Streaming current titration for coagulation of high turbidity water

Abstract

A jar test is commonly used to determine the chemical coagulation conditions in water treatment plants (WTPs). However, due to the frequent and intermittent turbidity measurements, and time-consuming determination for achieving optimal coagulation conditions, the jar test is not appropriate for the samples which are rapidly changing water turbidities. As an alternative, a streaming current detector (SCD) can be used by achieving electrically neutral conditions. A SCD can quantify the negatively charged particles by measuring the current of water samples. In this study, SCD titration was conducted to rapidly determine the optimal coagulation dosage for highly turbid waters (50∽600NTU) prepared with suspensions of kaolin (100∽1000mg/L). Polyaluminum chloride (PAC) and poly-diallyldimethylammonium chloride (poly-DADMAC) were added as coagulants. To estimate the optimal dose, a SCD titration-coagulation model was constructed, and its suitability was verified statistically by multiple linear regression analysis. In both homogeneous (PAC-PAC) and heterogeneous (poly-DADMAC-PAC) titration-coagulation models, the residual turbidity of highly turbid kaolin samples was successfully lowered to less than 1NTU. The homogeneous model and the jar test showed a maximum difference of 3mg/L for the suggested coagulant dose. Our results suggest that SCD can be applied to rapidly and accurately determine the coagulation dosage for highly turbid waters in water treatment plant even during rainy season.