TABLE OF CONTENTS The activated sludge process relies on a dense microbial population being in mixed suspension with the wastewater under aerobic conditions. With unlimited food and oxygen, extremely high rates of microbial growth and respiration can be achieved resulting in the utilization of the organic matter present to either oxidized end products (i.e. CO 2, NO 3, SO 4 and PO 4) or the biosynthesis of new micro-organisms (Section 15.1). The activated sludge process relies on five inter-related components: the reactor, the activated sludge itself, the aeration/mixing system, the sedimentation tank and the returned sludge (Table 17.1 and Fig. 17.1). However, there is an increasing interest in replacing the sedimentation tank unit with either an internal or external membrane filtration unit to separate the solids from the final effluent (Section 20.8.5).
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