Supply Chain - Treatment Process Technologies - Sand Filters

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

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

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

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

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

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

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

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

The solution

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

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

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

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

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

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

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

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

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

Oakham Nitrogen Removal Trials: Supply chain - key participants

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

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

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

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

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

Lessons learned

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

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

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

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

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

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

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

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

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

Located near New Inn, South Wales, this innovative nature-based solution (NbS) project addresses the water quality impact from a storm overflow (SO) discharging into the Afon Lwyd during wet weather. Water quality modelling classified the existing high spilling asset as having a ‘Severe Impact’ on the river which under the Storm Overflow Assessment Framework (SOAF), prompted investigation, optioneering and construction of the most cost-effective solution to deliver a ‘No Impact’ outcome. Using a multi capitals assessment, the team evaluated cost, carbon and long term value to both nature and society. This showed that prioritising a nature-based solution delivered substantial a cost saving (£43m) and carbon savings (half the embodied carbon) against its grey equivalent solution, a 33,500m3 storage tank, alongside wider community and environmental benefits. Root cause and optioneering stage

During the optioneering stage, a range of interventions were assessed to address the storm overflow impact, including catchment‑scale rainfall disconnection, increased pass‑forward flow, nature‑based treatment and conventional storage. Catchment disconnection was discounted due to the high levels of customer disruption required, while increasing pass‑forward flow was not feasible due to downstream hydraulic constraints. Given the overflow’s location adjacent to open land by the river, a nature‑based solution was identified as the most effective and deliverable option.

[caption id="attachment_29039" align="alignnone" width="1200"] The field pre-construction used for occasional grazing, with the existing storm overflow situated within the trees to the right - Courtesy of Arup[/caption]

A two-stage approach was chosen to maximise success, with an aerated reed bed providing initial intensive solids capture followed by two Integrated Constructed Wetland (ICWs) in series, providing effluent polishing and an opportunity for the industry to research wetland treatment in this application.

The favourable topography enabled a gravity system, eliminating the need for lifting flows and in turn, reducing operational energy demands. The field’s proximity to New Inn’s residents also allowed for place-making features for the local community, such as footpaths, an outdoor classroom and natural play areas, enhancing community engagement and educational opportunities.

The indirect monetary value of these wider benefits was captured in the decision-making stage via the use of CIRIA’s B£ST estimation tool, which estimated £12m in realised benefits over the next 40 years across social, natural and other capitals; something none of the grey solutions offered.

[caption id="attachment_28938" align="alignnone" width="1200"] Site layout - Courtesy of Arup[/caption] Design stage: New compound

The existing storm overflow (SO) was located amongst trees on the edge of the field. The incoming pipe laid in the eastern corner of the field meant the SO could be relocated into a new compound, which will contain the following chambers and plant:

Screening chamber: The screening chamber houses an orifice flow control and a new mechanical screen that removes solids from excess flows. Only flows above the permitted pass‑forward rate are diverted to the reed bed, ensuring that the treatment process receives appropriate, pre‑screened volumes. Bypass chamber: This chamber is designed to divert the highest flows from the catchment before they enter the nature‑based solution. The flow threshold is set so that around 95% of the total discharge volume still passes through the NbS, with the bypass only operating during the most dilute, peak‑flow conditions. MCC kiosk: New kiosk to house the motor control centre. Aeration blower kiosk: An acoustically insulated kiosk to house the blowers for the aerated reed bed.

Design for Manufacture and Assembly principles were adopted to several elements of the compound. The screening and bypass chamber were fabricated off site by FP McCann Ltd, reducing the need to cast these chambers in situ.

Both the kiosks were prefabricated off-site by Morgan Marine Ltd to save time and reduce on-site activities in the construction phase.

[caption id="attachment_28921" align="alignnone" width="1200"] The new compound (March 2025) - Courtesy of Welsh Water[/caption] Design stage: Reed bed & integrated constructed wetlands

The design team carried out a catchment Flow & Load Survey to ensure a better understanding of the design parameters required to achieve the ‘No Impact’ outcome. The survey gave insight into the challenges around pollutant loads in intermittent discharges, with varying concentrations of biochemical oxygen demand (BOD) and ammonia found in the excess diluted sewage; especially the difference between accommodating the ‘first flush concentration’ and weaker dilutions as a storm event continued.

Working collaboratively with the reed bed and ICW suppliers early in this stage, increased confidence in achieving the necessary pollutant removal in the final effluent.

