Isolation of microalgal strain from algal-bacterial aerobic granular sludge and examination on its contribution to granulation process during wastewater treatment in respect of nutrients removal, auto-aggregation capability and EPS excretion

Abstract Nutrients removal together with auto-aggregation capability of an isolated microalgal strain Chlorella sp. A-1 from mature algal-bacterial granules was examined under illumination at a light/dark cycle of 12 h/12 h or 0 h/24 h. Then its contribution to granulation process was evaluated in sequencing bath reactors(SBRs). The strain Chlorella sp. A-1 with a fast biomass growth and high auto-aggregation index(82.4% on day 5) achieved 93–96% of N and P removals when treating wastewater containing 50 mg-NH4-N/l and 5 mg-PO4-P/l after 5-day cultivation at the light/dark cycle of 12 h/12 h. The inoculated strain Chlorella sp. A-1 in SBRs was observed to help the fluffy activated sludge to transform into a little bit tight structure initiating the formation of algal-bacterial granules. Total extracellular polymeric substances(EPS), especially tightly bound EPS excreted from the strain was found to contribute more to algal aggregation. The isolated Chlorella sp. A-1 is probably the crucial biological factor for algal-bacterial granule formation.