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Anaerobic sequencing batch reactors and its influencing factors: an overview.

Anaerobic sequencing batch reactors (ASBR) operate in four cyclic steps: feed, reaction, settling and discharge. ASBRs allow typical biological anaerobic metabolism from substrate consumption to methane and carbon dioxide production. Microorganisms in an ASBR are exposed to variable substrate concentrations over the duration of the cycle, resulting in high rates of substrate conversion and efficient biomass flocculation and settling. High substrate concentrations at the beginning of a cycle result in high metabolic activity and substrate removal. Low substrate concentrations towards the end of the cycle result in low biogas production and allow for good sludge settling. However, the cycles should be as frequent as possible while allowing for completion of each of the four stages. Operating by batches enables the solids residence time to be independent of the hydraulic retention time without recourse to a settling tank, since the reactor functions as a decanter whenever the stirring mechanism is turned off. This review presents an overview of the ASBR process and the various factors influencing its performance.