Column Simulated Experiment Study Of Emulsified Oil In-Situ Removal Of Hexavalent Chromium In Groundwater

Emulsified soybean oil used as a carbon source in situ bioremediation for various types of groundwater pollutants has become a research focus in recent years. This study take Cr(VI) polluted groundwater as the research object, emulsified soybean oil as an electron donor, base on the laboratory column experiment, the removal rate of Cr(VI) and effect of emulsified soybean oil injected on aquifer medium’s permeability has been studied. Furthermore, in order to improve the Cr(VI) removal efficiency, nitrate dosage, Cr(VI) initial concentrations, emulsified soybean oil dosage are adequately considered, respectively. The conclusions of this study were as follows:The results of column experiment showed that the reaction cycle of emulsified soybean oil injected for the first time was longer than the second time, which was relation to chromium salts toxic effects on microorganisms and emulsified soybean oil’s low degradation. The hydraulic conductivity of soil column reduced 58.44 percents to 73.68 percents after injected, but then returned to 20 percents to 50 percents of the initial hydraulic conductivity with the increasing volume of effluent.Column experiments run for a total 64 days, twice injected with 80 m L of emulsified soybean oil. The influent Cr(VI) concentration was 15 mg/L and the lowest effluent Cr(VI) concentration was 2.46 mg/L. Cr(VI) removal amounts calculated were 32.60 mg and 91.26 mg. And the removal rate could reach 29.20 percents and 72.13 percents, respectively. The whole experiment process of Cr(VI) removal rate was 52.01 percents. According to the assessment of emulsified soybean oil utilization rate, it is found that when 1 m3 polluted groundwater containing 15 mg/L Cr(VI) treated, 9.69 L emulsified soybean oil is needed.In the Cr(VI) static experiments in which emulsified soybean oil as the sole carbon source, the addition of nitrate play an important role in the removal of Cr(VI). When the nitrate concentration is 10 mg/L and emulsified soybean oil injection volume is 2m L, the attenuation rate constant K of Cr(VI) was 0.304 d-1 and the removal rate was 100%, per unit volume of the emulsified oil to remove Cr(VI) was 5.0 g/L. In the simulation column experiments, the unit volume of emulsified soybean oil removal Cr(VI) in group 1 was lower than in group 2, due to the lack of nitrogen and the loss of emulsified soybean oil. Cr(VI) initial concentration has a significant impact on the removal of Cr(VI), high Cr(VI) concentration(15 mg/L) can inhibit microbial activity, thereby affect the Cr(VI) removal efficiency.