Supply Chain - Treatment Process Technologies - Activated Sludge Plant

The Seagahan Water Treatment Works (WTW) is located approximately six miles south of Armagh in Northern Ireland and serves communities in Edanveys, Corran, and Roughfort via a single gravity-fed main from the Seagahan impounding reservoir. The Seagahan Treatability Improvements Project is a strategic initiative within the Water Non-Infrastructure work stream, designed to address persistent operational and compliance challenges at NI Water’s 23 water treatment works. Seagahan WTW currently treats an average of 10 million litres per day (MLD), with a design capacity of 16.3 MLD and plays a critical role in regional water supply. Project need

In recent times Seagahan WTW has faced ongoing issues including:

Elevated trihalomethanes (THMs) and turbidity in final water. Inadequate contact time for disinfection. A failing soda ash system. Chlorinated backwash water and backwash capacity issues.

Unaddressed, these deficiencies could pose risks to regulatory compliance, limit future growth capacity, and increase the potential for Cryptosporidium contamination.

[caption id="attachment_26493" align="alignnone" width="1200"] Seagahan WTW & Seagahan Reservoir - Courtesy of NI Water[/caption] Project scope

The Seagahan WTW Treatability Improvements Project has implemented a series of targeted upgrades to enhance water quality, improve operational resilience and maintain compliance. Key interventions included:

Replacement of the soda ash plant. Installation of automatic coagulation dosing system to analyse trends. New orthophosphoric dosing system. Replacement of valves and actuators. Upgrade of one rapid gravity filter with glass media.

These upgrades are informed by a treatability appraisal conducted by Arup, which identified critical shortfalls and recommended improvements to ensure the facility could meet current and future regulatory standards.

Project team

NI Water engaged Arup and Murphy DAWSON-WAM (MDWAM) early in the project through an Early Contractor Involvement (ECI) approach, fostering a collaborative environment that allowed the project to evolve efficiently. As Principal Contractor, Murphy DAWSON-WAM, supported by strong coordination across all parties, successfully delivered the project on time and within budget. Arup played a dual role, providing NEC Project Management and Supervision throughout the construction phase, while also leading design reviews and approvals. Their involvement extended to managing stakeholder engagement within NI Water and liaising with external bodies such as the Department for Infrastructure.

A key success factor was the strong working relationship developed with NI Water’s Operations, which enabled a clear understanding of practical operability challenges. This collaborative approach informed strategic decisions around infrastructure layout, including pump and panel positioning, freeing up space for storage and maximising the use of existing buildings. These efforts not only streamlined project delivery but also ensured the long-term resilience of water treatment at Seagahan WTW.

[caption id="attachment_26484" align="alignnone" width="1200"] BIM model of existing GAC building - Courtesy of Murphy DAWSON-WAM[/caption] Seagahan WTW: Supply chain - key participants Client: NI Water Project manager: Arup Main contractor: Murphy DAWSON-WAM (MDWAM) Process & MEICA designer & contractor: Murphy Process Engineering Civils designer & contractor: DAWSON-WAM Ltd Civils design: RPS Formwork: Raptic Ltd Chemical storage & batch tanks: Spirotech Chemical dosing pumps: ProMinent Fluid Controls (UK) MCC works: Pronto Automation Systems Ltd Static mixer: TPS Filtration Chemical storage tank: Forbes Technologies Limited Air scour blower: AERZEN Machines Design & planning

ECI with MDWAM and Arup enabled a collaborative and informed approach from the outset of the project. Arup provided up-front technical input through treatability studies, which were instrumental in shaping Business Case submissions and developing focused Basis of Design reports. This proactive engagement supported scope progression and ensured a robust design strategy. Throughout the process, NI Water stakeholders were actively involved in decision-making, fostering transparency and alignment across all phases of delivery.

As designs evolved, a number of design review workshops were held which involved the use of walkthrough models to highlight pinch points and process walk-throughs.

