Degradation Of Isothiazolinone In Circulating Cooling Water By Ultraviolet Advanced Oxidation Technology

In recent years,isothiazolinone(CMIT-MIT)fungicides have been widely used in circulating cooling water systems to inhibit the growth and reproduction of microorganisms.The residual CMIT-MIT in circulating cooling water is discharged into the environment,which poses a great threat to the natural environment and human health.Therefore,it is of great significance to find an efficient method to remove CMIT-MIT from circulating cooling wastewater.At present,UV-based advanced oxidation process has become a feasible technology for the oxidation degradation of CMIT-MIT due to its advantages of high efficiency and environmental protection.In this work,UV/hydrogen peroxide(UV/H2O2)and UV/persulfate(UV/PS)processes were used to remove CMIT-MIT from circulating cooling wastewater.The degradation performance,influencing factors,degradation mechanism,product toxicity and economy of CMIT-MIT were studied.The main research contents were as follows:The degradation kinetics of CMIT-MIT was studied by UV/PS process.The degradation process conformed to the pseudo-first-order kinetic model.The degradation rates of 30 mg/L CMIT-MIT were 72%and 91%after 20 min treatment in UV and UV/PS(60 mg/L)systems,respectively.When the dosage of PS was 60 mg/L,the TOC removal rate of MIT-MIT solution reached 34.7%after 40 min ultraviolet irradiation.The results of quenching experiment showed that the free radicals that degraded in UV/PS system were SO4·-and ·OH,and the contribution rates of their degradation were 32.12%and 0.93%,respectively.In the UV/PS system,the removal rate of CMIT-MIT and the apparent rate constant increased with the increase of PS dose.Acidic conditions were more conducive to the degradation of CMIT-MIT.The presence of chloride ions,sulfate ions and nitrate ions in circulating cooling water had no obvious effect on the removal of CMIT-MIT by UV/PS,while the presence of carbonate ions significantly inhibited the degradation rate of CMIT-MIT.The results of ion chromatography and nuclear magnetic resonance hydrocarbon spectroscopy showed that the inorganic ions produced after degradation were chloride ions and sulfate ions,and the organic products were methylamine hydrochloride.The results of cytotoxicity test showed that the toxicity of the solution after UV/PS treatment was significantly reduced.In conclusion,UV/PS process is an efficient and safe process,which has a good development prospect in the degradation of CMIT-MIT.UV/H2O2 system was used to study the degradation kinetics of CMIT-MIT,and the degradation process was consistent with the pseudo-first-order kinetic model.The degradation rate of 30 mg/L CMIT-MIT was 90%after 20 min treatment in UV/H2O2(0.3 mM)system.When the dosage of H2O2 was 0.3 mM,after 40 min ultraviolet irradiation,the DOC removal rate of CMIT-MIT solution reached 35%.The quenching experiment results showed that hydroxyl radical is the degradation free radical in UV/H2O2 system,and its contribution rate to the degradation of CMIT-MIT is 46%.In the UV/H2O2 system,the removal rate of CMIT-MIT increases with the increase of H2O2,and the rate constant changes linearly with the concentration of H2O2:kobs=0.234×[H2O2]+0.062;The removal rate of CMIT-MIT decreased with the increase of the concentration of CMIT-MIT,and its removal rate constant decreased with the increase of the initial concentration of CMIT-MIT.The two are inversely proportional function(y=3.8/x).Different pH(4-10)had no significant effect on the degradation of CMITMIT.The presence of chloride ion,sulfate ion,nitrate ion and ammonium ion in circulating cooling water has no obvious influence on the removal effect of CMIT-MIT.The presence of carbonate ions can significantly inhibit the degradation rate of CMIT-MIT.The results of ion chromatography and nuclear magnetic resonance hydrocarbon spectrum showed that the main organic compounds produced after degradation were methylamine hydrochloride and formic acid,and inorganic ions were chloride and sulfate ions.The results of dissolved organic carbon reduction test showed that UV/H2O2 treatment process could reduce the toxicity of CMIT-MIT and improve the biochemical properties of CMIT-MIT,which provided an important basis for the degradation of fungicide pollutants by advanced oxidation technology combined with biotechnology.According to the data of power efficiency evaluation index(EEO),the EEO decreased with the increase of oxidant concentration.When the PS dosage was 60 mg/L(0.312 mM),the EEO value was 218.1 kWh·m-3,which was 40%lower than that of UV degradation alone.When the dosage of H2O2 was 0.3 mM,the EEO value was 198.6 kWh·m-3,which was 46%lower than that of UV degradation alone.Compared with UV/PS process,UV/H2O2 process had relatively low energy consumption in the degradation of CMIT-MIT,which has greater economic advantages in practical applications.