Nitrogen and phosphorus removal from an abattoir wastewater in a SBR with aerobic granular sludge

The formation and performance of granular sludge was studied in an 8l sequencing batch reactor (SBR) treating an abattoir (slaughterhouse) wastewater. Influent concentrations averaged 1,520 mg l(-1) volatile suspended solids (VSS), 7,685 mg l(-1) Chemical oxygen demand (COD), 1,057 mg l(-1) total kjeldahl nitrogen (TKN), 217 mg l(-1) total P. The COD loading was 2.6 kgm(-3)d(-1). The SBR was seeded with flocculating sludge from a SBR with an 1h settle time, but granules developed within 4 days by reducing the settle time to 2 min. The SBR cycle also had 120 min mixed (anaerobic) fill, 220 min aerated react, and 18 min draw/idle. The granules had a mean diameter of 1.7 mm, a specific gravity of 1.035, a density of 62 g VSS l(-1), a zone settling velocity (ZSV) of 51 mh(-1), and a sludge volume index (SVI) of 22 ml g(-1). Without optimizing process conditions, removal of COD and P were over 98%, and removal of N and VSS were over 97%. Nitrification and denitrification occurred simultaneously during react. The results indicate that conventional SBRs treating wastewaters with flocculating sludge can be converted to granular SBRs by reducing the settle time.