| PCBs (Polychlorinated biphenyls) is a kind of persistent organic pollutants with three effects of "carcinogenic, teratogenic and mutagenic", which can cause serious harm to ecological environment and human health through migration of soil, air, water, organism and other medium for a long time. Due to the early backwardness of dismantling process, PCBs in transformer oil and acid pickling waste liquor was disposed optionally, which has caused serious pollution in solid waste dismantling area, the study on the pollution characteristics and repair technology is very imperative, which would provide scientific basis for local ecological effect and human health.The contaminated soil along typical solid waste dismantling area in Taizhou is selected as the study object. On the basis of analyzing the pollution characteristics of PCBs in the field, this article investigates the removal mechanisms of PCBs through indoor experiment and numerical simulation and studies the repair technology in order to provide technical parameters and scientific basis for soil pollution of Polychlorinated biphenyls repair. The main results are as follows:(1) The soil in solid waste dismantling area has suffered serious pollution of PCBs, approximately 47% of the land has been polluted at different degree, The maximum is 937ng·g-1, the key pollution area are mainly distributed along the solid waste dismantling area in Taizhou. The rice and vegetables turn up different degree of overproof PCBs, and the agricultural products and soil contaminants presented a certain correlation.(2) The concentration range of ΣPCBs in the surface soil is 71.26-113.06 ng·g-1 with a mean of 92.39 ng·g-1. Seven kinds of indicative PCBs monomer are detected, PCB28 content is the highest, accounting for 36.52% of the total. The order of average content is:PCB28> PCB52> PCB101> PCB153> PCB138> PCB180. In the soil profile, most of PCBs lies in the humus layer, with depth increaseing, the content gradually reduces and it would reduce to 95% below 40 centimeters. From the point of monomer composition, the vertical migration ability of PCBs recedes with the increase of number of chlorine atoms. The concentration range of SPCBs in sediment is 246.74-621.76 ng·g-1, which is far above the soil. The concentration range in river water is 72.36-90.66 ng·L-1, which is far higher than the standard limit.(3) Comparing the proportion of various monomer of PCBs in different media, the proportion of PCB28 in sediment is lower than in the soil and river water, while the proportion of highly chlorinated PCBs (PCB153,138 and 180) in the sediment is higher than that of soil and river water, the more the chlorinated atomic number is, the smaller solubility in water, and the easier to be adsorbed by particles.(4) The surfactent Tween80 is used for static elution repair of the field contaminated soil and the fresh artificial contaminated soil. When the concentration of eluent is 5000 mg·L-1, the elution rate of PCBs in the fresh artificial contaminated soil and the field contaminated soil are 43.7% and 23.6% respectively, with the aging time extending, the elution rate gradually decreases, and that of highly chlorinated PCBs is less than the lowly chlorinated PCBs.(5) The Tween80 and meteoric water are used to leach the contaminated soil respectively. The removal rate of Tween80 is up to 40%, while that of meteoric water is quite low, this indicates that after aging for a long time, the pollutant in the in situ soil is hard to be removed under natural conditions.(6) Comparing the remediation effect of PCB28 in water phase under different flow of AS (Air Sparginng), different medium and different temperature. The result shows that, the bigger flow of AS leads to the faster removal rate and better effect, but excessive flow is easy to cause disturbance of soil medium, and that is finally designed at 40 ml/min in the experiment. The removal speed of sand is faster than soil, and the removal rate greater than soil. In addition, high temperature is in favour of transformation from NAPL phase and liquid phase to the gas phase, and the removal speed is faster than low temperature.(7) The T2VOC multiphase flow model of TOUGH software program is used to simulate the aeration repair effect of two different medium of sand and soil under the aeration flow of 40 ml/min, the results show that the digree of fitting the simulated data and experimental results is high, the model can simulate and indicate the process of the Polychlorinated biphenyls migration.(8) The resistant microbes are screened out from the contaminated soil and are domesticated,and study the growth characteristics of indigenous microorganism. The best living environment of microbe is decided:pH=7 and tempereture of 30 ℃, the growth condition of bacterial strain is the best. When PCBs concentration in soil is in the range of 9-15μg·L-1,microbial degradation began to play a major role, the utilization of PCBs is the highest, and the degradation effect is the best.(9) After domestication about resistant microorganisms,the microbial air sparging is carried out in the best survival environment with pH at 7 and tempereture at 30 ℃. The removal rate near the sparging mouth is the highest and up to 73.7%, and that can reach 60.3% at he bottom of soil column, the comprehensive removal rate reaches 90% after Microbia repair.(10) The T2VOC model is chose and the visualized PetraSim interface program is utilized to establish a two-dimensional and a three-dimensional isothermal model.repairing and predicting three-phase flow simulation of PCB28 in different scales of actual pollution sites in different aeration methods.The results show that T2VOC can simulate and analyse the diffusion and pollutants repair of Polychlorinated biphenyls, indicate the three-phase flow migration of water, gas, NAPL and pressure change, provide technical support for the theory of soil aeration of groundwater and soil,and then guide the process of pollution repair. |
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