Cultivating aerobic granular sludge in a developed continuous-flow reactor with two-zone sedimentation tank treating real and low-strength wastewater.

A continuous-flow reactor with two-zone sedimentation tank (CFR-TST) was developed to evaluate the formation of aerobic granular sludge (AGS). Micropowder made of excess sludge was added for a while in the CFR-TST, and selection pressure associated with settling time was created by the two-zone sedimentation tank. To avoid AGS disintegration, an airlift system for sludge return was used. The results show that AGS (mean particle size of 105µm; sludge volume index of approximately 26mL/g) was formed successfully in the CFR-TST. The micropowder induced bacterial attachment by acting as nuclei. The two-zone sedimentation tank made the well settling granules (i.e., heavy sludge) always retained in the CFR and poorly settling flocs (i.e., light sludge) washed away. After granulation, the contents of extracellular polymeric substances and metal precipitations in sludge increased, and the microbial community changed obviously. Additionally, the effluent concentrations of CODCr and NH4+-N were relatively low after granulation.

Analysis of bacterial, fungal and archaeal populations from a municipal wastewater treatment plant developing an innovative aerobic granular sludge process.

Mature granules and flocs from aerobic sludge were collected from the wastewater treatment plant (WWTP) treating both municipal and industrial effluents in Haining city China. This plant has been operating under conditions favoring aerobic granular sludge formation, for over 3 years, suggesting that the granules, which stably retained under changing effluent conditions, may contain unique microbial populations. Microbial analysis indicated that the granular sludge was primarily composed of Planctomycetes, Proteobacteria and Bacteroidetes from the bacterial phyla. Interestingly, microbial communities were also observed to be stratified between the structural features of the sludge. For example, Euryarchaeota was found to make up the majority of the archaea found in the granules while Methanosaeta was dominant in the flocs. Additionally, granules were found to contain, 34 phyla and 222 genera of bacteria, 4 phyla and 13 genera of fungi, and 2 phyla and 17 genera of archaea. While flocs contained, 32 phyla and 203 genera of bacteria, 6 phyla and 26 genera of fungi, and 2 phyla and 12 genera of archaea. This biodiversity signifying a preservation of bacterial and archaeal population in granules, and fungal populations in flocs may result from the sedimentary characteristics of the granules. This suggests microbes uniquely associated in the granules are playing a key role in structure formation and stability of the granular ecosystem, which is maintained by the longer sludge retention time.