Fuzzy Logic Process Control of HPO-AS Process

Abstract

The high purity oxygen activated sludge process requires more advanced controls as compared to the conventional activated sludge process. Feedback controllers have difficulty controlling process disturbances due to process delays and noisy signals, and cannot adjust to extreme upsets, such as stormwater flows. Four fuzzy logic control systems were developed for average conditions, and are superior to conventional feedback control systems in conserving energy, reducing dissolved oxygen (DO) variations, and stabilizing feed and exit gas flow rates. A direct control strategy, using feedforward aerator speed control and feedback stage 4 DO control, is the best among the four systems. For plants without variable speed aerators, feedforward control based on influent flow rate to adjust the stage 1 pressure setpoint, with feedback stage 4 DO control, is best. To address stormwater flows an adaptive fuzzy logic control system was developed. The control system can immediately shift to a new state to adapt to large changes in influent flow rate. The system prevents DO depletion under wet weather conditions, and conserves oxygen and energy during dry weather conditions.