Preference was for the new soda ash storage silo to be located indoors, restricted space for which was determined in the existing GAC building. MDWAM introduced innovative methods, including a 3D scan of the existing GAC building, to validate the feasibility of initial design proposals and facilitate the reuse of existing storage space. The volume and design of the storage silo were influenced by these constraints. The 3D scanning of the existing GAC building was instigated in the absence of record drawings, with new equipment designed to fit head height constraints and roller door access for installation.

A key design decision identified during a design review meeting was the introduction of a structural steel mezzanine platform level to locate the new MCC as floor space was limited.

During the initial investigations, the team identified gaps in the existing information relating to original structures, highlighting the need for further exploration. In several instances, monitoring data was unavailable, so dosing pump and process design had to be guided by SCADA trend analysis where possible. Temporary instruments were also set up during ECI to capture critical analytical data that was otherwise missing. These proactive measures ensured that design decisions were grounded in accurate, site-specific information, ultimately enhancing the reliability and efficiency of the final solution.

[caption id="attachment_26491" align="alignnone" width="1200"] (left) Mezzanine platform: MCC & holding tank and (right) soda ash bulk storage silo - Courtesy of NI Water[/caption] Construction & implementation

The project was delivered within a live operational environment, requiring meticulous planning and coordination to ensure continuity of service and safety. Construction on site began in December 2023 and completion was at the beginning of July 2025. The works were sequenced to minimise disruption to ongoing treatment operations, with close collaboration between the design, construction, and operations teams throughout. A key inherent risk exists when interfacing with existing operational works, live instruments and electrical assets, and this collaboration and careful planning helped to ensure no negative effect on network assets or output during the upgrade.

Early challenges included the failure of legacy equipment originally earmarked for reuse, such as manganese blowers and seized valving arrangements. These issues were addressed through rapid redesign and procurement, ensuring the programme remained on track. Spatial constraints within the site presented further complexity, particularly during the construction of the new dosing chamber and associated pipework diversions. Temporary works and phased excavation strategies were implemented to maintain access and operational integrity.

Modifications to the clean water tanks (CWT1 and CWT2) were carried out under confined space protocols. The installation of actuated valves and bell mouth fittings required innovative approaches due to restricted access openings. Sequencing was critical, with CWT2 brought back into service prior to converting CWT1 into a dedicated un-chlorinated backwash tank.

[caption id="attachment_26492" align="alignnone" width="1200"] Static mixer chamber roof & CWT1 inlet pipe - Courtesy of NI Water[/caption]

All works were delivered on a live site, with embargo periods and planned maintenance activities carefully managed. Temporary dosing systems were installed to facilitate safe changeovers, and effective stakeholder engagement with NI Water operations teams ensured that risks were mitigated and service continuity maintained. The new soda ash plant was commissioned in April 2025 and has since been used as the pH controlling process, taking over from the old system.

The project also included the installation of a new potable water supply to the site, with future-proofing measures incorporated to support additional connections. Engagement with DfI Roads and NI Water Distribution Teams ensured compliance and coordination with wider infrastructure planning.

Process enhancements

As part of the project, several process-driven improvements were implemented to enhance operational reliability, chemical dosing accuracy, and overall treatment efficiency.

Soda ash system upgrade: The existing soda ash silo was experiencing structural issues and material bridging, leading to inconsistent dosing. A new soda ash system was installed, comprising a silo with integrated shakers, blowers, and a batch tank. A third mixing/maturation tank was introduced to stabilise pH levels and eliminate dosing spikes. Strategically positioned at the opposite end of the building, it also shortens suction lines and improves soda ash solubility. This upgrade ensures consistent material flow and improved pH control, particularly important given the variable pH levels observed due to temperature fluctuations in Seagahan Reservoir.

[caption id="attachment_26487" align="alignnone" width="1200"] Soda ash mix tank A & B - Courtesy of NI Water[/caption]

Potable water protection measures: To prevent back siphonage and protect potable water quality, the supply to the backwash tank was removed following its conversion to an un-chlorinated backwash tank. A new supply line was established from the main distribution network, ensuring compliance with water safety standards.

