Thames Water advances £21M Cirencester STW upgrade, preps £240M Oxford STW contract
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Thames Water is undertaking a £21M works to increase capacity at Cirencester sewage treatment works (STW) and is readying a £240M contract for upgrading its Oxford STW.
Cirencester capacity upgrade
The works at the Cotswolds capital’s STW will improve the quality of effluent released at the works and increase the site’s capacity, helping to combat the challenges of climate change and population growth.
The STW can currently treat up to 269l/s of wastewater but the works will see it almost double this capacity to 484l/s.
As part of this upgrade, contractor Tilbury Douglas is constructing a new 9,000m2 high infiltration reed bed (HIRB). This natural filtration system provides a final treatment of water before it is returned to the environment. The HIRB will add treating capacity of up to 114l/s.
Thames Water says that this increase in capacity will greatly reduce the risk of storm overflows during periods of heavy rainfall and return a better quality of effluent to the river.
Work started on site in summer 2023 and is expected to complete in spring 2025.
“As custodians of this important infrastructure we need to ensure our sites are resilient to the pressures of climate change and population growth so we can continue to provide reliable services to our customers,” Thames Water project manager Paul Parfrey said. “This upgrade to our network will help protect customers and the health of the rivers and waterways.”
Gloucestershire County Council executive member for communities and public safety Lisa Spivey said that she was “impressed by the size of the [reed] bed” on a recent visit to the Cirencester STW.
“By using this system, Thames Water should be able to increase treatment capacity which is desperately needed,” she added. “All too often we are seeing storm overflows meaning sewage discharging into our local rivers and waterways. I hope that this reed bed will lead to less discharges into rivers like the Churn, Thames and Coln.”
Cirencester STW is one of 250 wastewater sites that Thames Water is planning to improve.
Contract for major upgrade of Oxford STW
One of the largest STW that Thames Water is planning to upgrade is Oxford and it has this week alerted the market to a future opportunity to work on this major project in a contract that is expected to be worth £240M.
The periodic indicative notice put out by the water company lists the goals of the upgrade works as:
- Compliance with a new quality permit consisting of an ammonia consent reduction from 3mg/l to 1mg/l; and a Tot-P reduction from 1mg/l to 0.25mg/l
- Increase flow to full treatment from 1,040l/s to 1,802l/s
- Increase in the storm tank capacity from 6,831m3 to 18,167m3
- Replace inlet works and upgrade the effluent treatment process with a new 170,000PE stream
- Increase dissolved oxygen level in the final effluent channel
- Address existing effluent stream process capacity pinch points
- Increase the throughput capacity of sludge treatment process
- New power supply, HV ring main, fibre optic network and SCADA upgrade
At this point Thames Water has not released details on the length of the contract or how many suppliers it is looking to appoint.
There will be a launch event held via Teams on 10 September and the publication of the contract notice is expected in early October.
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