Sewage-treatment plant construction work

Tender description

Design, construct and commission resilience works to the current Mogden Sewage Treatment Works (STW) with the scope summarised as follows: • improve the capacity of preliminary treatment; • improve the resilience and capacity of primary and secondary treatment; • improve the resilience of the Sludge and Digester Streams and prepare them for AMP8 work; • provide additional onsite energy generation; • enable the works to meet its flow and quality consent for population growth. Contract award is expected to be May 2021 and the project is required to be complete by March 2025, unless the Options for AMP 8 works are instructed. The contractor will be required to carry out the works without adversely impacting on the integrity of the STW and in accordance with the current permits. Mogden Sewage Treatment Works (STW) is the second largest STW in the Thames region and the country. Its catchment area in the west of London stretches from Chiswick to the north and west of Heathrow Airport. The design flow to full treatment capacity is 1 064 Mld. The works which are the subject matter of this contract opportunity are to provide for growth, resilience and consent compliance to a design horizon of 2 036 with the population equivalent (PE) projected to be 2.4 million; the contract will also include related planning, design and engineering services. The scope of this project comprises the following activities: Upgrades to the inlet pumping station and preliminary treatment to provide capacity, resilience and protection to downstream processes, including: • high voltage (HV) and low voltage (LV) electrical infrastructure; • additional screenings capacity on the East side; • improved grit distribution and capacity on the west side. Capital maintenance improvement works on the East Side Primary Settlement Tanks (PSTs) 1-8. Capital maintenance work and improved process control, to increase the resilience of the activated sludge plants (ASPs) including: • C battery blower replacement and ASP works including RAS system improvements; • D battery blower replacement; • E battery blower power supply; • remove flow restriction on North Final Settlement Tanks (FSTs) on Batteries A&B. New sludge treatment facilities to increase capacity, improve asset reliability and provide resilience. This includes: • additional thickened sludge blending tank with odour control; • new raw sludge thickening streams including thickeners and strain presses with the associated pumps and polymer system; • modifications to the sludge import facility to improve the throughput of the sludge stream; • digester modifications including capital maintenance work on mixing systems, replacement of roofs and preparatory works for a future sludge scheme by enabling sequential primary digestion; • replace the existing gas forwarding compressors and installation of a fourth Combined Heat and Power (CHP) engine; • capital maintenance works to replacement or upgrade existing HV and LV Switchboards; • modifications to the power management system and upgrade of the site SCADA (supervisory control and data acquisition) system Other works to upgrade the capacity of the existing systems for the 2036 growth scenario. The contractor shall also be responsible for submitting the application for planning consent, if required.