Supply Chain - Treatment Process Technologies - Treatment Stage - Secondary

As part of the UK government’s Green Recovery programme, Severn Trent initiated a series of transformative projects aimed at enhancing river water quality and ecological health. Among these, the deployment of ozone treatment technology at Frankton, Itchen Bank, and Ludlow Sewage Treatment Works marked a pioneering step in UK wastewater management. Delivered under the Bathing Rivers initiative, the ozone scheme targeted the reduction of faecal indicator bacteria and micro-pollutants in final effluent, with the goal of improving river water quality in the River Leam and River Teme catchments by March 2025. The scheme introduced ozone disinfection as an additional treatment stage at the end of the sewage treatment process. Ozone is already widely used in drinking water treatment across Europe but this is the first time it has been trialed in wastewater treatment in the UK. Technical overview of ozone treatment

The ozone treatment systems installed at Frankton, Itchen Bank, and Ludlow STWs were designed to deliver high-efficiency disinfection while maintaining operational safety and adaptability. Each site features three ozone contact tanks arranged in series, forming a single downward-flow water path.

Ozone (O3) gas is introduced via ceramic dome diffusers at the base of the first two tanks, creating a cloud of fine bubbles that maximises the surface area for gas-liquid interaction. This counter-current flow (water moving downward while ozone bubbles rise) enhances mass transfer efficiency and ensures thorough mixing.

[caption id="attachment_26787" align="alignnone" width="1200"] Installation at Ludlow STW - Courtesy of Severn Trent[/caption] The third contact tank provides an extended reaction time, allowing any residual ozone to complete its disinfection process before effluent discharge. To prevent environmental harm, excess ozone is captured in sealed airspaces and directed to destructors via vacuum pipework. These destructors use catalytic conversion to break down ozone safely, with the resulting air vented at high level outside the containerised plant.

Each site’s ozone dosing is governed by a dual-mode control system. In fixed dosing mode, operators can set a constant ozone dose proportional to flow, typically within the 1–7 mg/l range. During commissioning, a 2 mg/l dose was identified as optimal for achieving target water quality. Adaptive control allows the plant to respond dynamically to changes in effluent quality, maintaining treatment efficacy while minimising ozone consumption.

Safety was a core design principle. Each contact tank was equipped with anti-siphon loops, non-return valves, and water-in-pipe detectors to prevent back flow and ensure safe operation. The ozone plants were housed in pre-assembled containers with integrated gas monitoring systems, enabling rapid deployment and minimising on-site construction. These modular units also facilitated maintenance and future scalability. Ozone gas monitors are a required item of personal protective equipment for operatives of the ozone plants.

Site information

Frankton STW, located in Warwickshire, is a biofilter works with chemical dosing for phosphate removal. The ozone plant was integrated with a tertiary solids removal (TSR) system to meet suspended solids requirements. The ozone systems at all three sites include two generators and three contact tanks, with a target dose range of 1–7 mg/l.

The integration of ozone treatment at the sites required careful coordination with existing infrastructure and process flows. The TSR unit plays a critical role in preparing the final effluent for ozone contact by reducing suspended solids to below 25 mg/l, the threshold necessary for effective ozone transfer and reaction. The ozone plant is housed in modular, containerised units, allowing for rapid installation and minimal disruption to site operations. These units include built-in safety systems such as gas detectors, sealed airspaces, and automated destructors to manage residual ozone.

The Itchen Bank and Ludlow ozone plants operate in the same way as Frankton’s except they are fed by liquid oxygen, as opposed to compressed air at Frankton.

The system includes safeguards such as anti-siphon loops, non-return valves, and residual ozone monitors. The destructors featured pre-heaters and catalytic converters to safely break down residual ozone before venting. The system is fully automated, with built-in fault detection and bypass capabilities to maintain operational continuity. The plant’s design emphasised safety, efficiency, and adaptability, contributing to improved effluent quality and reduced environmental impact.

