Influence of three selection pressures on aerobic granulation in sequencing batch reactor

Abstract

Aerobic granulation is a promising biotechnology for wastewater treatment. The formation and development of granules and the pollutant removal are closely associated with hydrodynamic shear force, settling time and volume exchange ratio (VER), which are proved to be the selection pressures. Three different values of shear force (2, 3 and 4 cm/s), settling time (3, 5 and 10 min) and VER (25, 50 and 75%) have been experimented in sequencing batch reactor (SBR) in seven trials for the optimal performance of aerobic granulation. Higher shear force could develop smaller and more compact granules with better settling behaviour, but chemical oxygen demand (COD) removal is not found to improve beyond a value of 97.9% for shear force above 3 cm/s. A settling time as low as 3 min could result in very good biomass growth and formation of granules with sludge volume index (SVI) as low as 23 ml/g. Aerobic granulation is not successful at a long settling time of 10 min. Higher the VER, the lower is the SVI and the more efficient is the COD removal.