AUTOMATIC-CONTROL FOR CHEMICAL DOSING IN LABORATORY-SCALE COAGULATIONPROCESS BY USING AN OPTICAL MONITOR

The feasibility of applying an optical monitor in the automatic contro l of coagulation was assessed in this study. Prior to simulation testi ng, a series of batch tests was performed to determine the optimum sta te of dosing corresponding to the monitor's output. The results indica te that floc density decreased as floc size increased under the same c oagulant dosage. Moreover, ratio output of the monitor could provide a n index for evaluating the change trend of flee size in flocculation a nd for predicting the potential of flee settling. An automatic control system was designed and connected to a laboratory-scale water treatme nt process. A computer in the automatic control system received all th e ratio values with respect to the progressive dosing. After determini ng the dosage, the system terminated the function of control. This con trol system started performing a new test for determining another opti mum dosage when the fluctuation of inflow turbidity was more than a de signated value. Simulation tests demonstrated that the PDA monitor wit h a designed control system could be successfully applied in the on-li ne control of coagulation dosing. The recommended control parameters f or the control system was also identified. Copyright (C) 1996 Elsevier Science Ltd