Effluent turbidity control in direct filtration

This paper studies the effluent turbidity control of a deep bed rapid sand filter run by direct filtration method. In spite of the highly nonlinear filter dynamics, the maximum filter run time and optimum alum usage are achieved. The disturbances such as the filter flow rate and the effluent (raw water) turbidity that directly affect the effluent turbidity are compensated successfully. The required alum dose is directly dosed into the filter by a dosage pump controlled by the main computer. Since the extraction of a mathematical model of a sand and polymer based filter is very difficult and many times impossible, fuzzy control is preferred to control the filtration. An integral controller is used in parallel to the fuzzy controller to enhance the control performance for steady state errors.