Laboratory-scale sequencing batch reactor (SBR) activated sludge processes were operated using synthetic wastewater to clarify the effects of sludge retention time(SRT) and organic substrates on the accumulation of bio-P-bacteria. The accumulation of bio-P-bacteria could be enhanced by wide variation in concentration of organic substrates by giving a short fill period and sufficient anaerobic conditions. However, the accumulation could not be enhanced in the reactor operated with SRT less than 25 d in spite of the higher, more than 0.1 d−1, specific growth rates observed in the isolated strains of bio-P-bacteria. The specific growth rates of bio-P-bacteria were estimated at 0.040 d−1, 0.030 d−1 and 0.035 d−1 in the SBR activated sludge processes fed with sodium acetate (A), glucose and polypeptone (GP) and polypeptone (P), respectively. Therefore, a large sludge retention time would be necessary for the accumulation of bio-P-bacteria. Volatile fatty acids (VFA), such as sodium acetate (A), seemed to be more effective than other organic substrates (GP and P) for the accumulation of bio-P-bacteria in activated sludge ecosystems.

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