The various effects of hydrogen phosphate and bicarbonate in the degradation of some pollutants in the UV/chlorine and the UV/H2O2 processes

Abstract

In this study, the degradation kinetics of three target pollutants (i.e., levofloxacin (LEV), P-nitrosodimethylaniline (RNO), and basic fuchsin (BF) in four UV-based Advanced Oxidation Processes (UV/AOPs) (i.e., UV/NaOCl/HPO₄²⁻, UV/NaOCl/HCO₃⁻, UV/H₂O₂/HPO₄²⁻, and UV/H₂O₂/HCO₃⁻) were comprehensively investigated. The results showed that LEV and RNO were resistant to UV irradiation, chlorination, and H₂O₂ when applied separately, but significantly degraded in UV/AOPs. The chlorination process and alkaline conditions were beneficial to the degradation of BF. In UV/AOPs, the degradation rates of the pollutants were enhanced remarkably with different rate constants which were dependent on the dosage of oxidants, and the presence of HPO₄²⁻ and HCO₃⁻. This enhancement is due to the generation of reactive species (i.e., •OH, RCS, and secondary reactive radicals like PO₄^2•-, and CO₃^•-). The study also investigated the role and contribution of the reactive species to the degradation of the pollutants in UV/AOPs. The study demonstrated the difference in the degradation kinetics of the pollutants in UV/H₂O₂/(HPO₄²⁻ or HCO₃⁻) and UV/NaOCl/(HPO₄²⁻ or HCO₃⁻) in which the contribution of each oxidizing factor was determined. Acidic conditions were beneficial to the degradation rate of the pollutants in all UV/AOPs, except BF in UV/NaOCl. Seawater and river water were demonstrated to significantly promote the degradation rate of pollutants in UV/NaOCl/(HPO₄²⁻ or HCO₃⁻) but depressed it in UV/H₂O₂/(HPO₄²⁻ or HCO₃⁻). In addition, a typical PPCP (pharmaceutical and personal care product) (here LEV) was selected for further LC-MS analysis to determine its degradation pathway. The results provide a novel alternative strategy in the use of HPO₄²⁻ and HCO₃⁻ in UV/NaOCl and UV/H₂O₂ to increase the removal efficiency of organic pollutants.