Remediation Of PAHs Contaminated Soil By Dielectric Barrier Discharge Plasma And Pulse Corona Discharge Plasma

Recently,petroleum exploitation, industrial development and exhaust emission etc. have brought more and more polycyclic aromatic hydrocarbons(PAHs) to the environment. The soil is a very complicated heterogeneous system, and it has aggregated much PAHs because of its hydrophobic property. Domestic and foreign scholars have paid graeat attention to the bioremediation and phytoremediation methods to remedy PAHs contaminated soil, however, few of them could remediate the contaminated soil rapidly. Based on this, non-thermal plasma technology was used to remediate the typical PAHs-pyrene contaminated soil with dielectric barrier discharge(DBD) and Pulse Corona Discharge(PCD), the influencing factors: gas parameter and soil parameter were analyzed to compare the energy efficiency of the two discharge methods, the byproducts during the degradation and the mechanism of degradation were also studied. In addition, the feasibility of remedying the petroleum contaminated soil with PCB was also studied. The structure change and the composition of the petroleum pollutants before and after treatment were studied. The experimental results are as follows:(1) DBD with AC power of high frequency was used to remedy the pyrene contaminated soil. The degradation characteristics of pyrene were studied by the the electrical parameter, gas parameter and soil parameter, the results showed that the degradation efficiency could reach 67.9% when the discharge voltage was 33.8k V, the electrode gap was 14 mm, the gas flow rate was 1L/min and the initial pyrene concentration was 100mg/kg. It could improve the degradation rate to increase the discharge voltage or reduce the electrode gap. The degradation rate of pyrene would reduce when the initial pyrene concentration increased, however, the energy efficiency would increase. The removal rate was higher under alkalinity condition, however, the change the soil p H would influence adsorption status of pyrene in the soil particles, and the recovery rate would reduce.(2) The active species produced during DBD was analyzed qualitatively by Optical Emission Spectroscopy, the byproducts and mechanism of pyrene degradation were researched by ATR-FTIR and GC-MS. O3, O?, OH? and NOx played an important role in the degradation of pyrene. These active species could damage the structure of pyrene, which was oxidized and ringopened, therefore, low molecular organic compounds containing nitrogen andoxygen were generated.(3) PCD system was introduced to study the effect of remediation of pyrene in the soil in the system. After 60min’s treatment of PCD system, the degradation rate were respectively 45.5%, 52.5% and 53.0% when the pick voltages were 25 k V, 30 k V and 35 k V. The variation of pyrene degradation accords with the first order kinetic equation with the increase of the peak voltage and pulse frequency, and the reaction rate constant of pyrene increased. The removal effect of pyrene by PCD under different gas atmospheres was air> oxygen> nitrogen.(4) The treatment rates and energy efficiencies(G50) of pyrene by DBD and PCD were compared from the perspective of the principles and the characteristics of the discharge modes and the structures of the reactor. When the pyrene was treated by DBD, he degradation rate was high and the pollutants were decompensated relatively completely, but it was easily affected by the electrical parameters. When it was treated by PCD, the treatment effect was stable and energy efficiency was high, and its G50 value was 3.76mg/k J, which was 10 times more than that by DBD when the peak voltage was 30 k V and pulse frequency was 30 Hz.(5) The abatement of petroleum from contaminated soil by DBD was studied, the structures and compositions of the petroleum before and after treatment were analyzed. After 60min’s treatment by DBD, the degradation rate reached 76.93% when the peak voltage was 30 k V, the pulse frequency was 50 Hz, the electrode gap was 14 mm and the soil moisture content was 1.44%. When the initial pyrene concentration reduced, the removal rate of petroleum \ increased. The TOC removal rate reached 24.4% when the soil with the petroleum concentration of 2500mg/kg was remedied by PCD. The optimum soil moisture content suitable for reaction by plasma was 9.2%. The PAHs in the petroleum contaminated soil mainly composed of naphthalene and substituted benzene. Good petroleum removal effect was obtained by PCD plasma.