Physical and chemical characteristics of granular activated sludge from a sequencing batch airlift reactor

Granular activated sludge was cultivated in a sequencing batch airlift reactor fed with a synthetic sucrose-rich wastewater for 68 days. The formation of granular activated sludge and its physical and chemical characteristics were investigated. With the granulation, the specific gravity and surface hydrophobicity of sludge increased, but the specific surface area and the concentrations of carbohydrate and protein in the extracellular polymeric substances decreased. Microscopic examination showed that the morphology of the mature granular sludge was nearly spherical (0.5–1.2 mm in diameter) with a clear outline, and had a strong structure. The granular sludge had good settleability, as indicated by a low sludge volume index of 23 ml/g and a high settling velocity of 18–31 m/h. Compared with activated sludge flocs, the granules were regular and dense and exhibited high biomass retention.