Anaerobic phosphate release from activated sludge with enhanced biologicalphosphorus removal. A possible mechanism of intracellular pH control

The biochemical mechanisms of the wastewater treatment process known as enh anced biological phosphorus removal (EBPR) are presently described in a met abolic model. We investigated details of the EBPR model to determine the na ture of the anaerobic phosphate release and how this may be metabolically a ssociated with polyhydroxyalkanoate (PHA) formation, lodo-acetate, an inhib itor of glycolysis, was found to inhibit the anaerobic formation of PHA and phosphate release, supporting the pathways proposed in the EBPR metabolic model. In the metabolic model, it is proposed that polyphosphate degradatio n provides energy for the microorganisms in anaerobic regions of these trea tment systems. Other investigations have shown that anaerobic phosphate rel ease depends on the extracellular pH. We observed that when the intracellul ar pH of EBPR sludge was raised, substantial anaerobic phosphate release wa s caused without volatile fatty acid (VFA) uptake. Acidification of the slu dge inhibited anaerobic phosphate release even in the presence of VFA. From these observations, we postulate that an additional possible role of anaer obic polyphosphate degradation in EBPR is for intracellular pH control. Int racellular pH control may be a metabolic feature of EBPR, not previously co nsidered, that could have some use in the control and optimisation of EBPR. (C) 1999 John Wiley & Sons, Inc.