A Flood Consequence Assessment (FCA) was completed as part of the planning application and the findings required the reed bed and wetlands to be moved further away from the river, reducing the size of the originally allocated footprint. The revised layout however, still provided sufficient treatment area (3,000m2 for the reed bed and a combined ICW treatment area of 2,400m2) and created additional space for the public to enjoy.

Planning & stakeholder engagement

The planning application was critical to the success of this project, which was well received by local councillors and relevant bodies, in part, due to the extensive up-front work done by Arup’s planning team. Arup specialist teams carried out predictive odour and noise modelling of the solution to address concerns raised by the planning authority. The project team also engaged extensively with the local community through both in-person and online events, ensuring the design met local needs and preferences.

To align with the Sustainable Approval Body (SAB) requirements as part of planning approval, the design team implemented sustainable drainage features across the site. The maintenance track and vehicle areas in the compound were constructed from permeable TruckCell™ paving, made from recycled plastic, whilst vegetated swales and depressions were incorporated alongside the impermeable access track and footpaths. This reinforced the project’s low‑carbon and sustainable design ethos.

[caption id="attachment_28924" align="alignnone" width="1200"] Maintenance track constructed out of TruckCellTM - Courtesy of Arup[/caption] Pont-y-felin Lane: Supply chain - key participants Main designer/contractor: Morgan Sindall Infrastructure Lead designer & planning team: Arup Reed bed: Natural Wastewater Solutions (NWS) Integrated constructed wetland: Salix River and Wetland Services Vesi Environmental Ltd Aeration blowers: AERZEN Machines Precast screening & bypass chambers: FP McCann Ltd Chamber covers: Steelway Brickhouse Mechanical screens: Huber Technology Mechanical installation: Industrial Pipework Services MCC: Lloyd Morris Electrical Ltd MCC kiosk: Morgan Marine Ltd TruckCell™ paving: ABG Geosynthetics Construction stage

Construction started in January 2024, with Morgan Sindall Infrastructure mobilising to bring the nature-based solution system online before the regulatory deadline of 31 March 2025. The team navigated challenges including invasive species within the compound area and persistent groundwater during the large excavations, requiring an extensive dewatering activity (under approved Abstraction Licences).

Working with the sub-contractors, Natural Wastewater Solutions (NWS) for the reed bed, and Salix River and Wetland Services and Vesi Environmental Ltd for the integrated constructed wetland, 33,904 tonnes of soil were removed and the ground re-profiled. 30,000 tonnes was re-used off site, whilst 3,000 tonnes was recycled and re-used on site, with the final 904 tonnes taken to landfill, due to the presence of Japanese knotweed.

[caption id="attachment_29040" align="alignnone" width="1200"] Site drone photos throughout construction (January 2024 - June 2025) - Courtesy of Welsh Water[/caption]

Due to the impermeable nature of the soil, the reed bed and constructed wetland both required under-draining to minimise the impact on the groundwater table. Once the under-drains were installed, the basins were constructed, which included the following:

12,000 plants throughout the three basins, including: Phragmites planted for the reed bed and; Lesser pond sedge, reed sweet grass, lesser reedmace and water mint for the ICWs. 6,100m2 of liner across the three basins. 17,500m of aerated pipeline installed. 3,710 tonnes of stone.

The site team pushed to see the first flows through the system just 12-months later, ahead of the 31 March deadline and handled the heavy rainfall from Storm Eowyn on 24 January without any issue.

Monitoring

A robust sampling regime is currently underway to understand the performance of the individual stages and final effluent from the nature-based solution. This will inform future permitting of these types of solutions in cooperation with the environmental regulator, Natural Resources Wales (NRW).

The initial sampling results are promising, with significant reductions in BOD, ammonia, total suspended solids (TSS) and phosphorus in the final effluent. River water quality sampling upstream and downstream of the outfall is also being carried out to understand the impact of the scheme on the Afon Lwyd.

[caption id="attachment_28926" align="alignnone" width="1200"] Integrated constructed wetlands (October 2025) - Courtesy of Arup[/caption] Research

Welsh Water is participating in the Chemical Investigation Programme (2025–2030) with UKWIR, where samples from the wetlands are currently being used to help understand bio-accumulation of emerging substances such as pharmaceuticals in intermittent discharges.

Conclusion

With the site due to open to the public soon, Pont-y-felin Lane exemplifies a paradigm shift in storm overflow management, demonstrating how nature-based solutions can deliver technical excellence, environmental restoration, and community enrichment, all while setting a precedent for low-carbon infrastructure in the water sector. The forward‑thinking optioneering, combined with the client’s commitment to selecting a nature-based solution, over traditional ‘grey’ options, has resulted in a scheme that proves natural solutions can deliver more sustainable outcomes, for less.

