Severn Trent WINEP Batch 5 Programme (2026)

Sutton in Ashfield STW sludge thickening tanks - Courtesy of MWH Treatment

Severn Trent’s Water Industry National Environment Programme (WINEP) Batch 5 Programme encompasses phosphorus removal improvements at five wastewater treatment sites in north Nottinghamshire. The desired outcome of the programme is to accelerate delivery of Water Framework Directive (WFD) objectives by reducing phosphorus in wastewater discharges and in doing so, improving approximately 500 km of rivers across the Severn Trent region sooner, and delivering the benefits of cleaner rivers to customers and the local environment.

Project drivers

MWH Treatment was contracted to complete all detailed design, construction and commissioning activities for the WINEP workstream at Mansfield, Sutton, Edwinstowe, Retford and Mattersey Thorpe Sewage Treatment Works, as part of Severn Trent’s Green Recovery Programme. The works were required at all five sites to facilitate rising population in the catchments and the new Total Phosphorus permit requirements.

Retford STW: Sludge tank feed pipework – Courtesy of MWH Treatment

Mansfield STW

Mansfield STW currently serves a population equivalent (PE) of 97,463, however, the size of the catchment is expected increase to 104,435 PE, by the design horizon of 2038. The current final effluent permit for Total Phosphorus is 1 mg/l, which being tightened to 0.2mg/l by March 2027.

Existing works

The existing wastewater stream process at Mansfield STW consists of an inlet works, four storm tanks, three primary settlement tanks (PSTs), an activated sludge plant (ASP), and ferric sulphate dosing plant.

The site is also a sludge digestion centre, therefore has a digestion route comprising three batch thickening tanks, two surplus activated sludge (SAS) belt thickeners, two predigestion storage tanks, two anaerobic digesters, two digested sludge tanks, two centrifuges, and polymer dosing.

Scope of works

The works required modifications to the existing full flow to treatment (FFT) controls, replacement of existing PST desludge pumps, scraper bridges, and the primary sludge transfer main from the desludging well to the batch thickening tanks, construction of a new primary settlement tank, final effluent online iron and pH monitoring telemetry outstation, motor control centre, secondary ferric sulphate dosing plant, CoMag tertiary solids removal plant from Xylem Water Solutions (Evoqua) with associated pumping station and polymer dosing plant, a return liquors pumping station, and a washwater booster set for the TSR.

Sutton STW: Tunnelling works for pipe install – Courtesy of MWH Treatment

Sutton in Ashfield STW

Sutton in Ashfield STW is an activated sludge plant serving a PE of 35,107, which is forecast to increase to 40,257 by 2038. In addition to this 14.7% population increase, the Total Phosphorus permit is being tightened.

Existing works

The current treatment process comprises an inlet works with two storm tanks, two primary settlement tanks, and two separate Nitrifying Activated Sludge Plants (NASPs) with two final settlement tanks for each NASP followed by deep bed sand filtration (DBSF) for tertiary solids removal. A 30m³ ferrous chloride dosing rig is in place for phosphorus removal. Sludge treatment includes co-settling and consolidation of primary sludge and surplus activated sludge.

Scope of works

The scope of works required the addition of 60m³ of ferric sulphate dosing upstream of existing PSTs and upstream of the new TSR, Mecana tertiary solids removal plant from Eliquo Hydrok Ltd, TSR feed pumping station, dirty back wash return pump and pipework, PST desludge pumps, three sludge holding tanks, pre-TSR monitoring, iron and pH final effluent monitoring, and the construction of a new laboratory, telemetry outstation and motor control centre (MCC).

Edwinstowe STW

The existing biological filter works at Edwinstowe STW treats 2019 PE of 16,697 which is expected to rise to 17,898 by the 2038. This anticipated growth along with a tightened Total P permit of 0.49 mg/l are the main drivers for the improvement works.

Existing works

The existing site comprises an inlet works receiving pumped flows with 2D inlet screens and grit removal, two storm tanks, two primary settlement tanks, six biofilters (four rectangular and two circular), three humus settlement tanks, tertiary solids removal plant in the form of two Dynasand filters, and two sludge holding tanks.

Edwinstowe STW: Ferric sulphate dosing plant – Courtesy of MWH Treatment

Scope of works

Upgrades at Edwinstowe STW include ferric dosing plant with crude and secondary dosing points, caustic dosing plant with crude dosing point, inlet pumping station, combined TSR and recirculation pumping station, a Mecana tertiary solids removal plant from Eliquo Hydrok Ltd with associated clean and dirty back wash tanks, three sludge holding tanks, a telemetry outstation and motor control centre, a washwater booster pumping station, and online iron and pH final effluent monitors.

Retford STW

Retford STW is a medium sized trickling filter works, with tertiary sand filtration treating 76 l/s (1 DWF). The works has ferric sulphate dosing to meet an existing 2 mg/l Total Phosphorus permit. The works at Retford were required to ensure that the STW met a tightened a Total P limit of 0.3mg/l in the final effluent.

Scope of works

To meet the tightened Total P permit, a tertiary solids removal plant from Bluewater Bio and associated pumping station was selected. In addition, the scope of works required clean and dirty backwash tanks, a return liquors pumping station, ferric sulphate chemical dosing system with crude and secondary dosing applications, three batch tanks for primary sludge thickening, final effluent online iron and pH monitors, and the replacement of the FFT control penstock, the biofilter distributor drives, and the PST desludge pumps.

