Drum roll for pumping station
Large sewer overflows can present a problem in London. Thames Water Utilities is currently tackling the issue by dealing with stormflows at Abbey Mills pumping station
As part of the AMP3 programme Thames Water Utilities dealt with unscreened combined sewer overflow (CSO) discharges into the River Thames. The existing CSO at Abbey Mills pumping station was identified as the most suitable site for this work.
The Abbey Mills site was first identified and developed by Joseph Bazalgette as a key part of his great scheme for the main drainage of London in the 1860s. The site consists of four pumping stations by the River Lee, near Stratford in east London. It is one of the largest sewage pumping stations in the UK. The pumping stations at Abbey Mills serve two main catchments, primarily the area of central London and the low-lying areas of West Ham and the Isle of Dogs. At Abbey Mills the sewage from these catchments is lifted into the northern outfall sewer to pass to Beckton WwTW.
Excess stormflows are discharged unscreened into the River
Thames. The future pumping capacity of these pumping stations may reach as high as 50m3/s.
The project is of exceptional size. Nowhere in the world has such a large installation been attempted on stormflows with a known high-solid content. It was envisaged the solids loading for this vast London catchment could be significantly higher than encountered on normal WwTWs, particularly during the first flush after a storm.
The first flush is when the debris collected in the sewer network, following a long, dry period, is flushed through by large stormflows. All of this ‘stored’ debris will be scoured from the sewers and has to be dealt with by the CSO screens.
Network North Alliance, a partnership arrangement between Thames Water, Barhale, Engenica and FaberMaunsell, was charged for the delivery of this challenging project. Brackett Green, one of the largest screen makers in the world, was brought in at an early stage for the firm’s vast experience and expertise in all types of sewage fine screening equipment. The project was divided into two phases.
Phase one was to be built to prove the screen could be installed and relied upon to be fully operational at short notice, potentially during unmanned operation, knowing the Brackett Green drum screens have to accept whatever arrives at the site in whatever quantities.
During storm event
New ideas were incorporated into the screen cleaning mechanism and careful control of flow velocities through the unique, thick plate, perforated panels was an essential feature of the whole design. The result was the construction of the largest capacity sewage screen ever built in the UK and the largest capacity single screen in operation on storm duty anywhere in the world. Designed to screen up to 14m3/s through 6mm tapered hole panels and capable of withstanding a hydrostatic load of 140 tonnes during overload conditions, the screen is definitely unique.
Built to extreme accuracy with a diameter of 10m and a width of 3.5m, the screen has a rotating structure weighing in excess of 40 tonnes. Following successful completion of phase one, phase two is now under way, comprising the installation of two further screens and increasing the site capacity to 40m3/s.
The screenings handling plant was a challenge of equal complexity. This was designed to handle the huge quantity of screenings the drum screens will remove from the storm overflows during storm conditions. The experience gained by Network North Alliance and Brackett Green in this field has been second to none.
As the problem of visual pollution grows in the major cities around the world, Thames Water Utilities and its close associates are confident they can deliver the most viable solution to the difficult problems large sewage overflows present.