Fuzzy control of a coagulation reaction for the treatment of high-turbidity water

A fuzzy logic controller (FLC) was used for the automatic control of coagul ation reactions. A laboratory-scale water treatment plant (rapid mixing, fl occulation and sedimentation), operated under continuous-flow mode, was use d to simulate reaction conditions. Streaming current (SC) and pH were chose n as process outputs; while alum and base doses were chosen as control proc ess inputs. They were monitored on-line, and transduced through an FLC. Usi ng raw water with initial turbidity of 600 NTU, a residual turbidity of les s than 2.5 NTU was obtained. Raw water with an ultra-high initial turbidity (a kaolinite concentration of 1000 mg/dm(3)) was also tested. A residual t urbidity of less than 6 NTU was obtained under these conditions. In additio n, for the study of dynamic responses of the system to shock loadings, raw water with an initial turbidity of 798 NTU was spiked with 1 dm(3) of 100 g /dm(3) kaolinite suspension. The system was first perturbed by the impulse input of solid loading, and its residual turbidity increased to 16 NTU. How ever, the system rapidly regained stability, and a residual turbidity of le ss than 8 NTU could be obtained. It was demonstrated that the fuzzy logic c ontroller functions satisfactorily and is robust in the treatment of water of ultra-high turbidity.