collaborated not only with Severn Trent, but also with the ongoing AMP7 Caustic Dosing Rig Scheme, and the AMP8 Infra Scheme. This collaborative approach was undertaken across both design and on‑site construction; supporting Severn Trent in meeting regulatory permit requirements.

During outline design, MMB led discussions with Severn Trent to collectively develop the scope to set up an efficient programme that is affordable and meets the process performance to ultimately determine the minimum viable product. Crucially the revised solution is now positioned to hit the regulatory permit date.

Whilst having a presence on site. MMB has ensured a constant liaison with the two other contractor parties each week in both design and on-site activities. Discussions are held on weekly basis as a minimum to manage construction interfaces between the contractors and Severn Trent as well as maintaining the Construction (Design and Management) boundaries between each party.

Deliveries and construction traffic have been planned weekly ensuring safety of site personal and minimising disruptions caused to the other parties. This proved to be essential for keeping with the one-way road system established on site.

[caption id="attachment_30527" align="alignnone" width="1200"] PST excavation works (December 2025) - Courtesy of Mott MacDonald Bentley[/caption] Conclusion

The upgrade of Lichfield Sewage Treatment Works addresses both significant forecast population growth and the need to meet tightened environmental regulations. Through Early Contractor Involvement, Mott MacDonald Bentley worked closely with Severn Trent to review and challenge the original outline design, identifying substantial cost and programme risks that threatened the December 2026 regulatory compliance date.

A focused optioneering process allowed the team to evaluate existing asset’s capacities, challenge standard design assumptions, and develop a streamlined minimum viable product solution that aligned with the relaxed River Trent discharge permits whilst remaining affordable. Early site investigations, proactive risk management, and detailed design undertaken at pace were key to improving delivery certainty.

Overall, the project demonstrates how early contractor involvement and a strong collaborative working environment can unlock value, manage risk, and deliver a solution on time, within challenging regulatory and budgetary constraints.

The requirement of the Burnley Integrated Catchment Scheme is the River Water Quality Improvement for the Water Framework Directive (WFD) driver identified in the Water Industry National Environmental Programme (WINEP) to achieve a ‘Good’ status in the defined reaches of Pendle Water and the River Calder. The project, which commenced in 2020, is one of United Utilities’ largest AMP7 investments and is being delivered by Advance-plus, a joint venture between MWH Treatment, J Murphy & Sons (JMS) and Stantec UK. In previous articles published by Water Projects, United Utilities has shared the project journey from concept, solution design development, and construction. This case study focuses on the project team’s experience in achieving effective project outcomes. Project requirements & summary

To meet ‘Good’ status in Pendle Water and the River Calder, the treatment capability at Burnley Wastewater Treatment Works (WwTW) had to be enhanced to achieve compliance with the new treated effluent permit standards, coupled with management of storm discharges in the defined reaches, to achieve compliance with the WFD 99%ile wet weather intermittent standards. There are eight regulatory drivers attached to this WFD element of the scheme.

The project also includes two additional regulatory drivers for U_MON3 spill monitoring and U_MON4 flow monitoring.

Through complex river water quality and network modelling, the lowest whole life cost integrated catchment solution was determined and developed.

The Integrated Catchment Solution comprised four sites, which are all inter-dependent in delivering the regulatory outputs.

[caption id="attachment_26729" align="alignnone" width="1200"] Modification of existing PSTs 6, 7, 8 and 9 - Courtesy of United Utilities[/caption] Burnley WwTW

Serving a domestic population equivalent of approximately 107,000 plus trade load, Burnley WwTW has undergone a significant upgrade during this AMP7 project with the scope comprising the design, construction, and commissioning of:

A new Evoqua BioMag® activated sludge plant (ASP) from Xylem Water Solutions. The BioMag® system enhances conventional biological wastewater treatment by using magnetite (an iron oxide powder) to ballast the microbiological floc, creating an increase in mixed liquor suspended solids (MLSS) in the ASP and enhanced performance in the final settlement tanks (FSTs). A new 64-panel, 12,000m3 detention tank constructed by A-Consult Ltd with associated feed pumping station. A new additional (4th) primary settlement tank. A new 2500 l/s interstage pumping station (pass forward of FtFT and RAS flows). Refurbishment of the four existing FSTs. A new surplus activated sludge (SAS) thickening process. A new ferric and caustic chemical dosing plants. New MCCs, SCADA upgrade and power upgrade. U_MON3 event duration monitoring on spills to storm tanks. U_MON4 flow monitoring.

