Comparative investigation of acetaminophen degradation in aqueous solution by UV/Chlorine and UV/HO processes: Kinetics and toxicity assessment, process feasibility and products identification.

The degradation of acetaminophen (ACM) was comparatively studied by UV/chlorine and UV/HO systems. An apparent reduction in the removal rate was observed above the optimum pH levels of 7.0 and 3.0 in UV/chlorine and UV/HO processes, respectively. The relative contribution of each oxidizing agent in ACM removal using the two advanced oxidation processes (AOPs) was evaluated. Even though hydroxyl radicals, with the contribution percentage of 90.1%, were determined as the primary oxidizing species in ACM removal using the UV/HO process, reactive chlorine species (RCS), with 43.8% of contribution percentage, were also found to play a pivotal role in ACM removal using the UV/chlorine process. For instance, dichlorine radical (Cl) showed an acceptable contribution percentage of 32.2% in the degradation of ACM by the UV/chlorine process. The rate of ACM degradation significantly rose to 99.9% and 75.6%, as higher amounts of oxidants were used in the UV/chlorine and UV/HO processes, respectively, within 25 min. The introduction of HCO ions and humic acid remarkably decreased the rate of ACM degradation in both techniques used in this study. The presence of NO and Cl ions did not considerably affect the removal rate in the UV/chlorine process. The acute toxicity analysis revealed that a more pronounced reduction in the ACM solution toxicity could be achieved by the UV/HO process compared to the UV/chlorine process, which should be ascribed to the formation of chlorinated products in the UV/chlorine treatment. Eventually, plausible oxidation pathways were proposed for each process.