Developing Surrogate Indicator for Prompt Adjusting of Ozonation Operation: Insight from Pilot-Scale Treatment Using China’s South-to-North Water Diversion Project Feedwater

Energy-intensive ozonation processes could potentially evolve to flexible ozone (O3) dosing strategies that depend on variations of feedwater quality. Herein, we demonstrate a surrogate indicator using UV absorbance for timely indicating O3 performance on controlling disinfection byproduct (DBP) formation tendency, which could enable prompt adjustment of O3 operation in practical drinking water treatment plants (DWTPs). We specifically focused on treating the water sourced from the central route of China’s South-to-North Water Diversion (SNWD) Project at periods of high algae activity. We found that ozonation, positioned between the sand filter and carbon filter in a pilot-scale DWTP process, showed limited removal of typical DBP chloroform (CHCl3) formed during prechlorination. However, it notably enhanced the elimination of CHCl3 precursors and subsequently lowered the water’s susceptibility to secondary chlorination. Further, combining parallel factor analysis, Pearson correlation analysis, and two-dimensional correlation spectroscopy, we identified differential UV absorbance at 300 nm (ΔA300) as a rapid detection proxy for assessing ozonation efficacy in controlling the DBP formation tendency in DWTP. The formation of CHCl3 is highly dependent upon precursors of tryptophan and humic/fulvic acid II, which can be effectively indicated by ΔA300. Additionally, the secondary chlorination induces a positive relationship between the CHCl3 formation tendency and ΔA300 at the primary reaction stage. As reaction time extends, this correlation becomes negative, which warrants careful consideration in practical use. Meanwhile, the influence of the ozone dosage and NaClO dosage is negligible on the ΔA300 predictivity. Overall, this study advances the understanding of a surrogate indicator framework for prompt and real-time monitoring of ozonation performance.