[caption id="attachment_26791" align="alignnone" width="1200"] Tank installation at Itchen Bank - Courtesy of Severn Trent[/caption] Ozone Treatment Plants: Supply chain - key participants Civil engineering & groundworks: Kier Ozone plant supplier: Curio Group Liquid oxygen supplier: Air Products Monitoring & compliance

Each site will follow a rigorous monitoring protocol over a two-year trial period. Spot sampling for E.Coli and Enterococci will be conducted fortnightly, with continuous monitoring of ozone dose, concentration, and residual levels. Action limits were defined for by-products such as bromate, with automatic shutdown protocols in place. Data will be submitted quarterly to the Environment Agency, with a final report due after 24 months.

Environmental outcomes

The ozone treatment trials delivered measurable improvements in final effluent quality across all three sites, with expectation to significantly reducing concentrations of faecal indicator bacteria such as E. coli and Enterococci, as well as trace pharmaceuticals including carbamazepine and metformin. These reductions directly contribute to enhanced river health in the Leam and Teme catchments, supporting aquatic biodiversity and improving conditions for river recreational use.

By removing contaminants that are typically resistant to conventional treatment methods, ozone disinfection helps to mitigate risks to both human health and sensitive fluvial ecosystems. The improved effluent quality also reduces the impact of final effluent discharges, aligning with the goals of the Bathing Rivers programme and supporting compliance with emerging water quality standards.

The modular design of the ozone plants, pre-assembled in shipping containers, enabled rapid deployment and minimised disruption to existing site operations. This approach not only reduced construction time and carbon footprint but also provided a scalable model for future installations. The closed-loop ozone systems, equipped with real-time monitoring and automated destructors, ensures safe operation.

Together, these outcomes demonstrate how advanced oxidation technology can be harnessed to deliver tangible environmental benefits, setting a precedent for innovation in wastewater treatment across the UK.

[caption id="attachment_26790" align="alignnone" width="1200"] (left) Frankton STW ozone treatment plant from Curio Group and (right) liquid oxygen storage tank from Air Products at Itchen Bank STW - Courtesy of Severn Trent[/caption] Innovation & impact

These projects were not only the first of their kind in UK wastewater treatment marking a milestone in environmental engineering. The projects showcased how advanced oxidation processes can be safely and effectively integrated into existing infrastructureand the use of modular, containerised ozone plants allowed for rapid deployment with minimal disruption.

Conclusion

The ozone treatment projects at Frankton, Itchen Bank, and Ludlow STWs exemplify technical excellence, environmental stewardship, and innovative thinking. By improving final effluent quality and river health, Severn Trent Water has set a new benchmark for sustainable wastewater management. This submission highlights the transformative potential of ozone technology and its role in achieving cleaner, safer water for all.

From an ecological perspective, the reduction of faecal indicator bacteria and pharmaceuticals in final effluent is having a measurable impact on river health. The improved water quality supports biodiversity, enhances recreational value, and contributes to long-term resilience in the River Leam and River Teme catchments.

The rigorous monitoring and compliance framework, ensures that environmental protection remains central throughout the trial.

Ultimately, the success of these ozone treatment schemes reflects Severn Trent’s commitment to innovation, collaboration, and sustainability. By pushing the boundaries of conventional wastewater treatment, the programme has delivered lasting benefits for communities, ecosystems, and the wider water industry.

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.

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.

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 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 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.

Dearne Reach is a 4.3-hectare Integrated Constructed Wetland (ICW) in Clayton West, Huddersfield, designed to enhance water quality along 4km of the River Dearne. Delivered by Mott MacDonald Bentley on behalf of Yorkshire Water, this ICW will reduce levels of un-ionised ammonia and improve storm flow treatment in line with the salmonid fundamental intermittent standards. To deliver this nature-based solution, Mott MacDonald Bentley excavated 13 wetland cells covering over 44,000m2 (equivalent of 7 football pitches!), creating space to house more than 350,000 wetland plants. Project background

As an alternative to the traditional grey infrastructure solution, which initially would have entailed 7,000m3 of additional storm storage and a 4.5km diversion of final effluent to a lower river reach, the Dearne Reach ICW offers a sustainable approach to pollution mitigation. Funded by Yorkshire Water as part of their capital delivery programme, it is currently the largest ICW developed in the UK to improve water quality while increasing storm storage resilience.

