Sludge pre-recycle control of dynamic enhanced biological phosphorus removal system: An application of on-line fuzzy controller

This study presents a specific process control strategy, i.e. sludge pre-recycle control, for a dynamic enhanced biological phosphorus removal system by integratedly considering two factors: appropriately controlling F/M ratio in the anaerobic zone, and eliminating hydraulic shock in the secondary clarifier. Fuzzy logic inference is also introduced while constructing an on-line controller owing to the ill-defined characteristics of the dynamic enhanced biological phosphorus removal system. For comparison, continuous-flow pilot plant experiments with automatic monitoring and real-time control facilities are performed using two control strategies: sludge pre-recycle control and conventional (F/M)_an control. Experimental results indicate that similar effluent ranges of dissolved COD and dissolved phosphate can be obtained from the two strategies due to their similar (F/M)_an ratios. However, reliability analysis reveals that sludge pre-recycle control improves the effluent total SS concentration significantly more than conventional (F/M)_an control because of the reduction of hydraulic loading in the clarifier.