Anaerobic wastewater treatment is the biological treatment of wastewater without the use of air or elemental oxygen. There are a number of applications that focus on the elimination of organic pollutants from wastewater, slurries and sludges.
These organic pollutants are transformed by anaerobic microorganisms to a gas containing methane and carbon dioxide, known as "biogas".

(COD)"chemical oxygen demand" is know in the wastewater engineering field as the measurement of weight it takes to oxidize organic pollution chemically.
This weight of oxygen referred to as the COD is in essence a measure of organic matter content or concentration. The best way to appreciate anaerobic wastewater treatment is to compare its COD balance with that of aerobic wastewater treatment.
Through the Anaerobic Treatment, methane, a valiable fuel, is produced by converting the COD from wastewater.
Only a slight amount of COD is converted to sludge; and very little inputs are necessary to operate such a system.

With the Aerobic Treatment the COD in wastewater is greatly to converted sludge, a heavy waste product, and is not so cost effective for removal.
Aerobic wastewater treatment plants basically produce waste sludge.
Essential oxygen has to be continuously supplied by aerating the wastewater requiring a high demand and expense in kilowatt hours to operate the aerators.
For the most part environmental engineers are aware that anaerobic processes are used to stabilize sludge such as a sludge digester at municipal treatment plants.
As a matter of fact "high rate" anaerobic wastewater treatment technologies can also be utilized to treat and dilute the concentrated liquid organic wastewaters such as; breweries, factories, petrochemical, farming, rivers, lakes,
Anaerobic technologies can have a very beneficial impact on munical wastewater sewage treatment.
Anaerobic treatment is used by full scale plants and have been documented world-wide for the treatment of industrial effluents.
Anaerobic technologies are not only suitable for the elimination of bulky COD they can also be utilized for the biodegradation or biotransformation of toxic priority pollutants.
Microbial communities in anaerobic environments can either cause the oxidation of the pollutants resulting in its mineralization to benign products for example CO2, or they can cause the reductive biotransformation of pollutants to less toxic substances for example: dechlorination of polychlorinated hydrocarbons.
It's possible for anaerobic bioremediation to occur in bioreactors, for example in the treatment of industrial effluents which contain toxic pollutants, or it can occur on location in groundwater or sediments at sites that are contaminated.
Amid the most successful applications of anaerobic treatment for the oxidation of toxic pollutants is the case of the treatment of effluent in the plastic industry containing high concentrations of terephthalate.
These effluents are commonly elevated in COD and aerobic treatment would result in extreme sludge production.
A complex microbial community of anaerobes is feasible to maintain in bioreactors permitting the total conversion of terephthalate to carbon dioxide and methane in high rate anaerobic bioreactors.
(PET) polyethylene terephthalate industry has now fully accepted anaerobic technology as the main biological treatment of wastewater technology for effluents.