Hampstead Norreys STW – Wastewater Asset Assurance Programme
Replacement pumping, high-level pipework and a new balancing tank arrangement, installed while the works stayed in service.
The Brief
Woodhams delivered a mechanical installation package at Hampstead Norreys Sewage Treatment Works as part of Thames Water’s Wastewater Asset Assurance Programme.
The works formed part of a wider upgrade to improve treatment resilience, flow management and operational reliability at the site, focusing on the replacement, modification and integration of key mechanical process assets.
The scope covered mechanical process pipework, replacement pumping equipment, valves, humus sludge pumping modifications, balancing tank connections and the mechanical interfaces with existing treatment assets.
Hampstead Norreys remained operational throughout. The works had to be sequenced around live process flows, temporary pumping arrangements and low-flow windows, keeping treatment continuity and discharge consent compliance protected — and keeping sludge tanker movements running uninterrupted.
The Solution
Balancing tank arrangement. Woodhams carried out the works to the new balancing tank, with mechanical connections for forward flow, high-flow bypass and storm overflow pipework. The tank was designed to manage flows through the works and support the site’s Flow to Full Treatment requirements, with mechanical access provision to enable future inspection and wash-down of the hydro brake and storm overflow weir.
FFT pump replacement. The existing progressive cavity FFT pumps were decommissioned and removed, with new progressive cavity pumps installed to deliver 7.0 l/s. The mechanical scope included the associated suction and delivery pipework, isolation valves, non-return valves, air valves and revised pipework arrangements to suit the new installation. The existing macerator units were removed from the process arrangement, with pipework modifications to accommodate the new pump configuration and simplify the mechanical installation.
Humus settlement tank modifications. Woodhams re-levelled the HST outlet weir and modified the HST outlet pipework and the recirculation pumping station feed pipework, to ensure free discharge over the outlet weirs and reduce the risk of surcharging or flooding within the process. Further works included modifications to the existing humus tank discharge chamber, reducing the weir level to improve flow conditions.
Humus sludge pump replacement. The existing humus sludge pumps, valves and associated pipework were removed and replaced with new duty/standby progressive cavity units, complete with instrumentation, pipework and valving, each designed to return humus sludge to the Primary Settlement Tank through the existing below-ground pipework at up to 1.2 l/s. The installation included non-return valves, isolation valves and air valves for each pump, together with lagging and trace heating to the new pumps and pipework — improving the reliability and maintainability of the site’s sludge handling process.
Process pipework and mechanical interfaces. The package included FFT pipework from the balancing tank to the new FFT pumps, excess flow pipework from the balancing tank to the downstream storm flow arrangement, storm overflow pipework from the balancing tank to the downstream chamber, and new humus tank outlet pipework to the existing recirculation pumping station. Woodhams also modified the existing blending chamber, removing the existing overflow weir from service, filling the weir to chamber coping level, removing redundant fixings and making good the chamber to prevent debris build-up.
The Result
Key activities included coordinating pipework connections to existing assets, managing temporary pumping requirements during process changeovers, maintaining treatment flows during the pump replacement works and ensuring sludge tanker movements were not disrupted. Close coordination with Thames Water operations allowed outages to be planned, interfaces with live assets managed and redundant mechanical equipment removed safely.
The completed package improved the reliability and maintainability of key treatment assets — the FFT pumping arrangement, the humus sludge pumping system, the HST outlet arrangement and the associated process pipework — supporting Thames Water’s wider asset assurance objectives.
Woodhams’ experience in wastewater environments allowed the team to identify interface issues early, plan safe installation sequences and coordinate works around live process constraints, combining mechanical pipework installation, pump replacement, valve installation and process asset modification in one package.
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