Challenge for Formation of Aerobic Granular Sludge in a Continuous-Flow Reactor

Abstract

Formation of aerobic granular sludge was investigated using a laboratory-scale continuous-flow reactor. Although it is generally thought that aerobic granular sludge can be formed only when a sequencing batch reactor (SBR) is used, formation of aerobic granular sludge was observed using a continuous-flow reactor in this study. The formation was observed only when nitrification well occurred in the reactor, and any indication of the aerobic granulation was not observed in the presence of nitrification inhibitor. Therefore, it was considered that existence of nitrifying bacteria is responsible for formation of the granular sludge. It has been reported that existence of slow growing organisms like nitrifying bacteria induces formation of granular sludge when an SBR is used. Hence, it was considered that formation of aerobic granular sludge is possible in the presence of certain population of nitrifying bacteria even when a continuous-flow reactor is used. To our best knowledge, this is the first study that indicates the possibility of forming aerobic granular sludge in a continuous-flow reactor where organic wastewater is fed. These findings will contribute to dissemination of aerobic granular sludge technology because continuous-flow reactors are more widely used all over the world than SBRs.