Aligning with Yorkshire Water’s WFD drivers and net zero ambitions, this project pioneers an ICW tailored for intermittent storm overflows, distinguishing itself from conventional ICWs that require constant inflow. Its innovative design ensures effective management of stormwater variability and will contribute to driving continuous innovation in nature-based solutions across the water industry.

[caption id="attachment_25943" align="alignnone" width="1200"] Construction of the first cells - Courtesy of MMB[/caption] Integrated constructed wetlands

Constructed wetlands are engineered ecosystems that harness natural processes to treat wastewater, stormwater, and industrial effluents. Sometimes described as ‘nature’s kidneys’ because of their ability to filter and clean wastewater by mimicking natural wetlands, these systems use porous media beds and emergent plants to remove contaminants through physical, chemical, and biological mechanisms.

Various treatment wetland types exist, including free water surface wetlands - also known as integrated constructed wetlands (ICWs).

ICWs allow water to flow above the soil through aquatic plants, enabling the removal of suspended solids, nutrients, and pathogens. These passive systems, closely resembling natural wetlands, rely on processes such as adsorption, precipitation, sedimentation, and filtration to improve water quality.

[caption id="attachment_25944" align="alignnone" width="1200"] Cell construction - Courtesy of MMB[/caption] Advantages for Dearne Reach

The ICW at Dearne Reach offers numerous advantages:

Water quality improvement: Effective removal of nutrients, heavy metals, pathogens, and organic pollutants. Carbon sequestration: Capturing carbon within plant biomass and soil, contributing to achieving net zero goals. Biodiversity enhancement: Providing habitats for birds and other wildlife, supporting ecological balance. Community benefits: Creating green spaces for public enjoyment and research opportunities. Versatility: Adapting to varying wastewater loads and flows, making it highly efficient at stormwater management. Low operational costs: Passive systems with minimal maintenance and no chemical requirements over decades, unlike conventional treatment plants. Plantings

At Dearne Reach, 52 different species of plants have been designed to sit in 13 adjacent cells in which over 350,000 plants adsorb nutrients from storm overflow discharges and wastewater flowing out of the Clayton West Wastewater Treatment Works.  These have been specifically selected for the treatment capacity, and alongside the enhancement of existing hedgerows across the site, has enabled a staggering 38% biodiversity net gain in terrestrial habitats.

[caption id="attachment_25945" align="alignnone" width="1200"] Liner installation - Courtesy of MMB[/caption] Variable stormwater discharges

The project introduced an ICW specifically designed to treat intermittent storm overflows. Unlike traditional ICWs, which are effective only with constant inflow, this innovative design can handle the variability and unpredictability of stormwater discharges. The wetland is divided into multiple cells, each optimised for maximum retention time and pollutant removal.

Advanced hydraulic controls and computational fluid dynamics (CFD) simulations were employed to model and optimise the flow through the wetland, ensuring effective treatment of fluctuating volumes and pollutant loads.

Pumping station & rising main

A new wetland pumping station has been designed to raise up to 350 l/s of flows from Clayton West WwTW to the ICW through a new rising main constructed using HDD trenchless methods. Once the water reaches the head of the wetlands, the entire system is passively flowing through two precast concrete distribution chamber structures and fourteen 1.4m wide cascades to transfer the water through each of the 13 cells.

Harnessing solar power

The innovative design harnesses solar power to operate a level sensor and flow meter chamber to successfully manage stormwater variability whilst achieving a passive system ICW with no additional power requirements. The introduction of the solar panels mean that the flow monitoring chamber could be installed to provide future quantity and quality monitoring data, which can be shared to support the evidence base of these emerging infrastructures.

As the largest ICW developed in the UK, its unique design and successful results will contribute to driving continuous innovation in nature-based solutions for storm management across the water industry. It stands as an excellent example of the power of collaboration between civil engineering and nature-based solutions to mitigate the impacts of climate change and promoting sustainable development.

