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

Abstract

A fuzzy logic controller (FLC) was used for the automatic control of coagulation reactions. A laboratory-scale water treatment plant (rapid mixing, flocculation and sedimentation), operated under continuous-flow mode, was used to simulate reaction conditions. Streaming current (SC) and pH were chosen as process outputs; while alum and base doses were chosen as control process inputs. They were monitored on-line, and transduced through an FLC. Using raw water with initial turbidity of 600 NTU, a residual turbidity of less than 2.5 NTU was obtained. Raw water with an ultra-high initial turbidity (a kaolinite concentration of 1000 mg/dm³) was also tested. A residual turbidity of less than 6 NTU was obtained under these conditions. In addition, 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 dm³ of 100 g/dm³ kaolinite suspension. The system was first perturbed by the impulse input of solid loading, and its residual turbidity increased to 16 NTU. However, the system rapidly regained stability, and a residual turbidity of less than 8 NTU could be obtained. It was demonstrated that the fuzzy logic controller functions satisfactorily and is robust in the treatment of water of ultra-high turbidity.