United Utilities has awarded a contract to upgrade its Davyhulme wastewater treatment works in Manchester to meet European Union Directive requirements with a potential value of between £123 million to £171 million.

Laing O'Rourke Construction Ltd and Imtech Water Waste and Energy Ltd have been awarded the contract – three organisations were in the bidding for the work. Some of the work is likely to be sub-contracted out, although the value or proportion likely to be sub-contracted to third parties is not known at this stage.

The contract comprises the design, procurement, construction and commissioning of a new process treatment facility to achieve a lower final effluent (FE) ammonia consent. Davyhulme is United Utilities largest WwTW, treating wastewater from a population equivalent of about 1.1 million from Greater Manchester and discharges its final effluent (FE) to the Manchester Ship Canal.

The future FE consent is driven by Davyhulme's inclusion in the National Environment Programme as a result of the receiving Manchester Ship Canal being designated under the Freshwater Fish Directive in 2003. The revised consent will also meet the requirements of the Water Framework Directive.

A new activated sludge plant (ASP3) is required to replace one of the existing ASP streams at Davyhulme (ASP1, or ASP2) - the new ASP3 stream will treat 60 % of incoming flows. A new inlet works is also required as part of the scope of works, which will replace part of the existing ASP2 inlet works and reduce flow to the existing ASP1 / storm inlet works. Refurbishment of the plant and equipment on the retained existing ASP stream are also required.

The new ASP3 stream will consist of primary settlement tanks (PST), fine bubble diffused air (FBDA) type ASP, final settlement tanks (FST) and mechanical thickening of Surplus Activated Sludge (SAS). It will be required to produce a treated effluent to meet the future FE consent.

FE from the new ASP3 stream will re-join the existing final effluent culvert, prior to discharge into the Manchester Ship Canal. The new treatment facility will be totally independent of the existing biological aerated flooded filter (BAFF). Odour abatement technologies are also required for the more odorous technologies.

The contract covers:

• Design, construction and commissioning of the new works.
• Works to ensure compliance with the requirements of the EPR permit:
• Internal site roads within the new treatment facility areas;
• New site access road from the new treatment facility to a new site entrance;
• Construction of a new primary sub-station building;
• Modifications to existing site high voltage electrical infrastructure;
• Ancillary and accommodations works — site drainage and return;
• Electrical instrumentation control and automation (EICA) and a distributed control system (DCS).

Due to the strategic importance of Davyhulme WwTW as a part of United Utilities’ wastewater treatment facilities no unauthorised disruption to the existing plant will be allowed throughout the construction and commissioning process. The operation and throughput of the existing plant must be maintained at the current level throughout the construction period - duration of the contract is thirty months.