Orthogonal Experiment For Remediating Diesel Contaminated Soil By Enhancing Bioventing

Bioventing (BV) is a widely applied bioremediation technology for removal of organic compounds from unsaturated soil. It can be used to treat light and heavy components of petroleum contamination and can reduce the cost of tail gas treatment comparing with Soil Vapor Extraction. This laboratory experiment selected five main influencing factors: initial contamination intensity, venting mode, pore volume number during soil venting, the ratio of carbon, nitrogen and phosphate, soil water content. The orthogonal experiment was simulated and optimized using diesel as target contaminant in one dimension soil column filled with permeable, homogeneous sands on the condition of the column vent intermit 18h every day to find out the optimal combination that could achieve the maximum removal rate.It is shown that when the diesel mass concentration of the sand was 1% and the soil water content was 4.88%, the removal rate of natural attenuation column could achieve 30.58% after 143 days. However, in the orthogonal experiment, the maximum removal rate was 65.48% of the 12 soil columns, the minimum was only 4.00%. The results of range analysis showed the order of these factors for influencing the effects of BV remediation was soil water content, contamination intensity, the ratio of carbon, nitrogen and phosphate, pore volume number during soil venting, and venting mode. When the diesel mass concentration of the sand was 4%, air injecting at the bottom of column, the pore volume number during soil venting was 4, the ratio of carbon, nitrogen and phosphate was 100:20:1 and soil water content was 4.88%, that would reach a larger removal rate.Biodegradation was the main way of the diesel contaminants removal by computing the total removal rate of the diesel contaminants, the removal rate of volatilization, complete biodegradation rate and non-complete biodegradation rate after 143d BV remediation. The biodegradation rate was more than 77% of the total removal ratio, while the volatilization ratio was relatively small.The pore volume number of ventilation and soil water content mainly influenced volatilization; initial diesel concentration, soil water content and the ratio of carbon, nitrogen and phosphate mainly influenced gravity action; in addition, except the venting mode, biodegradation was influenced by the other four factors by analyzing the diesel distribution curve of soil column profile under different time.Soil moisture content was a main factor to influence the change of average concentration in diesel contamination area. When soil water content was no less than 75% of the maximum water holding capacity, it would inhibit the removal of the average concentration of diesel in soil.To the hydrocarbon components(C₉,C₁₀,C₁₂,C₁₆,C₁₈,C₂₂) measured in this experiment, the removal of heavy hydrocarbon component(C18,C22) was more difficult than light hydrocarbon component, and the time of the maximum removal rate was the later stage of experiment, about the days of 114 to 143.