Crossness Sewage Treatment Works upgrade plans serve two million people. It is one of Europe’s largest treatment plants. The scheme totals £400m. It includes a new wind turbine.
Crossness already burns sludge. This generates 20% of its energy. The wind turbine will raise this to 50%. It will generate half of the total energy needs for the sewage treatment works. The upgrade will also reduce Crossness’ carbon footprint.
The work responds to new Environment Agency standards. They demand increased capacity and effluent quality by March 2014. The investment will aim to minimise smells. It will increase capacity to cope with heavier rainfall. It will also meet new climate change needs.
Improvement work has started. The new equipment should be fully operational by 2014.
The earliest part of Crossness was built in 1865. It was part of Sir Joseph Bazalgette’s pioneering plan. This plan managed London’s sewage. Crossness is on the south bank of the Thames in Abbey Wood. It is in the London Borough of Bexley. It serves many areas. These include Richmond Upon Thames, Wandsworth and Merton. Also Lambeth, Southwark, Lewisham and Greenwich. And parts of Sutton and Bromley.
On the eastern boundary is a 20ha nature reserve. It maintains one of the last areas of grazing marshland in London. The reed-fringed ditches support a variety of wildlife. Wading birds also live here.
At approximately 70ha, the plant treats enough sewage. It can fill 20 Olympic-sized swimming pools each hour. The sludge-powered generator has been running since 1998. It can produce up to 6MW of energy. That is about three quarters of the site’s electricity needs.
During heavy rainfall, wastewater is diverted. It goes into storm tanks until the rain has subsided. During storms, so much wastewater enters Crossness. Partially treated wastewater has to be discharged. It flows into the Thames. Thames Water admits only partial success in controlling odour.
The sewage is processed in five stages.
First, the inlet works screen items. These include wood, bricks, rags and paper. Also plastic and grit.
Second, primary settlement uses gravity. It settles the finer solids as raw sludge.
Third, the remaining ‘settled sewage’ flows. It goes to the biological treatment plant. This is for secondary treatment. Polluting organic matter and ammonia are consumed. Bacteria do this.
Fourth, the resulting ‘mixed liquor’ passes. It flows for final settlement. The treated effluent flows over the weirs. It becomes clean water. It is strictly monitored. Then it is discharged to the Thames.
Fifth, sludge treatment thickens and mixes sludge. It mixes raw and activated sludge. Then they are pumped to the sludge-powered generator.
The total flow arriving at Crossness will remain the same. But the proportion of flow fully treated will rise. That means less risk of storm overflow into the river. Less wastewater entering the Thames will help boost oxygen levels. This will improve the habitat for fish and other aquatic life.
Crossness also aims to reduce the number of days. It wants to reduce days that litter flows into the river. It also wants to reduce days that untreated sewage flows into the river. It will use two new boats to remove rubbish. Thousands of sewers become blocked each year. This is because of household items being flushed away. These items should be properly disposed of.
Crossness proposes to keep a similar design. It will keep the new works and machinery. The design will be similar to the existing equipment. The works will be relatively low lying. It will not be obvious outside the site. The new development will stay well within the boundary. However, the wind turbine will be visible from some distance.
Thames Water is submitting a planning application. It goes to the London Borough of Bexley. It requests permission to undertake the improvements. The council is consulting organisations. These include local residents’ groups. Also the Greater London Authority. And the Environment Agency and Natural England. Ofwat has approved funding.