A huge project to increase the capacity of one of London’s major sewage works by fifty per cent is now half-way to being complete, Thames Water announced today.

Mogden sewage works in Isleworth has been under going a major refurbishment since August 2010 as part of a London-wide scheme to invest £675m in all five sewage works in the capital.

These upgrades will increase the amount of sewage the sites can treat, greatly reducing the need to use the storm tanks and, because they will very rarely be full to capacity, for storm discharges to the river. Additionally this work will also improve the standard to which we treat sewage at each of the works, further boosting the quality of the River Thames.

The huge transformation at Modgen, costing £140m, will also ensure that the site can cope with the projected increase in population in the area served by the works.

Nick Fawcett, Thames Water’s Head of Programme Delivery, said: “We have done the bulk of the construction work and we’d like to thank the neighbours for bearing with us. “We’ve done everything we can to minimise disruption but the worst part is over, the foundations are in place and by spring this year half of the new works will be operating. “We still have a 200-strong team working on the site but the focus of the activity is now shifting from civil engineering – such as building foundations and tanks, to mechanical engineering and electrical installation, which will help to get the tanks up and running.” The completion of the inlet area in spring – where the sewage enters the site and is screened to remove large objects – and the primary tanks – where the heavy particles are then removed – means the existing primary tanks can be refurbished so they too are covered and odour-controlled as soon as possible.

Nick added: “Soil is still being stored on the embankment while we build the remaining tanks but this will be removed by the end of this year, ahead of the completion in March 2013.” Work is also being done to install additional power generators as an extra back-up so the site can still run even in the rare event of an electricity outage.

As a final stage, native trees, shrubs and herb-rich grassland will be planted on the site to encourage wildlife and to improve the view for neighbours.