Potential causes of high performance of pure-oxygen aerobic granules in SBR under high organic loading condition

Aerobic granules were cultivated using pure oxygen aeration (POAG) in SBR for wastewater treatment under high organic loading condition (HOLC) to reveal its performance and potential causes. Compared to conventional granules and activated sludge, mature POAG with more compact and dense structure were formed in a shorter term using pure-oxygen aeration in SBR. The system shows high and stable COD and NH4+-N removal efficiencies with an average value of 91% and 84%, respectively, under HOLC. Adequate dissolved oxygen (DO) supplied by pure-oxygen aeration is the prerequisite explaining the elevated performance. POAG have more stable compact granular structure and elevated biomass than that of conventional biogranules and bioflocs under HOLC. High EPS content facilitate the formation of POAG and maintain its integrity and stability of spatial structure, which is in favor of biomass growth. Abundant catalase synthesized by its biomass ensure the ability to hydrolyze and mineralize organic substance under HOLC. A great deal of dehydrogenase secreted by POAG play a critical role in maintaining its metabolism under HOLC, which in turn enhance multiplication capacity of living organism in POAG and elevate removal performance of organic pollutants from wastewater.