Ship Canal ruling impacts UU’s sewage plant

United Utilities is to spend £35m on a new cleaner waste water treatment facility at Davyhulme in Trafford to satisfy stricter environmental regulations.

The new process treatment facility is aimed at achieving a lower final effluent ammonia consent at Davyhulme, UU's largest waste water treatment works, serving a population of 1.1 million from the Greater Manchester conurbation.

Davyhulme discharges to the Manchester Ship Canal.

The future final effluent 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. This revised consent will also meet the requirements of the Water Framework Directive.

Davyhulme WwTW consists of two parallel treatment streams downstream of a common inlet sewer. Both ASP1 and ASP2 streams have screening, grit removal and primary settlement prior to non-nitrifying aeration tanks (provided with surface aeration) and final settlement. The effluent from the ASP1 and ASP2 final settlement tanks is treated together in a common tertiary biological aerated flooded filter for nitrification, from which FE is discharged to the Manchester Ship Canal.

Sludge treatment at Davyhulme WwTW is currently undergoing refurbishment and expansion as part of the Sludge Balanced Asset Programme project to treat raw sludge up to 91 000 tonned dry solids sludge per annum. The major components of SBAP are a reception / screening facility of indigenous, followed by thickening, and imported liquid sludge's and a reception and storage facility for sludge cake imports. Sludges are subject to digestion pre-treatment by thermal hydrolysis followed by mesophilic anaerobic digestion. Digested sludges can be dewatered, using centrifuges and exported to land or may be either transferred to the United Utilities Shell Green incineration facility via the Mersey Valley Sludge Pipeline.

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