Sewage treatmant

Sewage treatment

The water you use to clean your teeth, shower and bath and to flush the toilet becomes sewage - we treat 480 millions of litres of it every day.

Other sewage we treat includes rainwater from roads, roofs and gardens as well as industrial effluent - mainly liquid organic waste from industries such as food factories and diary product manufacturers.

We have invested hundreds of millions of pounds to improve sewage treatment and over the past five years our treatment works have regularly achieved more than 99.9% compliance with environmental standards.

Almost all sewage is organic which is why water recycling centres (sewage treatment works) use natural, organic processes. 

The sewage goes through the following processes:

  • debris, rags and large objects, are removed using screens
  • sewage flows into tanks where the solids sink to the bottom and are removed as sludge
  • the sewage is treated biologically - the liquid passes through media with bacteria growing on them, such as filters of stone or plastic. The bacteria feeds off the waste, helping to clean the water.

Another form of biological treatment we use is the activated sludge process. Bacteria are mixed with the waste in large tanks using equipment which either blows or beats air into the mixture.

The cleaned effluent leaves the recycling centre (treatment works) and flows into local rivers or the sea. The treated effluent enters settlement tanks where any remaining solids settle leaving water which is ready to be returned to the environment.

Treated sludge, also known as biosolids, is a by-product of our treatment process.

We treat sludge in anaerobic digesters to produce agricultural fertiliser and renewable energy.