Haloacetic acid formation enhanced by the release of Fe deposits in full-scale drinking water distribution systems

The formation of disinfection byproducts (DBPs) has been well studied in relatively static and controlled reactor conditions during chlorination, yet the possible formation of DBPs in actual drinking water distribution system (DWDS) is poorly explored. In this study, we monitored the variations of DBPs, fulvic-like/humic-like components (C1) and protein-like (C2) components from finished water at five water treatment plants to corresponding tap water in looped DWDS utilizing iron pipes. Additionally, we measured the Fe concentrations in tap water and characterized Fe composition in both bulk water (Fe particles) and deposits on pipe walls (Fe deposits). It was observed that trihalomethane concentrations in tap water were 1 % - 34 % higher than those in finished water, while the variations of haloacetic acid (HAA) concentration were closely associated with C2 and Fe concentrations. Solid characterization revealed that the Fe deposits primarily consisted of carbon (99 %) and iron (1 %), whereas Fe particles in bulk water contained approximately 89 % carbon and 8 % iron. The variations in HAA concentrations could be attributed to the irregular release of C2 components, which are rich in carboxyl groups and can form ligands with FeOOH in Fe deposits. These findings of this study can contribute to a better understanding of the deposit impacts on DBP variations, as well as the behaviors of organic matter in looped DWDS. • THM concentrations increased while HAA concentrations fluctuated in the DWDS of different months. • Protein-like substance (C2) was related to the HAA concentration variations in different DWDS. • C2 can be combined with FeOOH in deposits by bridging between carboxyl and hydroxyl groups. • C2 can be released with the releasing of Fe deposits result in HAA formation.