What happens to my waste water?

What happens to my waste water?

Sewage is the dirty waste product generated from water after it's been used. Besides human waste, it also contains food, detergents, oils, metal residues, sand and sometimes harmful chemicals.

As well as treating waste from the sewers, we also collect surface water or rainwater and return it to the watercourses. All these waste products must be removed before we can return the treated, cleaned sewage, or effluent, back into rivers or streams.

Stage 1

Sewage passes through screens to remove any large pieces of debris such as plastic, paper and rag or wipes. The liquid then flows through channels to remove grit that's been washed in from places like roads. The sewage then rests in large settlement tanks where fine particles sink to the bottom to form sludge. Severn Trent Connect takes the sludge away regularly for further treatment so that it can be used as a fertiliser product.

Stage 2

Severn Trent Connect treats the settled sewage using special bacteria. The bacteria feed on organic matter and turn it into carbon dioxide, water or nitrogen. There are two methods:

1. The traditional method is to use biological filters which encourage bacteria to grow in deep beds of irregularly shaped stones. Gaps between the stones are full of air which allow the bacteria to breathe. The liquid is filtered through the stones.

2. A more modern method is called activated sludge treatment. Air is bubbled through the liquid to encourage bacteria to grow. Once the bacteria have cleaned the sewage, the liquid is passed into settlement tanks before flowing back into the river.

Stage 3

In order to meet even higher standards set by the Environment Agency, cleaned water can be put through a final filtration process either using shallow beds of gravel or reed beds to give the water a final 'polish' before it's returned to the water courses.


Facts and figures

  • Severn Trent Connect treats over 700 million litres of waste water per annum
  • More than half (63%) our daily water consumption at home originates from the bathroom and the toilet
  • You could fit a double-decker bus inside some of the UK's biggest sewers