Fenton-like Remediation Of DDT Contaminated Soil

In recent years,with the implementation of China's environmental protection policy,a large number of pesticide production enterprises have been shut down and relocated,resulting in a large number of contaminated sites containing persistent organic pollutants.These contaminated sites have the characteristics of high concentration,high toxicity,strong bioaccumulation and high residual.Therefore,it is of great research significance and practical value to explore the soil technology which is efficient,rapid and environmentally safe to repair these residual contaminated sites.In this paper,DDT is a typical representative of organochlorine pollutants.An environmentally friendly Fenton system consisting of zero-valent iron?ZVI?,disodium edetate?EDTA?and air?Air?was established.The removal effect of three different zero-valent iron powders on DDT was systematically studied.The removal effect,repair rate and repair mechanism of DDT pollution were systematically studied.To build a ZEA-like Fenton system,and because the water environment is simple and easy to analyze compared with the soil,EDTA/Air,ZVI/EDTA,ZVI/Air and ZVI/EDTA/Air were first carried out in the water.The four-system control experiment and three zero-valent iron materials for the degradation of DDT were carried out.Based on this,three ZEA systems based on three different zero-valent iron powders were established.Based on the control experiments,the effects of reaction time,zero-valent iron addition,EDTA concentration,initial concentration of DDT,temperature and other factors on the removal of DDT in soil were studied,and the structure and surface morphology of zero-valent iron were analyzed by scanning electron microscopy and XRD.The reaction mechanism and mechanism were discussed.The main conclusions are as follows:?1?During the construction of ZEA-like Fenton system,the experimental results show that the system has a removal effect on DDT.As the reaction time increases,the removal rate increases,but the removal rate gradually decreases.The removal rate of DDT from four systems:ZVI/EDTA/Air?ZVI/Air?ZVI/EDTA?EDTA/Air,and the removal rate of three other zero-valent iron powders to DDT:Amorphous zero-valent iron?Nano zero-valent iron?zero-valent iron.?2?In the study of repairing DDT-contaminated soil by ZEA system bases on zero-valent iron powder,the experimental results show that factors such as zero-valent iron dosage,EDTA concentration and initial concentration of DDT have a crucial impact on the removal of the system.The contaminant content is 187mg/kg,the EDTA concentration is 0.4 mmol/L,the iron powder dosage is 8g/L,the air exposure rate is 1L/min,the solid-liquid ratio is 1:8,and at the room temperature?25°C?,the removal effect is the best,the highest removal rate of DDT reached 58.6%.At the same time,the reaction rate constant K_obsbs also reaches a maximum value of 0.105 h^-1.?3?In the study of the repairing of DDT pollution in soil by ZEA system based on the nano-zero-valent iron powder,when the iron powder is increased,the removal rate increases at the first and then decreases,and the optimum nano-zero-valent iron powder dosage is 8g/L;When the EDTA concentration is increased,the removal rate also increases at the first and then decreases.The best concentration of EDTA is 0.4mmol/L.With the increase of initial concentration of DDT,the removal rate of DDT increases at the first and then decreases.When the initial concentration of DDT is 187mg/L the removal effect is the best,the removal rate reached a maximum of 62.6%,and at the same time,K_obsbs reached 0.121h^-1.?4?In the study of repairing of DDT pollution in soil by ZEA system based on amorphous zero-valent iron powder,when the iron powder is increased,the removal rate increases at the first and then decreases,the reaction rate constant increased first and then decreased,the influence of EDTA concentration and the initial concentration of DDT are similar to that of iron powder.When the dosage of amorphous zero-valent iron powder is 8g/L,the concentration of EDTA is 0.4mmol/L,and the initial concentration of DDT is 187mg/L,the removal rate is the highest.It is 79.1%,while K_obsbs reaches a maximum of 0.192h^-1.