[caption id="attachment_25941" align="alignnone" width="1200"] All cells constructed - Courtesy of MMB[/caption] Collaborative approach

To successfully design and build a wetland on the scale of Dearne Reach it was clear from the project outset that a collaborative design approach would be key to both a successful programme and commercial output. Therefore, collaboration between the design team, digital delivery team and geotechnical experts was fundamental. The challenges facing the site included, high shallow perched groundwater, sandy, gravelly clay requiring high degrees of compaction, and a requirement for over 13,000m3 of material for topsoil reuse. Alongside construction on a complex site within a coal mining legacy area, with archaeological potential and intersecting with a public right of way.

Dearne Reach ICW: Supply chain: key participants Principal designer & contractor: Mott MacDonald Bentley Outline design: Stantec UK Pressure testing: Ant Hire Groundworks: Lowthers Groundwater treatment: Siltbuster Group HDD rising main: Joseph Gallagher Ltd Liner suppliers: SIG Construction Accessories Precast structures: Craven Concrete Ltd Headwalls: Althon Ltd Treatment works package: HB Tunnelling Electrical package: Circle Control & Design Systems Ltd MCC installation: Technical Control Systems Ltd Communications instruments: Churchill Controls Ltd Wetland plant suppliers: Salix River and Wetland Services Grass & flower seed: Hurrells & Mclean Seeds Ltd Erosion protection: Geogrow Gate valves: Affco Flow Control (UK) Ltd Actuators: Glenfield Invicta Ltd Instrumentation: Marlec Instrumentation: IFM Electronic Ltd Flow meter: SIRIS Environmental Pipework: Aquaspira Ltd [caption id="attachment_25946" align="alignnone" width="1200"] Planting completed in all the cells - Courtesy of MMB[/caption] HDPE pipework & couplers: Westwood Pipelines Ltd HDPE pipework & couplers: Radius Systems DI pipework: George Green (Keighley) Ltd DI pipework: Electrosteel Castings (UK) Ltd DI pipework: UTS Engineering Ltd Metalwork: Fabtek Duct pits: Advanced Infrastructure Systems Pipe supports: Midland Fixings Ltd Drainage pipework: Wolseley UK ltd Drainage pipework: Myers Building Supplies Drainage pipework: Keyline Civils Specialist Ltd Pumps: Xylem Water Solutions Lifting gantry: Peter Cassidy (Leeds) Ltd Welfare cabins: Nixon Hire | Wernick Group Bolt-sets: BAPP Industrial Supplies Bolt-sets: VULCAN Industrial Fasteners RoadCem access roads: DNS Aggregates: Hague Plant ltd Concrete: Heidelberg Materials Plant hire: Lynch Plant Hire Plant hire: Grantham Industries Ltd Plant hire: Flannery Plant Hire (Oval) Ltd [caption id="attachment_25937" align="alignnone" width="1200"] Filling the first cells with water - Courtesy of MMB[/caption] Construction achievements

During construction, several notable achievements were made:

Groundwater management: As a result of high groundwater levels on the site, the system hydraulics were analysed, and cell height adjusted. This optimised the cut-fill balance and ensured no material import would be required to construct the embankments, ultimately preserving resources and reducing material waste whilst ensuring there would be no flotation risk

Bypass pipework reductions: Through the development of robust future access and maintenance plans, an opportunity was realised to eliminate unnecessary bypass pipework infrastructure. Initially, this had been proposed to allow each cell to be isolated for future maintenance. The removal of this pipework scope significantly reduced the carbon footprint and project costs.   

Sustainable lining solution: As the existing ground did not have a suitable impermeability to protect the underlying groundwater, the ICW had to be lined. To avoid the use of extensive plastic on site, a geosynthetic clay liner was used to create a self-sealing, resilient hydraulic barrier while minimising environmental impact.

Archaeological and geological integrity: The team ensured the coal mining legacy areas remained undisturbed, with archaeological trenching conducted site-wide to ensure any potential pre medieval features were not disturbed during construction.

RoadCem technology for sustainable access: Traditional concrete access roads were replaced with Roadcem soil stabilisation technology to reduce the required material import and associated carbon footprint with use of extensive artificial concrete.

Biodiversity commitment: 350,000 locally sourced plants were installed, arranged in seven planting zones, achieving a 38% biodiversity net gain in terrestrial habitats.