Centralised control via MCC panels: Motor Control Centre (MCC) panels were installed to provide centralised control of all newly commissioned equipment. This integration enhances operational oversight and simplifies maintenance procedures.

Efficiency gains in backwashing: The transition to unchlorinated water for backwashing has led to reduced chemical wastage and improved backwash efficiency, especially during periods of poor water quality. This required careful reconfiguration of valving arrangements and blanking off interconnections between tanks to prevent contamination of clean water leaving the site.

Flow monitoring & chemical dosing control: A dedicated flow meter chamber was constructed to monitor flow rates of orthophosphate and chlorine dosing. The flowmeter also interfaces with an actuated valve to regulate the filling of CWT1, now designated as the backwash tank. This setup allows for precise control of chemical dosing and tank filling operations.

To protect operatives, the chlorine and orthophosphate are installed in separate chambers to reduce the risk during leaks. This item was identified during a hazard identification meeting.

[caption id="attachment_26488" align="alignnone" width="1200"] Orthophosphoric dosing plant - Courtesy of NI Water[/caption]

Hydraulic improvements: The upstand level of CWT2 was increased to enhance hydraulic head, supporting improved flow dynamics across the system. An actuated valve was installed to prioritise flow between the backwash line and CWT2, ensuring that neither system is starved during simultaneous operations.

Water recovery gains: The backwash system was previously a bottleneck to reliable output, following review a hydraulic restriction in the lamellas was identified and addressed which allowed a greater flow to pass through them to reach their design capacity. This improved the overall efficiency and removed the bottleneck, providing headroom in the dirty wash water system and ultimately providing the works with more frequent backwashing facilities.

Innovations, cost savings & carbon reduction

The Seagahan WTW Treatability Improvements Project incorporated a range of innovative and sustainable measures that enhanced delivery and long-term operational performance. By maximising existing assets and deploying efficient technologies, substantial carbon and financial savings were achieved, both in construction and ongoing operation.

A 3D scan of the GAC building was undertaken to address the absence of reliable as-built records. This enabled accurate coordination with the BIM model and informed the design of new equipment, including a bespoke mezzanine platform for the MCC panels, optimising use of available space.

Sustainability was embedded throughout the project. Excavated material was reused on-site for landscaping and reprofiling, eliminating disposal costs and reducing carbon emissions. Modular blocks were re-purposed for use on other sites, supporting circular economy principles.

The introduction of a third process tank and the use of un-chlorinated water for backwashing improved chemical efficiency and reduced waste, particularly during periods of algal blooms. Additional measures included the installation of a spill tank with integrated safety features and the design of dosing skids with enhanced access and flushing capabilities.

These innovations supported efficient delivery, reduced environmental impact, and aligned with NI Water’s long-term sustainability goals.

[caption id="attachment_26483" align="alignnone" width="1200"] Soda ash transfer pumps - Courtesy of NI Water[/caption]

The project exemplifies sustainable infrastructure delivery, with substantial environmental and financial benefits realised through three key initiatives:

Embodied carbon avoidance: By re-purposing existing infrastructure rather than constructing a new 100m2 facility, the project avoided significant carbon emissions and capital expenditure - This approach resulted in an estimated carbon saving of 60 to 90 tonnes of Co2e and a cost saving of £350,000 to £500,000. Energy-efficient equipment: The installation of high-efficiency motors helped reduce operational energy consumption - This measure contributes an annual carbon saving of 2 to 5 tonnes of Co2e and an annual cost saving of £216 to £432. Process optimisation: Enhancements in chemical dosing reduced both chemical usage and sludge production - These improvements yield an annual carbon saving of 2 to 10 tonnes of Co2e and a cost saving of £1,000 to £2,000.

