Impact of seasonal variations and water quality parameters on the formation of trihalomethanes and haloacetic acids in drinking water treatment processes

Abstract

In this study, the combined effects of seasonal variations and water treatment processes on the formation of disinfection by-products (DBPs), focusing on trihalomethanes (THMs) and haloacetic acids (HAAs) within a full-scale conventional drinking water treatment plant, were investigated. The seasonal analysis revealed that autumn exhibited the highest levels of disinfection by-product formation potential (DBPFP), with trihalomethane formation potential (THMFP) and halo acetic acid formation potential (HAAFP) reaching 255 μg/L and 241 μg/L, respectively, likely due to increased organic matter from leaf fall and runoff. In contrast, winter exhibited the lowest concentrations, with THMFP at 150 μg/L and HAAFP at 56 μg/L. It is attributed to lower temperatures that limit organic matter reactivity. Correlations between 24 water quality parameters and DBPFP types were also examined, identifying critical parameters with the highest correlations. These parameters, including UV₂₅₄ absorbance and total organic carbon, were used to develop regression models sensitive to seasonal changes and treatment stages. Among the treatment units, the coagulation and aeration stages achieved notable reductions in THM precursors, whereas HAA precursors were less effectively removed, persisting into secondary treatment stages. Chloroform was the predominant THM species, with a peak concentration of 100 μg/L in autumn, decreasing to 76 μg/L in summer, possibly due to increased volatilization in warmer months. For HAAs, dichloroacetic acid displayed the highest seasonal variability, peaking in autumn at 28 μg/L. These findings highlight the need for seasonally adaptive treatment strategies, particularly during high-risk autumn periods when DBPFP levels are elevated. This study provides actionable insights into optimizing treatment protocols to improve DBP control, emphasizing seasonal adjustments’ critical role in ensuring compliance with water quality standards.