The final effluent quality for the new works at Burnley WwTW is to comply with both WRA (spot samples) and UWWTD (composite samples):

Design Permit WRA Parameter Average 95% ile Upper Tier Limit BOD 9 mg/l 50 mg/l Solids 40 mg/l Ammonia 2 mg/l 12 mg/l Total P 0.25 mg/l Iron 4 mg/l 8 mg/l Design Permit UWWTD Composite Samples Parameter Compliance Requirement Upper Tier Limit BOD 25 mg/l (or 70% removal) 50 mg/l COD 125 mg/l (or 75% removal) 250 mg/l Total P 2 mg/l (or 80% removal) [caption id="attachment_26728" align="alignnone" width="1200"] Evoqua BioMag® activated sludge plant - Courtesy of United Utilities[/caption] Burnley WwTW Catchment Strategy: Supply chain - key participants Client: United Utilities Construction Delivery Partner: Advance-plus JV MWH Treatment (Advance-plus jv) J Murphy & Sons (Advance-plus jv) Stantec UK (Advance-plus jv) Civil design detention tank: COWI UK Ltd Physical modelling: Hydrotec Consultants Ltd Dewatering design: OGI Groundwater Specialists Ltd Dewatering: Alba Dewatering Services Ltd Concrete construction: STAM Construction Ltd Detention tank shaft: Joseph Gallagher Ltd Pump station shaft: EJ Kelly Sheet piling: Sheet Piling (UK) Ltd PCC driven piling: Van Elle Concrete cutting: Holemasters Temporary works/shoring: MGF Ltd Precast post tensioned tanks: A-Consult Ltd Precast roof sections: Macrete (Ireland) Ltd Precast shaft segments: FP McCann Blower building: Saredon Steel Buildings Ltd BioMag® building: Gallaway Construction Ltd Access metalwork: Tushingham Steel Fabricators Evoqua BioMag® process: Xylem Water Solutions BioMag® mechanical installation: Alpha Plus Ltd [caption id="attachment_26724" align="alignnone" width="1200"] Detention tank water test - Courtesy of United Utilities[/caption] Civils & pipework: SGC Civil engineering Ltd Pumping station mechanical installation: Fluid Sealing & Engineering (FSE) Transformers: Winder Power Electrical installation: PICOW Engineering Group MCCs: Technical Control Systems Ltd Systems integration: Tata Consultancy Services SAS glass coated steel tank: Stortec Engineering Ltd Dosing systems: NPS Engineering Group PST fixed scraper bridge: EPS Water Epoxy coated carbon steel pipework & wall starters: Freeflow Pipesystems Ltd SAS drum thickeners: Huber Technology Odour control system: Air-Water Treatments Ltd PST odour covers: Corporate Engineering Ductile iron pipework: Saint Gobain PAM UK Ductile iron pipework: Electrosteel Castings (UK) Ltd FST scraper bridge refurbishment: Jacopa Ltd Blowers: Sulzer Pumps Wastewater Ltd Aeration system: Suprafilt Ltd SAS tank air mixing system: Utile Engineering Submersible pumps: Xylem Water Solutions Valves: AVK UK Ltd Standby generators: DTGen Kiosks: Industrial GRP Ventilation: Air Technology Systems Ltd Lindred Road CSO (PEN0056)

Work at this existing combined sewer overflow (CSO) site comprised the construction of an online 1,950m3 detention tank to store storm waters during times of heavy rainfall and reducing discharges to the watercourse. New pumps within the tank return the effluent to the sewer for onward treatment at Burnley WwTW. A new MCC and power supply were installed for this facility.

[caption id="attachment_18286" align="alignnone" width="1200"] Lindred Road detention tank during construction - Courtesy of United Utilities & Advance-plus[/caption] Altham Outfall Fennyfold CSO (BUR0026)

This existing CSO site is located in the local town of Padiham and on the sewer network that transfers flows to Hyndburn WwTW for treatment. The solution at this site was to construct a new chamber over the downstream sewer, install a new ‘real time’ controlled actuated penstock valve that regulates and optimises flows passed forward to Hyndburn, whilst reducing spills from the existing CSO. A new control kiosk was also provided.

Hyndburn WwTW

Value engineering and engagement with the Environment Agency enabled a no-build solution to be accepted at Hyndburn WwTW site, with only the optimisation of existing storm tank emptying system necessary for compliance.

