Dynamic and distribution of ammonia-oxidizing bacteria communities during sludge granulation in an anaerobic-aerobic sequencing batch reactor.

The structure dynamic of ammonia-oxidizing bacteria (AOB) community and the distribution of AOB and nitrite-oxidizing bacteria (NOB) in granular sludge from an anaerobic-aerobic sequencing batch reactor (SBR) were investigated. A combination of process studies, molecular biotechniques and microscale techniques were employed to identify and characterize these organisms. The AOB community structure in granules was substantially different from that of the initial pattern of the inoculants sludge. Along with granules formation, the AOB diversity declined due to the selection pressure imposed by process conditions. Denaturing gradient gel electrophoresis (DGGE) and sequencing results demonstrated that most of Nitrosomonas in the inoculating sludge were remained because of their ability to rapidly adapt to the settling-washing out action. Furthermore, DGGE analysis revealed that larger granules benefit more AOB species surviving in the reactor. In the SBR were various size granules coexisted, granule diameter affected the distribution range of AOB and NOB. Small and medium granules (d<0.6 mm) cannot restrict oxygen mass transfer in all spaces of the sludge. Larger granules (d>0.9 mm) can result in smaller aerobic volume fraction and inhibition of NOB growth. All these observations provide support to future studies on the mechanisms responsible for the AOB in granules systems.