Overall, the combined impact of these measures in the first year is estimated to deliver a total carbon saving of 64 to 105 tonnes of Co2e and a cost saving of between £351,216 to £502,432.

Project outcomes

The Seagahan WTW Treatability Improvements Project was successfully delivered on time and within budget driven by early contractor involvement, innovative design solutions, and a shared commitment to operational excellence and sustainability. With this project NI Water has been able to enhance operational efficiency, enable real-time monitoring via advanced SCADA telemetry, and has future-proofed the system for further instrumentation upgrades. Collaboration between the client, project manager, contractor and other key stakeholders was central to the execution of the project and its overall success.

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.

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.

Bolnhurst Water Recycling Centre (WRC), located near Keysoe in Bedfordshire, is currently undergoing a major upgrade to comply with new phosphorus discharge limits introduced under the Water Industry National Environment Programme (WINEP). Anglian Water, working through its @one Alliance, has designed and constructed a novel treatment solution that is now approaching the commissioning stage. The project combines a first-of-its-kind algae-based photo bioreactor system in-between primary and final settlement. By doing so, it is expected to not only secure immediate compliance with the new 0.5 mg/l phosphorus consent but also provide a sustainable, low-carbon model for nutrient management across the wider region. Non-traditional treatment option

Rather than relying on conventional chemical dosing or energy-intensive tertiary plants, the scheme has been designed to demonstrate how compact, modular, prefabricated technology can provide a chemical-free and carbon-efficient alternative. Once operational, the Bolnhurst system will act as a reference site for future phosphorus removal schemes in Anglian Water’s AMP8 programme.

[caption id="attachment_26780" align="alignnone" width="1200"] Exterior view of greenhouse - Courtesy of @one Alliance[/caption] The challenge

Under WINEP, Bolnhurst WRC is required for the first time to achieve an effluent phosphorus concentration of 0.5 mg/l. This is a stringent limit, particularly for a rural treatment works with no existing phosphorus removal capability. The site’s existing assets were an inlet wet well, followed by a series of RBCs, that were at the end of their lifespan, and a small lagoon that provided settlement.

Without intervention, Bolnhurst would have been unable to meet the new consent, exposing Anglian Water to regulatory penalties and increasing nutrient loading in the receiving watercourse. Achieving the new standard required a complete wastewater treatment package, instead of just a tertiary treatment process. The challenges on site included:

Restricted footprint: Little available space for conventional plant such as tertiary cloth filter packages and dosing units. Ageing assets: Existing assets were at the end of their design life and there was limited biological treatment and no inlet screen or primary settlement phase. Operational continuity requirements: Treatment must be maintained during construction. Carbon reduction commitments: The solution must align with Anglian Water’s net zero 2030 target. [caption id="attachment_26779" align="alignnone" width="1200"] Photo-bioreactor tanks installation phase - Courtesy of @one Alliance[/caption] Optioneering

Anglian Water tasked the @one Alliance to provide a robust solution that provides a variety of benefits to the local communities and environment. Initially, a range of potential treatment options were considered during the feasibility design, however following a multi-criteria assessment covering cost, carbon, footprint, operability and resilience, an innovative algae-based photo-bioreactor technology was selected as the preferred option.

The solution

Supplied by ALGAESYS S.A., the central feature of the upgrade is the 200m2 algae-based photo-bioreactor system. This is a low energy, chemical-free system for primary, secondary and tertiary treatment, capable of removing solids, organic matter, nitrogen and phosphorus, as well as reducing pathogens. At Bolnhurst WRC, this robust decarbonised technology harnesses naturally occurring algae to capture dissolved phosphorus and other nutrients from secondary effluent. The algae assimilates phosphorus as it grows, enabling P-removal without the need for chemical precipitation.

The bioreactors are designed to operate in modular tanks, equipped with LED lighting to help out in the depths of winter, and controlled aeration to keep the algae alive. Once established, the algal biomass can be periodically harvested, with the potential for beneficial reuse as an agricultural soil conditioner. There is also potential for the wastewater to be used for data centre cooling, instead of precious potable water; as AI data centres grow in the UK.

