Biofilm-Derived Disinfection Byproducts in Water Distribution: Precursor Roles and Toxicity under Various...

Biofilms in drinking water distribution systems (DWDS) serve as important reservoirs of disinfection byproduct (DBP) precursors. This study systematically investigated the formation and toxicity of DBPs from extracellular (EOM) and intracellular organic matter (IOM) of pipe biofilms under five disinfection methods. EOM consistently produced higher DBP yields than IOM, with ozone (O₃)/chlorine (Cl₂) generating the highest levels due to a synergistic oxidation-halogenation effect. Monochloramine (NH₂Cl) disinfection resulted in low DBP additive toxicity for both EOM (493) and IOM (100), and the zebrafish embryo toxicity test also confirmed that NH₂Cl induced the weakest adverse effects. Although disinfection altered the content and proportion of proteins, polysaccharides, and deoxyribonucleic acid (DNA) in biofilms, these changes alone could not fully explain the observed DBP formation patterns. Targeted analysis identified ten major biofilm components, including d-glucosamine, 2-deoxy-d-ribose, and several amino acids. However, their contribution to the formation of the aforementioned DBPs was generally low, indicating that uncharacterized precursors predominated in most scenarios. Despite their limited quantitative contribution, potential reaction pathways for four amino acids with high DBP formation potential were summarized. The contribution of specific biofilm components to DBP formation identified and evaluated in this paper provides important insights for DBP control in DWDS.