Development of automatic coagulant dosage control technology for rapid change of raw water quality parameters

Abstract

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.

State of the Art of Online Monitoring and Control of the Coagulation Process

“…Sangu et al [49,50] described an automatic coagulant dosage control method that relies on the measurement of residual aluminum concentrations in the rapid mixing stage. The technique should be especially applicable for rapid changes of raw water turbidity.…”

Self-adaptive cycle-to-cycle control of in-line coagulant dosing in ultrafiltration for pre-treatment of reverse osmosis feed water

“…The above approach was successfully implemented for the one specific feed water source for which the correlation was determined, but the control approach was found to be deficient at two other sites. More recently, a feed-back control approach was reported for coagulant dose adjustment, also for a coagulant-sedimentation process, whereby the residual aluminum concentration in the mixing tank served as the metric for assessing coagulation efficiency [43,44]. Deployment of the approach was successful for reducing source water of turbidity from 0.5 -100 NTU to below 1 NTU.…”