Process optimisation: update to previous report

New primary settlement tank No. 4

New primary settlement tank (PST) No. 4 desludge pump run/dwell timers have been optimised to provide primary sludge concentration to a target of ~3.5% ds w/w. Daily PST No. 4 sludge blanket dips are undertaken by ADP and UU Operations undertook routine measurement of primary sludge concentration to inform any occasional minor changes to desludge pump run/dwell timers. The set-points for the run/dwell timer of the PST No. 4 desludge pumps typically range from 9-12 minutes for the run phase and 45-60 minutes for the dwell phase. These set-points will be adjusted in the future to accommodate changes in operational conditions at the site, including those related to the current sludge treatment center. [caption id="attachment_26733" align="alignnone" width="1200"] PST4 with odour control cover - Courtesy of United Utilities[/caption] Interstage pumping station The new interstage pumping station (IPS) has been commissioned with close consideration of the operating level set-points as determined during detailed hydraulic design. Further optimisation of the recycled activated sludge (RAS) control flow rates was undertaken following an exceptionally dry and warm weather period during April-June 2025 which has then resulted in supplementary further optimisation of the IPS control set-points. To maintain a stable hydraulic gradient for control of RAS (via gravity) from the final settlement tanks, the IPS top water level has been further optimised at 2.5m set-point with an operating level set-point control band optimised across a 0.5m depth (as per design). The IPS pumps minimum/maximum operating speeds (32.5Hz and 50Hz respectively) have been further optimised to provide stable control to level set-point across the 0.5m operating level band and avoiding, as much as possible, pump start/stops during dry weather flow periods where pump minimum performance exceeds received flows into the pumping station. The IPS has operated generally in accordance with the initial duty/assist/assist cascading level control with PID control loop tuning set-points remaining generally unchanged since original turn of flows in early October 2024. Further optimisation of the IPS process control set-points is not envisaged in the future. [caption id="attachment_26725" align="alignnone" width="1200"] Interstage pumping station - Courtesy of United Utilities[/caption]

Process air blowers: The new process air blower package was initially commissioned with support from the supplier, Sulzer Water & Wastewater. The majority of operational set-points within the blower package system are standard defaults and did not require further optimisation. The assist blower start/stop changeover set-points were optimised during a subsequent Sulzer site visit to ensure stable operational transition, avoid unnecessary noise and prevent nuisance under/over pressure process trips.

The process air blower discharge header control set-point has been further optimised to 640 mbarg in attempt to minimise dissolved oxygen depletion during storm events. The occasional depletion of dissolved oxygen remains an issue during the extraordinary rate of change of incoming flows and loads often associated with these storm events.

The addition of alternative ‘Storm Mode’ process control may ultimately be required to fully remedy the situation. Further optimisation of the process air blower process control set-points may therefore be required in conjunction with implementation of future ‘Storm Mode’ process control philosophy.

New primary ferric sulphate dosing: Extensive and routine jar-testing to monitor the optimal primary ferric dose molar ratio dose to achieve target residual orthophosphate and Total Iron concentrations was undertaken during May and June 2025.

The primary ferric molar ratio dose providing optimal phosphate and iron control (~1mg/l orthophosphate and <20mg/l Total Iron concentrations in PST effluent), as determined during the Summer Completion Test, was 4.15 MR. For reference, the ‘as-commissioned’ diurnal orthophosphate base load profile is shown below.

[caption id="attachment_26740" align="alignnone" width="1200"] Burnley WwTW: Orthophosphate diurnal load profile - primary ferric LUT set-points (as commissioned November 2024) - Courtesy of United Utilities[/caption]

A summary of initial and subsequent primary ferric dosing MR dose ‘optimisation’ is provided below:

28 November 2024 Dosing commences at 5MR 11 December 2024 Dosing increased to 6MR to target 1mg/l orthophosphate in PST effluent 20 December 2024 Dosing reduced to 5MR in response to ASP ammonia breakthrough spikes 24 December 2024 Dosing reduced to 4MR in response to ASP ammonia breakthrough spikes 2 January 2025 Dosing paused in response to observed ASP ammonia breakthrough spikes 9 January 2025 Dosing recommenced at 2MR 11 February 2025 Dosing increased to 3MR to target 1mg/l orthophosphate in PST effluent 25 February 2025 Dosing increased to 3.5MR to target 1mg/l orthophosphate in PST effluent 6 March 2025 Dosing increased to 3.75MR to target 1mg/l orthophosphate in PST effluent 17 March 2025 Dosing reduced to 3.5MR in response to ASP ammonia breakthrough spikes 24 April 2025 Dosing increased to 3.75MR to target 1mg/l orthophosphate in PST effluent 30 April 2025 Dosing paused in response to observed FST iron breakthrough spikes 3 May 2025 Dosing recommenced at 4.5MR following jar testing 8 May 2025 Dosing reduced to 4.15MR in response to jar test results N/A No primary ferric MR change since 8/5/25

Routine, minor, operational changes to the primary ferric dosing set-points will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future; and most notably, in response to envisaged seasonal variation and catchment characteristics.

