Last edited 17 Jun 2019

Waste water

The term ‘waste water’ (or wastewater) is sometimes used to refer to all water that has been used in homes, businesses, industry, agriculture and so on, as well as rain that falls on roofs, roads, and landscape, that then enters the sewerage system.

However, the term waste water is more accurately used to refer only to water that has been used in homes, businesses, industry, agriculture and so on, whilst water from rainfall is referred to as ‘surface water run-off’. NB The term or ‘sewage’ refers specifically to a mixture of waste water and excrement.

Sewers (or sewerage) refers to the infrastructure used to transport waste water to treatment facilities or to disposal points.

Types of sewer include:

Combined sewers can cause pollution problems when heavy rainfall events cause them to overflow.

NB A drain is a pipe that serves only one building waste water to a sewer. A lateral drain is a section of drain positioned outside the boundary of a building, connecting with the drains from other buildings to become a sewer.

The treatment of waste water generally involves:

  • Screening.
  • Primary settlement.
  • Sludge treatment and biological treatment.
  • Final settlement.
  • Return to watercourses (where it may be referred to as effluent, secondary effluent, or treated effluent).

Where properties are not connected to the sewerage infrastructure they may have septic tanks. These are tanks installed underground that separate waste water into solids and water that can be safely discharged into a septic drain field (seepage field or leach field). Material that does not break down naturally in septic tanks must be periodically removed and disposed of.

Rather than discharging directly into sewers, surface water run-off may be collected and stored. This can help reduce flooding during heavy rainfall events. Sustainable urban drainage systems (SuDS) aim to mimic 'natural' drainage by adopting techniques to deal with surface water run-off locally, through collection, storage, and cleaning before allowing it to be released slowly back into the environment.

Suitable surface water run-off (sometimes referred to as ‘grey water’ as it excludes sewage), such as run-off from the roofs of buildings, may be ‘reclaimed’ and treated to be re-used in WCs, urinals irrigation, washing machines and so on.

The terms black water, brown water, foul water, or sewage, refer to water that has come into contact with faecal matter or urine. Black water can be harmful to health and may contain bacteria, viruses, protozoa and parasites. Globally, most black water is discharged back into the environment without having been treated. This results in significant environmental damage and health problems.

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