In Enhanced Biological Phosphorus Removal ( Ebpr ) Processes

Phosphorus is an essential element for every living organism, but when it exceeds certain limit in water bodies, it will cause serious environmental issues, such as eutrophication. P accumulation in water bodies can be caused by non-point sources, such as agriculture land runoff, as well as from point sources such as wastewater effluent discharges. In order to avoid eutrophication of water bodies the regulatory agency have traditionally pushed for the removal of phosphorus at wastewater treatment plants rather than regulating the non-point sources; this has been done imposing strict limits on wastewater effluents to natural watershed. At the same time, phosphorus stock on the earth is a limited resource, and its quantity is decreasing steadily, due to its use in the fertilizers production. In order to support the population growth on the earth, phosphorus recovery, especially from wastewater streams has to be considered. Biological processes that remove phosphorus from wastewater, are called Enhanced Biological Phosphorus Removal (EBPR in short) processes, and produce a P rich sludge that can be treated to recover phosphorus in forms that could be used as fertilizers. Several processes have been developed to recover P from EBPR plants, such as Waste Activated Sludge Stripping to Remove Internal Phosphorus (WASSTRIP) and the PhoStrip processes. P recovery within EBPR plant often involved an anaerobic holding tank, where P is released due to PAO activity as well as bacteria decay. However, the impact of EBPR process operating conditions on P-release capacity and kinetics are not fully understood.