| Bio-venting is an in-situ remediation technique combined with physical treatment and biological treatment.lt had been effectively used for removal of volatile organic compounds from soil due to its high efficiency and low treatment cost. The experiment was investigated in the laboratory using diesel fuel as a model contaminant, performed in one dimension porous column filled with yellow earth. The removal effect and regulation of different influencing factors(ventilation methods, initial diesel concentration, soil moisture, ventilation rate) in the contaminated soil were studied. The diesel fuel degrading bacterium was enriched and isolated from the diesel fuel contaminated soil which using diesel fuel as the sole carbon and nitrogen source. The strain was screened and identifdied through morphological observation and16SrDNA sequence analysis, respectively. The factors influencing its degradation efficiency were analyzed. To explore the effectiveness of SVE-BV on diesel fuel contaminated fields, a field demonstration of SVE-BV remediation was carried out on the soil in Guangzhou province at the time. The main results of the study were as follows:(1)Pumping and injecting had the same removal regulation. Although the removal rate of pumping is faster than injecting, but the remediation efficiency is only2.28%higher than injecting. The TVOC of tail gas before and after ventilation also had the same changing regularity, but the value after ventilation was relatively higher. The TVOC had been determined every one hour, two hours and three hours in the8hours’ ventilation one day, the fluctuating degree of TVOC was one hour>two hours>three hours. Available phosphorus and Effective nitrogen were highly related to the diesel biodegradation efficiency in the soil.(2)The diesel fuel degrading bacterium.designated as DB, was enriched and isolated from the diesel fuel contaminated soil which using diesel fuel as the sole carbon and nitrogen source in this paper.The strain was identified as identified as Acinetobacter calcoaceticus through molecular biology. The results of the single factor experiment showed that the optimum condition for strain DB was at diesel fuel concentration of4g/kg and SDBS6g/kg, the total addition amount of H2O2was20mL/kg and methanol was5mL/kg. The degradation rate of the soils which was added the bacteria, non-added and sterilized by sodiumazide was69.82%,22.12%and13.65%, the half-life was37d,165d and347d, respectively, when the proposed bacteria grow under the optimum condition condition during62d bioremediation experiment. DB is a high efficient degradation bacterium can be used in the bioremediation diesel contaminated soil.(3)The diesel removal in the column was influenced by volatilization and biodegradation. The downward migration impact which caused by the gravity influenced the diesel, s distribution on the space in column. The removal rule of diesel columns with different sampling port was decided by the three actions together. The diesel content in different soil columns were decreased with different degrees. Initial diesel concentration and ventilation rate are the main factors that influence the removal of diesel, then the soil moisture content. Diesel can reach the maximum removal rate when diesel concentration of lOg oil/kg soil, moisture content is20%, the ventilation rate is150mL/min. The changes of pH and the loss of water were little in the process of experiment. Available phosphorus and available nitrogen content all reduced, the catalase and dehydrogenase increased firstly and then decreased. But every influencing factor of different soil columns reduced with different degrees.(4)A field demonstration of SVE-BV remediation was carried out, the results showed that the TPH removal rate of different soil depths were between74.12%and85.24%after more than there months SVE and one month BV remediation. The highest removal rate of TPH was64.88in the prophase by SVE, TPH in soil has been further removal by BV,and37.46%of TPH has been removed at the depth of lm, which has reached the best remediation effect. When SVE performed50days the volatile organic compounds of low molecular weight were almost removed according to the variation of TVOC about horizontal, vertical pumping gas pipeline and sampling port. All these proved the experiment has come into trailing period, and then followed by BV will greatly reduce the cost. Effective phosphorus and available nitrogen showed a decreased tendency in different depth of soil, especially in the BV process which the biodegradation palys a dominant role. Volatile organic compounds were mostly removed during the process of BV, which also accompanied by biodegradation. |
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