Public right of way enhancements: Social value was equally important to the project and the team collaborated with the local council to enhance the public right of way, improving accessibility with a wheelchair-friendly, 2m-wide footpath along the perimeter of the ICW, featuring timber fencing for optimal wetland viewing points to support community health and well-being.   

Carbon savings: The project has achieved a 60% reduction in embodied carbon and 40% reduction in operational carbon across its lifecycle – delivering a more environmentally friendly solution in comparison to the original grey infrastructure solution.

[caption id="attachment_25940" align="alignnone" width="1200"] Fully planted wetland - Courtesy of MMB[/caption] Innovative digital construction

From the outset, early collaboration with Mott MacDonald Bentley’s digital delivery team identified an opportunity to pilot the use of intelligent plant machinery, alongside a ‘Smart Construction Dashboard’ during the build.

Prior to mobilisation on site, the model and delivery programme was shared for upload into the Smart Construction/Earthbrain software. These platforms initially use Artificial Intelligence to generate an efficient delivery output, detailing size, type and number of machines required. They also generate a powerful earth shifting model, highlighting the most efficient distribution workflow for the cut/fill material to travel and be placed.

This was most useful to compare the tendered assumptions and check for any oversights in the planning phases. This approach improved accuracy, efficiency, and most importantly, improved health and safety standards on site. This marked a first-of-its-kind trial for deploying intelligent plant in the construction of a nature-based solution.

The site team reported significant benefits, particularly given the scale of the excavation, such as:

Model-driven excavation optimised material use, eliminating unnecessary cutting/filling and promoting a right-first-time methodology. Automated systems reduced manual surveying and minimised plant-people interaction, ensuring safer site operations. Precision excavation reduced material waste while moving 65,000m3 (117,000 tonnes) of soil, limiting reliance on imported fill. [caption id="attachment_25939" align="alignnone" width="1200"] Wetland plants developing - Courtesy of MMB[/caption] Successes & summary

The Dearne Reach ICW Project exemplifies sustainable development by delivering a low-carbon stormwater management solution. Leveraging natural processes such as sedimentation, filtration, and biological uptake, the wetland effectively removes pollutants and reduces the ammonia levels in stormwater in line with the salmonid fundamental intermittent standards. This enhances water quality and strengthens local biodiversity, aligning with global climate adaptation efforts.

The project’s innovative approach to managing stormwater discharges aligns with Yorkshire Water’s efforts to mitigate and adapt to the effects of climate change. It stands as an excellent example of the power of collaboration between civil engineering and nature-based solutions to mitigate the impacts of climate change and promoting sustainable development.

This first-of-its-kind trial has set a new benchmark for future wetland and nature-based solution projects across the water industry, with lessons learned shared to inspire continuous innovation in sustainable construction.

Southern Water’s Sandown Water Supply Works (WSW) supplies water to the Isle of Wight. The works treats water from the River Eastern Yar, a ‘flashy’ river with wide swings in turbidity and colour. The works treats river water by coagulation and flocculation, clarification, filtration, activated carbon adsorption and disinfection. The works provides a steady supply and allows the rate of extraction to be reduced in winter so groundwater levels can recover. Due to the nature of the river catchment area, during periods of heavy rainfall, the works has seen significantly lower-level pH in the raw water. Background

Weather has a major impact on raw water quality. Typically, rainfall increases flow in the river and, with it, turbidity. Colour, an indicator of natural organic matter, reduces in wet weather and increases in drier spells. Climate change has increased the intensity of rainfall, and this reduces the pH of the river water, making control of coagulation, which depends on colour, turbidity and pH, more difficult.

Higher turbidity during storm conditions requires a higher coagulant dose, and this further depresses the pH. This issue has, on several occasions, resulted in a shut-down of the works which struggled to meet treated water quality goals. Southern Water notified the DWI of this process issue and were issued with an improvement notice which required a long-term solution to be implemented by 28 February 2025.

[caption id="attachment_27251" align="alignnone" width="1200"] BIM image of the new dosing kiosk - Courtesy of Trant Engineering[/caption] Outline design

Southern Water engaged Trant Engineering to develop and implement a solution. Trant had a dedicated team at Sandown working on other schemes and had good working relationships with the Southern Water Project Team and Operations. This meant that they already had a good understanding of the problem and were able quickly to propose a solution consisting of chemical storage, pH control and a caustic soda dosing system together with all the associated piling, reinforced concrete plinths, paths, slabs and buried service ducts.