[caption id="attachment_26778" align="alignnone" width="1200"] Photo-bioreactor tanks installation phase - Courtesy of @one Alliance[/caption]

Given the restricted site footprint, the bioreactor plant was designed as a compact, modular system. Prefabricated units were assembled off-site and delivered to Bolnhurst for rapid installation. This approach minimises site disruption, lessens health and safety risks, reduces construction carbon, and allows future expansion by adding additional modules if required.

To integrate the algae system into the existing WRC, a number of supporting works were delivered:

New inlet pumps and screens with an automatic duty/standby rotation and a safe maintenance access platform. Re-purposed RBC discharge tank, which is now used as a backwash attenuation tank. Tertiary sand filters, located externally to the greenhouse, which improves access and maintainability. Bespoke MCCs, control panels and SCADA integration. New TSFR flow meter & final effluent sample point. Backfilling of existing lagoon.

With the regulatory deadline preceding full commissioning of the algae plant, a temporary lamella clarifier with ferric dosing from Siltbuster Group was installed. This interim system is already in place and is expected to secure compliance ahead of the statutory deadline, ensuring Anglian Water avoids permit breaches while final commissioning of the permanent works is completed.

[caption id="attachment_26781" align="alignnone" width="1200"] Installed bioreactor tanks prior to seeding - Courtesy of @one Alliance[/caption]

Once fully commissioned, the Bolnhurst phosphorus removal project is expected to deliver a broad set of benefits:

Regulatory compliance: Consistent achievement of the 0.5 mg/l phosphorus consent, protecting local water quality and Anglian Water’s environmental performance. Carbon reduction: A more detailed carbon analysis is currently underway, and should verify that it is on track to make a more than 50% carbon reduction against baselines. Resource recovery: Captured phosphorus, stored in algal biomass, can be harvested for reuse in agriculture, supporting circular economy principles. Energy efficiency: Optimised pumping and modular process design are expected to reduce energy consumption by up to 80% compared with conventional systems. Resilience and flexibility: Modular units can be adapted or expanded in future, while prefabrication simplifies replacement or upgrade activities. Knowledge transfer: Lessons from Bolnhurst will inform the wider roll-out of algae-based phosphorus removal in Anglian Water’s AMP8 programme. [caption id="attachment_26783" align="alignnone" width="1200"] Algae photo-bioreactors being seeded - Courtesy of @one Alliance[/caption] Bolnhurst WRC: Supply chain - key participants

The constrained nature of the site necessitated careful planning of construction logistics, lifting operations, and traffic management. Prefabrication was central in reducing working at height, hot works, and confined space entries.

Project delivery relied on a wide network of supply chain partners coordinated through the @one Alliance:

Project delivery: @one Alliance Principal contractor: Mott MacDonald Bentley Civil engineering: Hercules PLC MEICA: Waveneys Photo-bioreactor & PSC design: ALGAESYS S.A. Sludge tank: Stortec Engineering Ltd MCC requirements: TES Group Emergency safety shower: Hughes Safety Showers MCERTS: SIRIS Environmental Pumps: Xylem Water Solutions Temporary lamella plant hire: Siltbuster Group [caption id="attachment_26785" align="alignnone" width="1200"] Surplus biomass tank - Courtesy of @one Alliance[/caption] Commissioning

During commissioning, strict controls are in place to manage the co-existence of temporary and permanent treatment streams, ensuring no risk of environmental non-compliance. Operator training is being carried out in parallel to ensure that the new processes are understood and embedded before handover.

Expected outcomes

Once the algae-based system is fully operational, Bolnhurst WRC will be one of the first sites in the UK to meet phosphorus consents through a large-scale, chemical-free process. The project is expected to demonstrate the feasibility of algae systems as a mainstream alternative to chemical dosing, while provide real-world performance data for AMP8 phosphorus removal planning. This will also potentially reduce Anglian Water’s dependency on chemical supply chains & finally, showcase how modular prefabrication can overcome footprint constraints on small rural works.

