Effluent suspended solid control of activated sludge process by fuzzy control approach

The influent flow rate and substrate concentration normally vary with time in a municipal wastewater treatment plant (MWWTP). The treatment units must be operated dynamically to prevent the process from failing, reducing treatment efficiency, and creating a lack of stability. Using real time operation data to control the dynamic activated sludge process (DASP) systematically is an alternative approach to the expert system, which is based on experts' knowledge and/or operators' experiences and whose control rules are typically difficult to be derived by a systematic approach. The fuzzy control theory based on modified Newton's method can make real-time control feasible and is adopted in this study. The theory is definitely a systematic approach toward deriving optimum control strategies on-line. The optimum control strategies derived from the proposed approach are verified by experimental results that indicate that the forecast and control abilities of fuzzy model are sufficient. The proposed systematic approach only requires on-line monitored data, not experts' knowledge and operators' experiences, to adequately control the complex system. This feature is possible despite the fact that the system information is not clearly described, the kinetic model and related parameters are unknown, or the dynamic behaviors of the process are not thoroughly understood. Moreover, a comparison is also made in this study of the results between F:M ratio and fuzzy control strategies. That comparison reveals that the F:M control might not be appropriate for DASP when municipal wastewater is treated. The fuzzy control strategies confirm that the operating concepts for DASP are similar to those for a steady-state condition and can make the effluent quality better and more stable. The only difference between both systems is that time delay problems arise in DASP, but not in steady-state ASP.