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Biological wastewater treatment with activated sludge followed by a liquid-solids separation step has been an established process for over a century. Effective liquidsolids separation can be made through biological or chemical flocculation. Biological flocculation involves the aggregation of organic and inorganic components into flocs through the action of microbes and their by-products, i.e. extracellular polymeric substances (EPS). Adverse conditions can promote floc break-up, i.e. deflocculation, reducing effluent quality and increasing overall treatment costs. It is essential to have a better understanding of the biological flocculation process and factors influencing it, especially in cyclically conditioned (aerobic/anoxic/anaerobic) treatment processes.The exposure to low dissolved oxygen (DO) (<0.5 mg/L) conditions has been reported to promote deflocculation. However, in this dissertation studies, sludge from three different sources repeatedly showed a lack of deflocculation even after 24 hours subject to low DO and substrate depletion. Divalent cationic interactions, high bound EPS content and the activities of facultative bacterial communities were factors argued to have contributed to increased floc integrity, and which helped mitigate the deflocculation under low DO conditions. The importance of facultative bacterial communities on floc maintenance and mitigation of deflocculation under low DO conditions was confirmed through microbial inhibition experiments. Deflocculation, in the form of floc erosion, was observed under low DO conditions only when microbial inhibitory conditions were promoted using a mitochondrial uncoupler, sodium azide. Sodium azide also exhibited interactive tendencies with the EPS, which was confirmed through EPS fluorescence quenching studies and this was another mechanism through which floc integrity could be influenced. It was the microbial communities, their activities and metabolic by-products (EPS), and not necessarily the short-term DO