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.

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

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

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

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

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

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

Site information

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

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

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

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

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

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

Environmental outcomes

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

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

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

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

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

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

Conclusion

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

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

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

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

Thurleigh Water Recycling Centre (WRC) is located just outside the village of Thurleigh in North Bedfordshire, around six miles from Bedford. The site plays a vital role in Anglian Water’s water recycling network, helping protect local waterways and maintaining environmental compliance. This project forms part of Anglian Water’s Water Industry National Environment Programme (WINEP), a national initiative focused on improving water quality and ecological health. WINEP supports the UK Government’s Water Framework Directive, which requires water companies to achieve good ecological status in rivers and water bodies. Problem To meet the Water Framework Directive, Thurleigh WRC needed to significantly reduce phosphorus levels in its final effluent. Excess phosphorus can cause algal blooms, oxygen depletion and damage to aquatic ecosystems. Thurleigh’s consent limit was set at a stringent 0.5 mg/l - beyond what existing assets could consistently achieve. Failure to meet this requirement risked breaching Anglian Water’s AMP7 commitments, potentially leading to regulatory penalties and reputational impact. Environmentally, reducing phosphorus was essential for improving river quality and supporting biodiversity. Solution Anglian Water tasked the @one Alliance with delivering the scheme. The team adopted an innovative £3.2m biological algae treatment system (I-Phyc) in place of traditional chemical dosing. The I‑Phyc system uses algae’s natural ability to absorb nutrients. Key components included: 11 process tanks and eight conditioning tanks with LED lamps and automated wipers. A new cloth filter for efficient algae harvesting. An air‑mixing system with dual blowers to maintain optimal oxygen levels. A new PLC‑controlled kiosk for real-time monitoring. Dual-channel phosphate monitors for accurate compliance tracking. Feed and backwash pumping stations. A DNO power upgrade for resilient electrical supply. This integrated solution not only meets regulatory targets but also sets a new benchmark for sustainable, low‑carbon water treatment; reflecting Anglian Water’s values of Always Exploring, Do the Right Thing and Build Trust. [caption id="attachment_28297" align="alignnone" width="1200"] The Thurleigh WRC biological algae treatment system from Industrial Phycology Ltd - Courtesy of @one Alliance[/caption] Thurleigh WRC: Supply chain - key participants Successful delivery relied on strong collaboration across the supply chain. The combined expertise of the project partners ensured high-quality design, compliance, and installation of a first-of-its-kind system: Project delivery: @one Alliance Principal contractor: Barhale MEICA & civils design: RSE (Ross-shire Engineering) Archaeology survey: Dalcour Maclaren Ltd Ecological survey: Greenwillows Associates Ltd I-Phyc algal reactor design & supply: Industrial Phycology Ltd Site electrical & mechanical delivery: RSE (Ross-shire Engineering) I-Phyc reactor electrical & mechanical delivery: Advanced Process Air blowers: Aerzen Machines MCC: Paktronic Engineering Co. Ltd Telemetry equipment: Dodd Group (Eastern) Ltd Safety shower: Hughes Safety Showers Ltd Civils works: DLO (@one Alliance Direct Labour) Challenges Introducing Anglian Water’s first algae-based phosphorus removal system brought several challenges: Supplier integration: Working with new technology required onboarding suppliers unfamiliar with @one Alliance processes. Close collaboration ensured alignment with standards and successful delivery. Operational transition: Adopting a biological alternative to chemical dosing required training, operational changes and robust risk management to ensure a smooth handover. Archaeological delays: Archaeological investigations during enabling works caused delays, but were essential to protect local heritage and meet statutory obligations. Despite these challenges, the project team maintained strong collaboration and proactive planning to keep the programme on track. [caption id="attachment_28298" align="alignnone" width="1200"] Completed biological algae treatment system - Courtesy of @one Alliance[/caption] Carbon savings Construction generated 205 tCO2e of capital carbon. However, the I‑Phyc system absorbs 46 tCO2e annually, meaning the project will offset its carbon footprint within four years. Further operational carbon savings include: The need for chemical transport and storage is removed. Lower sludge handling and disposal. Once fully optimised, the algae will absorb carbon equivalent to 2,190 trees per year. Conclusion The Thurleigh WRC I-Phyc Phosphorus Removal Project showcases how the @one Alliance and Anglian Water collaborate with the supply chain to bring new sustainable technologies to site. As Anglian Water’s first chemical‑free, algae‑based phosphorus removal system, Thurleigh provides a scalable model for future AMP8 schemes; achieving regulatory compliance while reducing carbon and operational costs.