The broader significance lies in proving that regulatory drivers can act as catalysts for innovation, driving adoption of lower-carbon and more sustainable wastewater technologies.

[caption id="attachment_26782" align="alignnone" width="1200"] (left) Sand filters and (right) DAF - Courtesy of @one Alliance[/caption] Conclusion

The Bolnhurst Water Recycling Centre Phosphorus Removal Project represents a landmark step towards sustainable nutrient management. As it moves into final commissioning, the scheme is poised to deliver compliance with stringent phosphorus limits, while simultaneously advancing Anglian Water’s goals on carbon reduction, circular economy, and resilience.

By combining an innovative photo-bioreactor system with conventional treatment, the project demonstrates how small, space-constrained WRCs can meet demanding environmental standards without reliance on chemicals or energy-intensive processes.

Once operational, Bolnhurst will stand as a reference site for the industry, providing valuable insight for future projects and reinforcing the role of the @one Alliance in delivering innovative, low-carbon infrastructure that safeguards both communities and the environment.

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.

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.

Everton Water Recycling Centre (WRC) is a small treatment works in Bedfordshire, serving around 200 homes and a population of roughly 600. Located downslope from Everton village (220 ft above sea level), the works benefits from a 14% gradient, allowing wastewater to flow to the site by gravity before being treated and discharged to the River Ivel. To meet the Environment Agency’s AMP7 requirements, Everton WRC needed to significantly reduce phosphorus in its discharge. Without action, the site would fail to comply with Environmental Permitting Regulations (EPR). Anglian Water was required to meet new consent limits of 1 mg/l phosphorus and 8,000 µg/l iron under the Water Industry National Environment Programme (WINEP). Solution

Anglian Water tasked its @one Alliance with identifying an effective and innovative solution to this issue. The conventional approach, iron dosing, would have needed major civil works, a new concrete base, modifications to the existing process, and an ongoing supply of iron chemicals. This would create ongoing costs, increased carbon emissions from deliveries, and higher operational complexity.

Instead, the team chose to challenge convention by developing Anglian Water’s first Integrated Constructed Treatment Wetland (ICTW) as a nature-based alternative. The final design created a three‑cell wetland covering 18,320m² (around 2.5 football pitches).

[caption id="attachment_28098" align="alignnone" width="1200"] Start of turf stripping - Courtesy of@one Alliance[/caption]

To build a wetland of this size, Anglian Water purchased the required land from a local farmer who owned the field downstream of the existing works. The existing outfall pipeline ran parallel to the farmer’s field and Tempsford Road, carrying the treated wastewater out towards the River Ivel. To feed the wetland, the team bypassed the start of that pipeline, diverting the water through the gravity-fed wetland before cutting back into the existing pipeline at the new wetland outfall location.

Planting

Over a six-month construction and planting period, the team excavated the three wetland cells and planted more than 110,000 native plants, including:

Emergent wetland plant species

Lesser pond sedge (Carex acuitiformus) Reed Sweet Grass (Glyceria maxima) Lesser reedmace (Typha angustifolia) Yellow flag (Iris pseudacorus)

Marginal wetland plant species

Water mint (Mentha aquatica) Purple loosestrife (Lythrum salicaria) Brooklime (Veronica beccabunga) Flowering rush (Butomus umbellatus) Gipsywort (Lycopus europaeus) Marsh cinquefoil (Potentilla palustris) Marsh marigold (Caltha palustris) Meadowsweet (Filipendula ulmaria) Water forget-me-not (Myosotis scorpioides) [caption id="attachment_28094" align="alignnone" width="1200"] View of site accommodation, Everton WRC, and the wetland site - Courtesy of@one Alliance[/caption] Challenges

