Waste Water Treatment

Topics: Sewage treatment, Wastewater, Activated sludge Pages: 23 (7313 words) Published: November 8, 2011
Sewage treatment

The objective of sewage treatment is to produce a disposable effluent without causing harm to the surrounding environment and prevent pollution.[1] Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer). Using advanced technology it is now possible to re-use sewage effluent for drinking water, although Singapore is the only country to implement such technology on a production scale in its production of NEWater[2]. Contents

1 Origins of sewage
2 Process overview
o2.1 Pre-treatment
2.1.1 Screening
2.1.2 Grit removal
2.1.3 Fat and grease removal
o2.2 Primary treatment
o2.3 Secondary treatment
2.3.1 Activated sludge
2.3.2 Surface-aerated basins (Lagoons)
2.3.3 Constructed wetlands
2.3.4 Filter beds (oxidizing beds)
2.3.5 Soil Bio-Technology
2.3.6 Biological aerated filters
2.3.7 Rotating biological contactors
2.3.8 Membrane bioreactors
2.3.9 Secondary sedimentation
o2.4 Tertiary treatment
2.4.1 Filtration
2.4.2 Lagooning
2.4.3 Nutrient removal Nitrogen removal Phosphorus removal
o2.5 Disinfection
o2.6 Odour Control
3 Package plants and batch reactors
4 Sludge treatment and disposal
o4.1 Anaerobic digestion
o4.2 Aerobic digestion
o4.3 Composting
o4.4 Incineration
o4.5 Sludge disposal
5 Treatment in the receiving environment
o5.1 Effects on Biology
6 Sewage treatment in developing countries
7 See also
8 References
9 External links

[edit] Origins of sewage
Sewage is created by residential, institutional, and commercial and industrial establishments and includes household waste liquid from toilets, baths, showers, kitchens, sinks and so forth that is disposed of via sewers. In many areas, sewage also includes liquid waste from industry and commerce. The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. Most sewage also includes some surface water from roofs or hard-standing areas and may include stormwater runoff. Sewerage systems capable of handling stormwater are known as combined systems or combined sewers. Such systems are usually avoided now since they complicate and thereby reduce the efficiency of sewage treatment plants owing to their seasonality. The wide variability in flow, affected by precipitation, also leads to a need to construct much larger, more expensive, treatment facilities than would otherwise be required. In addition, heavy storms that contribute greater excess flow than the treatment plant can handle may overwhelm the sewage treatment system, causing a spill or overflow. Modern sewered developments tend to be provided with separate storm drain systems for rainwater.[3] As rainfall travels over roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. (See urban runoff.)[4] Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include retention basins, wetlands, buried vaults with various kinds of media filters, and vortex separators (to remove coarse solids). Sanitary sewers are typically much smaller than storm sewers, and they are not designed to transport stormwater. In areas with basements, backups of raw sewage can occur if excessive...
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