Biofilm bacterial community transition under water supply quality changes in drinking water distribution systems

In this work, the bacterial community transition characteristics of pipe wall biofilms and the iron release behaviors under water supply quality changes were investigated through pilot-scale experiments. Test pipelines that were harvested from actual drinking water distribution systems (DWDS) in a northern city in China were transported to the water source site of China's South-to-North Water Diversion Project for supply water switch experiments. Some main water quality parameters closely related to iron release in DWDS, such as SO4 2-, Cl -, HCO3 -, pH and Ca2+ hardness, were adjusted to observe their effects on the biofilm bacterial community. Microbial samples collected from pipe biofilms were analyzed using Illumina MiSeq sequencing of the 16S rRNA gene. The results showed that the bacterial community composition and diversity of pipe biofilms with different water supply histories were significantly different but tended to be the same after one month of switching to new water. The level of bacterial richness and diversity increased after increasing the SO4 2-, Cl-and HCO3 -of the supply water but decreased after increasing the pH of the water. The relative abundance of corrosive bacteria did not change greatly with the increase of these water quality parameters. The 16S predicted gene functions demonstrated that the relative abundances of metabolic enzymes involved in iron and sulfur redox were rather low (< 0.1%) and had no obvious difference in the different experimental phases. It was shown that chemical interactions other than microbial processes played the main role in iron release during the water supply transition period. Opportunistic pathogencontaining genera such as Burkholderia, Ralstonia, Mycobacterium, Acinetobacter, and Pseudomonas were detected; this detection implied that more effective disinfection measures should be considered to ensure the microbial safety of drinking water.