Insight Into Hydro-chemo-biological Processes In Water Table Fluctuation Zone Of BTEX Contaminated Aquifer

With the rapid development of petrochemical industry in recent years,the pollution of petrochemical industry in the environment is becoming more and more serious.Especially for groundwater and soil environment pollution,once the problem is found,it has often caused irreversible consequences because of its latency and concealing.Due to low density and insolublity of BTEX,it usually floats and migrates near the groundwater table.While the groundwater table frequently changes with the impacts of mining or recharging,rainfall and other factors,the zone between the high and low groundwater levels is known as the Groundwater Table Fluctuation?GTF?zone.Thus,the migration and transformation of BTEX in this zone is specific due to the water fluctuation and the consequent oxidation-reduction environment changes.This article relied on the National Natural Science Fund Project ?Fate and transport of BTEX under natural and air sparging remediation in the fluctuation zone of groundwater table?,and applied the indoor one-dimensional sand column simulation experiments to investigrate toluene attenuation and physical,chemical,biological effects in the groundwater table fluctuation.The results could give contributions to clarify the process of contaminants migration and transformation in the underground environment,further provide scientific theoretical basis for the removal of pollutants.Through the indoor experiment and the systematic data analysis,main results of this paper are described in detail as follows:1.The toluene attenuation with the water migration during GTF was in accordance with the first-order decay model.The toluene attenuation rates varied in different porous media types,6.4 mg·L^-1·d^-1 for medium sand,5.3 mg·L^-1·d^-1 for fine sand-clay media under GTF conduction,while for non-fluctuation seniors the rates were only 0.57 mg·L^-1·d^-1 for medium sand,0.59 mg·L^-1·d^-1 for fine sand-clay media.The residual amount of toluene in sand media and under GTF conditions was less than that in sand-clay media combined with non-fluctuation.It can be inferred that GTF could significantly accelerate the rate of toluene migration especially in sand media.2.With the increasing of accumulated effluent,the reduction reaction occurred in different conductions with the order of NO₃-> Fe³⁺ > SO₄^2-> CO₂.Under the experimental four senorios: sand media-flutuation?SF?,sand-clay media-fluctuation?SCF?,sand media-non fluctuation?SNF?,sand-clay media-non fluctuation?SCNF?,each conversion time of REDOX electron process started and ended at different points which normally were delayed by fluctuation especially in sand media.3.The detected microbes OTU were different under different hydraulic conduction,and had obvious changes in media at different times.The results indicating that the change of microbial population under GTF was significantly greater than non-fluctuation.And the change of microbial population under sand-clay media was significantly greater than sand media.Shannon index,Simpson nidex,and Pielou index showed different trends in different conductions.4.During toluene attenuation,the physical activity dominated in the early stage,followed by chemical activity.For the numbers of result,a positive correlation existed between the organic matter and the OTU.The particle size of meida was positively correlated with the OTU,while the specific surface area of media was negatively correlated with the OTU.The relationship between Pseudomonas and TOC,NO₃-,SO₄^2-was strongly correlated under the conduction of medium sand-fluctuation,and strong correlation between Acinetobacter and HCO₃^-,NO₂-,Fe³⁺ in the conduction of SCF was also obtained.