Supply Chain - Treatment Process Technologies

Ringsend Wastewater Treatment Plant, owned by Uisce Éireann, is located on the Poolbeg peninsula and treats the majority of wastewater generated in Dublin, along with additional flows from parts of counties Kildare and Meath; accounting for approximately 40% of all wastewater produced in Ireland. As the largest wastewater treatment plant in the country, it represents a critical piece of infrastructure serving Dublin and its surrounding areas. Originally designed for a population equivalent (PE) of 1.64 million, the plant has undergone a €550m capital investment programme in recent years to refurbish and expand its capacity to 2.4 million PE. This upgrade ensures that the facility can accommodate ongoing economic and population growth within the Greater Dublin Area, while also safeguarding the sensitive habitats of Dublin Bay Special Area of Conservation. Drivers & process selection

Ringsend WwTP was not capable of meeting the Urban Wastewater Treatment Directive (UWWTD) standards due to overloading and insufficient nutrient removal capacity. To address this, upgrading the secondary treatment process stage was identified as key intervention, and this was to be delivered under the following five separate contracts:

The Process Proving Contract. Capacity Upgrade Contract. Block 2 full Nereda® retrofit. Block 3 full Nereda® retrofit. Hybrid 2 (hybrid Nereda® retrofit of remaining 4 blocks). [caption id="attachment_31692" align="alignnone" width="1200"] Upgraded secondary treatment blocks - Courtesy of Uisce Éireann/Murphy[/caption]

Nereda® Aerobic Granular Sludge (AGS) Technology is biological wastewater treatment which has been developed in the Netherlands under a unique public-private partnership between the Delft University of Technology, the Dutch Foundation for Applied Water Research (STOWA), the Dutch Water Boards and Haskoning. Within a Nereda® reactor, throughout a simple three-step cycle, the purifying biomass in Nereda® grows naturally as compact aerobic granular sludge, with superb settling properties. An important feature of the granules is that aerobic and anoxic/anaerobic zones co-exist. This enables a large variety of biological processes to happen simultaneously, like nitrification, denitrification and biological phosphate removal.

There were several advantages for introducing Nereda® treatment technology to Ringsend WwTP. The plant already had a Sequencing Batch Reactor (SBR) system for secondary treatment with minimal space for expansion and the Nereda® system could be retrofitted to the internals of the 24 existing SBR tanks.

The Nereda® process also provides improved nutrient removal (nitrogen and phosphorus) which was required to comply with the EPA Wastewater Discharge Licence for the plant.

Ringsend WwTP Secondary Treatment: Project Delivery Partners Design consultant & ER (all contracts): TJ O’Connor & Associates Ltd Egis Group Haskoning Group Process Proving main contractor: Celtic Anglian Water CUC main contractor: PJ Hegarty/Veolia Water Ireland JV Block 2 main contractor: FaCT3 Consortium: Celtic Anglian Water TES Farrans Block 3 main contractor: Ward & Burke Construction Hybrid 2 main contractor: Murphy Process Engineering [caption id="attachment_31693" align="alignnone" width="1200"] Ringsend WwTP Site - secondary treatment upgrade in progress - Courtesy of Uisce Éireann[/caption] Process Proving Contract

Given the specific requirements of the upgrade project, the Nereda® Aerobic Granular Sludge Treatment technology provided a potentially promising solution, however, it had not been proven on a plant the scale of Ringsend WwTP.

To confirm the application of the Nereda® AGS treatment process specifically to this plant and allow for optimisation of the application in the existing reactor cells, a process proving programme was implemented.

This contract consisted of retrofitting one of the four existing SBR cells in Block 3 with Nereda® internals and Nereda® control process optimisation to validate the retrofit design and proposed treatment process. The Process Proving Contract was completed by the existing plant operator, Celtic Anglian Water (CAW), as a variation to their Design, Build, Operation and Maintenance contract for an overall contract value of circa €10m.

Capacity Upgrade Contract

The €70m Capacity Upgrade Contract (CUC) was the first upgrade for the secondary treatment at Ringsend and was completed by PJ Hegarty/Veolia Water Ireland JV.

The design and build element of the CUC involved the piled construction of six new reinforced concrete treatment tanks in a two-tier arrangement with three tanks in the upper tier and three tanks in the lower tier. The six treatment tanks have a total volume of approximately 50,000m3, and have been designed and constructed to use the Nereda® biological treatment technology.

The Capacity Upgrade Contract scope also included the design and construction of a new pumping station and various ancillary elements. This upgrade increased the plant’s capacity by 400,000 PE (from 1.64 million to 2.14 million PE).

[caption id="attachment_31691" align="alignnone" width="1200"] Capacity Upgrade Contract in operation - Courtesy of Uisce Éireann[/caption] Block 2 Retrofit

The Block 2 Retrofit was completed by CAW/TES/Farrans Consortium (FaCT3) for an overall contract value of circa €50m. This involved retrofitting the four existing SBR cells in Block 2 on the upper deck of the existing secondary treatment units with Nereda® treatment process technology along with an upgrade to the intermediate pumping station. The full scope of this contract included:

Phased retrofit of the high lift pumps serving the upper deck SBRs located in the intermediate lift pumping station. Phased retrofit of the existing aeration system manifold pipework serving the upper deck SBRs. Modification to Block 2 centre core and provision of inlet and selection shafts for Block 2. Retrofit of Block 2 (Cells 2A, 2B, 2C and 2D) with Nereda® Aerobic Granular Sludge Technology equipment. Provision of sludge buffers and water level correction buffers within Block 2. Electrical and instrumentation, control and automation equipment. Metal salts dosing distribution system. Odour control treatment and associated collection system. Miscellaneous items including SAS discharge, washwater utility, compressed air, hoisting facilities, drains etc. [caption id="attachment_31695" align="alignnone" width="1200"] Retrofitted Block 2 back in operation - Courtesy of Uisce Éireann/Murphy[/caption] Block 3 Retrofit

The €40m Block 3 Retrofit was completed by Ward & Burke Construction. This involved retrofitting three of the four existing SBR cells in Block 3 on the upper deck of the existing secondary treatment units with Nereda® technology. The fourth cell had been previously retrofitted as part of a process proving advanced works contract. The full scope of this contract included:

Phased retrofit of the existing aeration system manifold pipework serving the upper deck SBRs. Modification to Block 3 centre core. Retrofit of Block 3 (Cells 3A, 3C and 3D) with Nereda® AGS technology equipment and upgrading of Reactor (Cell) 3B which has already been fitted with Nereda® equipment. Provision of additional sludge buffers and water level correction (WLC) buffers within Block 3; 3A and 3C only. Electrical and instrumentation, control and automation equipment. Metal salts dosing distribution system. Odour control extraction/ collection system. Miscellaneous items including SAS discharge, washwater utility, compressed air, hoisting facilities, drains etc. Hybrid 2

The €70m Hybrid 2 Contract was completed by Murphy Process Engineering Ltd, which involved retrofitting sixteen existing SBR cells in Block 1 on the upper deck and Blocks 4, 5 and 6 on the lower deck of the existing secondary treatment units with hybrid Nereda® process technology.

The works consisted of the installation and implementation of replacements or upgrades to the existing elements of the SBR reactors to maintain or modernise their functionality and to provide robustness for the future. The full scope of this contract included:

Civil works Survey of existing tank structure. Inspection/replacement of movement joints. Remedial works after demolishing the existing walkways, aeration grid and other plant. Mechanical works Replacement of walkways. Replacement of equipment (RAS pump, mixers). Replacement of valves and piping. Replacement of air mains and aeration grid. Replacement of surge boxes. [caption id="attachment_31696" align="alignnone" width="1200"] Sludge coolers - Courtesy of Uisce Éireann[/caption] Electrical works Replacement of MCC at centre core. Replacement of some instruments. Replacement of cables and cable containment. Replacement of building services (lighting, etc.). Automation works Reprogramming of Block PLCs. Reprogramming of Hybrid Nereda® controllers. Integration in SCADA system. Construction interfaces/complexities

The five contracts were delivered with the added complexity of working within Ireland’s largest WwTP, which remained operational throughout. The secondary treatment upgrades were undertaken alongside significant upgrades to sludge treatment and ancillary systems, including biogas, UV, CHP, and SCADA.

To ensure all upgrade contracts maintained progress and the plant was operational at all times required a great deal of interface coordination between the contractors and the existing operator of the plant. All work activities and plant shutdowns (partial and full) were planned and discussed well in advance. The projects could not have been successfully delivered without the level of collaboration that was achieved between all stakeholders.

[caption id="attachment_31694" align="alignnone" width="1200"] Upgraded secondary treatment blocks - Courtesy of Uisce Éireann/Murphy[/caption] Summary

The secondary treatment upgrade at Ringsend WwTP was completed in December 2025 with the completion of the Hybrid 2 contract. All projects have been successfully delivered on programme and within budget which is a great achievement by all stakeholders.

The plant’s capacity has been upgraded from 1.64 million PE to 2.4 million, and can now accommodate increased demand from the growing requirements of the Greater Dublin Area. The success of the Nereda® Aerobic Granular Sludge treatment process has ensured that Uisce Éireann are now compliant with their obligations under the UWWTD for nutrient removal.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The new MMB outline design consisted of the following:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The village of Highampton is located approximately 11 miles north-west of Okehampton in mid-Devon, with a population of around 400 people. Due to a reduction in permitted phosphorus discharge levels under the Water Industry National Environment Programme (WINEP), an upgrade to Highampton WwTW was required to ensure compliance with the Environment Agency consent limit of 3.3 mg/l total phosphorus in the final effluent. South West Water and Galliford Try, selected a nature-based solution as a low‑carbon additional treatment stage to achieve the tightened annual average consent limit, which was due to come into effect on 31 March 2026. Background & project scope

The Highampton WwTW P-Removal Project involved the installation of a reactive media filter bed complete with associated feed pumping station and monitoring equipment.

In 2022/2023, in collaboration with ARM Ltd, South West Water and Galliford Try successfully trialled the UK’s first full-scale reactive media filter bed at Wilmington WwTW. Following the success of this trial, the same ARMPhos™ technology was selected for the scheme at Highampton.

The scope to be delivered by Galliford Try to make these improvements under the WINEP were:

84m2 media bed and associated pumping station, pipework and control instrumentation. ARMPhos™ media bed for P removal to meet the new phosphorus permit of 3.3 mg/l. [caption id="attachment_31217" align="alignnone" width="1200"] Works site prior to the start of construction - Courtesy of Galliford Try[/caption] ARMPhos™ phosphorus removal system overview

The ARMPhos™ reactive media bed operates downstream of the existing works as a tertiary process to reduce phosphorus in the final effluent via a chemical reaction with the ARMPhos™ media layer. The system operates on a 40% bypass philosophy (40% treated through the bed and 60% by-passed) with flows being re-mixed in the level control chamber.

The reactive media, based on apatite, offers two modes of action; an initial adsorption/crystallisation phase of phosphate onto the apatite, which stimulates the second phase of crystallisation of complex calcium/phosphate out of solution onto the adsorbed crystals.

The adsorption phase is driven by attraction of phosphate ions to the naturally occurring cations, principally aluminium and iron, occurring within the apatite. These bind the phosphate to the apatite until all the binding sites become saturated. The loading rate up to saturation is understood and depending on the P loading rate and volume of media it can take several years before this stage is complete.

The bound phosphate subsequently crystallises which seeds the second mechanism which is the crystallisation of calcium/phosphate complexes which form naturally in solution. There is some overlap of these two mechanisms. The adsorption phase is finite, but the crystallisation phase goes on indefinitely and system performance is ultimately limited by the reduction in hydraulic conductivity of the media.

At this point refurbishment is required, though this may occur 10-15 years after commissioning if the system is designed and installed correctly, and loads remain within design parameters. Traditional reactive media P removal solutions using slag or other naturally occurring minerals generally only display the adsorption step.

