Urban waste water, commonly referred to as sewage, is generally a mixture of domestic waste water from baths, sinks, washing machines and toilets, waste water from industry and rainwater run-off from roads and other surfaced areas.

Sewage needs to be adequately treated before it’s discharged into rivers, estuaries or coastal waters. Otherwise it could damage the environment, including fish and other aquatic life.

Proper collection, treatment and discharge of waste water, and correct disposal or re-use of the resulting sludge helps to protect and improve water quality in the UK.

Sewage is treated by two different processes as standard.  Primary treatment involves settling out much of the solid matter, followed by secondary treatment which uses bacteria that ‘digest’ and break down organic substances. Sometimes, further (tertiary) treatment is required to protect sensitive water environments. This can involve disinfecting the treated effluent to protect bathing or shellfish waters. It can also involve the removal of phosphorus or nitrates (nutrients present in sewage) to protect sensitive waters.

Discharges from sewage treatment works are controlled through Environmental Permits issued by the Environment Agency – and monitored to ensure that they do not damage the environment.

Key facts and figures

• The UK has approximately 9,000 sewage plants in total.
• Approximately 2,000 sewage plants serving populations and industries generate sufficient organic load to require secondary treatment under the urban waste water treatment directive.
• The UK currently has 589 water bodies made up of lakes, rivers, estuaries and coastal waters identified as sensitive areas since 1994.
• The total area of standing water bodies (lakes, estuaries and coastal waters) identified as sensitive areas is around 2,745 km².
• The total length of river stretches identified as sensitive areas is around 19,466 km.

Urban waste water treatment directive

The urban waste water treatment directive (91/271/EEC) has the objective of protecting the environment from the adverse effects of untreated ‘urban waste water’, more commonly referred to as ‘sewage’.

The directive establishes minimum requirements for the treatment of significant sewage discharges.  It was adopted by European Union member states in May 1991 and transposed into legislation across the UK by the end of January 1995.

Article 10 of the water framework directive cites the urban waste water treatment directive’s requirements as providing a significant contribution to water protection as part of the raft of measures highlighted under the framework directive.

Sensitive areas

An important aspect of the urban waste water treatment directive is the protection of the water environment from nutrients, (specifically compounds of nitrogen and phosphorus), and/or nitrates present in waste water where these substances have adverse impacts on the ecology of the water environment or abstraction source waters.

Under the Directive the UK is required to review environmental waters at four-yearly intervals to determine whether they are sensitive to the effects of sewage discharges and if so, identified as sensitive areas with nutrient reduction provided at relevant sewage plants.  Another category of sensitive area relates to other directives’ water bodies that are protected by tertiary treatment for the purposes of their parent directives.

• Read more about sensitive areas in the UK

Implementation of the directive

Defra has responsibility for policy on implementation of the Directive in England, the Department of the Environment in Northern Ireland, the Scottish Government in Scotland and the Welsh Government in Wales.  Their environmental regulators, (the Environment Agency for England, Northern Ireland Environment Agency, Scottish Environment Protection Agency, and Environment Agency Wales), have responsibility for monitoring discharges from treatment plants for compliance with the directive’s treatment standards.

Directive and transposing legislation across the United Kingdom

• The urban waste water treatment directive (consolidated) (European Union web site)
• The Urban Waste Water Treatment (England and Wales) Regulations 1994 and 2003 Amendment Regulations
• The Urban Waste Water Treatment Regulations (Northern Ireland) 1995 and 2003 Amendment Regulations
• The Urban Waste Water Treatment (Scotland) Regulations 1994 and 2003 Amendment Regulations.

Key publications and documents

• UK public information – Article 16 report  (current Article 16 report – to be updated in 2012)
• Latest UK Article 15 submission covering 2008 data.