Caustic dosing: An initial set-point of 7.1 pH units was adopted for interstage pH process control upon commencement of the Summer Completion Test. This control set-point has been further optimised on occasion and in agreement with/request by United Utilities Operations to 7.15 pH units to either reduce chemical consumption or in consideration of prevailing final effluent alkalinity measured value.

Routine, minor, operational changes to the interstage pH setpoint considering prevailing final effluent pH and alkalinity will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future.

[caption id="attachment_26726" align="alignnone" width="1200"] Chemical dosing area - Courtesy of United Utilities[/caption]

Liquid polyelectrolyte dosing: The ‘sweetening’ dose set-point of 25 l/h per FST has been retained and a storm event %FtFT trigger setpoint of 75% (in line with Evoqua recommendation). During periods of low FtFT, the 25 l/h ‘sweetening’ dose set-point results in the liquid poly system batching around four times per day; ensuring that a fresh, but matured, make-up solution is available at all times in readiness for flash increase in FtFT or prolonged storm event.

The poly dose proportional set-point has been gradually reduced to the current value of 0.6 mg/l as active product. It is noted that the product selection and amount of liquid polyelectrolyte dosed is subject to EA permitting and, as such, strict limits on maximum poly dose rate applies (currently 3.2 mg/l maximum as active product).

Further optimisation of the liquid poly ‘proportional’ dose process control set-points is not envisaged as necessary in the future.

[caption id="attachment_26734" align="alignnone" width="1200"] New assets at Burnley WwTW - Courtesy of United Utilities[/caption]

Magnetite addition & recovery: Magnetite, an iron oxide powder, is added to the activated sludge process via the BioMag® system to provide mixed liquor enhanced settleability in the final settlement tanks by microbiological floc ‘ballasting’.

The new works was operated during Q1 of 2025 to maintain the magnetite : MLSS ratio at the target of approximately 2:1, which was necessary to achieve the necessary mixed liquor settleability performance as measured by Specific Stirred Volume Index (SSVI).

Control to the target ratio is effected by management of magnetite ‘top-up’ addition, and in consideration of daily surplus activated sludge wastage volume, which relies upon having a disposal route for SAS. Mixed liquor settleability performance matured naturally during Q2 of 2025 and the magnetite : MLSS ratio was coincidentally reduced to target of 1:1 by the reduction of magnetite ‘top-up’ addition to the design anticipated amount of 500 to 600 kg/d.

The historic magnetite : MLSS ratio data is shown in the graph below. It can be seen that magnetite : MLSS ratio has trended down since the Summer Completion Test and as such, the ‘top-up’ magnetite loading set-point has been increased slightly to compensate.

Routine operational changes to the daily magnetite loading rate will therefore remain a business-as-usual activity associated with normal wastewater treatment works operation in the future. [caption id="attachment_26722" align="alignnone" width="1200"] MLSS minus magnetite (true MLSS) and true MLSS : Magnetite ratio on-site tests and laboratory results - Courtesy of United Utilities[/caption]

Recycled activated sludge control: Further optimisation of the RAS control set-points was undertaken following the extended period of exceptionally dry and warm weather period during April-June 2025. During this dry weather period the RAS flow rate was maximised to design limitation of 1,040 l/s to best manage potential for denitrification within the FSTs and avoid rising sludge and scum formation where possible. RAS control to ‘FtFT Mode 1’ was adopted for control of RAS flows during the Summer Completion Test in accordance with a three-tiered banded philosophy as follows:

FtFT flow (l/s) RAS flow (l/s) <600 400 >600 <1000 600 >1000 750

The RAS control system has operated stably for many months, and no significant further optimisation is envisaged. However, routine operational changes to the RAS control rate or mode of operation will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future.

Activated sludge plant: Routine control of MLSS concentration has remained by the conventional method of monitoring food to micro-organism ratio (F/M) to the design target ~0.08d-1, by assessment of sludge age against target of ~14 days and then by manual adjustment of the surplus activated sludge daily wastage volume.