HighamptonWwTW: Supply chain - key participants Main designer & contractor: Galliford Try Reed bed designer & contractor: ARM Ltd Environmental & Geotechnical: Ground Consultants Ltd Ecology: Ead Ecology Pumps: NOV (Mono Pumps) Fencing: Topan Group [caption id="attachment_31220" align="alignnone" width="1200"] New site fencing and field reinstatement around the new reactive media construction - Courtesy of Galliford Try[/caption] Carbon savings

This nature-based solution has an extremely low carbon footprint. The process is passive, and apart from pumped flow to the bed it consumes no other power. Apart from changes of the depleted media (currently estimated every 10 to 15 years) the process has a very low carbon footprint. The process also benefits from further carbon reductions compared to other phosphorus removal processes as it requires no regular deliveries of chemicals or produces any sludge for export.

Galliford Try also reduced their carbon footprint during construction, as all excavated material generated was re-used on site in the construction of the filter. This not only reduced carbon associated with the export of spoil but also vastly reduced the quantity of imported material required including concrete.

As can be seen in the desktop study below, the reactive media bed process can provide significant reductions in operating carbon when compared to other  phosphorus removal options.

Phosphorus removal options Chemical dosing Chemical dosing & TSR ARMPhos™ Power (kgCO2e/yr) 196 1327 544 0.233 kgCO2e/yr (UK Government GHG Conversion Factors for Company Reporting 2021) Additional sludge transport 582 582 0 0.96 kgCO2e/yr for HGVs, 80km round trip (GHG Conversion Factors for Company Reporting 2021) Chemical transport 1635 1635 0 0.96 kgCO2e/yr for HGVs, 800km round trip, 4 deliveries/year plus proportion of bulk delivery Chemical manufacture 1716 1716 0 Total additional operating carbon  4129 kgCO2e/yr 5260 kgCO2e/yr 544 kgCO2e/yr Summary

This innovative scheme provided the Galliford Try Team with many challenges in design and delivery as described above. The use of this technology removed the requirement for any additional chemical-based treatments. This reduces not only day-to-day operator interventions but also removes the constant costs and carbon impact of maintaining a chemical style treatment process.

This solution achieves the phosphorus permit without risking the aluminium permit and reduces reliance on poly-aluminium chloride and ferric; both of which are hazardous materials due to acidity and which require storage and handling. They pose a serious risk to aquatic life if they enter waterways directly or via surface water drains. It is also safer for operators as there is no requirement for them to handle chemicals.

Additionally, successful chemical dosing at wastewater treatment works, which experience periods of low/no incoming flow,s are at greater risk of breaching the permit consents due to the accuracy of the dosing required and ensuring the chemicals are homogeneously mixed within the process flow.

With this being an installation of a naturally based reactive media filter bed, this also provided an ecological enhancement to the existing site environment and its surroundings. The technology also enabled the total carbon to be reduced in comparison to traditional phosphorus removal methods. The use of this system also allowed Galliford Try to reduce their operational maintenance hours as well as achieving a low visual impact.

The completed project helped to reduce phosphorus discharge into the local river, whilst not having any detrimental effect on alkalinity levels or increases in aluminium content, which would be commonly found in traditional methods of removal.

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 Phosphorus Removal Enhancement Programme (PREP) Batch is a group of projects within United Utilities. These projects provide improvements delivering the Environment Agency (EA) Water Industry National Environmental programme (WINEP) outputs for a future population growth based on a 2035 design horizon. With a focus on ensuring the lowest ‘whole life cost’ solution, the team recognized the opportunity to employ a phased approach along with repeatable template solutions. They have both developed solutions within the batch and drawn on solutions from the wider programme of work to meet the lowest whole life cost. Treatment works details The PREP Batch consists of improvement works to meet tightened final effluent total phosphorus permits at five existing wastewater treatment works (Bury, Worsley, Rochdale, Tyldesley and Chorley WwTWs) situated in the north Manchester area; with a joint population equivalent of 504,410. The £15m programme of work is being delivered by United Utilities’ Construction Delivery Partner (CDP) Framework Advance-plus, a joint venture between MWH Treatment, J Murphy & Sons and Stantec UK. The contract was awarded in January 2020 with construction commencing in January 2021. [caption id="" align="alignnone" width="1200"] Tyldesley WwTW ferric dosing unit installation - Courtesy of Advance-plus[/caption] Worsley WwTW: FtFT 12,010m3/d: Total P permit: 0.5 mg/l Treatment is via settlement and activated sludge process, after secondary settlement the treated wastewater is pumped to a BAFF plant and discharged to Astley Brook, which is a tributary of the River Glaze. The project scope includes new primary ferric dosing equipment, refurbishment/replacement of existing ferric dosing equipment for secondary dosing, additional sludge storage and mixing facilities, provision of caustic dosing for alkalinity correction, provision of on-site storm detention tank and associated pumping station and asset renewal of existing primary settlement tank de-sludge pumps. Anticipated completion is 1 March 2022. Bury WwTW: FtFT 203,904m3/d: Total P permit: 0.4 mg/l Treatment is via settlement and activated sludge process, after secondary settlement the treated wastewater is pumped to a BAFF and discharged to the River Irwell. The project scope is for the provision of new primary and secondary ferric dosing equipment, and replacement of existing rectangular primary tank scraper bridges and rail systems. Anticipated completion is 30 March 2022 for the chemical dosing plant, and 1 August 2022 for the replacement primary settlement tank bridges. Rochdale WwTW: FtFT 116,986m3/d: Total P permit: 0.4 mg/l The works is a large conventional activated sludge plant treating domestic and commercial flows. It includes storm overflow and settlement, screening and grit removal, primary settlement followed by ASP incorporating conventional final settlement tanks, there is no dedicated tertiary treatment. The project scope is for the provision of new primary and secondary ferric dosing equipment. Anticipated completion is 17 September 2021. [caption id="" align="alignnone" width="1200"] Tyldesley WwTW ferric dosing unit installation - Courtesy of Advance-plus[/caption] Tyldesley WwTW: FtFT 16,243m3/d: Total P permit: 0.8 mg/l Serving the metropolitan area of Wigan, treatment is via settlement and biological filters, after secondary settlement the treated wastewater is pumped to a NTF plant for ammonia removal, then to a COUF plant and discharged to the river. The scope of works is for new primary ferric dosing equipment, additional sludge storage and mixing facilities, provision of caustic dosing for alkalinity correction and new FtFT flow control. The anticipated completion date is 2 February 2022. Chorley WwTW: FtFT 80,006m3/d: Total P permit: 0.4 mg/l The works is a large conventional activated sludge plant treating domestic and commercial flows. The works includes storm overflow and settlement, screening and grit removal, primary settlement followed by ASP incorporating conventional final settlement tanks, tertiary solids removal is provided for the secondary settled effluent through a rapid gravity filter. The scope of works here is for the provision of new primary and secondary ferric dosing equipment, additional sludge storage and mixing facilities, odour control and provision of caustic dosing for alkalinity correction. Works should be completed by 30 March 2022. Phased delivery approach The notional solution for the five projects contained in the PREP Batch was chemical treatment of the effluent, and tertiary treatment to achieve the required phosphorus consent levels. Following a review of the existing treatment processes by United Utilities, a phased delivery approach was proposed as it became clear that upgrades to the existing chemical dosing systems allied with other plant improvements could meet the consent levels, negating the need for tertiary treatment. Therefore, a two phase approach has been adopted. The first phase of the works was programmed to provide new or upgrades to the existing chemical dosing systems on each site. If proven successful, the requirement for tertiary treatment will be removed from the final solution, which could provide a significant cost saving across the five projects (circa £1m per project). To support the plan, collaborative planning sessions were undertaken to create a programme that would allow the chemical treatment to be commissioned first and tested to ensure the consent was achieved, but allow time for the installation of tertiary treatment should there be any issues. [caption id="" align="alignnone" width="1200"] Bury WwTW PST MCC DfMA solution - Courtesy of Advance-plus[/caption] Phosphorus Removal Enhancement Programme: Supply chain - key participants Project delivery: Advance Plus MWH Treatment J Murphy & Sons Stantec UK Dosing equipment: Northern Pump Suppliers Ltd (NPS) Sludge storage tanks: Stortec Engineering Ltd Systems integrators: Tata Consultancy Services (TCS) Systems integrators: Cougar Automation Ltd MCCs: Lloyd Morris Electrical Ltd MCCs: BGEN PST bridges at Bury WwTW: JK Fabrications Ltd Design templating As the AMP7 delivery programme needed to move at pace, the decision was made to develop a template solution on early projects, known as donor projects and then utilise the template on the remaining recipient projects. The PREP Batch’s delivery schedule made it both a donor project for some assets and a recipient project for other assets. Chemical dosing equipment was a key focus for templating with other asset types of sludge storage, pumping stations, MCC kiosks, sampling systems and ICA equipment all areas for template development. A key principle of the templating effort was the need to ensure that once a template had been developed, it had client support from an engineering, operations and maintenance perspective. [caption id="" align="alignnone" width="1200"] Tyldesley WwTW caustic dosing unit - Courtesy of Advance-plus[/caption] The approach taken was to take early designs outside the project environment and review them in a joint forum made up of the clients’ design leads, contractor’s designers and supply chain representatives. The designs were then reviewed by representatives for the Operations and Maintenance community and any comments incorporated. These designs were then locked down for reuse. Using this approach had several benefits: Working with the client’s design leads, Advance-plus were able to discuss and challenge asset standards which led to a number of agreed deviations making significant savings against the budget. These discussions were underpinned by a joint desire to ensure the designed assets were operable and maintainable with a common sense approach. Advance-plus, working collaboratively with C2V+ (United Utilities other construction delivery partner) brought shared ideas, shared effort and ensured that the template outputs would be delivered across the whole AMP7 programme. This would ultimately benefit United Utilities with common assets across their region. Supply chain input also ensured that the designs being developed were deliverable, with the supply chain giving excellent advice on the most effective way to deliver an idea. Operations and Maintenance team input ensured Advance-plus were able to fine tune the details of operability and maintainability and gave the final agreement to the templates. The templates could then be reused in the knowledge that they had everyone’s support. Once a template was agreed, multiple units would be delivered which meant Advance-plus were able to give the supply chain workload visibility and the ability to forward plan manufacturing. [caption id="" align="alignnone" width="1200"] Bury WwTW - (left) template POA arrangement and (right) valve chamber and spill tank - Courtesy of Advance-plus[/caption] The PREP Batch benefited from the work provided by other donor projects for chemical dosing, with the whole dosing area being developed including, storage, dosing equipment, tanker area, blind tank, showers, hose reels etc. The donor project developed the total design solution from P&ID’s, layouts through to ICA requirements. The solution for large external tank ferric and caustic dosing (smaller size dosing rigs are delivered within a kiosk solution) were reviewed by the joint team, with a significant focus on the layout of the storage area. Northern Pump Suppliers (NPS), one of United Utilities framework suppliers for chemical dosing equipment, supported the design development of the template bringing a wealth of experience to the discussions. Also, by having the United Utilities’ design leads involved, clarity on specification requirements could quickly be discussed and approach agreed, with NPS able to confirm how the solution would be delivered. The PREP Batch was therefore able to take all this design effort and implement it across the projects within the batch. This significantly reduced the timescales and effort needed to develop this batch of work. Furthermore, the supply chain for the majority of the equipment needed was already in place with purchase agreements. This again improved the ability to deliver this element of work reducing the time taken. [caption id="" align="alignnone" width="1200"] Rochdale secondary dosing - Courtesy of Advance-plus[/caption] Areas of development that the PREP Batch provided as a donor project Two key areas of development that the PREP Batch provided as a donor project were sludge storage and MCC kiosks. Sludge storage Through collaborative meetings, a number of solutions were put forward by both construction delivery partners. The need for access to the top of sludge storage tanks became a key area of focus. The discussions centered on the reason for access stairs to the top of the tank. It transpired that this access was required solely to maintain the ultrasonic level instrumentation at the top of the tank, so the team got to work to establish if something different could be done. The electrical engineers liaised with the supply chain and established that a radar or vibronic instrument would fulfil the same duty and more importantly the instruments do not need direct access for maintenance and can be tested and calibrated remotely. This allowed the staircase to be removed, which brought about significant savings to the delivery of this asset type. This solution is now being utilised on other projects across the programme. [caption id="" align="alignnone" width="1200"] (left) Worsley WwTW caustic dosing and (right) sludge storage tank from Stortec Engineering Ltd at Worsley - Courtesy of Advance-plus[/caption] MCC kiosks The PREP Batch supported the development of a modularised MCC kiosk solution. Early in the programme of work it was recognised that the majority of the MCCs would be a similar layout. Advance-plus engaged MCC framework suppliers Lloyd Morris Electrical Ltd, to establish a principle for a range of standard layout and sizing of MCCs and kiosks. Furthermore, Advance-plus required off site manufacturing to be undertaken wherever possible, and wanted the MCC delivered in its kiosk fully tested. Using the PREP Batch as the donor, Lloyd Morris Electrical Ltd developed a range of sizes for small, medium and large kiosk requirements. As the MCC and kiosk are built on a transportable base, and to minimise on site works, the MCCs have been raised off the ground therefore negating the need for full concrete bases with cable trenches. Overall, the templating approach is bringing benefits to the PREP Batch and across the programme. United Utilities has a consistent asset across the region making operator and maintenance familiarity better. Significant efficiency advantages are being seen in this approach which is supporting United Utilities’ aspirations to deliver the best whole life cost solutions. [caption id="" align="alignnone" width="1200"] Worsley WwTW sludge MCC DfMA assembly - Courtesy of Advance-plus[/caption] Progress update At the time of writing (September 2021), the design has been completed for all five sites, and each are now at various stages of construction, commissioning and optimisation. At Bury and Rochdale WwTWs, the ferric dosing systems have been installed and commissioned and both are in the optimisation period. Both Worsley and Tyldesley WwTWs are in the construction phase, with civils construction complete and M&E installations are underway. Demolition work has commenced at Chorley WwTW. All projects are tracking to programme with the ability to establish if the phased delivery approach is working on programme.

