An automatic coagulant dosage control technology for water purification plants was developed to deal with rapid changes of feed water quality. Control logic was developed to decide coagulant dosage based on aluminum concentration in the mixing tanks. A coagulant-sedimentation process apparatus was installed in December 2010 in a water purification plant, and the coagulant dosage control test using feed water was started. The developed system was confirmed to be effective for managing settled water turbidity and adequacy of coagulant dosage. For actual changes of feed water quality at the water purification plant over more than one year, the developed system was able to maintain settled water turbidity at less than 1.0 mg-kaolin/L in the period of high feed-water turbidity.

An automatic coagulant dosage control technology for water purification plants was developed to deal with rapid changes of raw water quality parameters. Control logic was developed to decide coagulant dosage based on aluminum concentration in rapid mixing tank water based on results of semi-pilot scale experiments. This logic enabled quick feedback on the excess or lack of coagulant. It was found that the aluminum residual rate, which was proposed as an indicator of coagulation reactions, could be given as a function of coagulant dosage and turbidity. The effectiveness of the control logic was verified in semi-pilot scale experiments. Settled water turbidity was within ±0.5 NTU of target value even when raw water turbidity increased rapidly up to 100 NTU.