Optimization of activated sludge reactor configuration: kinetic considerations

To evaluate and design staged activated sludge systems it is necessary to determine the biomass requirement for a given configuration. This depends on both kinetics and treatment requirements. We present a procedure to determine the optimum reactor configuration for a range of influent and effluent substrate concentrations, half saturation coefficients, and number of tanks in series for both inhibitory and non-inhibitory substrates. Dimensionless plots of the results show the minimum biomass requirement of the series relative to that for a single CSTR and the optimal relative sizes of the tanks. The plots may be used directly for staged system design and lead to the following conclusions: three tanks in series is generally best, high influent substrate concentrations and stringent discharge requirements increase the benefit of staging, and optimal tank sizing is significantly better than using equal sized tanks.