Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on the environment. It is also possible to reuse it. This process is called Reclaimed water.
One common process in wastewater treatment is phase separation, such as sedimentation. Biological and chemical processes such as oxidation are another example. Polishing is also an example. The main by-product from wastewater treatment plants is a type of sludge that is usually treated in the same or another wastewater treatment plant.
The term "wastewater treatment" is often used to mean " sewage treatment".
Types of treatment plants
Wastewater treatment plants may be distinguished by the type of wastewater to be treated. There are numerous processes that can be used to treat wastewater depending on the type and extent of contamination. The treatment steps include physical, chemical and biological treatment processes.
Types of wastewater treatment plants include:
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Sewage treatment
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Industrial wastewater treatment plants
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Agricultural wastewater treatment plants
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Leachate treatment plants
Sewage treatment plants
Industrial wastewater treatment plants
Agricultural wastewater treatment plants
Leachate treatment plants
Leachate treatment plants are used to treat leachate from
. Treatment options include: biological treatment, mechanical treatment by
ultrafiltration, treatment with
Active Carbon filters, electrochemical treatment including electrocoagulation by various proprietary technologies and reverse osmosis membrane filtration using disc tube module technology.
Unit processes
The unit processes involved in wastewater treatment include physical processes such as settlement or flotation and biological processes such oxidation or anaerobic treatment. Some wastewaters require specialized treatment methods. At the simplest level, treatment of most wastewaters is carried out through separation of
from
, usually by sedimentation. By progressively converting dissolved material into solids, usually a biological floc or
biofilm, which is then settled out or separated, an effluent stream of increasing purity is produced.
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Phase separation
Phase separation transfers impurities into a non-aqueous phase. Phase separation may occur at intermediate points in a treatment sequence to remove solids generated during
oxidation or polishing. Grease and oil may be recovered for fuel or
saponification. Solids often require
dewatering of
sludge in a wastewater treatment plant. Disposal options for dried solids vary with the type and concentration of impurities removed from water.
[Ajay Kumar Mishra Smart Materials for Waste Water Applications
]
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Sedimentation
such as , grit, and sand may be removed from wastewater by gravity when density differences are sufficient to overcome dispersion by turbulence. This is typically achieved using a grit channel designed to produce an optimum flow rate that allows grit to settle and other less-dense solids to be carried forward to the next treatment stage. Gravity separation of solids is the primary treatment of sewage, where the unit process is called "primary settling tanks" or "primary sedimentation tanks".
Biological and chemical processes
Oxidation
Oxidation reduces the biochemical oxygen demand of wastewater, and may reduce the toxicity of some impurities. Secondary treatment converts organic compounds into carbon dioxide, water, and biosolids through oxidation and reduction reactions.
Biochemical oxidation (secondary treatment)
Chemical oxidation
Advanced oxidation processes are used to remove some persistent organic pollutants and concentrations remaining after biochemical oxidation.
Anaerobic treatment
Anaerobic wastewater treatment processes (for example UASB, EGSB) are also widely applied in the treatment of industrial wastewaters and biological sludge.
Polishing
Polishing refers to treatments made in further advanced treatment steps after the above methods (also called "fourth stage" treatment). These treatments may also be used independently for some industrial wastewater. Chemical reduction or pH adjustment minimizes chemical reactivity of wastewater following chemical oxidation.
See also
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List of largest wastewater treatment plants
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List of wastewater treatment technologies
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Water treatment
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