Sewage Treatment

Sewage Treatment Works

The major sewage treatment in the Thame catchment is managed by Thames Water. There are 31 major works in our catchment which all discharge into our river. stw

Everything that goes through these Sewage Treatment Works (STWs) is treated so that it is at a level that has been deemed as suitable by the Environment Agency, this is known as consenting. The outfalls at the works are tested on a regular basis to ensure that they meet the consented levels, this includes both in-house testing and spot checks by the Environment Agency (EA). If the levels are breached during EA checks, then the works must work quickly to make necessary improvements in order to avoid becoming a ‘failing works’.

Unfortunately, even with the limits enforced, sewage treatment still has a major impact on our rivers as STWs are allowed to discharge elevated levels of phosphate, nitrate and ammonia into the Thame; this is quite common in rural river catchments. On top of this, Thames Water is placed under increasing pressure because of the extensive development happening in areas such as Aylesbury.

Sewage Treatment

The process of sewage treatment, credit: Thames Water

To find out more about the sewage treatment process click here

Small Sewage Treatment Works

In some areas, there are much smaller sewage treatment works which are council run, these are also referred to as Housing Acts Works (HAWS). These works are also monitored and consented by the Environment Agency.

For information on HAWS in South Oxfordshire click here.

Septic Tanks

Many rural homes are not connected to a major or small sewage treatment works. When this happens, each home will have its own treatment system, known as a septic tank or a cesspit. These will discharge directly into our waterways, making it difficult to monitor them regularly. There are many regulations that work to try and prevent pollution entering our rivers from these systems.
If you have your own septic tank, then you can find advice on maintenance and regulations in our section on ‘advice for households‘. If you are planning on installing your own sewage system then you can get advice on permits and compliance here.

You can help us monitor sewage treatment works an septic tanks around the catchment by taking part in regular water quality testing of riverfly monitoring.