• Monochloramine Advanced Oxidation for Removal of Trace Organics in Wastewater

      Saez, Eduardo; Ben, Aaron Casey; Arnold, Robert; Farrell, James (The University of Arizona., 2019)
      Monochloramine and free chlorine are both common disinfectants and candidates for Advanced Oxidation Processes (AOP). Results from this study show that free chlorine in the form of HOCl and OCl- has faster degradation kinetics for emerging pollutants. Unfortunately, free chlorine only becomes stable after chlorine demand is satisfied. Monochloramine on the other hand, forms instantaneously upon the addition of chlorine in the presence of ammonia and is a relatively stable compound. Advanced Oxidation Processes using UV 254 light with monochloramine has not been thoroughly investigated. In this study, monochloramine AOP is used to degrade p-cresol to illustrate its oxidative effectiveness. Monochloramine AOP is then compared to chlorine AOP; Chlorine AOP can achieve 90% p-cresol degradation after 15 minutes while monochloramine AOP degraded approximately 65% p-cresol after 15 minutes; both results operated at concentrations of 100 µM oxidant, under UV 254 light with an incident irradiance of 10.38 W/m2 , with an initial p-cresol concentration of 10 µM, and using deionized water buffered with 10 mM phosphate buffer at pH 7. The viability of Monochloramine AOP in wastewater is tested in this study; unfortunately, monochloramine AOP only achieves 10% p-cresol reduction in 15 minutes under UV 254 irradiation for wastewater experiments. Lastly, breakpoint curves are generated while under 15 minutes of UV 254 irradiation to directly compare how the molar ratio of Cl2:NH3 affects AOP degradation of p-cresol.
    • UV/Chlorine Advanced Oxidation Processes: Factors Influencing p-Cresol Transformation Kinetics

      Sáez, Avelino E.; Thakur, Shruti Salil; Arnold, Robert G.; Sierra, Reyes (The University of Arizona., 2018)
      During the last 10 years, endocrine disrupters like nonylphenol (NP) have become a major concern in wastewater and water resources. Existing wastewater treatment plants are not designed to remove and/or degrade these emerging pollutants efficiently. In addition, NP is persistent in the aquatic environment, moderately bioaccumulative, and toxic to aquatic organisms. As a result of NP’s high chemical stability and/or low biodegradability, advanced oxidation processes (AOPs) are being considered for the removal from wastewater and water resources. This research project investigated the kinetics of the degradation of p-cresol, a surrogate used for a common endocrine disrupter, p-nonylphenol by UV/Chlorine AOP. A bench-scale study using a cylindrical glass batch reactor equipped with a low pressure (LP) UV lamp showed that the UV/Chlorine AOP was more efficient than either UV/H2O2 AOP or UV and chlorination alone for the degradation of p-cresol at pH 6 in Milli-Q water. The pseudo first-order rate constant was 5.8 times higher for the UV/Chlorine AOP than for the UV/ H2O2 AOP at a given chemical molar dosage and pH 6. The degradation of p-cresol followed pseudo-first-order reaction kinetics, and the degradation rate constants (kobs) were a function of the p-cresol dose, chlorine dose, solution pH, and the presence of natural organic matter (NOM). Degradation of p-cresol greatly increased with increasing chlorine dose and decreasing solution pH during the UV/Chlorine AOP. Additionally, the presence of NOM in the solution inhibited the degradation of p-cresol. UV photolysis, chlorination, and reactive species (hydroxyl radical (•OH), chlorine radical (•Cl) and chlorine monoxide radical (•OCl)) contributed to the degradation of p-cresol. A MATLAB® mathematical model was designed to stimulate the degradation of p-cresol under various operating parameters. However, the formation and toxicity of the chlorinated by-products should be further assessed.