Enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) is a wastewater 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 are absent) prior to the aeration tank. Under these conditions a group of heterotrophic bacteria, called polyphosphate-accumulating organisms (PAO) are selectively enriched in the bacterial community within the activated sludge. These bacteria accumulate large quantities of polyphosphate within their cells and the removal of phosphorus is said to be enhanced.

Generally speaking, all bacteria contain a fraction (1-2%) of phosphorus in their biomass due to the its presence in cellular components, such as membrane phospholipids and DNA. Therefore as bacteria in a wastewater treatment plant consume nutrients in the wastewater, they grow and phosphorus is incorporated into the bacterial biomass. When PAOs grow they not only consume phosphorus for cellar components but also accumulate large quantities of polyphosphate within their cells. Thus, the phosphorus fraction of phosphorus accumulating biomass is 5-7%. This biomass is then separated from the treated water at end of the process and the phosphorus is thus removed. Thus if PAOs are selectively enriched by the EBPR configuration, considerably more phosphorus is removed, compared to the relatively poor phosphorus removal in conventional activated sludge systems.