Kinetic study on the degradation of organic pollutants in UV/persulfate and in other advanced oxidation processes: Role of radicals and improvement of the degradation rates

Abstract

Kinetic degradation of five typical pollutants including clothianidin (CLO), levofloxacin (LEV), p-nitrosodimethylaniline (RNO), paracetamol (PCM), and basic fuchsin (BF) by UV/persulfate (UV/PS) and other advanced oxidation processes (AOPs) (i.e., UV/H2O2, Fe2+/H2O2, electrochemical process, UV/PS/heat, UV/PS/Fe2+, UV/PS/Fe2O3, and UV/PS/rGO) were studied. The result showed that all pollutants were effectively degraded by UV/PS with different degradation rates. The oxidizing factors contributing to the pollutant degradation in UV/PS were studied, showing that UV is the predominant contributor to CLO degradation, while its contribution is negligible in the degradation of other compounds. •OH and SO4•- were the main radicals contributing to the degradation of all pollutants in UV/PS, except CLO. The second-order rate constant of •OH and SO4•- towards pollutants was determined according to the competition kinetic model, to be in the range of 109-1010 M−1 s−1. The degradation rate of pollutants in different AOPs were varied, because the oxidizing factors and their role in AOP systems directly affect the degradation efficiency of pollutants. In all AOPs, •OH radical played a major role in their degradation. The presence of water matrices has different influences on the degradation rates of pollutants. For example, 10 mM NO2- inhibited the degradation of pollutants to 99.1%, whereas Br-, SO42-, and F- had a lower inhibitory effect on their degradation. HPO42- can improve the degradation rate of BF, but it also significantly inhibited the degradation of PCM. The results also revealed that UV/PS/Fe2+ and UV/PS/rGO can remarkably increase the degradation efficiency of all pollutants, while using α-Fe2O3 and heat were less efficient. In addition, other parameters including COD removal, energy consumption, and toxicity assessment were also investigated to evaluate the potential application of UV/PS in practice.