Retford STW: Bluewater Bio FilterClear TSR – Courtesy of MWH Treatment

Mattersey Thorpe STW

Mattersey Thorpe STW is another biofilter works currently serving a PE of 5,976 which is expected to rise by approximately 5% by 2038. The works treats a DWF of 1,631 m³/d (18.9 l/s) and FFT of 4,596 m³/d (53.2 l/s) which is to remain unchanged for the 2038 design horizon. The Total Phosphorus permit is being tightened to 1.2 mg/l.

Existing works

The existing treatment process STW comprises an inlet works followed by two circular primary settlement tanks, five biofilters and two circular humus tanks.

Scope of works

Undertakings at Mattersey Thorpe STW included a ferric sulphate chemical dosing system and crude dosing point at the PST discharge chamber, replacement of five filter bed drives, FFT control modifications, a recirculation pumping station, final effluent monitoring and associated telemetry, a new sludge holding tank, and the construction of new laboratory.

Mattersey Thorpe STW: Ferric sulphate dosing plant – Courtesy of MWH Treatment

Severn Trent WINEP Batch 5: Supply chain – designers & contractors

• Principal contractor & designer: MWH Treatment
• Designers: Stantec UK
• Management consultancy: VISION Consulting
• Ground investigations: RSK Geosciences
• Ecologist: Middlemarch Environmental Ltd
• Civil sub-contractors: CR Civil Engineering
• Civil sub-contractors: M2 Civils Ltd
• Shaft sinking: Active Tunnelling Ltd
• Shaft sinking: HB Tunnelling Ltd
• FRC: Smithform
• Piling: Keller Ltd
• Piling: Technik Ground Solutions Ltd
• Mechanical installation: Fluid Sealing & Engineering
• Mechanical installation: Watermark
• Mechanical installation: Tushingham Steel Fabricators Ltd
• Electrical installation: Elsym Installations
• Electrical installation: Main Electrical
• Electrical installation: Southern & Redfern Industrial Solutions

Retford STW sludge thickening tanks – Courtesy of MWH Treatment

Severn Trent WINEP Batch 5: Supply chain – plant & equipment suppliers

• Ferric dosing plant: Colloide
• Poly dosing plant: NPS Engineering
• Caustic dosing plant: Lintott Control Systems
• PST scraper bridges: EPS Water
• Static mixers: Statiflo International Ltd
• Sludge & backwash tanks: Balmoral Tanks Ltd
• MCCs: RSE Control Systems (Blackburn Starling)
• TSR plant – CoMag ballasted clarification: Xylem Water Solutions
• TSR plant – FilterClear multimedia filter: Bluewater Bio Ltd
• TSR plant – Mecana cloth filters: Eliquo Hydrok Ltd
• Pipework: Saint Gobain PAM UK
• RAM pumps: EMS Industries Ltd
• Submersible & mixer pumps: Xylem Water Solutions
• Washwater booster sets: KGN Pillinger
• Electric actuators: Rotork
• FE monitoring: Servitech International Ltd
• Biofilter drives: Drive Systems Ltd
• Showers, eye baths & hoses: Aqua Safety Showers International Ltd
• Demolition works: Derby Demolition
• Scafolding: Lindway

Innovations & sustainability commitments

With five projects included in the overall programme, MWHT was able to realise a number of cost, time, and carbon savings, including:

1. Batch‑level procurement of MCCs, sludge tanks, GRP kiosks, and other standardised items across the programme has delivered notable cost savings.
2. VISION Consulting was engaged early on to implement a Commitment-based Management model. This was successful and resulted in a 22% time saving overall against the initial programme.
3. The designs for the sludge tank bases at Sutton in Ashfield STW were adopted at Edwinstowe and Retford, resulting in a time and cost saving at the design stage.
4. During the excavation at Edwinstowe STW, it became apparent that the ground was made up of good quality sand. By using a U1 Exemption, this sand was reused as ducting surround on Edwinstowe and the other schemes in the batch. This was also completed with the type one stone used for the compound and car park from Mattersey forming the sub-base fill of the TSR at Mansfield.
5. At Mansfield, the sludge connection for the PST was originally planned to connect into the existing sludge feed pipework at a depth of approximately 6m. This would have required extensive excavation and significant temporary works. To mitigate this, a timber heading tunnel was constructed, allowing the pipework connection to be made underground. This approach resulted in significant carbon, programme, and cost savings.
6. Solar panels used on the welfare at four of the five sites to enable electric vehicle charging to be fully sustainable.
7. Close to 70% of all procurement was from suppliers located within a 30 mile radius. This resulted in lower delivery costs, lead times and carbon emissions.

Mansfield STW: Primary settlement tank – Courtesy of MWH Treatment

Social value

This programme has committed to delivering social value within the local communities at the five sites. This has been completed by volunteering with Forestry England to cut back growth around the ancient oak trees in Sherwood Forest, the site teams volunteering time at the local food bank, and replacing a section of concrete at the local primary school. This had been an issue for a number of years and had resulted in trip hazards for the pupils entering class.

The old concrete was broken out and replaced over the Easter half term, eliminating any disruption to the pupils learning and rectifying the trip hazard issue.

Progress to date

At the time of writing, May 2026, all five projects have progressed well. MWH Treatment is looking to hand over Mattersey Thorpe in the coming weeks, Edwinstowe and Retford are coming into the commissioning phase.

The civil and mechanical installations at Sutton in Ashfield STW are nearing completion, with the EICA due to start by the end of May 2026. At Mansfield STW, the civils works are progressing as planned.