Automatic control of the activated sludge process—II. Efficacy of control strategies

Through the use of computer simulation, the efficacies of the following strategies for control of the activated sludge process were evaluated: single loop feedback control; multiple loop feedback control; single loop feedforward control; feedforward/feedback control; and multiple loop feedforward control. The best improvement in system performance was found with multiple loop feedforward control although the full benefits of the technique could not be achieved due to saturation of the manipulated variables. During the research two types of plants were simulated: Case I in which the concentration of suspended solids in the final effluent decreased as the MLSS concentration entering the settler increased, and Case II in which the effluent suspended solid increased. The best choices for the measured and controlled variables in the multiple loop feedforward control systems depended heavily upon the type of behavior exhibited by the final settler.