Stabilization and destabilization of microbial ecology in drinking water distribution systems

Lihua Chen (PhD Candidate),  Gertjan Medema (promotor Delft University of Technology), Walter van der Meer (promotor), Gang Liu (promotor Research Center for Eco-Environmental Sciences (RCEES), Chinese Academy of Sciences (CAS)

Duration: 2017-2021

Funding:

Introduction
The supply of safe drinking water is important to public health. The main challenge of drinking water utilities is to deliver drinking water to customers that is microbiologically safe and biologically stable. The treated water enters drinking water distribution systems (DWDSs) together with particles, cells, and nutrients, which subsequently contribute to biofilm formation and loose deposits accumulation during water distribution. The origin and development of biofilm and loose deposits in DWDSs is, meanwhile, the accumulation process of inorganic and organic contaminants over a period of decades. In return, the release of such material accumulated in distribution systems to bulk water can result in the deterioration of tap water quality, which has been commonly observed as higher turbidity and particle loads, and/or higher cell numbers, and/or greater presence of specific bacteria in tap water compared to treated water.

Keywords
microbial ecology, drinking water distribution systems, biosafety of drinking water

Scientific and technological challenges
Driven by the development of water purification technologies and the tighten of drinking water regulations, efforts have been made to improve the treated water quality, including: the use of alternative water sources, upgrading water purification technology at water treatment plant, and shifting of disinfection strategies. These operations constitute the causes of irregular changes in supply water quality, which might induce transition effects that disturb the stabilized microbial ecology in DWDSs. The destabilization of DWDSs microbial ecology may lead to serious water quality risks, such as the water discoloration observed in large area of Beijing, China, when the supply water quality was improved in 2008; and the recent Flint drinking water crisis in Michigan, U.S., where elevated blood lead was detected in children after water source change. Besides, reversible shifts in microbial communities were observed after the disinfectant strategies switching from chlorination to chloramination, which is expected to moderate the production of by-products. In some emergency cases, high concentration of chlorine will be used temporarily for guaranteeing drinking water biosafety, which might cause the destabilization of the original niche of microbial ecology in DWDSs, being worthy of attention. It is critical to understand the real profiles of microbial ecology in DWDSs, and bring the theoretical measurements forward to practical management

Research goals
In this study, the fate of microbial communities, opportunistic pathogens and antibiotic resistance genes (ARGs) in unchlorinated and chlorinated DWDSs will be investigated to systematically understand and evaluate the biosafety of drinking water under regular operations. The transition effects under irregular changes caused by switching supply water quality and disinfection strategies will be observed in both field and pilot scale, bridging the theory to practice.