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

Abstract

The formation and performance of granular sludge was studied in an 8 l sequencing batch reactor (SBR) treating an abattoir (slaughterhouse) wastewater. Influent concentrations averaged 1520 mg l −1 volatile suspended solids (VSS), 7685 mg l −1 Chemical oxygen demand (COD), 1057 mg l −1 total kjeldahl nitrogen (TKN), 217 mg l −1 total P. The COD loading was 2.6 kg m −3 d −1. The SBR was seeded with flocculating sludge from a SBR with an 1 h 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 m h −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.