Use of Halide Radicals in Water Treatment

Abstract

The increasing population and a reduction in freshwater resources has made the reuse of water imperative [1-3]. Advanced oxidation processes (AOPs) enable the safe reuse of wastewater through the removal of persistent pollutants. The highly reactive nature of reactive species, like hydroxyl radicals is limited by their reactivity with ubiquitous compounds like dissolved organic matter (DOM)[4, 5]. The use of halide radicals can help improve the efficiency of UV-based AOPs. This thesis investigates the mechanism of halide radicals in three different systems: a) the use of iodine radicals in functionalized fullerenes b) the use of UV/chlorine as an advanced oxidation process and their potential for removal of pharmaceutical pollutants in DOM-rich waters c) the use of pulsed UV irradiation for the UV/Cl AOP. The aim of this thesis is to analyze these processes, their efficiency, and their mechanism for potential applications in point of use water treatment systems. In the first part of the study, the functionalized fullerenes were analyzed for their AOP mechanism under UV395 irradiation. Several photochemical pathways were explored to determine the extent and mechanisms of interference of I- in the photosensitization of singlet oxygen by cationic fulleropyrrolidinium ions and rose bengal. Triplet excited state sensitizer lifetimes were measured via laser flash photolysis to probe the role of I- in triplet sensitizer quenching. The results were compared with past inferences for the fullerene photosensitizer systems. The presence of iodine results in an overestimation of photosensitization, due to the reactivity of iodine with probes and indicators used in photosensitivity experiments. In the second part of the study, the potential use of the UV/chlorine process was analyzed for the removal of three pharmaceutical pollutants: acetaminophen, carbamazepine and sulfamethoxazole. In particular, the ability to use UV305 with hypochlorite instead of the traditional UV254 with hypochlorous acid was evaluated. The ability of the UV/Cl AOP at pH 8 under UV305 irradiation to generate ozone- a strong, selective oxidant- as the dominant reactive species is useful especially in DOM-rich waters. The results were assessed for different system conditions. The third part of the research investigated the potential use of intermittent irradiation in the UV/Cl system and its impact on the efficiency of the AOP. The pulsed UV/Cl AOP was studied for different frequencies and duty cycles and the results were studied for optimization.