Chapter Iv: the Impact of System Operation and the Biochemistry of Enhanced Biological Phosphorus Removal on the Occurrence Ofanaerobic Stabilization

Improved design strategies at BNR plants should include cost reductions so that the consumers and water authorities will be more willing to build EBPR plants instead of conventional activated sludge plants. Through efficient design, actual savings in construction and operation costs can be realized. For this reason, anaerobic stabilization of COD needs to be seriously considered during design for direct energy savings at the plants. The existence of anaerobic stabilization has been demonstrated through experimental work (Randall et al., 1984; Randall et al., 1992; Wable and Randall, 1994). Evaluation of operational data from existing plants (Barker and Dold, 1995 and 1996) has also indicated the definite presence of anaerobic stabilization at plants that include anaerobic zones as part of their operation. By exploring the biochemical reactions taking place in EBPR process, particularly the involvement of the storage mechanisms, namely PHA, poly-P and glycogen storage, the potential mechanisms of the anaerobic stabilization of COD in EBPR systems was explored. The resultant balances pointed out the importance of glycogen metabolism in terms of conserving carbon and providing a sink for the reducing equivalents produced under aerobic conditions. This mechanism is different from those observed in anoxic-aerobic and conventional aerobic activated sludge systems, and appear to be at least partially responsible for the observed anaerobic stabilization of COD.