Degradation Mechanism Of Chlorinated Organic Pollutants In Soil By Persulfate Activation Technologies

DDT?1,1,1-trichloro-2,2-bis?p-chlorophenyl? ethane? is a commonly used organochlorine pesticide, which is of environmentally persistent, long-time residual,bioaccumulative, semi-volatile, long-distance mobility and high toxicity. It has been banned now, but with the development of China's urbanization, a large number of organochlorine pesticide plants were shut down and relocated. There are a lot of organochlorine pesticide residues existed on the original site and have a lot of potential hazards to the surrounding population and environment. Therefore, developing an efficient method for organochlorine pesticide is imperative.Degradation of DDT in aqueous solution by nanoscale Fe⁰ activation of persulfate was investigated, of temperature, DDT concentration, persulfate and nanoscale Fe⁰ ratio,reagents dosing sequence and gas atmosphere. The formation of intermediates were analyzed by GC-MS, and we suggested a possible degradation pathway of DDT.Micro/nanoscale Fe⁰ was used to activate persulfate to degradate DDTs in site contaminated soil. Using other activation methods to degradate organic pollutants in Nantong and Wuxi contaminated soil. The main contents and conclusions are as follows:1 Degradation of DDT by nanoscale Fe⁰ activation of persulfate was studied. Mass balance experiments showed that nanoparticle Fe⁰ only made reductive dechlorination,73%-100% of DDT reduced section conversed to DDD and DDE. The system of persulfate activated by nanoparticle Fe⁰ could complete mineralize DDT with DDD and DDE generated only 20%-28%. Nanoparticle Fe⁰ activation of persulfate could also quickly degraded DDD and DDE and their degradation from hard to easy order of : DDE> DDT>DDD. When nano-Fe⁰/PS molar ratio of 1:1, DDT degradation rate was the highest. When nanoparticle Fe⁰ concentrations was higher, reduction was the dominant role in the system,when persulfate concentration was higher, oxidation dominant the system. The degradation rate of DDT increased with increasing temperature, but reduced with increasing concentration of DDT. Reagents dosing order also had a significant impact on DDT degradation, PS added first would had a higher degradation rate of DDT. The degradation rate of DDT increased when in the air and lower when exposed to O2. Using the GC-MS to determine the molecular of DDT degradation intermediates, the rusult suggested a possible degradation pathway of DDT which had an oxidation and reduction process.2 We used the PS activated by micro/nanoparticle Fe⁰ to degrade DDTs in soil, DDTs degradation rate increased slightly with increasing persulfate concentration. DDTs degradation rate increased significantly with micro/nanoparticle Fe⁰ molar ratio increased and DDTs degradation rate increased rapidly when the micro/nanoparticle Fe⁰/persulfate molar ratio of 4:1. Persulfate activated by micro/nanoparticle Fe⁰ could rapid degradate DDTs in soil, of 80% 24 h, but the soil accumulated a lot of DDD and DDE, DDD would continue to be degradated. Experiment by adding a surfactant to improve the solubilization of DDTs showed that the degradation rate of DDTs in Brij35 eluent was the highest when micro/nanoparticle Fe⁰/persulfate molar ratio of 4:1 and p,p'-DDT, o,p'-DDT and p,p'-DDE degradation rate could reach 100%, 100% and 86%.3 Base activation of persulfate had good removal efficiency of organic pollutants of a pesticide factory in Nantong site. The degradatation rate of pollutants were above 90%with 7.0 M sodium hydroxide and 50 g/L persulfate. Alkali alone could degradate pollutants to some degree, too. Ferrous ion activation of persulfate with persulfate concentration of 300 g/L and persulfate/Fe²⁺ molar ratio of 1:1, the degradation efficiency of pollutants were the best and the three kinds of pollutants degradation rate were 100%,50% and 40%. The degradation of organic matter in soil was less effective by Fenton reagent with the concentration of hydrogen peroxide was 0.8 M and H2O2/Fe²⁺ molar ratio of 1:1 and the removal of the three kinds of pollutants were 60%, 10% and 2%. Persulfate activated by alkali was more suitable for pesticides containing soil. Persulfate activated by Fe²⁺ also had some degradation effect and Fenton reagent was the worst.4 Fe²⁺ activation of persulfate degradated PAHs of a contaminated soil in a steel plant in Wuxi, while persulfate concentration of 150 g/L and persulfate/ Fe²⁺molar ratio of 5:1 or10:1, the removal rate of contaminants were higher, degradation of pollutants were52%-97% or 45%-100%. Add a complexing agent of ethylene diamine tetraacetic acid and citric acid or surfactants of Brij35?Hydroxypropyl-?-Cyclodextrin?, the removal of contaminants did not increase, but with a certain decrease. The degradation of organic matter in soil by Fenton reagent was less effective. When the H2O2 concentration of 100 m M and H2O2/ Fe²⁺molar ratio of 2:1, the degradation rate of pollutants could reach41%-52%. Increasing the concentration of H2O2 to 200 m M and 500 m M, degradation rate of contaminants were reduced to 26%-42% and 41%-50%.