Process Control of Activated Sludge Treatment, Phase II

Material balances on substrate and microorganisms were derived in conjunction with various mixing configurations thought to accurately describe the activated sludge process. These models include the completely mixed with bypass, plug flow, and plug flow with bypass. Two sets of kinetic mechanisms for substrate utilization and bacterial growth were employed. A feed forward controller was designed from linear approximations of the material balances derived in the completely mixed with bypass mixing model. Utilizing frequency response methods, the controller was found essentially identical to a completely mixed modeled controller developed in a prior investigation. Through computer simulation the controller\u27s effectiveness was tested. The controller maintained suitable effluent quality principally through proportional control on the influent flow rate. Additional proportional derivative control on influent substrate concentration produced further reductions in substrate levels; however, when employing realistic forcing functions,these reductions were minor. Comparison of mixing models was dependent upon the degree of substrate loading inflicted on the system. Bypassing had a detrimental effect on effluent quality and process control. Experimental studies were performed to find a representative kinetic and mixing model which reproduces the diurnal fluctuations of key activated sludge process parameters found at the Lexington Wastewater Treatment Plant. A suitable model was not found as experimental and theoretical results did not agree