United Utilities has gone out to tender with a major £120 million AMP6 contract to upgrade its Blackburn waste water treatment works and will hold a bidders day later next month.

The contract for wastewater treatment plant construction work, described as the Blackburn and Darwen WwTw Integrated Solution AMP 6, covers the design, procurement, construction and commissioning of a new process treatment facility at Blackburn. The work is aimed at achieving lower Final Effluent, Bacterial Oxygen Demand and Ammonia limits, whilst also complying with the requirements of the Bathing Waters and Shellfish Waters Directives for storm water spills.

Darwen WwTW is also required to improve the quality of its FE discharges and reduce the frequency and volume of storm discharges.

United Utilities said the Blackburn and Darwen WwTW Integrated Solution project is intended to provide a holistic engineering solution to address the multiple quality and maintenance drivers at the two works. There are significant process and operational risks associated with Blackburn and Darwen, including:

• the structural condition of the aqueduct structure.
• part of the catchment delivers unscreened flows to the works.
• existing Biological and Fine Filtration (BAFF) plant is only capable of handling 50 % of current Flow to Full Treatment (FTFT).
• screened sludge tanks are uncovered (former consolidation tanks).
• thickened sludge bypasses the strain press.
• the Enhanced Enzymic Hydrolyser (EEH) plant does not perform consistently.
• the retention time of the digesters is inefficient.
• Darwen inlet pumping station regularly floods.

Blackburn WwTW has had a number of projects delivered over the last two AMP investment periods. However, United Utilities said while the projects had delivered improvements in water quality, the further improvements required for AMP6 had led to a full review of the WwTW to identify a long term solution which meets both the maintenance needs at the site as well as the regulatory requirements.

The new works involve the closure of the existing Darwen WwTW with additional storm storage capacity to be built and a new transfer sewer to divert Darwen flows.

The work at the Blackburn WwTW will include:

• increase hydraulic and process capacity at the Inlet Works (Nabs Head);
• increase hydraulic capacity of the pipeline/aqueduct between the inlet works and main works;
• increase hydraulic and process capacity on the main works to treat increased flows to a higher standard including:
• new ‘brewery waste' treatment facility;
• new effluent screening facility for flows that bypass the inlet works;
• new primary settlement tanks ;
• new activated sludge plant;
• new final settlement tanks;
• new tertiary treatment plant;
• additional final effluent UV plant;
• extend existing hydro-generation plant;
• new sludge treatment assets
• Time limit for receipt of tenders or requests to participate is 10^th October 2014.

The pre-qualification questionnaire will be available from Friday 12^th September with interested suppliers invited to attend an introductory presentation in Widnes on Wednesday 17^th September. Deadline to confirm attendance at the bidders’ day is no later than close of business Wednesday 10^th September.

Click here to access the contract documentation.