UV/Chlorine Advanced Oxidation Processes: Factors Influencing p-Cresol Transformation Kinetics

Abstract

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.