Nitrification in sequencing batch reactors with and without glucose addition at 11 °C

Nitrification was investigated in two laboratory-scale sequencing batch reactors (SBRs) at 11 °C, one with glucose addition (G-Reactor) and the other without (N-Reactor). The characteristics of nitrification and the distribution of ammonia oxidizing bacteria (AOB) within activated sludge flocs in the two reactors were examined. A high specific nitrification rate existed in the N-Reactor, while a high volumetric nitrification rate existed in the G-Reactor. The proportion of AOB enriched in the N-Reactor was about three times that in the G-Reactor. The activated sludge flocs in the N-Reactor had a larger floc size and a higher biomass density than in the G-Reactor. AOB were mainly in a form of clusters in the activated sludge flocs in the N-Reactor, but were well dispersed throughout the flocs in the G-Reactor.