Clay Mills Sewage Treatment Works


MWH Constructors was responsible for the design and construction of a new activated sludge plant (ASP) at Clay Mills STW.

Claymills | United Kingdom


Project Overview

In the heart of the Severn Trent region lies Clay Mills, a restored Victorian sewage pumping station based on the north side of the River Trent flood plain near Burton upon Trent, Staffordshire, UK. This project involved a major extension to the existing sewage treatment works and provides improved treatment processes and increased capacity.

Clay Mills is an important site for Sever Trent Water, serving both domestic and industrial clients. Large amounts of industrial wastewater (predominantly from local breweries) contribute to a population equivalent of over 420,000.

Aerial image of Tres Rios

 Project Scope

MWH was responsible for the design and construction of a new activated sludge plant (ASP) at Clay Mills STW.

The principal driver for the project scope was phosphorus removal, although sludge treatment was also being improved. The scope includes, but was not limited to:

  • New ASP with associated final settlement tanks (FSTs)
  • Acid Phase Digestion (APD) with sludge heat exchanger plant
  • Sludge thickening plant
  • Additional 1MW Combined Heat and Power (CHP)
  • Refurbishment and conversion of existing percolating filters

The project includes a large amount of complex construction, including six 36m diameter concrete FSTs, a four-lane double-pass ASP, two acid phase digesters and various associated pumping stations, chambers and buildings.

In 2011, MWH Treatment was appointed as contractor for the Solution Development, Design, Construction and Commissioning of Clay Mills STW. This comprised quality and capacity enhancements and capital maintenance to Burton upon Trent’s 420,000PE works, including CHP; the construction of new 1.3 m³/s BioP ASP; six 35m diameter final tanks; demolition of existing filters and the conversion of others to nitrifying filters.

The site has progressed successfully and has proved to lead the way in innovation.

  • Off-site fabrication – saved £100K and 2 months on the programme through pre-cast FST
  • Innovative design – saved £100K by redesigning the two acid phase digesters to form a single tank – one wrapped around the other (a bagel). This has led to savings on piling, instruments, high pressure gas valves as well as reducing the area required – particularly important as Clay Mills was very tight for space.
  • Supply chain engagement – saved £22K pa in Opex through procurement evaluation of diffusers. At Clay Mills Suprafilt PTFE coated 12’’ membrane diffusers were selected, saving £22K and reducing fouling
  • Weholite Pipework – saved £200K on ductile iron and 15% on the installation time when used for low pressure gravity lines

Ground Improvement – saved over £350K and reduced lorry movements by using Piling Mat. Health and Safety – no reportable accidents to date.


Top performing considerate construction sites in the country

Silver awards at the National Considerate Constructors Scheme awards

Year MWHC won the Gold Considerate Constructors award

Lost time incidents

 Project Results

MWH is constantly using innovative methods to bring benefits to the client, a prime example of which is the use of pre-cast concrete. Rather than using time-consuming in-situ methods, the FST walls were pre-cast off-site. The use of pre-cast concrete tank walls created program efficiencies and reduced the need for working at height without the need for compromise.

Sludge from wastewater treatment and tanker imports is now processed in a new pre-treatment building providing buffer capacity (340 m3), poly dosing and sludge thickening equipment. Thickened sludge will then enters new acid phase digesters (two 832 m3 digesters in series) – where organic matter is broken down into volatile fatty acids before entering the existing digesters.

MWH has improved the original design of two separate APD tanks by combining them in an annular structure, i.e. with one tank wrapped around the other.  This redesign has resulted in savings in terms of both capital cost and land required.

Aerial image of Tres Rios