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.

Lanchester Sewage Treatment Works (STW), located west of Durham, formed part of Northumbrian Water’s Water Industry National Environment Programme (WINEP) during AMP7. The works is a biological filtration plant serving a population equivalent of 5,717, with projected growth of approximately 13.9% within the catchment by 2032. The primary objective of the project was to achieve compliance with new discharge consents driven by the AMP7 WINEP Water Framework Directive (WFD) requirements for phosphorus and iron, while maintaining compliance with existing consent limits for ammonia, biochemical oxygen demand (BOD), and suspended solids. Existing works

Flows to Lanchester STW gravitate from the catchment to the inlet works, which comprised two escalator screens and a grit detritor. The flows then pass to two primary settlement tanks and two biological filters. An interstage pumping station then lifts effluent from the filters to the north-west of the site, where it passes through two humus settlement tanks.

Prior to the AMP7 scheme, flows gravitated to reed beds located to the east of the site and, following final effluent sampling, were discharged to the receiving watercourse, Smallhope Burn.

[caption id="attachment_31042" align="alignnone" width="1200"] Google Maps image of Lanchester STW[/caption] Scope of works

To achieve compliance, the existing reed beds were decommissioned and replaced with new tertiary treatment plant. This involved the installation of a new tertiary pumping station downstream of the humus settlement tanks, which lift flows to three nitrifying submerged aerated filter (NSAF) units supplied by De Nora Water Technologies.

Effluent then gravitates to two Eliquo Hydrok Mecana tertiary solids removal (TSR) units before discharging from the site via the existing sample point to the receiving watercourse.

The NSAF and TSR units were constructed on reed beds 1A and 1B, following the clearance of overgrown vegetation and the backfilling of the beds to form a suitable level platform.

Additional scope of works included:

A tertiary MCC to power the new plant. An MCERTS tank from SIRIS Environmental for flow monitoring downstream of the Mecana units. A Grundfos washwater booster kiosk supplying hose points/hydrants around the site. New bunded Aquazone chemical dosing storage tanks and kiosk with associated points of application. Uprated pumps at the existing interstage pumping station. New ammonia sample chamber. [caption id="attachment_31050" align="alignnone" width="1200"] Existing biological filter beds - Courtesy of MMB[/caption] New consents

To achieve compliance, the new consents for Lanchester STW were as follows:

Parameter Current Value (2019) Future Value (2032) Discharge rate (FFT) 42.4 l/s 54.3 l/s Dry weather flow 1,261m3/d 1,261m3/d BOD 15 (50) mg/l 15 (50) mg/l TSS 80 mg/l 80 mg/l NH4N 6 mg/l 6 mg/l Total P * n/a 0.7 mg/l Fe * n/a 4 mg/l * Regulatory date of 22/12/24 for the new Total P and Fe consents. Lanchester STW: Supply chain - key participants Principal designer & contractor: Mott MacDonald Bentley ECC project management: Turner & Townsend Surveys: Castle Keep Surveys Tertiary solids removal: Eliquo Hydrok Ltd NSAF & blowers: De Nora Water Technologies UK Chemical dosing: Aquazone Washwater booster: Grundfos Electrical & cabling installation: Intelect (UK) Ltd MCC: Armah Switchgear Ltd MCC & NPG kiosk: NPS Engineering Group Systems integrator: IDEC Group Ltd - Aureos Pipework installation: North East Pipeline Solutions Ltd Bespoke drawpit chambers: NOV Fibre Glass Systems MCERTS: SIRIS Environmental Metalwork: ADL Fabrications Overpumping: Selwood Overpumping: Hydrainer Davit arms & testing: Peter Cassidy (Leeds) Ltd Precast cable troughs: FP McCann Ltd Hazardous waste removal: Teward Bros Nitrifying submerged aerated filter (NSAF) units

Three nitrifying submerged aerated filters (NSAF) from De Nora Water Technologies were installed at Lanchester to address ammonia and BOD consents. These were installed on reinforced concrete plinths alongside their supporting blower equipment. Safe and maintainable access to all units was provided via a steel access platform, fabricated and installed by ADL Fabrications.

To ensure compliance with ammonia consents during construction and prior to commissioning of the permanent assets, temporary hybrid submerged aerated filter (HSAF) units were deployed on site. These were fed via above-ground pipework and remained operational until the NSAF units were brought into service.

The timing of the NSAF installation was critical, as each unit required an approximate six-week seeding period to establish sufficient biomass on the media to effectively treat ammonia loads. A key concern during this period was the onset of Spring, when biological filters across the site underwent sloughing, allowing significantly higher loads to pass through the treatment process to the NSAF units. This created a risk of overloading the units if they were not adequately seeded. The seeding process was closely monitored to ensure that an appropriate level of treatment was maintained throughout. Once fully established, the NSAF units consistently achieved performance exceeding the required consent standards.

[caption id="attachment_31045" align="alignnone" width="1200"] De Nora NSAFs and associated access metalwork - Courtesy of MMB[/caption]

A key project objective was to provide adequate wetting and dilution of the biological filter beds during periods of low flow. This had been an existing issue at the site, posing a risk to media growth and, consequently, overall treatment performance.

During initial optioneering, a new pumping station was proposed to recirculate treated effluent from downstream of the NSAF units back to the filter beds. This would ensure a consistent flow regime, maintaining suitable conditions for sustaining the biological media.

This option was subsequently designed out and replaced with a gravity-fed recirculation pipeline, which automatically diverted NSAF effluent back to the head of the treatment process during periods of low flow. This approach delivered significant cost and carbon savings, while also removing the health and safety risks associated with constructing and operating a new pumping station.

The majority of the above-ground pipework associated with this system was fabricated in stainless steel and installed by North East Pipeline Solutions Ltd (NEPS).

The final arrangement was an efficient and robust pipework solution, supplying both the downstream TSR units and the site recirculation system entirely by gravity.

Mecana TSR

Two Mecana tertiary solids removal (TSR) units were supplied and installed by Eliquo Hydrok Ltd to enhance solids removal performance on site. The package plant comprised rotating filter discs, which captured suspended solids as flows passed through the units.

Mott MacDonald Bentley designed the reinforced concrete slab foundations to support the installation of the units. As with the NSAF units, the TSRs were constructed on the footprint of former reed beds. This required the reed beds to be drained and cleared of vegetation. All vegetation clearance works were undertaken with due consideration to ecological constraints, including regular monitoring for nesting birds to ensure compliance with environmental requirements before and during the works.

The site was regularly exposed to flooding risk during the enabling works, adding further complexity to the scheme. Close coordination between Mott MacDonald Bentley and Northumbrian Water  ensured that this was effectively managed through the implementation of over-pumping solutions.

[caption id="attachment_31043" align="alignnone" width="1200"] Eliquo Hydrok Mecana TSR and SIRIS Environmental MCERTS measurement tank - Courtesy of Mott MacDonald Bentley[/caption]

Following clearance, the reed beds were backfilled to the required levels using compacted Type 1 stone. The formation levels were carefully designed to support the hydraulic requirements of the gravity-fed systems. Upon completion, the installed TSR units had full road and footpath access, ensuring that all operational and maintenance activities could be carried out safely and efficiently.

Downstream of the TSR units, MCERTS-compliant flow monitoring was incorporated. Below-ground chambers were previously considered, however, an opportunity arose to utilise a standard MCERTS certified product, which was selected in preference. This solution comprised an above-ground PVC tank supplied by SIRIS Environmental - an MCERTS accredited company.

Adoption of this standardised unit removed the risk associated with constructing a bespoke chamber that may not meet MCERTS accreditation requirements, thereby simplifying the design and approval process. Consequently, the remaining design considerations were just the connecting pipework and slab levels, ensuring adequate freeboard was maintained to suit downstream hydraulic conditions.

An associated washwater booster set, supplied by Grundfos, was also installed. This system drew from the SIRIS MCERTS tank and distributed washwater to the new hydrant and hose points installed across the site.

Chemical dosing

To achieve the new Total P consents, new chemical dosing was supplied and installed by Aquazone, introducing new caustic and ferric dosing points across the existing site.

[caption id="attachment_31046" align="alignnone" width="1200"] The new chemical dosing set-up - Courtesy of MMB[/caption]

During optioneering, an integrated kiosk and tank arrangement was considered; a package also supplied by Aquazone on similar WINEP schemes. However, investigations identified that access to the site was via a bridge with width and weight restrictions of 3.3m and 32T respectively, which would prevent delivery of the integrated kiosk and tank arrangement.

Instead, the kiosk and tanks were delivered separately, with reinforced concrete containment bunds cast in situ to retain chemicals in the event of a catastrophic failure of the tanks.

The location of the new chemical dosing installation presented challenges for electrical ducting and dosing lines, due to a concrete road separating it from the new MCC. Several significant existing services were identified in this area through utility surveys, further constraining routing options.

An opportunity was identified to utilise bespoke prefabricated drawpit chambers manufactured by NOV Fibre Glass Systems. These chambers provided flexibility in size and shape, which was key for accommodating tight spaces with significant existing services. As a result, to avoid clashes and the re-routing of key ducts, the drawpit footprint was reduced accordingly. The duct entries were also set to precise angles and levels to suit the designed duct layout.

[caption id="attachment_31044" align="alignnone" width="1200"] NOV Fibre Glass Systems prefabricated drawpits - Courtesy of MMB[/caption] Reed bed replacement

The utilisation of land occupied by the existing reed beds was key to ensuring sufficient space was available for the new process plant and associated ancillaries. Biodiversity Net Gain (BNG) was a key consideration in the removal of two of the six existing reed beds. The resulting loss of habitat associated with these two beds was compliant with planning requirements under permitted development rights.

