Exploring Contaminant Fate within Plastic Water Infrastructure: The Nexus of Environmental Engineering and Material Science Frontiers

Plastic pipes are increasingly being used in potable water systems as corrosion resistant low cost materials. Despite the growth and installation of plastic pipes, gaskets, coatings, and liners in drinking water systems there are many knowledge-gaps with these materials. Lack of knowledge regarding contaminant fate within plastic water infrastructure systems present a possible emerging public health problem. For example, polyethylene plastic pipes are being installed in 75% of new building construction, and buried water service. For this dissertation research, water chemistry, environmental engineering, polymer and surface science and principles were applied to address several knowledge-gaps regarding plastic pipes. The first chapter of this dissertation focusses on reinforced plastic composites, materials sometimes used for water piping. Chapter 1 describes the influence of carbon nanofiber reinforcements on polyester composite water uptake and organic contaminant release. The experiments revealed that oxidized carbon nanofibers (CNFs) in the polyester composites significantly influenced water-composite interactions and organic contaminant leaching. Chapter 2 of this dissertation describes an investigation of the linkage between fixture water use and drinking water quality in a new green building. It was found that at the basement fixture, where the least amount of water use events occurred, greater organic carbon, bacteria, and heavy metal concentrations were detected. Different fixture use patterns resulted in disparate drinking water quality within the same residential building. Within Chapter 3, results of experiments conducted to determine the factors that influence Pb accumulation on the surface of low density polyethylene (LDPE) were discussed. Pb deposition onto LDPE as a function of time was modeled using the pseudo-1st-order equation, and an ozone based accelerated aging method for LDPE oxidation was developed. Greater Pb precipitation rates were found for aged LDPE compared to new LDPE at both tested pH values. However, at pH 11 less Pb surface loading on aged LDPE was detected compared to Pb loadings at pH 7.8. The final chapter of this dissertation explains an investigation into the abundance of metal deposition onto 1-year old crosslinked polyethylene (PEX) plumbing system. Results showed that total metal loadings differed between hot and cold water line pipe segments and water temperature influenced surface scales. A bench scale experiment revealed that the polyethylene surface served as a nucleation site for Fe crystals. This dissertation work provides a foundation for continued exploration of contaminant fate in water infrastructure