Cultivation of aerobic granular sludge in a conventional, continuous flow, completely mixed activated sludge system

Abstract

Aerobic granules were formed in a conventional, continuous flow, completely mixed activated sludge system (CMAS). The reactor was inoculated with seed sludge containing few filaments and fed with synthetic municipal wastewater. The settling time of the sludge and the average dissolved oxygen (DO) of the reactor were 2 h and 4.2 mg·L^-1, respectively. The reactor was agitated by a stirrer, with a speed of 250 r·min^-1, to ensure good mixing．The granular sludge had good settleability, and the sludge volume index (SVI) was between 50 and 90 mL·g^-1. The laser particle analyzer showed the diameter of the granules to be between 0.18 and 1.25 mm. A scanning electron microscope (SEM) investigation revealed the predominance of sphere-like and rod-like bacteria, and only few filaments grew in the granules. The microbial community structure of the granules was also analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Sequencing analysis indicated the dominant species were α, β, and γ-Proteobacteria, Bacteroidetes, and Firmicutes. The data from the study suggested that aerobic granules could form, if provided with sufficient number of filaments and high shear force. It was also observed that a high height-to-diameter ratio of the reactor and short settling time were not essential for the formation of aerobic granular sludge.

Keywords

aerobic granular sludge / completely mixed activated sludge system (CMAS) / continuous flow / shear force / filamentous bacteria / polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE)

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Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant No. 50878180).

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg