Polyphosphate-accumulating organisms (PAOs) are a group of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

that, under certain conditions, facilitate the removal of large amounts of

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

from wastewater in a process, called

enhanced biological phosphorus removal Enhanced biological phosphorus removal (EBPR) is a sewage treatment configuration applied to activated sludge systems for the removal of phosphate. The common element in EBPR implementations is the presence of an anaerobic tank (nitrate and oxygen ...

(EBPR). PAOs accomplish this removal of phosphate by accumulating it within their cells as

polyphosphate Polyphosphates are salts or esters of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic ring structures. In biology, the polyphosphate e ...

. PAOs are by no means the only bacteria that can accumulate polyphosphate within their cells and in fact, the production of polyphosphate is a widespread ability among bacteria. However, the PAOs have many characteristics that other organisms that accumulate polyphosphate do not have, that make them amenable to use in wastewater treatment. Specifically, this is the ability to consume simple carbon compounds (energy source) without the presence of an external electron acceptor (such as nitrate or oxygen) by generating energy from internally stored polyphosphate and glycogen. Most other bacteria cannot consume under these conditions and therefore PAOs gain a selective advantage within the mixed microbial community present in the activated sludge. Therefore, wastewater treatment plants that operate for

have an anaerobic tank (where there is no nitrate or oxygen present as external electron acceptor) prior to the other tanks to give PAOs preferential access to the simple carbon compounds in the wastewater that is influent to the plant. A PAO related to the ''

Betaproteobacteria Betaproteobacteria are a class of Gram-negative bacteria, and one of the eight classes of the phylum Pseudomonadota (synonym Proteobacteria). The ''Betaproteobacteria'' are a class comprising over 75 genera and 400 species of bacteria. Togeth ...

'' has been identified and named Candidatus Accumulibacter Phosphatis. Accumulibacter has been shown to remove phosphorus from EBPR plants in Australia, Europe and the USA. It can consume a range of carbon compounds, such as acetate and propionate, under anaerobic conditions and store these compounds as

polyhydroxyalkanoates Polyhydroxyalkanoates or PHAs are polyesters produced in nature by numerous microorganisms, including through bacterial fermentation of sugars or lipids. When produced by bacteria they serve as both a source of energy and as a carbon store. M ...

(PHA) which it consumes as a carbon and energy source for growth using oxygen or nitrate as electron acceptor. Recently, another PAO related to the ''Actinobacteria'' has been identified in wastewater treatment plants. These organisms appear to be limited to certain amino acids as carbon and energy source. The storage compound that they use to store the amino acids that these organisms take up under anaerobic conditions has not been identified. These bacteria have been observed in some EBPR plants in Denmark (where they were discovered) but their wider distribution is unknown.

References

{{DEFAULTSORT:Polyphosphate-Accumulating Organisms Biotechnology Waste treatment technology Bacteriology Phosphorus