Formation of chlorinated disinfection by-products and fate of their precursors in individual processes of a conventional water treatment plant assessed using high-resolution mass spectrometry†

Abstract

Dissolved organic matter (DOM) causes operational problems in water treatment plants (WTPs), most notably from precursors of disinfection by-products (DBPs) when reacting with disinfectants. Several WTPs have adopted chlorination not only for disinfection but also for controlling excessive algae in the raw water, which could result in additional DBPs. This study investigated the formation of chlorinated DBPs and their precursors during conventional water treatment processes. Raw water (RW), clarified water (CW), sand filtered water (FW), and finished water were collected from a WTP in Thailand. DOM in the samples was analyzed using Orbitrap mass spectrometry. In parallel, another set of samples (RW, CW, and FW) were chlorinated and subjected to the same analyses. Comparing both sets of samples, the DOM components were assigned to DBPs and precursors. Chlorination of the various samples from the WTP resulted in vastly different DBPs, with only 19 DBPs being common to all samples out of the 740 DBPs observed in this study. Furthermore, 134 of the DBPs could be traced to their precursors that were consistently present throughout the processes and even in the finished water. A clarifying tank was the most effective way to remove the precursors, removing or reducing in intensity 75.0% of the CHO precursors and 78.9% of the CHON precursors. Sand filtration had minimal effects on the precursors. Some DBP precursors remained in the finished water which could potentially cause the formation of DBPs in the water distribution system.