The proposed process solution treated chlorinated process water through dosing with sodium hydroxide within carrier water immediately prior to entering the contact tank. A measured dose is applied to the process, calculated by measuring pH and flow. The dose is then adjusted as required through a process feedback loop to maintain a required target pH set point.

Project scope Buried service duct installation. SFA piling works. Reinforced concrete plinths, paths and slabs. Gas service diversion. Diversion of incoming raw water mains. Chemical delivery area including delivery bund, interlocked delivery valving system, drainage works and chemical interceptor tank. Installation of safety shower. Installation of static mixer and chemical dosing point of application (POA) enclosure. Two bunded 5000L chemical storage tanks to store 28% concentration sodium hydroxide. Carrier water break tank. Carrier water hardness analyser and water softener system. Dosing pumps enclosure. Motive water pumps enclosure. pH Analyser Backboard. Process instrumentation, pressure sensors, level controllers and actuator valving. Dosing control panel with HMI. System integration with existing site controls. New dosing kiosk. Design & build

Because of space constraints, the incoming raw water mains had to be diverted. The dosing system required a pH analyser/controller mounted on a backboard with process instrumentation, pressure sensors, level controllers and automatic valves. Carrier water pumps and a water softener completed the dosing package with an adjacent dosing control panel with PLC and HMI.

Sandown WSW pH Correction: Supply chain - key participants Client: Southern Water Main contractor & civil works: Trant Engineering Civil design: AtkinsRéalis Piling works: Southern Piling Dosing system: Chemidose Limited Safety shower: Aqua Safety Showers International Ltd Control system, panels & systems integration: FW Marsh Static mixer: Statiflo International Ltd Kiosks: Morgan Marine Ltd Access fabrications: Toomers Ltd Challenges

There were several key challenges. Highly limited space available for the equipment required, extensive buried services, and challenging project delivery timescales to meet the regulatory outputs. Working closely with Southern Water and the established delivery partners Atkins Realis, Chemidose and F W Marsh, Trant’s team was able to complete the necessary Design, HAZOP and ALM process early in 2024.

The design was prepared with programme constraints heavily in focus and incorporated an off-site ready built kiosk with integral floor. This enabled the full kiosk fitout to be undertaken in parallel with the civils work on site and resulted in significant programme improvement. The dosing system was fully FAT tested offsite at Chemidose’s premises.

Space was tight to fit the kiosk on site, and tight within the kiosk to fit the process equipment needed whilst maintaining good access. A collaborative design process and a great team enabled this to be achieved within the constraints. Challenges were encountered on the civils design including unmapped significant pipework and unfavourable geotechnical conditions in the only viable location for the kiosk. The team moved quickly to resolve solutions which required a piled foundation to address the ground conditions and avoid loading the unmapped pipework whilst diversion was resolved.

[caption id="attachment_27253" align="alignnone" width="1200"] Local control panel with HMI - Courtesy of Trant Engineering[/caption] Installation & commissioning

The civil works and on-site preparatory M&E works were completed in parallel with the dosing kiosk fitout. This combined with the level of offsite fitout and testing substantially minimised the on-site installation period. The dosing kiosk was delivered to site as the civil works were completed, and a limited period of M&E works were required to connect into the existing site process.

The result

Within four weeks of the kiosk delivery, commissioning was able to commence. A successful commissioning period allowed project works to enter active service several weeks ahead of the DWI regulatory date for installation. The project achieved full formal handover well ahead of the DWI regulatory date for commissioning.

By close cooperation throughout the supply chain, commissioning was able to commence within four weeks of the kiosk delivery. Being familiar with the site, Trant’s Instrumentation, Control & Automation (ICA) team was able quickly to integrate the new controls, and the new works was in service and formally handed over several weeks ahead of the DWI regulatory date for installation.

The solution deployment has been successful in addressing the problem of low pH causing a need to shut down the works during periods of heavy rainfall and this success has been welcomed by all parties.