Thematic discussion While other existing wastewater databases often focus on percentage of sanitation coverage or pollution loads, AQUASTAT focuses on annual volumes at national level.
Terminology[ edit ] The term "sewage treatment plant" or "sewage treatment works" in some countries is nowadays often replaced with the term wastewater treatment plant or wastewater treatment station.
Alternatively, sewage can be collected and transported by a network of pipes and pump stations to a municipal treatment plant. This is called a "centralized" system see also sewerage and pipes and infrastructure.
Origins of sewage[ edit ] Main article: Sewage Sewage is generated by residential, institutional, commercial and industrial establishments. It includes household waste liquid from toiletsbathsshowerskitchensand sinks draining into 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 treated greywater being permitted to be used for watering plants or recycled for flushing toilets.
Sewage mixing with rainwater[ edit ] Sewage may include stormwater runoff or urban runoff. Sewerage systems capable of handling storm water are known as combined sewer systems.
This design was common when urban sewerage systems were first developed, in the late 19th and early 20th centuries. Heavy volumes of storm runoff may overwhelm the sewage treatment system, causing a spill or overflow. Sanitary sewers are typically much smaller than combined sewers, and they are not designed to transport stormwater.
Communities that have urbanized in the midth century or later generally have built separate systems for sewage sanitary sewers and stormwater, because precipitation causes widely varying flows, reducing sewage treatment plant efficiency.
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 basinswetlandsburied vaults with various kinds of media filtersand vortex separators to remove coarse solids. Industrial wastewater treatment In highly regulated developed countries, industrial effluent usually receives at least pretreatment if not full treatment at the factories themselves to reduce the pollutant load, before discharge to the sewer.
This process is called industrial wastewater treatment or pretreatment. The same does not apply to many developing countries where industrial effluent is more likely to enter the sewer if it exists, or even the receiving water body, without pretreatment. Industrial wastewater may contain pollutants which cannot be removed by conventional sewage treatment.
Also, variable flow of industrial waste associated with production cycles may upset the population dynamics of biological treatment units, such as the activated sludge process. Overview[ edit ] Sewage collection and treatment is typically subject to local, state and federal regulations and standards.
Treating wastewater has the aim to produce an effluent that will do as little harm as possible when discharged to the surrounding environment, thereby preventing pollution compared to releasing untreated wastewater into the environment.
Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment.
Some sewage treatment plants that are connected to a combined sewer system have a bypass arrangement after the primary treatment unit. This means that during very heavy rainfall events, the secondary and tertiary treatment systems can be bypassed to protect them from hydraulic overloading, and the mixture of sewage and stormwater only receives primary treatment.
Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically performed by indigenouswater-borne micro-organisms in a managed habitat. Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment.
Tertiary treatment is sometimes defined as anything more than primary and secondary treatment in order to allow ejection into a highly sensitive or fragile ecosystem estuaries, low-flow rivers, coral reefs, Treated water is sometimes disinfected chemically or physically for example, by lagoons and microfiltration prior to discharge into a streamriverbaylagoon or wetlandor it can be used for the irrigation of a golf course, green way or park.
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