Enhanced Coagulation for Removal of Natural Organic Matter and Disinfection Byproducts: Multivariate Optimization

Enhanced coagulation can remove dissolved organic carbon (DOC) that acts as a precursor to disinfection byproducts (DBPs). However, previous studies have not elucidated the effect of certain coagulation and settling parameters, such as the fast-mixing rate and settling time, on haloacetic acids (HAAs) and trihalomethanes (THMs). Furthermore, coagulant dosage, fast mixing power, and settling time play essential roles in the cost-efficiency of operation and construction of a water treatment plant. This study aims to present a novel investigation of the effects associated with the operational factors of coagulation-flocculation and sedimentation to achieve feasible solutions for management of DBPs. The simultaneous effects of pH (4.5-8.5), coagulant type (Fe3+/Fe3+ + Al3+ ratio), coagulant dosage, fast-mixing rate, and settling time were examined using a response surface methodology design. Accordingly, predictive models were generated by conducting 2 sets of experiments, which comprised 50 runs of jar tests that were performed in triplicate of 2 blocks for 2 natural drinking water sources in Newfoundland, Canada. The results were validated on four natural waters and two synthetic water samples. The multivariate optimization on THM4 and HAA5 resulted in a significant reduction in the fast-mixing energy by 59.9%, and a reduction of 23.4-41.1% in coagulant dosage. The results of natural organic matter fractionation on water samples revealed that the optimized coagulant dosage of 3.83-5.95 mg/mg DOC could remove up to 91.00%, 72.64%, and 70.79% of THM4, HAA5, and DOC, respectively, in natural water samples with a very hydrophobic acid (VHA) fraction of 0.67-0.81 VHA/DOC.

Automated summary

This study investigated the effects of coagulant dosage, fast mixing power, and settling time on haloacetic acids and trihalomethanes, aiming to provide feasible solutions for DBPs management. The predictive models generated through experiments validated on natural and synthetic water samples showed a significant reduction in energy consumption and coagulant dosage post-optimization. The study highlights the importance of multivariate optimization in achieving efficient water treatment processes.