Enhanced biological phosphorus removal in an anaerobic-aerobic sequencing batch reactor: characteristics of carbon metabolism.

Carbon metabolism of activated sludge performing enhanced biological phosphorus removal (EBPR) was investigated in a sequencing batch reactor (SBR), where glucose and acetate were supplied as carbon sources. There have been reports that EBPR often failed because of outgrowth of G-bacteria, which are able to use glycogen (or glucose) alone instead of glycogen and polyphosphate as an internal energy storage pool for the anaerobic uptake and storage of acetate. However, in this experiment, complete EBPR was achieved without proliferation of G-bacteria despite the supply of glucose in addition to the acetate. Additional one-cycle SBR operation was carried out to investigate the detailed metabolism of glucose and acetate. Acetate-using, phosphorus-accumulating organisms (PAOs) could use glucose as a source for the anaerobic polyhydroxyalkanoate (PHA) synthesis from acetate. However, glucose and acetate were metabolized separately through independent metabolic pathways by respective microorganisms: acetate-using PAOs, lactate-producing organisms (LPOs), and lactate-using PAOs. Glucose was rapidly converted to lactic acid by LPOs before acetate-using PAOs used the glucose as an energy source for the anaerobic PHA synthesis from acetate and the lactateusing PAOs anaerobically synthesized PHA from lactate at the expense of polyphosphate. The EBPR was accomplished by acetate-using PAOs and lactate-using PAOs independently when glucose acetate were supplied together.