Only small additional areas, required for the installation of the new MCC and chemical dosing kiosk, impacted further on habitat. For these areas, statutory credits were purchased due to their limited extent. In addition, to meet internal ecological standards, Northumbrian Water instructed the implementation of a separate off-site compensation scheme at a local farm to offset the habitat loss associated with the Lanchester site.

Electrical infrastructure upgrade

A new tertiary treatment MCC and Northern Powergrid (NPG) kiosk were installed as part of the scheme, alongside an upgrade and changeover of the site power supply to serve the new plant. NPG successfully undertook transformer and cabling replacement works during a planned outage, with a temporary generator installed to maintain continuity of supply throughout the upgrade.

The works required closely coordinated, time-critical planning between Mott MacDonald Bentley, Northumbrian Water, NPG, and electrical subcontractor Intelect UK Ltd to ensure the changeover was completed safely and without disruption to site operations.

Collaborative planning & digital tools

Close collaboration and constructive challenge between all parties involved was key to the successful delivery of the Lanchester scheme. To support this, Mott MacDonald Bentley hosted weekly Collaborative Planning sessions on site.

These sessions enabled the wider MMB team, including design, operations and commercial personnel, to engage directly with Northumbrian Water and the various subcontractors involved in the project.

This collaborative approach ensured the project was continually planned and monitored as a collective effort, facilitating timely discussions and identification of value-driven opportunities. It also promoted open communication, reducing the risk of isolated working. Risks were identified early, with clear actions assigned and tracked, helping to safeguard key regulatory milestones.

[caption id="attachment_31041" align="alignnone" width="1200"] 3D model of the new NSAF and TSR assets’ - Courtesy of MMB[/caption]

The collaborative planning sessions were further enhanced through the use of digital delivery tools. A 3D Revit model of the site was regularly reviewed during meetings to support design development, assess interfaces with NWG operations staff, and address buildability considerations. Model interrogation tools, including dimensioning and sectional views, were used to validate and clearly communicate design decisions. These discussions were often supplemented by joint site walkovers to align design intent with site conditions.

By ensuring regular client involvement in the planning process, the final solution was developed in a fully considered and collaborative manner, delivering compliance with regulatory requirements while also meeting the operational needs of the client.

Standard design & the MMB Production Hub

Increasing demand and workload to achieve regulatory dates has encouraged the use of standard products across the business to ensure consistent, fit for purpose solutions are identified in an efficient matter. This means eliminating re-work associated with bespoke design that could extend the construction programme.

At Lanchester, standard design practices and lessons learned from similar local projects were applied to develop the NSAF and TSR areas. Upon completion of the scheme, key learnings were shared with the MMB DfMA team. This included innovations such as the SIRIS MCERTS tank and prefabricated drawpits described above, both of which were identified as potential efficiencies for future schemes. These contributions are shared internally via the MMB Production Hub; a framework-wide resource designed to collate valuable insights, standardise solutions, and simplify design constraints. The Hub has already supported the optioneering phases of the initial AMP8 schemes and will continue to add value as more knowledge is captured and shared across the network.

[caption id="attachment_31047" align="alignnone" width="1200"] The new TSR plant - Courtesy of Mott MacDonald Bentley[/caption] Customer liaison

Site access was gained via a track shared with two local landowners. Following discussions between Northumbrian Water’s Treatment Works Manager and the project team, traffic management measures were strengthened. This included the introduction of a dedicated gate marshal during peak periods, reinforcement of access protocols with site staff and delivery drivers, and the establishment of a single point of contact for all stakeholder engagement.

The Customer Liaison Officer maintained regular contact with the affected landowners to confirm that these measures remained effective and to promptly address any concerns raised. A key lesson learned was that where shared access arrangements depend on safety-critical behaviours, consistent and visible controls, supported by proactive, empathetic communication and clear accountability, are essential to maintaining stakeholder trust and ensuring programme continuity.

Conclusion

By August 2025, the project scope had been successfully installed and commissioned. Key regulatory consent milestones for total phosphorus and iron were achieved by the regulatory date of December 2024, through the early installation and commissioning of critical treatment assets.

Bishops Lydeard Water Recycling Centre (WRC) falls within the South Somerset Council area, serving the adjoining villages of Bishops Lydeard and Greenway via a gravity sewer. The site discharges to Back Stream and on to the River Tone, serving a total population equivalent of approximately 3,056 PE (2040 forecast).  The WRC was identified by the Environment Agency under WINEP as requiring process improvements, including reduction of phosphorus levels in treated wastewater prior to release. Project drivers

Regulatory obligations included:

New MCERTS flow measurement installed at inlet works. New phosphorus consent (WFD_IMPg): 1.0 mg/l with AMP8 stretch target of 0.8 mg/l Total P. Iron (Fe): 3 mg/l 95%ile | 8 mg/l absolute maximum (ABS). Aluminium (Al): 1.5 mg/l ABS. Storm storage (WINEP U_IMP6): Increase in volume from 147m3 to 228m3. EDM (U_Mon3): Monitoring to and from the storm tank. [caption id="attachment_31173" align="alignnone" width="1200"] Site under construction - Courtesy of Envolve Infrastructure[/caption] Proposed solution

To meet the new consent permits, the following elements were required.

Phosphorus removal: Chemical dosing to be added to the existing treatment stream, including a ferric sulphate dosing system and also a sodium carbonate dosing system for alkalinity adjustment. Storm storage: A new 228m3 above-ground modular steel tank to be constructed on a reinforced concrete base with mechanical flushing bell. Key elements will include a storm return pump station, Copasac and sampling chamber, pump mixers, interconnecting pipework, penstock modifications, new MCC and control systems, and EDM instrumentation. Additional sludge storage: An additional 160m3 of sludge storage via a modular steel tank on a reinforced concrete base, together with a sludge transfer pumping station, interconnecting pipework, removal of the old RC sludge storage tanks, a new bunded tanker discharge point, and associated MCCs, control systems and instrumentation. Design & early contractor involvement (ECI)

Through early contractor involvement during the design phase, Envolve Infrastructure and Trant Engineering used their specialist sector knowledge to guide key constructability decisions across safety, quality, time and cost.

Envolve Infrastructure worked closely with all stakeholders to develop a construction methodology and programme sequencing that maintained uninterrupted existing processing throughout. Close coordination and collaborative working between the delivery teams, designers and Wessex Water Operations was necessary to deliver the scheme successfully, on time and without incident.

Bishops Lydeard WRC: Designers, consultants & contractors Project delivery: YTL Construction Design consultant: Sweco Principal & civil contractor: Envolve Infrastructure MEICA contractor: Trant Engineering Automation & commissioning: YTL Construction Pumping station: Matt Durbin Associates Wellpoint dewatering: Dewatering Services Ltd Temporary works: MGF Ltd [caption id="attachment_31165" align="alignnone" width="1200"] Multi media filtration plant pump station under construction - Courtesy of Envolve Infrastructure[/caption] Bishops Lydeard WRC: Suppliers of process plant & equipment Multi-media filtration plant: Bluewater Bio Ltd Moving bed biofilm reactor plant: Siltbuster Group Ferric chemical dosing: WES Ltd Alkalinity plant: Rospen Industries Above-ground storage tanks: Stortec Engineering Ltd Flushing bells: Eliquo Hydrok Ltd MCC, panel & kiosk: RSE Control Systems (GPS) Pipework: Saint Gobain PAM UK Pipework: Frazer Utilities Actuated penstocks: Glenfield Invicta Storm return pumps: Xylem Water Solutions Storm mixer pumps: KSB Ltd Valves: AVK UK Ltd Steelwork: Woodhams Group Precast headwall: Althon Ltd Site access bridge: Retro Bridge Ltd Coring: Drillcut (UK) Ltd ABB WaterMaster MCERTS flow measurement: ABB Pulsar Ultra 4 EDM monitoring: Pulsar Measurement [caption id="attachment_31161" align="alignnone" width="1200"] Storm tank under construction - Courtesy of Envolve Infrastructure[/caption] Challenges & mitigation

Ground conditions

Ground conditions across the site were inherently poor, with a high-water table and flood zone adjacent to the watercourse. Working through proposals during design and undertaking further site investigation, YTL Construction, Envolve Infrastructure and Sweco reached a value-engineered solution, replacing piled foundations with an increased thickness of structural granular fill, delivering cost, programme and environmental benefits.

Existing assets & site constraints

The limited space and positioning of existing assets required a phased construction approach to maintain access for both construction traffic and operational vehicles. A joint phased programme was developed alongside design development, ensuring the new storm tank, sludge tank, MMF plant and chemical dosing units were constructed and commissioned without impacting the existing works.

[caption id="attachment_31171" align="alignnone" width="1200"] New HV route into site - Courtesy of Envolve Infrastructure[/caption]

HV diversions

To create sufficient space for the new elements of work, the existing HV cable feeding the WRC, including a section of overhead cable, required diverting. Working alongside the power provider, Envolve Infrastructure undertook the necessary civils works to reroute the cable and clear space for the new MCC kiosk, sludge tank, alkalinity unit and pumping station.

Access bridge

The existing access bridge spanning the adjacent watercourse was found to be unfit for ongoing construction and tanker traffic. As the only means of access to the works, and the sole access point for an adjacent resident, the bridge could only be closed for vehicle access up to 7 days. Through careful planning and weekend working, Envolve Infrastructure successfully installed a new steel bridge with reinforced concrete abutments, minimising disruption to local residents and maintaining full operational continuity of the WRC.

[caption id="attachment_31164" align="alignnone" width="1200"] New access bridge installation - Courtesy of Envolve Infrastructure[/caption] Efficiencies, sustainability & environment

A collaborative approach was adopted throughout design to improve buildability, involving YTL Construction, design consultants, technical specialists and early contractor involvement. The YTL Construction Offsite Build (OSB) in-house team provided the design, manufacture and supply of pre-assembled standardised equipment, including:

Chemical dosing kiosks. Point of application boxes. Emergency showers. Washwater booster sets. Lighting columns.

This methodology delivered improved efficiency, reduced programme, enhanced health and safety, and reduced carbon through fewer vehicle movements and shorter on-site construction durations.

In addition to the existing biological treatment process, a new Moving Bed Biofilm Reactor (MBBR) from Siltbuster Group was installed to further improve biological wastewater treatment.

[caption id="attachment_31162" align="alignnone" width="1200"] Newly completed MBBR - Courtesy of Envolve Infrastructure[/caption]

Environmental mitigation measures included:

Engagement with the Environment Agency to plan works through classified watercourses. Use of HVO fuel for all plant and equipment. Replanting of hedgerows and trees with native species. Preservation and protection of local habitats and tree protection zones. Re-use of excavated material on site, reducing landfill and vehicle movements. Off-site manufacturing to reduce on-site carbon impact. Electrical & mechanical works

The Trant Engineering Wessex Water delivery team undertook the detailed electrical design, full M&E installation, testing and commissioning works for the scheme. The M&E scope encompassed the installation and integration of a new multi-media filtration (MMF) tertiary treatment plant from Bluewater Bio Ltd, MMF feed pumping station, wash water booster set, ferric sulphate dosing system, front end ferric dosing system, alkalinity dosing system, alkalinity dosing chamber, new sludge storage and transfer pumping station, decant tree, works return pumping station, storm storage tank, storm return and final effluent monitoring, together with all associated process pipework and instrumentation.

[caption id="attachment_31166" align="alignnone" width="1200"] Multi-media filtration plant - Courtesy of Envolve Infrastructure[/caption]

The project also included a substantial site-wide electrical infrastructure upgrade incorporating a new 200kVA power upgrade, new MCC kiosk, standby generator installation, DNO metering arrangements, power distribution, telemetry integration, site lighting and control systems. Trant Engineering undertook all LV electrical design, cable routing, containment, power and control installations, instrumentation integration and commissioning activities across the operational treatment works.

