Master of Science in Engineering (MSE)
Civil and Environmental Engineering and Construction
First Committee Member
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This work evaluated the impacts of blending several different high grade recycled waters with conventional source waters for direct potable reuse (DPR) applications. Bench-scale laboratory tests were conducted for recycled water-source water blends from four participating facilities that have either considered adopting DPR or have already implemented DPR as a feasible approach to overcome water scarcity. The chemical and biological stability of the finished waters was investigated after pipe rig incubation to simulate the quality of blended waters that had aged in a potable water distribution system. The effects of blend ratio, reclaimed water treatment, and source water quality were evaluated to understand disinfection by-product (DBP) yields, generation of metal corrosion products, and changes in bacterial densities in the effluents collected from the pipe rigs. Blending higher proportions of reverse osmosis (RO)-treated water reduced Total Organic Carbon (TOC) concentrations, which resulted in lower effluent Trihalomethane (THM) concentrations. Increased THM formation occurred in the ozone-biofiltered blends from Utility 2, resulting in concentrations exceeding the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Limit (MCL) of 0.08 mg/L. Elevated concentrations of THMs were associated with both the high concentration of organic precursors present, and the use of chlorine during secondary disinfection. Total lead concentrations exceeding the 15 g/L EPA action level were generally measured in samples with more negative Langelier Saturation Index (LSI) values. Regression analysis showed that the relationship between pipe rig effluent lead and LSI of the finished waters was significant at a 99% confidence level (p<0.01). For all utilities, pipe rig effluent for RO-treated blends typically contained higher effluent lead and copper concentrations compared to ozone-biofiltered blends; however effluent copper concentrations did not exceed the 1.3 mg/L action level. Corrosion potential of the RO-treated surface water blend from Utility 4 was presumably controlled when zinc orthophosphate was added as a corrosion inhibitor. Biological Activity Reaction Tests (BART™) results indicated that the sulfate reducing bacteria and the slime forming bacteria were the most predominant groups of microorganisms that appeared at the beginning of the reaction period (1-2 days). The results from this study can help advise drinking water facilities in selecting appropriate source waters and optimal blend ratios to augment water portfolios, while conforming to Safe Drinking Water Act regulations that safeguard public health.
Civil Engineering | Environmental Engineering
University of Nevada, Las Vegas
Grimaldi, Assumption, "Evaluating the Chemical and Biological Stability of Finished Waters Blended for Direct Potable Reuse in a Simulated Distribution System" (2017). UNLV Theses, Dissertations, Professional Papers, and Capstones. 3136.
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