Physicochemical characteristic and reaction activity of anoxic granular sludge in sequence batch reactor

Anoxic granular sludge was developed in sequencing batch reactors (SBR) fed with a synthetic wastewater for 200 days. The formation of granular sludge, physical and chemical characteristics and denitrification capacity were investigated. With the granulation, the specific gravity, and concentration of extracellular polymeric substances (EPS) with polysaccharide dominating increased. The pictures show that granular sludge was ellipsoidal (1.0-2.5 mm in diameter) with a clear outline and a strong structure, and inorganic nucleus inside. The granular sludge had good settling ability, was indicated by low SVI of 14.76 ml/g and high settling velocity of 25-46 m/h, 1.051 in specific gravity, 54.5% in MLVSS/SS, and exhibited high biomass retention with 8.2 gMLSS/l. The maximum (max.) specific denitrification rate (SDNR) of granular sludge was 0.1710gNO₃^--N/(gVSS·h) and 0.0942gNO_x-N/(gVSS·h) larger than that of floc sludge or municipal sludge. High nitrogen removal capacity of anoxic granular sludge was achieved by long-term running under single anoxic condition and denitrifying bacteria was trained or enriched.