As part of a subsequent side-stream enhancement package delivered towards the close of the scheme, Trant Engineering additionally provided all M&E installation and LV detailed design for the MBBR plant and blowers, MBBR feed pumping station and an associated MCC to serve the additional side-stream works. The design also incorporated provision for future expansion, with the site configured to accommodate two future DAF units with minimal additional modification requirements.

Key project outputs delivered by Trant Engineering included:

Storm storage capacity increase to approximately 310m3. Installation of EDM monitoring on the inlet and outlet of the storm tank. New tertiary multi-media filtration plant from Bluewater Bio Ltd for improved final effluent quality. Ferric sulphate dosing from WES Ltd, and alkalinity dosing from Rospen Industries for phosphorus removal. New sludge handling, transfer and return pumping assets. Site-wide electrical infrastructure and standby power upgrades. New MCCs, telemetry and process control integration. Installation and commissioning of MBBR side-stream treatment systems from Siltbuster Group. Future-proofed layout to facilitate potential DAF installation.

The successful delivery of these works enhanced treatment performance, increased operational resilience and ensured long-term compliance with tightening environmental discharge consents, demonstrating Trant Engineering’s capability to deliver complex integrated M&E and electrical design solutions within live operational wastewater environments.

[caption id="attachment_31172" align="alignnone" width="1200"] Sludge storage tank - Courtesy of Envolve Infrastructure[/caption] Project completion

Works commenced on site in October 2023, with all regulatory outputs achieved on 20 December 2024, representing the collaborative approach to project management, construction and commissioning across all partners. At the time of writing (May 2026), the newly completed works at Bishops Lydeard WRC are in full operation and continuing to deliver on scheme objectives for the local environment and the residents it serves.

This complex and highly successful project provides a significant improvement to the treatment process and quality of final effluent and delivers additional robustness against future storm events. It was delivered to the highest quality and health and safety standards.

Owned and operated by Dŵr Cymru Welsh Water, Corwen Wastewater Treatment Works (WwTW) is located north of Corwen town centre in north Wales. The works serves a predominantly rural catchment with a current population equivalent (PE) of around 2000 and comprises inlet pumping (of both foul and storm flows), primary settlement, stone media trickling filters, and humus settlement, with final effluent discharge into the River Dee. The River Dee is of high environmental importance and includes designated sensitive areas, including Sites of Special Scientific Interest (SSSI). Project background

Phosphorus in treated wastewater can lead to oxygen depletion, deterioration of habitat quality, and adverse impacts on sensitive aquatic ecosystems. As such, phosphorus control is a critical component in protecting the ecological status of receiving waterbodies, particularly those designated for environmental conservation.

With the River Dee designated as a Site of Special Scientific Interest, the regulatory direction set by Natural Resources Wales (NRW) is to progressively reduce permitted phosphorus discharges to support the achievement of ‘good ecological status’ under environmental water quality objectives. This has resulted in the introduction of tighter total phosphorus consents; in this case, a limit of 1.0 mg/l.

The introduction of the tightened total phosphorus consent required targeted upgrades to maintain compliance with the revised conditions. Dŵr Cymru Welsh Water undertook an assessment of the necessary modifications through its process design, defining the scope of works required to achieve compliance at Corwen while maximising the reuse of existing assets where practicable.

The scheme also presented an opportunity to address ageing infrastructure, improve hydraulic performance across the works, and enhance operational resilience within a site constrained by flood risk.

[caption id="attachment_31276" align="alignnone" width="1200"] Biofilter distribution bed - Courtesy of Eric Wright Water Ltd[/caption] Existing works & drivers

The primary driver for the scheme was to maintain regulatory performance in line with revised consent conditions. To achieve this, chemical precipitation using ferric sulphate dosing was required, integrated into the new inlet pumping main. Additional drivers included:

Ageing infrastructure, including inlet screening, the existing Dortmund-type primary settlement tank, the existing humus settlement tank, half-bridge scrapers and the biofilter distribution arms. Existing hydraulic constraints affecting distribution efficiency. Opportunities to improve operational flexibility within the inlet and settlement processes. Site flooding risk due to proximity to the River Dee. Design & delivery approach

The scheme was delivered under a design and build contract, with Eric Wright Water Ltd acting as principal contractor. Waterco Datrys undertook the multidisciplinary design, encompassing civil, mechanical, and electrical disciplines, supported by FBW Engineering.

A collaborative delivery model was adopted, with weekly coordination meetings held between Dŵr Cymru Welsh Water Process, Operations, and the delivery team. This approach ensured that operability, maintainability, and commissioning requirements were fully embedded within the developing design.

Corwen WwTW: Supply chain - key participants Client: Dŵr Cymru Welsh Water Principal Designer & Contractor: Eric Wright Water Ltd Civil & MEICA design: Waterco Datrys Piling contractor: Van Elle EICA design: FBW Engineering Services Ltd EICA contractor: Lloyd Morris Electrical Ltd Mechanical contractor: Whitland Engineering Ltd Precast concrete: Shay Murtagh Precast Ltd Half-bridge scrapers: Eric Wright Water Ltd Inlet screen & screenings handling: Jacopa Limited Imports screen: Huber Technology Ferric dosing tank & associated equipment/kiosk: Colloide Safety shower & hose reels: Hughes Safety Showers Ltd Stainless steel sludge tanks: Stortec Engineering Ltd Sludge tank mixers: Xylem Water Solutions Pumps: Watson Marlow Ltd Pumps: Grundfos Pumps: KSB Ltd Pumps: Xylem Water Solutions Washwater booster pumpset: Dutypoint Ltd Static mixer: Statiflo International Ltd Access steelwork fabricator: Whitland Engineering Ltd [caption id="attachment_31279" align="alignnone" width="1200"] Jacopa inlet screen - Courtesy of Eric Wright Water Ltd[/caption] Inlet works & screening upgrade

Raw flow enters the works via a gravity sewer to the inlet pumping station wet well. The inlet works were upgraded to improve screening performance and operational resilience. A new 6 mm, 2D mesh Jacopa bandscreen was installed within the wet well, replacing the existing screening arrangements and maceration equipment. The new screen and screenings handling system provide enhanced removal of gross solids and rag material prior to pumping to downstream treatment processes and storm storage.

A high-level bypass arrangement, incorporating a manually raked screen, was also provided to ensure flow continuity in the event of mechanical failure. The bypass is set above known flood levels, maintaining operability during extreme events.

Inlet pumping main & ferric dosing

The pass-forward inlet pumping arrangement was reconfigured to discharge directly to full treatment, replacing the previous high-level channel. The new inlet main incorporates:

An MCERTS-compliant flow meter. Connections for sludge supernatant and humus return flows. Valved rodding points for cleaning and inspection. Ferric sulphate dosing via a static mixing arrangement. [caption id="attachment_31275" align="alignnone" width="1200"] Colloide ferric dosing tank and access platform - Courtesy of Eric Wright Water Ltd[/caption]

A 10m3 ferric sulphate storage tank has been installed, along with a dedicated dosing kiosk designed and supplied by Colloide. The dosing installation includes a bunded chemical delivery off-loading area with a contained drainage system, ensuring that any spills are safely managed in accordance with operational and environmental requirements.

The containment area is controlled via an actuated valve, configured to maintain functionality and resilience during flood events.

Primary settlement upgrades

A new radial primary settlement tank was constructed adjacent to the existing Dortmund-type tank. The new tank comprises a precast, above-ground circular structure and is fitted with a half-bridge scraper mechanism, an automated scum removal system, and a V-notch weir arrangement. Sludge draw-off is directed to the existing sludge handling infrastructure.

The existing primary settlement tank has been retained to provide operational flexibility and can be brought back into service during maintenance or outages of the new tank.

[caption id="attachment_31271" align="alignnone" width="1200"] Primary settlement tank - Courtesy of Eric Wright Water Ltd[/caption] Biofilters & hydraulic improvements

Downstream biological treatment is provided by two existing stone media biofilters. Upgrades were undertaken to improve hydraulic distribution and optimise treatment consistency.

Initial investigations identified hydraulic surcharge as being associated with the existing dosing siphon arrangement. This was addressed through removal of the siphon and the installation of a new inlet pipework configuration.

The scope of works included increasing the media depth, replacing the distributor arms, modifying the inlet pipework arrangement, and investigating hydraulic back-up between the primary settlement tank and the biofilters.

Humus settlement

A new humus settlement tank was constructed adjacent to the existing unit to increase overall settlement capacity and provide operational flexibility. The new tank comprises a precast, above-ground structure fitted with a half-bridge scraper mechanism, an automated scum removal system, and a V-notch weir arrangement.

New peristaltic pumps were installed to serve both humus settlement tanks, returning humus sludge to the primary settlement tank for co-settlement.

[caption id="attachment_31273" align="alignnone" width="1200"] Humus settlement tank - Courtesy of Eric Wright Water Ltd[/caption] Final effluent & washwater systems

A new final effluent kiosk was installed, housing online monitoring instrumentation for phosphorus, iron, suspended solids, and pH.

Final effluent is reused for washwater applications across the site, including inlet and imports screening. A new pumping station was constructed to provide both final effluent washwater supply and outfall pumping, improving the resilience of final effluent sampling and settlement processes during periods of high river levels.

Where potable washwater is required, a new Dutypoint booster system provides a reliable supply to the chemical dosing and sludge handling areas. This arrangement ensures clear segregation between process effluent and potable systems, enhancing operational safety.

[caption id="attachment_31280" align="alignnone" width="1200"] Final effluent chamber and sampling chamber - Courtesy of Eric Wright Water Ltd[/caption] Sludge handling & storage

Sludge handling arrangements at Corwen WwTW were upgraded as part of this scheme to improve operational resilience, segregate sludge streams, and enhance overall handling efficiency.

Two new above-ground stainless steel storage tanks, supplied by Stortec Engineering Ltd, were installed to provide dedicated storage for indigenous sludge. This improves process stability and enables more controlled sludge management across the works. In addition, a dedicated imports reception facility was constructed to allow tanker deliveries of cess and sludge to be received, screened, and stored safely on site.

The imported sludge system includes an integrated screening unit, supplied by Huber Technology, to remove gross solids prior to pumped transfer into a new above-ground stainless steel imports tank, also supplied by Stortec Engineering Ltd.

[caption id="attachment_31272" align="alignnone" width="1200"] Sludge tanks & imports screen platform - Courtesy of Eric Wright Water Ltd[/caption] Electrical & ICA

Key elements of the electrical and ICA upgrades included:

Upgrade of the incoming power supply and transformer capacity. Installation of a new kiosk housing the main MCC, with provision for future expansion. Integration of PLC and HMI control systems. Installation of MCERTS-compliant instrumentation for flow and sludge monitoring. Innovations

A number of innovations were adopted for the successful delivery of the project:

The use of precast concrete settlement tanks, from Shay Murtagh Precast Ltd, reduced programme duration and construction risk. A collaborative delivery approach enabled efficient progression of a complex scheme within tight timescales. Asset reuse was maximised wherever practicable: The inlet screening solution was designed to utilise the existing wet well, avoiding the need for a new structure. Existing biofilter beds were refurbished to improve treatment capacity and performance. The existing humus tank was retained, with mechanical elements replaced while preserving the structurally sound concrete infrastructure. [caption id="attachment_31278" align="alignnone" width="1200"] Installation of the MCC kiosk - Courtesy of Eric Wright Water Ltd[/caption] Construction constraints

Flood risk

The site is located adjacent to the River Dee and is subject to regular flooding. Critical electrical and mechanical infrastructure was therefore installed on elevated platforms or protected within chambers constructed above the design flood level.

The outfall chamber was sealed and fitted with a non-return valve to allow site floodwater to drain to the outfall while preventing backflow. Process chambers and inlet works upgrades were designed to maintain operational resilience during flood conditions.

