Remediation Of Contaminated Soil With BHCs And DDTs

Although the usage of organochlorine pesticides (OCPs) has been banned in China for nearly30years, concentrations of BHCs and DDTs in soils are still high due to their low degradation rates. The function of land use changes after a number of old pesitides manufacturing field closed. Manufacturing plants and equipments of former organochlirine manufacturing corporations may contaminate surrounding soil heavily. If soil contaminated with BHCs and DDTs heavily was not treated safely, it is possible to be pollution source and cause serious threat to environment. The accumulation of BHCs and DDTs in human body has a strong risk on human health. Rapid and efficient BHCs and DDTs remediation meathod are essential. Three remediation methods and optimazition of remediation parameters were investigated in soil contaminated with BHCs and DDTs. Soil enzyme activities after remediation were also analysed. The results showed as follows:1. A washing experiment of four kinds of alcohols (methanol, ethanol,1-propanol,2-propanol) and four kinds of surfactants (Tween80, Tween60, SDS, TX-100) was conducted to select an optimum solvent for BHCs and DDTs. Results indicated that the removal rates of alcohols were better than that of surfactants. Ethanol was the best eluent with removal rate of total contamitants87.18%in single soil washing. The optimum parameters of ethanol were a15min of contact between soil and ethanol by ultrasonic equipment, a1/20soil-solvent ratio and three cycles of ethanol washing. A relative satisfactory remediation efficiency also achieved when5.0g soil was washed by ethanol. Evaporation was used to recycle ethanol, and greater than90%of the ethanol in the spent washing fluid was recovered. The ability to recycle cosolvent solutions provides a mechanism for cost reductions of the remediation strategy.2. Removal efficiencies of BHCs and DDTs by thermal desorption were investigated. It was obtained the main reason influenced thermal desorption was temperature. Removal rates could be increased by increasing treatment temperature. Higher temperature needed shorter time in order to achieve the same removal efficiency. Inceasing thermal time caused inceasing removal efficiency in the same temperature. The total contaminants concentration decreased from3115.77mg/kg to0.33mg/kg after thermal treating at500℃for30min. The desorption efficiency was99.9%. Thermal desorption of OCPs polluted soil was shown to be governed by first-order kinetics model. Soil moisture decreased the rates for OCPs, so soil needs to be air-dried before remedition.3. Photo-Fenton degradation experiments were carried out to degrade BHCs and DDTs in contaminated soil. The optimum conditions were obtained at pH3for3mmol/L Fe2+dosage,375mmol/L H2O2, using a500W presure mercury lamp for90min. The most important factor influnced degradation rates were the concentration of H2O2. The degradation efficiency was strongly influenced by pH value, light intensive and reaction time. Fe2+dosage has little influence on degradation process. Compared with other two methods, photo-Fenton degradation obtained lower remediation efficiency.4. Five kinds of soil enzyme activities (urease, polyphenol oxidase, acid phosphatase, alkaline phosphatase and invertase) of contaminated soil, ethanol treatment soil and thermal treatment soil were evaluated. Soil enzyme activities changed after remediation. Five kinds of enzyme activities increased after ethanol washing. Urease, polyphenol oxidase activities increased but acid phosphatase, alkaline phosphatase and invertase activities reduced78.75%,27.29%and38.85%after thermal treatment relative to the contaminated soil, respectively。...