A comprehensive investigation of bacterial communities in sediment and bulk water in a chlorinated drinking water distribution system

Abstract

The accumulation of pipeline sediments within drinking water distribution systems (DWDS) has garnered widespread attention because of their roles as microbial reservoirs. However, previous investigations predominantly concentrated on microbial occurrence in unchlorinated DWDS sediments but largely overlooked chlorinated systems and failed to characterize the spatial distribution patterns of potential pathogens along the DWDS. This study systematically examined bacterial communities in both the sediment and bulk water phases across a chlorinated DWDS through the seasonal collection of 96 samples. Physicochemical water quality parameters, such as turbidity and residual chlorine, exhibited relative stability throughout the network. As anticipated, sediment samples showed substantial particulate accumulation (summer: 1.13 ± 0.61 Log₁₀ NTU; winter: 1.07 ± 0.45 Log₁₀ NTU). Microbial biomass proved significantly elevated in sediments (summer: 4.78 ± 0.65 Log₁₀ gene copies/mL; winter: 4.99 ± 0.42 Log₁₀ gene copies/mL) than water samples (summer: 3.98 ± 0.50 Log₁₀ gene copies/mL; winter: 4.06 ± 0.57 Log₁₀ gene copies/mL; p < 0.05), with similar patterns emerging for the potentially pathogenic fungi, Mycobacterium spp., and Legionella spp. Notably, no longitudinal accumulation gradient of microbial biomass was detected along the pipeline network in either the sediment or water samples. Interestingly, the winter sediment samples displayed peak microbial biomass levels. Seasonal variation exerted a substantial effect on microbial community composition, with turbidity and residual chlorine demonstrating stronger correlations with biomass in summer than in winter. These findings underscore the necessity for regular sediment removal from chlorinated DWDS as a critical preventive measure against waterborne pathogen proliferation and disease transmission.