Effect of pipe materials on chlorine decay, trihalomethanes formation, and bacterial communities in pilot-scale water distribution systems

In this study, the influence of pipe materials on chlorine decay, trihalomethanes formation, as well as on microbial community composition of the biofilms formed on the pipe walls in a model full-scale water distribution system was investigated. The chlorine decay experiment showed that the turbulent flow model fitted the experiment data of chlorine decay well, with stainless steel pipe that had the highest rate constant of chlorine decay, and followed by ductile iron pipe and polyethylene pipe. Meanwhile, the formation of trihalomethanes under the three different pipe materials followed the order as: polyethylene pipe > ductile iron pipe > stainless steel pipe. Microbial community analysis showed that biofilm from polyethylene pipe had much higher diversity than that from the ductile iron pipe and stainless steel pipe. In addition, clear differences in the bacterial community structure among biofilms of different pipe materials were observed. The ductile iron pipe biofilm was mainly composed of Enhydrobacter (33.84%), Propionibacterium (8.08%) and Acinetobacter (5.59%). The polyethylene pipe biofilm contained Sphingomonas (25.25%), Streptococcus (7.64%), Ralstonia (4.83%), Pseudomonas (4.63%), and Escherichia-Shigella (4.71%). The stainless steel pipe biofilm was abundant with Flavobacterium (24.76%), Arcicella (12.03%), and Acidovorax (8.98%). Moreover, the occurrence of opportunistic pathogens was detected, especially in the biofilm of polyethylene pipe, followed by ductile iron pipe and stainless steel pipe. The integrated findings in this study suggest that ductile iron pipe and stainless steel pipe are more suitable as plumbing material than polyethylene pipe in drinking water distribution systems.