Ground conditions

Ground conditions comprised variable made ground overlying clay, gravel, and silt deposits. Due to variability in bearing capacity, and the importance of hydraulic levels across the works to ensure efficient hydraulic performance, piled foundations were adopted for key structures, including settlement tanks and sludge storage tanks.

Live site operation

The project was delivered within a fully operational treatment works. Maintaining compliance throughout construction required careful sequencing, temporary bypass arrangements, and the staged commissioning of new assets.

These activities were managed and delivered by Eric Wright Water Ltd in collaboration with Dŵr Cymru Welsh Water.

[caption id="attachment_31274" align="alignnone" width="1200"] De-sludge return pump platform - Courtesy of Eric Wright Water Ltd[/caption] Conclusion

The Corwen WwTW phosphorus upgrade scheme delivers a targeted process intensification and infrastructure renewal project within a constrained and operationally sensitive site.

The introduction of ferric dosing, combined with upgraded settlement processes and improved hydraulic control, ensures compliance with the tightened 1.0 mg/l phosphorus consent. The scheme has also significantly enhanced site resilience through the implementation of flood protection measures and electrical infrastructure upgrades.

The works were delivered while maintaining continuous treatment, demonstrating effective coordination between Dŵr Cymru Welsh Water, the design team, and the contractor. The upgraded works now provide a robust and flexible asset capable of meeting current compliance requirements while accommodating future operational demands.

In addition to achieving regulatory compliance, the scheme supports Dŵr Cymru Welsh Water’s wider ambition to protect and enhance the natural environment, particularly the rivers and catchments across Wales. By improving treatment performance, operational resilience, and long-term asset reliability, the project contributes to sustainable wastewater management and helps deliver meaningful environmental improvements within the communities it serves.

The completed works therefore represent not only an investment in infrastructure resilience, but also a positive step towards safeguarding water quality for future generations.

One of Anglian Water’s strategically important water treatment works in the south of the region has recently undergone a major upgrade to its disinfection infrastructure, strengthening both primary and final disinfection to meet regulatory requirements and enhance long-term operational resilience. The works treats groundwater abstracted from multiple satellite borehole sources, which is blended on site with imported water from the wider strategic network. While this integrated supply arrangement provides flexibility and resilience, it also introduces additional complexity in managing water quality risk. Coupled with increasingly stringent regulatory expectations, this complexity required a robust, future-ready approach to disinfection. Project background

The treatment works is a critical asset within the Anglian Water supply area, serving a diverse mix of residential, commercial and rural communities.

Raw water from three satellite borehole sites is blended at the works before undergoing aeration and iron and manganese filtration as part of the treatment process. In addition to local groundwater, the site now receives imported water via the Strategic Pipeline Network.

While this blended water enhances resilience of supply, it introduces additional regulatory considerations; particularly in relation to microbiological risk. As a result, the site was required to comply with Regulation 26 of the Water Supply (Water Quality) Regulations, which mandates appropriate primary disinfection where a risk to water quality is identified. [caption id="attachment_31444" align="alignnone" width="1200"] The completed DN500 carbon steel pipework - Courtesy of @one Alliance[/caption]

At the same time, elements of the existing final disinfection assets were approaching the end of their effective service life. This presented an opportunity to address multiple drivers through a single, coordinated programme, strengthening compliance, improving resilience and maximising value through integrated delivery.

In response, Anglian Water, working through its @one Alliance, successfully delivered two closely aligned schemes at the site:

A Regulation 26 UV primary disinfection project, and; A final disinfection enhancement and resilience project.

Delivered in parallel within a shared construction footprint, the schemes were deliberately integrated to optimise cost, programme, carbon and operational outcomes. This case study sets out the background to the investment, the solution that was implemented and the benefits delivered for customers and the wider region.

The issue

The central challenge was to deliver a fully compliant and resilient disinfection solution on a live operational site, while maintaining continuous water supply throughout construction and commissioning.

This required the team to achieve full Regulation 26 compliance for blended supplies, enhance final disinfection resilience and monitoring, and integrate new assets seamlessly with existing treatment processes and control systems. This had to be delivered within a constrained site footprint, with tight hydraulic tolerances and minimal tolerance for disruption to operations or customers.

[caption id="attachment_31442" align="alignnone" width="1200"] The completed works including the new 1500 litre emergency shower from Aqua Safety Showers International Ltd - Courtesy of @one Alliance[/caption] The solution

The @one Alliance implemented a strategic and meticulously planned solution that brought together two distinct but complementary schemes into a unified delivery. By integrating Regulation 26 primary disinfection with final disinfection enhancement, the approach ensured regulatory compliance, strengthened operational resilience and optimised construction within a constrained operational environment.

To achieve Regulation 26 compliance, a new UV primary disinfection process was installed upstream of the treated water reservoirs. The system was designed to operate effectively across the full range of site flows, providing robust protection under all operational scenarios. The UV system was designed to operate across the full range of site demand conditions, ensuring resilience during both normal and peak operating scenarios.

A defining feature of the solution was the re-use of two kiosk-housed UV units.  These existing UV assets were held within the Anglian Water estate & were re-purposed and fully refurbished, validated and recommissioned, and avoided the need for new equipment manufacture and reducing embodied carbon.

Rather than procuring new plant, the units were relocated to site and comprehensively modified to operate together as a permanent installation. This included diversion and cut-in of treated water pipework to route flows through the UV process, mechanical, electrical and control modifications to enable combined operation, and full reactor servicing, validation and re-issue of commissioning documentation.

The Regulation 26 works also incorporated the installation of two new glass traps downstream of the UV units, a new SWORPS flowmeter and associated instrumentation, and a new power supply fed from the existing MCC via an additional feeder. The new assets were fully integrated with site operational systems and security requirements. Extensive civils works were delivered alongside, including concrete base slabs for the kiosks, pipework support plinths, drainage, ducting, draw pits and new access paths.

[caption id="attachment_31443" align="alignnone" width="1200"] The newly installed pipework & kiosk - Courtesy of @one Alliance[/caption]

Sodium hypochlorite final disinfection dosing equipment was installed to provide robust residual disinfection prior to storage and distribution. This therefore doses into the SPA main where it enters the site and this has been enabled by the excellent collaboration between the two delivery vehicles on behalf of Anglian Water.

Both schemes were deliberately designed and constructed within the same area of the site, allowing shared use of kiosks, civils, pipework routes and instrumentation. This integrated approach reduced duplication, minimised construction impacts and delivered efficiencies in cost, programme and carbon, while providing a resilient and future-ready disinfection solution.

Supply chain: Key participants Project delivery: @one Alliance Principal contractor: Skanska UV health check: Trojan Technologies Site engineering services: East Anglian Site Engineering Ltd Ecology surveys: Norfolk Wildlife Services Ltd Topographical & drone surveys: Randall Surveys LLP Mechanical & electrical: Field Systems Designs Ltd Civil engineering & pipework: Claret Civil Engineering Ltd MCCs, PLC investigations & UV light units: CEMA Ltd MCC modifications: TES Group WAC testing: Endeavour Testing Ltd Valves: AVK UK Ltd Pumps: Flowserve Pumps: KSB Ltd Pumps: SPP Pumps Ltd Pumps: Xylem Water Solutions Pumps: Grundfos Pipework: Saint Gobain PAM UK Telemetry: Dodd Group Static mixer (with lances): Statiflo International Ltd Flow switches, meters & pressure sensors: IFM Electronics Flow meters: Emerson Turbidity monitors: Hach Level switches: RS Components Ltd Level floats: Xylem Water Solutions Final water free chlorine analytical monitors: Evoqua Pressure indicators/gauges: WIKA Hypo package & modifications: Amentum Safety shower: Aqua Safety Showers International Ltd Civils materials: Wolseley Ltd Site set-up: Wernick Group Vegetation clearance: Chevron Green Services Ltd Kiosk lift: Cadman Cranes Ltd Site security: BauWatch UK Ltd Security fencing: Burn Fencing Ltd [caption id="attachment_31441" align="alignnone" width="1200"] The new hypo dosing system - Courtesy of @one Alliance[/caption] Benefits of the solution

The completion of the Regulation 26 and final disinfection schemes has delivered a wide range of regulatory, operational and long-term benefits, strengthening both water quality assurance and resilience.

The introduction of UV primary disinfection enables compliance with Regulation 26 requirements and strengthens protection against microbiological risks. This is complemented by enhanced final disinfection and improved monitoring, strengthening assurance that treated water consistently meets quality standards before entering storage and distribution.

Operational resilience has been significantly improved through the duty/standby configuration of the UV reactors and the dosing pumps within the sodium hypochlorite dosing system. This provides flexibility during maintenance and under variable demand as a result. Upgraded monitoring and shutdown systems further reduce the risk of asset failure and unplanned outages, supporting reliable day-to-day operation.

The project has also delivered clear cost and carbon efficiencies. Re-using existing emergency UV units avoided the manufacture and procurement of new plant, reducing both capital cost and embodied carbon. Additional efficiencies were achieved through shared civils infrastructure and kiosks, a reduced requirement for landscaping and retaining walls, and the coordination of construction activities within a single integrated programme.

Finally, the solution provides a future-proofed asset base. All new infrastructure was delivered in line with minimum asset standards, with design lives of 40 years for civil structures and 15 years for mechanical and electrical equipment. The completed schemes accommodate future changes in demand and supply arrangements, ensuring long-term resilience and a secure water supply for customers across the region.

[caption id="attachment_31446" align="alignnone" width="1200"] The completed DN500 carbon steel pipework - Courtesy of @one Alliance[/caption] Conclusion

The recently completed projects to comply with Regulation 26 of the Water Supply (Water Quality) Regulations and provide final disinfection demonstrate how integrated planning, intelligent asset re-use and collaborative delivery can achieve strong regulatory and operational outcomes.

By combining primary and final disinfection upgrades into a single, coordinated programme, Anglian Water and its @one Alliance have delivered a resilient, compliant and future-ready solution that safeguards water quality while delivering long-term value for customers.

This project stands as a clear example of how strategic investment in treatment infrastructure can balance regulatory compliance, operational resilience and sustainability, supporting a secure water supply for communities across the Anglian Water region for decades to come.

Longbridge STW, a key facility serving Warwick, Leamington Spa, and surrounding communities, is undergoing a significant, £56m transformation under the AMP7 programme. This ambitious expansion will nearly double the plant’s sewage treatment capacity from 734 litres per second to 1,261 litres per second, thus ensuring resilience and sustainability for a rapidly growing population. The upgraded facility will extend its catchment area to the south-west of Warwick incorporating new residential zones and a commercial trader in Lighthorne Heath, a newly constructed incoming sewer that will convey sludge from Campion Hills Water Treatment Works, as well as have to manage stormwater from multiple combined sewer overflows (CSOs), enhancing the system’s efficiency and environmental performance. Background

By 2038, the population served by Longbridge STW is projected to rise from 156,250 to 186,413 population equivalent (PE). In response, discharge consents will be tightened to meet stricter environmental standards:

Existing consent New consent Ammonia 5 mg/l Ammonia 4 mg/l BOD 20 mg/l BOD 13 mg/l Phosphorus 1 mg/l Phosphorus 0.2 mg/l Currently operating as a traditional filter works, the plant includes storm flows management, inlet, and primary treatment stages, followed by two secondary biological filter phases and tertiary sand filtration, as well as traditional sedimentation processes. The expansion will modernise this infrastructure to meet future regulatory and operational challenges. Project delivery

The project is being delivered through a strategic partnership between Severn Trent, acting as the client, and Mott MacDonald Bentley, serving as both principal designer and principal contractor - demonstrating a collaborative commitment to innovation, environmental stewardship, and community service.

[caption id="attachment_25596" align="alignnone" width="1200"] Google Maps view of the existing Longbridge STW - Courtesy of MMB[/caption] Project scope

This project involves a comprehensive upgrade of wastewater treatment infrastructure to meet stringent regulatory requirements and enhance operational efficiency.

