Developments in Enhanced Biological Phosphorus Removal (EBPR)

Abstract

Phosphorus removal using Phosphorus Accumulating Organisms (PAOs) has attracted significant interest in recent years for controlling nutrient pollution in the aquatic environment. Enhanced Biological Phosphorus Removal (EBPR) has been known for several decades since the concept of “luxury uptake” was proposed in 1965 but the mechanisms have not been understood until recently. Biological phosphorus removal may occur through growth associated coupling or storage within the biomass as polyphosphate. The latter mechanism is exploited in the EBPR systems. Until recently, Acinetobacter sp alone was thought to be responsible for EBPR., but it is now known that this may not be the case, although the organism(s) responsible for polyphosphate accumulation are still unknown. There are two biochemical mechanisms proposed for PAOs under anaerobic and aerobic conditions based on the reducing power required for the synthesis of polyhyroxyalkanoate (PHA) . A range of reactor configurations has been developed to accomplish EBPR essentially exploiting the anaerobic and aerobic metabolism of PAOs. The initial EBPR systems relied upon modifications to continuous flow activated sludge reactors incorporating the anaerobic stage prior to aeration basin for phosphorus removal and anaerobic and anoxic stages for nitrogen and phosphorus removal. More recently, Sequencing Batch Reactor (SBR) has been shown to be an effective reactor system for either phosphorus removal alone or for the removal of both nitrogen and phosphorus. Much of EBPR work over the last four decades has been done on low phosphorus concentration (about 15mg/L) domestic effluents. More recently, industrial effluents containing high phosphorus concentration (about 90 mg/L) have also been successfully treated by EBPR. The understanding of EBPR both in terms of mechanisms and reactor systems reached a level ensuring that EBPR is now more attractive alternative to chemical treatment for phosphorus removal.