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Chloramines in Water Reuse Scenarios: Impacts on Treatment and New Processes

  • Author(s): Patton, Samuel Douglas
  • Advisor(s): Liu, Haizhou
  • et al.
Abstract

The growth of industry, agriculture and human populations puts additional strain on the supply of safe drinking water around the world. Climate change induced droughts and human activity contaminate existing water sources and worsen the supply. Increasingly, outlooks on water stress indicate that millions more people will be living in areas of intense water stress. In response to these pressures, direct and indirect potable reuse has come to the forefront. But potable reuse requires advanced water treatment systems (AWTS) in the form of membrane filtration and UV-based advanced oxidation processes (UV/AOPs). With AWTS, chloramines are introduced to reduce biofouling in membrane systems but also co-exist in the UV/AOP steps of treatment.

The goal of this dissertation is to study the chemistry of chloramines and their impacts treatment efficiency. First, the photochemistry of monochloramine (NH2Cl) was studied. It was observed that its photolysis formed HO• and chlorine atom (Cl•) which could break down recalcitrant organic contaminants such as 1,4-dioxane (1,4-D). It was also found that upwards of 75% of 1,4-D removal was due to HO• in a UV/NH2Cl system. Further, it was determined that NH2• was ineffective at treating 1,4-D. Second, the impacts of oxidant mixing between chloramines and hydrogen peroxide (H2O2) was studied. It was determined that NH2Cl and dichloramine (NHCl2) both had similar mechanisms of action, forming Cl• and HO•. It was observed that NH2Cl was more efficient for 1,4-D removal. When mixed with H2O2, NH2Cl had negative impacts on 1,4-D removal by preventing H2O2 from absorbing photons and scavenging the radicals generated by H2O2. These results were replicated on the pilot and bench scale. Third, the mechanisms by which chloramines form, the breakpoint process could be exploited for organic contaminant removal. This process was shown to produce HO• and it was demonstrated that peroxynitrous acid was responsible. Lastly, the breakpoint process and chloramine photochemistry were combined in a new process which treated up to 30% of 1,4-D in 100 mJ/cm2 and over 50% at 1000 mJ/cm2. The outcomes of these projects allow engineers to design better AWTS and discovering a novel AOP for future applications.

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