The efficiency of biological wastewater treatment depends on the selection and growth of metabolically capable microorganisms and upon the efficient separation of microorganisms from the treated solution. In recent years, the Sequencing Batch Reactor (SBR) has been used to form compact and biologically efficient sludge, in the form of aerobic granules. Aerobic granulation technology is receiving increasing attention.;Granules were considered a special case of biofilm composed of self-immobilized cells. Aerobic granular sludge have a wide range of beneficial characteristics compared to activated sludge, most notably their high bioactivity and good settling property. A review summarizes the recent advance on aerobic granulation technology, including the operational factors, granular characterization, granulation models and its applications in Chapter 2. To date, the mechanism controlling aerobic granulation is still unclear and the factors resulting in granular instability and disintegration are not well investigated. The purpose of this study is to explore the causes of granule deterioration, which will be conducive to the practical application and propagation of aerobic granulation technology.;In this work, two types (bubble column and airlift) of completely aerobic SBRs were operated to form heterotrophic aerobic granules, and microbial investigations were conducted to correlate the reactor operation with the granular structure at the macro- and micro-scale. The results and discussion are divided into three sections: granular development and performance; microscopic investigation, and microbial characterization.;First, low food to microorganism ratio (F/M) was found to introduce the growth of flocculent biomass and result in granular disintegration, which was shown to not less than 0.2 in our study. Airlift SBR was more advantageous than bubble column SBR in cultivating stable granules.;Second, granular size was found to greatly influence granular stability and nitrite accumulation due to the mass transport limitation.;Third, granular surface porosity profiles showed an inverse relationship with granular age and size. The optimal granular diameter was less than 1.2 mm for our heterotrophic aerobic granules. A four-step granular life cycle was summarized.;Fourth, granule formation was reproducible using various inoculum sludges and microbial communities were highly dynamic through the operation time. Betaproteobacteria dominated mature acetate-fed granules.
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