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Two parallel sequential batch reactors were used to study the mechanism of developing enhanced biological phosphorus removal (EBPR) by individually feeding glucose or acetate as the major organic substrate. Bacteria taken from the same source were cultured under identical operating conditions simultaneously in the two reactors. Results showed that feeding acetate as the major substrate to the first reactor (reactor A) quickly induced the EBPR performance. However, feeding the second reactor with glucose (reactor G) failed to provide the EBPR performance even though reactor G was operated similarly to reactor A. The operating procedures for reactor G were then modified to provide higher glucose in the feed, longer anaerobic reaction time, shorter aerobic reaction time and limited DO levels. These modified procedures not only induced good EBPR performance in the system, but also enabled the system to maintain very stable operation for more than 2 months. Batch experiments were conducted to compare the metabolic characteristics between the two EBPR systems using acetate or glucose. The results showed that glucose was immediately transported into the bacteria and stored as glycogen and poly-β-hydroxyalkanoate (PHA). It was found that poly-β-hydroxyvalerate (PHV) accounted for most of the accumulated poly-β-hydroxyalkanoate for reactor G as compared to poly-β-hydroxybutyrate (PHB) for reactor A. Polyphosphate hydrolysis and PHA accumulation were lower in reactor G compared to reactor A. For reactor G, this may potentially result in the selection of glycogen as the principal energy source in the anaerobic condition, which explains the poor PO 4 -P removal efficiency in reactor G before the modified operating procedures were developed and successfully applied. KEYWORDSAcetate; glucose; enhanced biological phosphorus removal (EBPR); poly-β-hydroxyalkanoate (PHA); poly-β-hydroxybutyrate (PHB); poly-β-hydroxyvalerate (PHV); glycogen; polyphosphate; polyphosphate accumulating bacteria (bio-P bacteria); short chained fatty acid (SCFA); sequential batch reactor (SBR).

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