Joint Effects And Mechanism Research Of Common Coexisting Substance In Water On Degradation Of Organic Compounds By Co²⁺/PMS Process

Advanced oxidation processes based on highly reactive radicals such as hydroxyl radicals and sulfate radicals(SO4·-)are widely used in water treatment processes.SO4·-generated by bivalent cobalt-activated peroxymonosulfate(Co2+/PMS)are highly effective in degrading a variety of emerging organic pollutants.Due to the widespread presence of chloride,ammonia and dissolved organic contaminants in water,the Co2+/PMS process was inevitably interfered by these substances in water treatment applications,which affects the removal of organic pollutants and leads to the formation of other reactive species and by-products.In recent years,the influence of a single background constituent on SO4·-process has received extensive attention.However,a variety of background constituents commonly coexist in real water and their joint effects and mechanism on the degradation of organic pollutants in the Co2+/PMS process are still unclear,limiting the application of Co2+/PMS system in water treatment.This study systematically investigated the joint effects and mechanisms of three common coexisting background constituents(e.g.,chloride,ammonia and dissolved organic matter)on the removal of organic pollutants in the Co2+/PMS process.The results showed that the removal of bisphenol A and sulfamethoxazole in the reaction for 1 hour was 100%when 1 mmol/L chloride was added to the Co2+/PMS process,and their degradation rate decreased with the increase of chloride concentration.In the Co2+/PMS process in the presence of chloride of 1 mmol/L and ammonia of 1 mmol/L,the removal of bisphenol A and sulfamethoxazole decreased to 44%and 48%,respectively,indicating that the copresence of ammonia and chloride further inhibited the removal of organic pollutants.However,after the addition of dissolved organic matter of 2 mg/L,the removal of bisphenol A and sulfamethoxazole increased to 60%and 78%.respectively,indicating that the copresence of dissolved organic matter with chloride and ammonia effectively alleviated the synergistic inhibition of ammonia and chloride on the removal of organic pollutants.It was found that SO4·-rapidly reacted with chloride to generate oxidatively reactive chlorine species(e.g.,Cl·,ClO·,Cl2·-)and HOCl.HOCl is capable of oxidizing organic pollutants and quenching free radicals.The concentrations of radicals decreased with the increase of chloride concentration,resulting in the decrease of organic pollutant removal.Dichloramine which has low oxidation reactivity was formed from the reaction of ammonia and HOCl in the Co2+/PMS process in the copresence of chloride and ammonia under the reaction condition to this study.Dichloramine further consumed radicals and inhibited the removal of organic pollutants.When dissolved organic matter is added to Co2+/PMS process with the copresence of chloride and ammonia,part of HOCl was consumed by dissolved organic matter and results in the decrease of dichloramine formation,thus alleviating the synergistic inhibition of ammonia and chloride.In addition,dissolved organic matter is the precursor of disinfection by-products,and HOCl is an important intermediate and oxidant for the generation of chlorate and disinfection by-products.The existence of dissolved organic matter promotes the formation of disinfection by-products,while the reaction of ammonia with HOCl could effectively inhibit the formation of chlorate and disinfection by-products.This study revealed the influences of common coexisting constituents in water on the removal of organic pollutants,reactive species constribution and by-product formation in the Co2+/PMS process.The results showed that the effects of coexisting constituents in the real water on the degradation of pollutants in the Co2+/PMS process are complex.When multiple background constituents coexist,their influences on the Co2+/PMS process cannot be calculated by simple superposition.Therefore,when the Co2+/PMS advanced oxidation process is applied in real water treatment,the joint effects of various background substances in the real water need full consideration.