The competition between flocculent sludge and aerobic granules during the long-term operation period of granular sludge sequencing batch reactor

Abstract

The long-term operational stability of aerobic granular sludge reactor was investigated in this study. It was found that the fraction of flocculent sludge fluctuated from 5 to 35%, even with a settling time of less than 5 minutes and manual discharge of flocculent sludge during a steady state of more than 400 days. Although the microbial community structure of flocculent sludge was similar to that of granular sludge co-existing in the reactor, the specific growth rate, the observed biomass yield and the specific oxygen consumption rate of flocculent sludge were much higher than those of granular sludge with identical microbial community structures. Therefore, the presence of flocculent sludge in the granular sludge reactor is mainly because of the kinetic superiority of flocculent sludge over granular sludge, rather than microbial competition. Increasing mass transfer in the feast period or discharging excess flocculent sludge could enhance the growth of granular sludge and improve the stability of the long-term operation of the granular sludge reactor.