ABSTRACT
In this unit, biological treatment is explained and the components of conventional activated sludge are described. Factors affecting activated sludge and its operation and design parameters are detailed. Calculations for the loading parameters of the food to microorganism (F/M) ratio and solid retention time are shown, and a range of values is discussed. The substrate utilization rate, as used in the design of the process, is explained and solved example problems showing computations are presented. Factors affecting secondary clarification are discussed in detail, followed by a simulation by a settlometer test. The relationship of the sludge hypothetical return rate ratio and sludge volume index is derived, followed by solved example problems. Variations of activated sludge processes, including step aeration, contact stabilization and expended aeration, are described and illustrated with schematic diagrams. Oxygen uptake rate as it affects the DO level in an aeration tank is discussed.
