Date of Award
Fall 2022
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil, Construction, and Environmental Engineering
First Advisor
McNamara, Patrick J.
Second Advisor
Newton, Ryan J.
Third Advisor
Wang, Yin
Abstract
The drinking water distribution system (DWDS) provides a habitat particularly supportive to biofilm-forming bacteria that can attach to pipe walls. These biofilms comprise the majority of bacteria in the DWDS, yet they have been understudied with respect to the pipe material on which they form. Biofilms can accelerate disinfectant decay, promote corrosion of pipes, and harbor opportunistic pathogens (OPs). The choice of pipe material could have a long-lasting effect on the characteristics of the biofilms formed in DWDSs. In this study, the impact of pipe material on biofilms residing in full-scale drinking water pipes was investigated by obtaining biofilm samples from three utilities (Milwaukee, Waukesha, and Oak Creek) and four pipe materials (cast iron, ductile iron, copper, and lead). Quantification of biomass (ddPCR targeting the 16S rRNA gene) and characterization of the microbial communities (Illumina sequencing) provided insights into how pipe materials shape biofilm microbial communities. Within a single utility, cast iron and ductile iron pipes supported higher biomass densities than copper and lead pipes. Pipe material shaped the biofilm communities within a single utility and explained 12% of microbial community dissimilarity within the dataset; pipe sample type, which is inherently a function of pipe material because tubercles only formed in iron pipes, explained 30% of microbial community dissimilarity. Iron-associated genera dominated iron pipes (especially for cast iron), and various heavy-metal resistant bacteria were identified in each pipe material. This is the second study to characterize the microbial community within full-scale lead pipes. Utility was a stronger driver of microbial community dissimilarity (21%) than pipe material, but the interactions between utility and pipe materials should be better understood. The dominance of Mycobacterium specifically in ductile iron pipes of the chloraminated utility suggests that the interaction of this pipe material and disinfect ant may select for the OP-harboring genus. Further, corrosion-accelerating genera in cast iron pipes were not ubiquitous in all utilities, suggesting utilities could control microbial corrosion. Lastly, detection rates of putative OPs were similar by pipe material and utility, with high detections of Burkholderia cepacia and Ralstonia pickettii, which are considered OPs of emerging concern.