The scope includes:

A new inlet pumping station and inlet works. An additional primary settlement tank (PST). An activated sludge process pumping station (ASP PS). A new side-streamed activated sludge plant (ASP). Four final settlement tanks (FSTs). A ballasted coagulation tertiary solids removal plant (TSR) with its associated pumping station and process. A return activated sludge/surplus activated sludge (RAS/SAS) pumping station. Ferric dosing system. Sludge thickening plant that includes: Gravity belt thickeners (GBTs). Polymer dosing units. A return liquors pumping station. Thickened SAS tanks. Several other upgrades associated with achieving the new constraints. ECI & optioneering

Mott MacDonald Bentley (MMB) was engaged early in the project through several Early Contractor Involvement (ECI) contracts, which enabled a collaborative and improved approach to optioneering and outline design. During ECI 1, the team developed conceptual sketches for various treatment configurations and provided indicative cost estimates. This process allowed stakeholders to evaluate multiple options and select the most cost-effective and technically viable solution.

The optioneering phase focused on balancing performance, constructability, and whole-life cost. Technologies and layouts were assessed not only for their treatment efficiency but also for carbon footprints, Operational constraints, ease of installation, future maintenance, and integration with existing assets. The selected solution was then progressed under the ECI 2 contract, which involved developing the outline design, defining the scope of works, and establishing a target price. This early contractor involvement was instrumental in aligning design intent with delivery strategy, enabling the detailed design phase to commence while the Design & Build contract was being finalised.

[caption id="attachment_25602" align="alignnone" width="1200"] Longbridge STW process flow diagram - Courtesy of Mott MacDonald Bentley[/caption] Digital engineering

Digital engineering tools, including 3D modelling and clash detection, 4D modelling, Virtual Reality setups and Spatial AI Technology were used throughout the project to improve coordination and reduce construction risk. Modular construction methods were also employed where feasible to accelerate delivery and enhance safety.

The project integrates robust and sustainable technologies, underpinned by early collaboration and strategic design development. By adopting the collaborative and digitally enabled approach outlined above, the project team was able to commence detailed design significantly earlier than traditional delivery models would allow. This early start unlocked critical programme efficiencies, which are especially valuable given the tight deadlines facing the project.

In addition to schedule gains, the approach also delivered notable commercial efficiencies for the client through early cost certainty and reduced design rework. The optioneering and early engagement phases enabled the team to challenge initial assumptions and improve the originally envisaged carbon footprint of the scheme, aligning with broader sustainability goals.

Furthermore, the project is progressing strongly on its Biodiversity Net Gain (BNG) commitments, with proposals demonstrate a proactive approach to environmental enhancement.

[caption id="attachment_25593" align="alignnone" width="1200"] Chemical dosing system from another site - Courtesy of Colloide Ltd[/caption] Preliminary & primary treatment

Flow interception & distribution: All incoming flows to the existing inlet works are first intercepted at a newly constructed interception chamber. From this point, up to 1,261 litres per second (l/s) of flow to full treatment (FFT) will be directed to a new inlet pumping station. Any excess flow, typically stormwater, will be diverted to the existing inlet works, which are being re-purposed to handle storm events.

Inlet pumping station configuration: The new pumping station will operate in a duty/assist/assist/standby wet well arrangement, ensuring redundancy and operational flexibility. It conveys flows to the new inlet works, which will include three fine screens designed to remove ≥80% of solids larger than 6 mm, protecting downstream processes from clogging and wear and a vortex grit separator located downstream of the screens, which efficiently extracts grit and inorganic materials such as sand. This step is crucial for safeguarding mechanical equipment from abrasion and fouling.

Flow splitting & primary settlement: Post-screening and grit removal, the flow enters a splitter chamber that divides it in an 80:20 ratio; 80% of the flow is routed to the four existing primary settlement tanks (PSTs), and 20% will be directed to the newly constructed PST 5.

In the primary treatment stage, gravity-based sedimentation will be employed to remove a substantial portion of the remaining suspended solids. This step significantly reduces the organic and particulate load entering the secondary treatment phase.

Transition to secondary treatment: The clarified effluent from all PSTs will be conveyed to the activated sludge process (ASP) pumping station, marking the transition to the secondary biological treatment phase.

[caption id="attachment_25604" align="alignnone" width="1200"] Vortex grit chamber from another site - Courtesy of SPIRAC Ltd[/caption] Secondary treatment

The new ASP pumping station will transfer 48% of the total flows from PSTs to the new ASP distribution chamber, while the rest 52% will be lifted via existing Archimedean screw pumping station to the existing secondary treatment works.

The ASP distribution chamber will receive flows from both the ASP pumping station (PS) and the return activated sludge (RAS) PS, distributing it evenly across the four ASP lanes. Each lane will be configured with an anoxic zone followed by aerated zones; enabling efficient biological treatment.

Anoxic zone - denitrification phase: Primary settled sewage will be blended with RAS before entering the anoxic zone. The mixture will be introduced under low turbulence conditions to prevent oxygen ingress, which is essential for maintaining an anoxic (oxygen-depleted) environment.

In this zone, denitrifying bacteria will utilise nitrate (NO3-) as an electron acceptor, converting it into nitrogen gas (N2); a key step in nitrogen removal. Submersible mixers will be used to maintain plug flow and prevent solids accumulation.

Hydraulic separation from the downstream aerobic zone will be achieved using concrete baffles and full-width weirs, effectively preventing oxygen back-mixing.

The hydraulic retention time (HRT) in the anoxic zone will typically range from 1 to 3 hours under average flow conditions.

[caption id="attachment_25601" align="alignnone" width="1200"] ASP construction (summer 2025) - Courtesy of Mott MacDonald Bentley[/caption]

Aerated zone - nitrification & BOD removal: Following the anoxic phase, the flow will enter the aerated zone, where diffuser grids supply oxygen via turbo blowers. In this oxygen-rich environment, ammonia (NH3) will biologically oxidised to nitrate (NO3-) by nitrifying bacteria. Biochemical oxygen demand (BOD) is significantly reduced, enhancing effluent quality.

The aeration process will be dynamically controlled using dissolved oxygen (DO) sensors and ammonia analysers, ensuring optimal oxygen delivery and energy efficiency. For enhanced operational control, the aerated zone is divided into four control sub-zones, allowing for tailored aeration strategies based on real-time process conditions.

Tertiary treatment

Flow consolidation & chemical dosing: Effluent from the final settlement tanks (FSTs) and other existing process units will first be routed to a mixing chamber, where flows will be combined. Prior to entering the tertiary treatment stage, the combined flow will undergo chemical dosing with ferric sulphate. This step facilitates the precipitation of residual phosphorus, a critical requirement for meeting stringent discharge consents.

Tertiary solids removal (TSR) via ballasted coagulation: The chemically dosed effluent will be directed to the TSR plant, which employs CoMag® technology from Xylem Water Solution (Evoqua). This advanced process uses polymer and magnetite to form dense, fast-settling flocs. The magnetite acts as a ballast, significantly increasing the settling velocity of the flocs, thereby enhancing the removal of phosphorus-rich solids with high efficiency.

Magnetite recovery & sludge management: The settled sludge, enriched with phosphorus and magnetite, is conveyed to a magnetic recovery drum. Here permanent magnets will separate the magnetite from the sludge and the recovered magnetite will be recycled back into the process, while the phosphorus-laden sludge is directed to the sludge treatment line.

Final effluent monitoring & discharge: The treated effluent will exit the TSR plant and flow into a final effluent monitoring chamber, where key quality parameters such as suspended solids, phosphorus, and turbidity are continuously monitored against discharge consent limits. Once verified, the final effluent is discharged to the River Avon via a dedicated outfall chamber.

[caption id="attachment_25597" align="alignnone" width="1200"] Evoqua CoMag® plant from another site - Courtesy of Xylem Water Solutions[/caption] Longbridge STW: Supply chain - key participants Client: Severn Trent Principal designer & contractor: Mott MacDonald Bentley FRC: Bell Formwork & Civil Engineering Services Ltd Precast concrete: Naylor Concrete Products Ltd Evoqua CoMag® tertiary solids removal: Xylem Water Solutions Scraper bridges: Jacopa Ltd Inlet screens & grit removal: SPIRAC Ltd Electrical installation: Main Electrical Ltd ASP aeration: Suprafilt Ltd MCC: BGEN Ltd - Part of M Group Chemical dosing: Colloide Composite steel-reinforced pipes: Aquaspira Ltd Flow controls: AFFCO Flow Control (UK) Ltd Innovations, cost savings & carbon reduction

Smart Engineering: Innovative precast wall segment strategy: At Longbridge STW, there are four 32m diameter FSTs and one 27m diameter PST. Faced with tight timelines and complex site logistics, the design team opted for an innovative precast solution where Hydrotite waterstops are installed between each precast wall segment along the entire vertical joint to achieve watertight integrity throughout the structure.

Early engagement with precast supplier during the design development stage to provide precise pipe penetration details and sealing methods, thus avoiding any last-minute changes. Key Benefits of the precast approach included:

Cost savings: Reduced material waste and labour costs compared to traditional cast in situ methods. Accelerated programme: Faster installation significantly shortens the construction timelines. Ease of installation: Modular design signifies on-site assembly and alignment. Off-site fabrication: High quality production in controlled environment ensures consistency. Reduced site work: Minimised on-site activities and congestion. Enhanced safety: Reduces high-risk tasks such as reinforcement cutting and formwork handling. [caption id="attachment_25595" align="alignnone" width="1200"] Example of a precast concrete tank that will be used for the Longbridge PST & FSTs - Courtesy of Naylor Concrete Products Ltd[/caption]

Innovative grit removal upgrade: As part of MMB’s value engineering initiative, the project team reviewed the grit removal design to identify opportunities for cost and efficiency improvements. In ECI 1, a conventional 8.5m diameter detritor grit chamber was proposed. However, in ECI 2, the team recommended replacing it with a more compact 5m diameter vortex grit unit. This marked a first for Severn Trent, as this particular size of vortex unit had never been implemented before.

The key benefits are:

Procurement savings exceeded £100,000. Civil works and excavation costs significantly reduced. Construction timeline shortened, mitigating potential Health & Safety risks. Carbon footprint lowered due to reduced concrete and access metalwork.

This shift not only delivered immediate financial and programme benefits but also aligned with Severn Trent’s sustainability goals and set a precedent for future grit system designs. The success of this initiative demonstrates the power of collaborative engineering and bold innovation in driving smarter, greener infrastructure solutions.

Embracing digital innovation in construction delivery: As part of MMB’s commitment to smarter, safer and more efficient project delivery, the team have integrated several advanced technologies into the construction workflow:

OpenSpace AI enabled real-time progress tracking and improved coordination between design and site teams, reducing rework and enhancing transparency. Drone Surveys accelerated site analysis and topographical validation during early design stage. This enhanced safety by minimizing manual survey works in high-risk zones. 4D Construction Sequencing enabled proactive clash detection, supports programme optimization by identifying sequencing inefficiency before they impacted site operations. [caption id="attachment_25594" align="alignnone" width="1200"] OpenSpace AI walkthrough of ASP base - Courtesy of MMB[/caption]

These technologies not only modernised the delivery approach but also set a benchmark for future projects. Key benefits included:

Improved decision making through centralised, visual data. Reduced site visits and enhanced remote collaboration. Shortened construction timelines. A lower carbon footprint through efficient planning and reduced rework.

Procurement led design: Procurement led design is a strategic approach that flips the traditional design-first model by integrating procurement decisions early in the design phase; especially impactful in pipework systems, where material availability, cost, and constructability can dramatically influence outcomes.

Key benefits include early supplier engagement, material driven design decision and cost and constructability optimisation.