Like many capital projects, the Everton Integrated Constructed Treatment Wetland faced several challenges, including:

Land acquisition & planning: Securing land and planning approval took longer than anticipated and fell largely outside the delivery team’s control, creating uncertainty in the programme. Seasonal working: To avoid winter working risks, construction was strategically rescheduled to start in April 2025, enabling safer and more predictable delivery during drier months. Stakeholder coordination: The scheme involved multiple parties landowners, local authorities, and environmental regulators, requiring strong communication and alignment throughout. First-of-its-kind risks: As Anglian Water’s first ICTW, the solution carried natural risks around design validation and achieving stringent phosphorus and iron limits without chemical dosing. International appeal

As the UK’s first ICTW, the project has drawn international attention. In November 2025, Anglian Water hosted officials from the Mexican Embassy and Government during a UK trade mission exploring innovative water management approaches. Grant Tuffs, Regional Engagement Manager, noted that the visit strengthened international collaboration and highlighted the value of nature‑based solutions in modern water infrastructure.

The wetland has also been visited throughout the earlier stages of the project by Richard Fuller, local Bedfordshire Conservative MP, showcasing the positive and widespread attention this project has received throughout its lifecycle.

[caption id="attachment_28091" align="alignnone" width="1200"] Preparing the wetland cells - Courtesy of@one Alliance[/caption] Everton Wetlands: Supply chain - key participants Project delivery: @one Alliance Principal contractor: Skanska Wetland designers: Binnies Wetland designers: VESI Environmental Ltd Flood risk assessment: SWECO Topography surveys: Randall Surveys LLP Archaeological mitigation work: Headland Archaeology Ground investigation work: AF Howland Associates Specialist wetland construction: William Morfoot Ltd Wetland plants & planting: Salix River and Wetland Services Landscape planting & ecological surveys: Greenwillows Associates Ltd Enabling civil works: DLO (@one Alliance Direct Labour) Drone surveys & video footage/stills: Dronesmart Global Site security & construction timelapse: Wireless CCTV Ltd Flow meter supplier: Metasphere Ltd Flow meter installation: Dodd Group OSM chamber: SIRUS Security fencing & gate: Burn Fencing Ltd

Because no new dosing plant was needed, the existing site infrastructure and power usage remained unchanged. The planning and land acquisition process took three years, reflecting the complexity of delivering a first‑of‑its‑kind solution. This allowed the team to develop a robust, repeatable design for future wetlands planned across AMP8.

[caption id="attachment_28095" align="alignnone" width="1200"] Wetland cells prior to planting - Courtesy of@one Alliance[/caption] Successes

The Everton Integrated Constructed Treatment Wetland Project eliminated the need for chemical dosing, reducing lorry movements, operational carbon, and long‑term chemical costs. A deeper pond area was also created to encourage biodiversity and support local wildlife.

The Everton Wetland was completed in October 2025. With planting now established, full growth and system maturity are expected by Spring 2027. The plants have an indefinite lifespan but is likely to be between 30 and 50 years or more.

Overall, the project achieved an 84% reduction in carbon emissions, cutting the carbon footprint from 654 tCo2e to 104 tCo2e, largely due to balanced cut‑and‑fill earthworks that avoided imports and exports and the removal of 99% of anticipated concrete use.

[caption id="attachment_28097" align="alignnone" width="1200"] Wetland plants - Courtesy of@one Alliance[/caption] Conclusion

The Everton Wetland Project demonstrates how nature-based design can deliver regulatory compliance while providing long-term environmental, operational, and carbon benefits. By replacing chemical dosing with an ICTW, Anglian Water has reduced costs, cut emissions, increased biodiversity, and created a blueprint for future schemes.

As part of the £37m wetland programme, the lessons from the Everton Integrated Constructed Treatment Wetland Project will shape the next generation of wetlands to be delivered across AMP8. This project represents a significant milestone in the UK water industry’s shift toward sustainable, resilient infrastructure.