Routine monitoring of the biological load on the ASP and as-required operational changes to the daily SAS wastage volume to maintain F/M ratio and sludge age within an acceptable range will remain a business-as-usual activity associated with normal wastewater treatment works operation in the future. The historic F/M ratio and sludge age data is shown below.

[caption id="attachment_26739" align="alignnone" width="1200"] F to M ratio and sludge age - Calculated using on-site tests and laboratory test results - Courtesy of United Utilities[/caption]

Similarly, routine microscopic analysis has been undertaken by UU labs to monitor and track filamentous (and other indicator bacteria) abundance.

Summary/conclusion

The Summer Completion Test was carried out by Advance-plus over a 28-day period between 21 July and 18 August 2025. From the test results, it is concluded that the new works has successfully demonstrated compliance with the requirements of:

CT1: Final effluent water quality compliance with site WRA Regulatory Permit limits for BOD, TSS, ammonia, Total Phosphorus, Total Iron and pH. The final effluent water quality adequate compliance with asset standard for alkalinity residual (noting routine pH set-point change made during completion test in response to slight reduction in background alkalinity). CT2: Final effluent water quality compliance with site UWWTD Regulatory Permit limits for BOD and COD. CT3: Final effluent water quality compliance with site UWWTD Regulatory Permit limits for Total Phosphorus. CT4: Magnetite recovery rate of the BioMag® process.

Anglian Water are investing £10m to upgrade Ramsey Water Recycling Centre in Cambridgeshire to address regulatory compliance, improve treatment capacity and enhance environmental protection and water quality in local watercourses, including the nearby Ramsey High Lode. The project combines two critical schemes; storm tank capacity upgrades and increased flow to full treatment (FtFT), ensuring the site meets future demand, stringent environmental standards, and safeguards aquatic ecosystems during high-intensity rainfall events. The issues

The primary challenge driving this project was the inadequate storm volume capacity at Ramsey WRC. The existing storm tank could only hold 260m³, far below the required capacity set by the Environment Agency (EA).

Failure to increase the on-site stormwater storage capacity would result in a consent failure leading to the risk of environmental harm and regulatory penalties for Anglian Water.

Additionally, the site’s existing flow to full treatment infrastructure was outdated and in need of major repair and upgrade. The current system could not handle the additional flows required to meet future population growth and environmental obligations. Without intervention, Ramsey WRC faced operational inefficiencies and potential breaches of discharge permits.

To overcome these issues, Anglian Water tasked the @one Alliance to design a dual-scheme solution to address the stormwater storage and FtFT issues.

[caption id="attachment_28313" align="alignnone" width="1200"] Construction of the reinforced concrete slab for the new storm tank - Courtesy of @one Alliance[/caption] Storm tank upgrade

The new storm tank designed to significantly increase storage capacity and reduce overflow risk during heavy rainfall events. The new tank is 11.1m in diameter and 8.47m high. This provides an additional 693m3 of storage capacity bringing the total volume of stormwater storage to 953m3. This upgrade ensures compliance with Environment Agency requirements and future-proofs the site against climate change impacts and population growth.

To improve operational efficiency and safety, the design incorporates external dry well submersible pumps for automated cleaning. This innovation eliminates the need for manual cleaning and access platforms, reducing health and safety risks for maintenance teams.

Furthermore, the stormwater storage tank has been carefully integrated into the existing infrastructure, optimising the limited site footprint and minimising disruption during construction. This approach allowed the project team to deliver a high-capacity solution without extensive civil works or compromising ongoing operations.

[caption id="attachment_28307" align="alignnone" width="1200"] Construction of new Storm Tank 4 - Courtesy of @one Alliance[/caption] Flow to Full Treatment (FtFT) upgrade

The second element of the project focused on increasing the site’s ability to treat incoming flows during peak conditions.

Modular side-stream: Anglian Water implemented a modular side-stream solution supplied by Siltbuster Group, which offers flexibility and scalability within the constrained site layout. This system includes:

Three Lamella clarifiers for primary solids removal. Two moving bed biofilm reactors (MBBR) complete with blower skids for biological treatment. Three dissolved air flotation (DAF) units to polish effluent and remove residual solids.

These technologies work in harmony to deliver robust treatment performance even under challenging conditions.

Supporting this advanced treatment process are associated pumps, flow splitters, and access platforms, ensuring smooth operation and ease of maintenance.