Progress (as of September 2025)

Works started on site in Q1 of 2025. At the time of writing (September 2025), the construction works are progressing well, with ASP civil structures under construction and earthworks for other major assets nearing completion. Early engagement with subcontractors has helped maintain programme alignment and mitigate risks.

[caption id="attachment_25600" align="alignnone" width="1200"] ASP construction (summer 2025) - Courtesy of Mott MacDonald Bentley[/caption]

Key successes include the smooth transition from outline to detailed design, enabled by the ECI process, and strong collaboration across all stakeholders. The project remains on track to meet its regulatory deadline, with commissioning scheduled for mid-2027.

Future phases will focus on mechanical and electrical installations, commissioning, and performance optimisation to ensure long-term compliance and operational efficiency.

The Rivers Lugg and Wye have been identified as having high levels of phosphorus, which is causing eutrophication of these watercourses. Norton Wastewater Treatment Works (WwTW) discharges treated final effluent to the Norton Brook, a tributary of the River Lugg. Presteigne WwTW discharges treated final effluent directly into the River Lugg downstream of the Norton Brook confluence and Weobley WwTW discharges to Newbridge Brook, a tributary of the River Arrow and then River Lugg before joining the River Wye in Hereford. Norton WwTW Norton WwTW is a biofilter works located in Powys serving a population of 320. All wastewater flows arrive to the works by gravity and are treated on site before being discharged. The site previously had a descriptive consent and an unconsented storm discharge. The project driver was to reduce phosphorus to achieve a Total P of 0.65mg/l, with a regulatory completion date of 31 December 2021. Due to the proximity of Norton WwTW to Presteigne WwTW (approximately 3km), an identified option was to pump the Norton flows to the Presteigne catchment. An assessment of the hydraulic and biological capacity of Presteigne WwTW and the Presteigne sewerage network determined there was sufficient capacity to accept the pump-away solution whilst maintaining compliance with all permits. Therefore, the agreed solution was to replace Norton WwTW with a terminal pumping station, pump sewage into the existing sewer network draining to Presteigne WwTW. Consequently, the Norton WwTW would be decommissioned. [caption id="" align="alignnone" width="1200"] Norton SPS progressive cavity pumps - Courtesy of Morgan Sindall Infrastructure[/caption] Norton WwTW: Supply chain - key participants Designer: Arup Main contractor (WwTW & rising main): Morgan Sindall Electrical supply & installation: Protocol Control Systems (PCS) Ltd Inlet screens: Haigh Engineering Mechanical design/installation & steelwork: Industrial Pipework Services (IPS) Ltd Main pumps: Netzsch Pumps Washwater booster: Dutypoint Ltd MCC supply/install: Bridges Electrical Engineers Ltd Transfer to Presteigne Progressive cavity (PC) pumps were selected as the pumping method due to the complex nature of the 2km long rising main. The rising main has a number of peaks and troughs with washouts, air valves and sections operating under gravity. Furthermore, the inverted siphon section of the main may be susceptible to soft blockages which PC pumps were determined to be better suited to than submersible centrifugal pumps. Submersible pumps would be more susceptible to pressure fluctuations caused by potential air gulping in the downhill section of the main. The PC pumps are positioned on an above-ground slab along with valves and pipework to enable good operator and maintenance access. Split stator casing pumps were specified to provide ease of rotor replacement. To protect the PC pumps against ragging and wear, an inlet screen and grit chamber were set up upstream of them. The inlet screen is an Ace Screener® from Haigh Engineering Ltd, equipped with an integrated compactor and liquid separator unit. It is located beside the screen to facilitate the discharge of waste material into a skip. [caption id="" align="alignnone" width="1200"] Norton SPS: MCC kiosk and Haigh Engineering inlet screen - Courtesy of Morgan Sindall Infrastructure[/caption] Rising main Due to the length of the rising main, and the low flows coming into the pumping station on a regular basis, the output from the SPS would have been likely to suffer from septicity. This would cause particular odour problems as the discharge makes its way through the Presteigne network towards Presteigne WwTW. It was decided that potable water dosing be included within the design to reduce the risk of septicity. This has the added benefit of assisting in moving solids along the long rising main, which reduced the risk of soft blockages in the inverted siphon section of the main. During the construction of the rising main, a spider plough was utilised for sections within fields. This allowed for simultaneous excavation, pipe-laying, and covering to take place, resulting in minimal visual impact on the landscape. Additionally, this approach resulted in reduced staff involvement during this stage of construction, which was another advantage. A final air valve was required on the rising main before discharge, which is in close proximity to local housing and a children’s park. To prevent any odour-related complaints that might arise from the air valve, a carbon filter has been installed to scrub odours from the air released from the air valve. The chosen filter is a passive filter that can be easily installed within the air valve chamber. [caption id="" align="alignnone" width="1200"] Spider plough operation to construct the Norton WwTW pump away rising main - Courtesy of Morgan Sindall Infrastructure[/caption] Presteigne WwTW Presteigne WwTW is a biofilter works serving a population of 1,906 with a driver to reduce Total P to 1mg/l. The proposed solution is to provide chemical dosing at Presteigne to treat all the Presteigne network flows along with the additional pumped flows from Norton WwTW. The chosen system was ferric dosing with primary dosing upstream of the existing primary settlement tank (PST). A ferric delivery area design included a bunded tanker area in case of ferric spillages. This area had drainage with an interlock system, which meant the drainage penstock would close during ferric filling to prevent uncontrolled spillage to the environment. Innovative new dosing pipelines were utilised of flexible reinforced PVC type ‘hose-within-hose’ to provide double containment and an integral leakage detection system and alarm. This meant long continuous hose lengths can be run without breaks. An anti-ragging static mixer and pipework were located above ground to reduce health and safety risks, costs and environmental impacts associated with excavation works. To cope with the increased sludge production due to primary ferric dosing, a new sludge pumping station using PC pumps was designed. This is located alongside the existing PST de-sludge chamber. This was an above-ground element of mechanical plant, with access provided for operation and maintenance. Split casing pumps were specified to provide ease of rotor replacement. The progressive cavity pumps (duty/standby) couple directly into the sludge hopper chamber of the PST. [caption id="" align="alignnone" width="1200"] Presteigne WwTW: Ferric point of application (PoA) unit - Courtesy of Morgan Sindall Infrastructure[/caption] Alkalinity dosing was required as a result of the new ferric dosing. The identified solution for this was a small bag dosing plant with on-site mixing to create a liquid dose. A new point of application facility located on the side of the existing PST which discharges to the biological filter. It was determined that this point had enough hydraulic mixing for an effective alkalinity dose. The new works is achieving its ammonia consent with the current loading, but it had been identified that ammonia compliance could be a risk during AMP9. Nitrifying sand filters have been proposed as a technology to treat the ammoniacal nitrogen as a tertiary treatment solution. This has an added benefit of tertiary solids removal to give confidence in the total phosphorus consent. However, given the excellent performance of the works against consent and nitrifying capacity of the existing biofilters, the nitrifying sand filters will be phased into the works when required. Works included a new sampling arrangement with sampling kiosk, complete with an upstream diversion and reception chamber for when the nitrifying sand filter is constructed. Presteigne WwTW: Supply chain - key participants Designer: Arup Main contractor: Morgan Sindall Electrical supply & installation: Protocol Control Systems (PCS) Ltd Ferric dosing: Colloide Mechanical design/installation & steelwork: Industrial Pipework Services (IPS) Ltd Alkalinity dosing - BiCarb: Rospen Industries Primary settlement tank auto-desludge: SEEPEX UK Ltd Motor control centre supply & installation: GPS Group [caption id="" align="alignnone" width="1200"] Presteigne WwTW: Ferric dosing system and safety shower - Courtesy of Morgan Sindall Infrastructure[/caption] Innovations A number of innovations have been developed throughout the detailed design stage of Presteigne, including removing a number of pumping operations, thereby simplifying the process, and reducing costs and environmental impacts. The design also allowed for the removal of motorised mixing points for chemical dosing in favour of using the works hydraulics for mixing. Furthermore, a conventional solution would have called for an additional PST and humus settlement tank (HST) to provide redundancy to the works. By investigating the process performance, it was determined that the existing single PST and HST were sufficient across the operating range of the works. Therefore, the design proposed temporary bypass connection points upstream of both the PST and HST, with identified lay-down areas for temporary settlement units to be brought on site if required. This meant that the construction works could be completed within the existing site land boundary and saving capital and operational cost and carbon emissions. Weobley WwTW Weobley WwTW is a biofilter works located in Herefordshire serving a population of 1,153. All flows arrive to the works by gravity and are treated on site before being discharged. The works has P removal driver to achieve a Total P of 1.5mg/l. As at Presteigne WwTW, the proposed solution was to provide chemical dosing to reduce phosphorus. A ferric dosing system with primary dosing upstream of the existing PST complete with a ferric delivery area was provided. Given the added ferric dosing, it was expected there would be more sludge production. The existing sludge holding tanks had low abilities for controlling decant. The solution included for a new discharge tree with access arrangement to the existing sludge holding tanks for better operation. The existing works had no inlet screening, with only a macerator on site upstream of primary settlement. A Huber Technology RO9 screen with integrated screenings handling was installed in the existing inlet channel and provided new mechanical flooring with removable sections to provide flexibility for operating and maintenance of the screen. [caption id="" align="alignnone" width="1200"] Weobley WwTW: (left) Huber Technology inlet screen and (right) flow to full treatment pump station - Courtesy of Morgan Sindall Infrastructure[/caption] This provided significant cost and embodied carbon savings compared to a completely new screening installation. Downstream of the screen, an inlet flume was provided for flow measurement and control of the downstream lift pumping station. The flume was constructed off-site, allowing for greater dimensional accuracy than an on-site constructed flume, as well as reduced downtime for the site. A new lift pumping station for all incoming flows for treatment was required to provide a separate lift to the balancing tanks then the unscreened storm flows. The existing inlet pumping station was re-purposed as the storm pumping station, meaning the more efficient pumping station was operating for more of the time compared to the older storm pumping station, which only operated intermittently - hence saving on energy usage and operational carbon. An existing multi-use returns pumping station was used to pump humus returns and storm returns to the head of the works. This asset consisted of outdated and poorly operating pumps and valve work. A solution was developed to replace mechanical equipment within the existing dry-well, saving the need for a new complete pumping station. Weobley WwTW: Supply chain - key participants Designer: Arup Main contractor: Morgan Sindall Electrical supply & installation: Protocol Control Systems (PCS) Ltd Mechanical design & installation: Whitland Engineering MCC supply & installation: Lloyd Morris Electrical Ltd Pumps & package pump station: Xylem Water Solutions Potable water booster supply: Dutypoint Ltd Ferric dosing supply: Colloide Inlet screen supply: Huber Technology Safety shower supply: Hughes Safety Showers [caption id="" align="alignnone" width="1200"] Weobley WwTW: Ferric point of application units - Courtesy of Morgan Sindall Infrastructure[/caption] BIM BIM capabilities were utilised at all three sites to design the schemes, and the wider engineering team used site-wide 3D models to great effect to review the works and propose any improvements. Furthermore, this provided an engaging and relatable interface to present the schemes solution to stakeholders, as well as using engineering drawings. Project completion Welsh Water’s have invested £5.9m at the Norton and Presteigne WwTWs and £2.7m at Weobley WwTW. These phosphorous removal schemes are the first tranche to be completed of a programme of upgrades to existing wastewater treatment works that will improve water quality in the Wye and Lugg river basin catchments. Learnings from these schemes have been used by Arup and Morgan Sindall and shared with the Welsh Water Capital Delivery Alliance partners to improve scheme delivery of other rural wastewater treatment works. Through early engagement with chemical dosing suppliers, potable water designs and DfMA MCC suppliers, design enabling efficiencies in design and construction costs to be realised have been standardised. Norton & Presteigne WwTWs were commissioned in March 2022 and Weobley WwTW was commissioned in March 2023.