Chapter 4 Mechanisms of aerobic granulation

Abstract

This chapter focuses on the mechanisms of aerobic granulation. Aerobic granulation is a process of microbial self-immobilization without the support of a carrier. Similar to the formation of biofilms and anaerobic granules, aerobic granulation should be a multiple-step process in which a number of physico-chemical and biological factors should be involved. Many factors have been known to affect the formation of aerobic granules in sequencing batch reactor (SBR). Compared with continuous microbial culture, the main feature of SBR is its cycle operation—that is, each cycle consists of filling, aeration, settling, and discharging. In SBR, the settling time is likely to exert a selection pressure on the sludge particles. Only particles that can settle down within a given settling time would be retained in the reactor, otherwise they would be washed out of the system. Selection pressure in terms of upflow velocity has been recognized as a driving force toward successful anaerobic granulation in upflow anaerobic sludge blanket (UASB) reactors. Similarly, in aerobic granulation, a selection pressure should be created to promote the formation of aerobic granules in SBR.