Collaborative Research: Influence of Drinking Water Chemical Composition on Biofilm Properties and Decay of Disinfectant Residual: An Experimental and Modeling Study

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Tap water treated and monitored by the water distribution system has generally thought to be safe. However, several recent failures of water infrastructure that we rely on for this safety have highlighted the need to better understand and monitor the Nation's water quality. Recent research has shown that water quality can deteriorate from the source at the drinking water treatment plant to the taps in homes. A focus of this research is on in-building "premise plumbing", the least understood and monitored part of the water distribution system. Premise plumbing has the highest surface-to-volume ratios in the distribution system, making it susceptible to pipe surface chemical and biological reactions. In addition, water can often sit stagnant in small pipes for days, resulting in loss of residual disinfectant activity and resulting pathogen growth in pipe surface biofilms. This project will determine how to reduce the decay of disinfectant, the formation of toxic disinfectant byproducts, and the growth of pathogens in biofilms that grow on premise plumbing surfaces. This will be achieved by controlled experiments with disinfectants and molecular level characterization of the microbes present in the biofilm. Results will be shared with the drinking water industry, water regulators, and other stakeholders to develop best management practices for ensuring the safety of home drinking water.A systematic study is proposed to understand how, when, and where risk occurs in premise plumbing. The research is based on the following hypotheses: (H1) drinking water chemical constituents control the porous structure of premise plumbing biofilms; (H2) these biofilm properties control the mass exchange of disinfectant between the biofilm and bulk aqueous phases and consequently the residual concentrations of disinfectants; and (H3) laboratory biofilms grown in the presence of drinking water will have diffusion and reaction properties of biofilms occurring in premise plumbing networks supplied from those sources. A collaborative research program will test these hypotheses through a multi-stage research program. First, biomass growth under stagnant conditions with depleted disinfectant concentrations on PEX and PVC, common premise plumbing materials using tap water amended with anti-scaling and/or anti-corrosion chemicals to simulate treated drinking water. H1 will be tested by analyzing 3D porous structure of biofilm matrix based on optical coherence tomography of biofilms grown from these different waters. H2 will be tested by quantifying the interaction of disinfectant with biofilm via coupon- and pipe-section scale reactive transport experiments and modeling. H3 will be tested by quantifying free chlorine decay and formation of disinfectant byproducts in building scale experiments at the University of Illinois and Washington State University under different stagnation times. Successful completion of this research will transform our knowledge of biofilm growth and disinfectant chemistry in premise plumbing and help regulators and other stakeholders better manage water supply systems to protect human health.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.