| There is a wide variety of petroleum hydrocarbons in the nature, about 600 kinds, mainly including alkane, cycloparaffin and aromatic hydrocarbon. In the progress of production, processing and transport of oil, oil leak and the drain of waste water and solid waste can bring a large amount of petroleum contaminants into environment. Environment, especially water resource has been polluted unprecedentedly, which do great harm to human health and animals and plants life.A refinery, with the capacity of processing 100000 tons crude oils every year, is located in the west of the city, where limestone is uncovered, the distribution of the Quaternary incompact layer is scattered and the antifouling performance of groundwater is poor. Refinery and pipeline are located in the limestone without anti-seepage treatment and it's easy for waste water to go into groundwater to contaminate groundwater through karst-fractured zone. Karst-fractured groundwater has been polluted seriously. The treatment of groundwater contaminated with petroleum hydrocarbons is imminent. By summing up home and abroad related research of the natural attenuation technique of groundwater polluted by petroleum hydrocarbon, the law of natural attenuation of petroleum hydrocarbon in groundwater and biogeochemical of natural attenuation of petroleum hydrocarbon were studied. This study will be of importance in the pollution control and rehabilitation of karst-fractured groundwater polluted by petroleum hydrocarbon and the protection of groundwater.In this paper, the law of natural attenuation of petroleum hydrocarbon in karst-fractured groundwater was studied through static experiment, realizing the important mechanisms of natural attenuation of petroleum hydrocarbon. And biogeochemical of natural attenuation of petroleum hydrocarbon was researched through laboratory simulation of soil column and static experiment.In this paper, the main research contents include:1) The characteristics of karst-fractured groundwater and water-bearing media.The supplement, runoff and draining of karst-fractured groundwater and the characteristics of karst-fractured water-bearing media were found out through field investigation.2) The spatial and temporal distribution characteristics of petroleum hydrocarbon in karst-fractured groundwater.Based on hydrogeological conditions in the study area, environment geology in the study area is investigated to find out the pollution sources and the pollution ways of karst-fractured groundwater. The groundwater samples were collected in the study area and made the detection of petroleum hydrocarbon concentration, combining with the previous monitoring data to analyze the time and space distribution characters of karst-fractured groundwater petroleum hydrocarbon. The result shows that karst-fractured groundwater petroleum hydrocarbon in study area has been attenuation. The area of petroleum plume was 3.5km~2 in 1991, reducing to 0.85km~2 in 2015 and the highest concentration was 1.77mg/L in 1991, reducing to 0.18mg/L in 2015.3) The natural attenuation laws of petroleum hydrocarbon in karst-fractured groundwater.The natural attenuation laws of petroleum hydrocarbon were studied through static experiment, setting the sterile control experiment. Using SPSS software to fit dates that the concentration of petroleum hydrocarbon in water sample collected from static experiment, the first-order kinetic equation of natural attenuation of petroleum hydrocarbon was obtained. The result shows that the natural attenuation of karst-fractured groundwater petroleum hydrocarbon conforms to first-order decay kinetics, rate of decay being 0.013d-1. During the period of experiment, the contribution of biological action to natural attenuation of petroleum hydrocarbon is more than the non-living action.4) The biogeochemical of natural attenuation of petroleum hydrocarbon in karst-fractured groundwater.Biogeochemical of natural attenuation of petroleum hydrocarbon was studied through laboratory simulation of soil column and static experiment. The concentration of petroleum hydrocarbon, microbial activity, redox potential, electron acceptors(oxygen, nitrate and sulfate) and reaction products(bicarbonate radical, nitrite and sulfion) in water samples was detected. The result shows that in static experiment, the value of microbial activity increases at first then decreases, the value of redox potential decreases as time goes on, the electron acceptors including oxygen, nitrate and sulfate decreases, the nitrite increases at first then decreases, and the bicarbonate radical increases. In the laboratory simulation of soil column, there are three oxidation-reduction zones, including oxygen reduction zone, nitrate reduction zone and sulfate reduction zone. |
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