Development of microalgal-bacterial aerobic granules for ammonium removal from wastewater in a photo sequencing batch reactor

Abstract

Aerobic granular sludge was applied in a method with photo sequencing batch reactor (PSBR) under a constant light/dark cycle (18/6 h). Rapid aggregation of microalgae and bacterial biomass with the increasing production of extracellular polymeric substances (EPS) was recorded. EPS induced microalgal-bacterial growth led to the formation of microalgal-bacterial aerobic granules. Microalgal-bacterial aerobic granules showed maximum ammonium removal of 3.3 mg NH4+-N/L/h, equal to 333 mg NH4+-N/m2/h or 637 mg NH4+-N/mol photon or 0.05 mol NH4+-N/mol photon. Ammonium-nitrogen oxidation was carried out by oxygen produced from the microalgal photosynthesis, with simultaneous nitrification and denitrification in the aerobic and anaerobic zones, respectively. From this study it was observed that the microalgal-bacterial aerobic granules developed in a stirred PSBR and can treat domestic wastewater without external air supply, although the process of granules formation discontinued over time.