Sewage refers to the waste and wastewater produced by residential, commercial and industrial sources and discharged into sewers. It can also include stormwater when that water is drained into a sewer system. Sewage can contain dissolved and suspended mineral, animal matter and vegetable matter, as well as urine, faeces, bacteria and intestinal parasites. It may also contain paper, grease, cigarettes, soap, detergents, other cleaning products, pesticides, herbicides, fertilisers and a wide range of other contaminants - some of which may be derived from the sewer system itself e.g. metal from the pipes.
Sewage treatment is a process that removes contaminants from sewage. There are a variety of processes – physical, chemical and biological – that can be used to treat sewage. The level of treatment determines the quality of the water at the end of the process. Sewage treatment produces both a liquid effluent and a sludge.
The direct impacts of sewage treatment may include:
- Reduced water sediment load
- Reduced water feacal contamination
- Reduced water chemical contamination
- Reduced water nutrient concentrations
The outputs of sewage treatment may include:
- Wastewater for reuse (See: Irrigation with effluent water)
- Wastewater for release into natural environment (See: Wastewater release)
- Sludge for landfill
- Sludge for use as fertiliser (See: Fertiliser application)
Last updated 7 September 2010