The impact of chloride and nitrogenous ions on advanced oxidation processes: Radical formation, pollutant removal, transformation products, and toxicity changes
Su-Juan Pang, Nan Huang, Qingyuan Chen, Yeqing Chen, Wenjing Zhou
Abstract
Advanced oxidation processes (AOPs) have emerged as a promising technology for the removal of contaminants in water treatment. AOPs generate highly oxidative radicals, such as •OH and SO 4 • − , and many past studies have demonstrated that inorganic ions (e.g., chloride, nitrate, nitrite, and ammonium) in water can react with these radicals to form reactive chlorine species (RCS) or reactive nitrogen species (RNS). These species are involved in pollutant degradation and can affect the formation of toxic byproducts, leading to potential environmental risks. In this review, we summarize the formation pathways of RCS and RNS and the role of chloride and nitrogenous ions in AOPs and compare the effects of chloride and nitrogenous ions on the degradation rate and mineralization efficiency of pollutants. The effects of these ions are influenced by various factors, including the initial concentration of the ions, structure of the pollutant, type of oxidant, pH, and wavelength of the light. Furthermore, we discuss the formation pathways of chlorination or nitration products in the presence of chloride ions and nitrogenous ions. Most chlorination products are more toxic than their parent pollutants, whereas approximately 50 % of nitration or nitrosation products were more toxic than their parent compounds and 50 % were less toxic