Effectiveness Comparison Of Different Solvents In Organochlorine Pesticide (OCP)-Contaminated Soil Flushing And Optimization Of Flushing Parameters

With China's industrialization and urbanization, and the implementation process of "Stockholm International Convention," a great number of OCP manufacturing factories have been closed or moved off the relocation in recent years, and these sites pose a serious threat to human health and environmental safety. Therefore, it is urgent to remediate these sites. Screening of flushing solvents and optimazition of flushing parameters were investigated in two organochlorine pesticide (HCHs and DDTs, chlordane and mirex)-contaminated-site soils. The results showed as follows:(1) A flushing experiment of sixteen kinds of solvents (dichloromethane, acetone, ethyl acetate, petroleum ether, hexane, methanol, ethanol, propanol, isopropanol, rhamnolipid, hydroxypropyl-β-cyclodextrin (HPCD), sodium dodecyl sulfate, SDS, SDBS, Tween 80 and Triton 100) was conducted to select an optimum solvent for HCHs and DDTs, and chlordane and mirex-polluted soil flushing. Results indicated that in HCHs and DDTs contaminated soil, ethyl acetate is the best eluent with removal rates of 87.6% and 86.9% for HCHs and DDTs, respectively. The removal rates of the other organic solvents ranged between 61.6% and 87.0% for HCHs and DDTs, but the removal rates of surfactants were less than 4% for HCHs and DDTs. Organic solvents were better than surfactants in HCHs and DDTs polluted soil flushing. This phenomenon also occurred in chlordane and mirex-polluted soil. For mirex, the removal rates of organic solvents were about 80% with the exception of propanol (63.5%). For chlordane, the removal rates of organic solvents were more than 70% with the exceptions of petroleum ether (59.6%), hexane (49.3%) and propanol (42.0%). The removal rates of chlordane for Tween 80, cyclodextrin, Triton X-100 and rhamnolipid were 54%,20%,12.8% and 12.2%, respectively, and the other surfactants'were lower than 1%. And the removal rate of mirex was 29.6% for Tween80, 12.4% for Triton X-100,5.7% for rhamnolipid. Therefore, we can conclude that organic solvents like ethyl acetate, acetone and ethanol, act as better flushing solvents in OCP-polluted soil in the light of removal rate.(2) HPCD was used to wash both soils to investigate the following five aspects of elution conditions:flushing time, HPCD concentration, ratio of soil weight to volume of flushing solvent, elution temperature, and elution times. The results revealed that the optimal elution time was 0.5h. The eluted pesticide increasedwith the increase of HPCD. In 2g soil-10mL 100g/L HPCD system, the removal rates for HCHs and DDTswere 100% and 18.3%, respectively. While the flushing times increased to 3, the total DDTs removal rate was up to 29.1% in 2g soil -10mL 60g/L HPCD system. Increase in elution temperature could improve the removal rates of HCHs and DDTs. The results in chlordane and mirex polluted soil were similar to those in HCHs and DDTs contaminated soil.(3) Three kinds of surface active agent (Tween 80, Triton 100 and rhamnolipid) were used to wash chlordane and mirex contaminated soil for optimization of elution conditions, including elution time, concentration, temperature, and elution times. The results displayed that surfactant concentration is the key factor for removal rate. The removal rate of OCPs increased with an increase in ratio of soil weight to volume ofsurfactant solution. Elution time should be controlled in 1h with a high washing removal rate. High temperature (50,70℃) could decrease the removal rate of chlordane and mirex in polluted soil flushed by surfactant. Appropriate increase in elution times could get better results.(4) Flushing experiments with ethanol-water solution in HCHs and DDTs contaminated soil were carried out to determine elution time, ratio of ethanol to water, and flushing times. The results showed that at 180rmp 30℃, and 1:15 of soil weight to volume of ethanol solution, removal rate reached the highest in an hour. When the ratio of ethanol-water volume is 8:2 or 7:3,the elution rates of pesticide in soil was 76.8% and 73.6%; when the washing times were two, the removal rate reached 100% and 93.7%.