Tertiary solids removal: To further enhance effluent quality, the project has incorporated tertiary solids removal (TSR) through twin-stream pile cloth filters and disc filters from FLI Water Ltd, which provide an additional layer of protection for local watercourses.

Power supply: Recognising the increased power demands of these systems, the upgrade also includes a 315kVA electrical power enhancement, installation of a new LV switchboard kiosk, and integration of telemetry systems for real-time monitoring and control.

Collectively, these improvements enable Ramsey WRC to handle an additional 20 litres per second (l/s), bringing the total FFT capacity to 89.4 l/s, while ensuring compliance with stringent environmental standards.

[caption id="attachment_28314" align="alignnone" width="1200"] DAF tanks and access steelwork - Courtesy of @one Alliance[/caption] Challenges

Delivering this complex project posed several significant challenges that required innovative solutions and careful planning.

Space constraints: The existing site footprint offered very limited options for new installations, making it difficult to accommodate additional infrastructure without major disruption. The project team’s decision to adopt modular side-stream units provided the flexibility to position equipment efficiently within the restricted area. This approach minimised the need for extensive civil engineering works and allowed the team to make the most of the available space. Integration with existing assets: Maintaining continuous operations during construction was critical to avoid service interruptions. The team addressed this by retaining key components of the existing system, such as inlet works, screens and grit removal facilities. This strategy not only reduced costs and complexity but also ensured that the site remained fully functional throughout the upgrade process. Regulatory compliance and timeline management: With a design horizon extending to 2025, another significant hurdle was for the project needed to align with NEP FLOW Driver U_IMP6 and WINEP obligations. To meet these requirements, the team engaged stakeholders early and implemented a phased construction plan. Integration of multiple advanced technologies: The project faced technical complexity due to the integration of multiple advanced technologies, including lamella clarifiers, moving bed biofilm reactors (MBBR), dissolved air flotation (DAF) units, and tertiary solids removal (TSR) systems.

Coordinating these systems demanded robust design and commissioning strategies. The team mitigated risks by collaborating closely with specialist suppliers, ensuring seamless integration and reliable performance across all components.

[caption id="attachment_28309" align="alignnone" width="1200"] MBBR tanks - Courtesy of @one Alliance[/caption] Ramsey WRC: Supply chain - key participants Client: Anglian Water Project delivery: @one Alliance Principal contractor: Skanska Civils installation: Hercules PLC Stormwater storage tank: Hayes GFS Ltd Modular side-stream solution: Siltbuster Group TSR disc filter: FLI Water Ltd Mechanical & electrical installation: Waveney Pumps Ltd Air blowers: AERZEN Machines Access steelwork: Steelway Power upgrade: UK Power Networks MCC & kiosk: Max Wright Ltd Pumps: Xylem Water Solutions Gorman-Rupp pump supply: Hydromarque Ltd Verderflex peristaltic pumps: Verder Ltd Pipework: Saint Gobain PAM UK Site security & construction timelapse: Wireless CCTV Ltd Asbestos removal: Oracle Solutions Coordination & collaboration

The successful delivery of the Ramsey WRC upgrade was underpinned by a highly coordinated and collaborative supply chain strategy. Given the complexity of the dual-scheme approach, combining storm tank capacity upgrades with advanced flow to full treatment (FFT) enhancements, the project required contributions from multiple Tier 2 contractors and specialist suppliers, each playing a critical role in achieving the technical and regulatory objectives.

[caption id="attachment_28312" align="alignnone" width="1200"] Lamella settlement and access steelwork - Courtesy of @one Alliance[/caption] Conclusion

Work commenced in August 2024 and at the time of writing (January 2026) is scheduled for completion in the upcoming months; ensuring that all regulatory deadlines are met without delays.

The Ramsey Water Recycling Centre upgrade stands as a clear demonstration of Anglian Water’s commitment to resilience, regulatory compliance and environmental stewardship. By investing £10m into advanced treatment technologies and storm capacity improvements, the project not only addresses immediate operational and regulatory challenges but also future-proofs the site for AMP8 and beyond.

This strategic investment ensures that Ramsey WRC can continue to meet the growing demands of population increase and the tightening environmental standards that govern water recycling operations.

The flow to full treatment element of the investment is on track to achieve an 77% reduction against Anglian Water’s capital carbon baseline, which is key to supporting Anglian Water’s commitment to reaching a net zero organisation by 2030.

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.