Simulation of Aerobic Biodegration of BTEX Plume in Groundwater
Petroleum hydrocarbons leaked from storage tanks of gas stations and tank farms can contaminate soil and groundwater. However, the constituents of gasoline can be biodegraded naturally. Aerobic biodegradation is the major attenuation process for these constituents such as BTEX. If the concentration of dissolved oxygen in the groundwater is enhanced whether by natural infiltration or artificially induced, the biodegradation can be accelerated. Furthermore, the oxidants introduced in the remediation process for oxidizing contaminants can also promote biodegradation by increasing the content of oxygen in the underground saturated layer. In this study, the aerobic biodegradation of BTEX plume in aquifer is modeled with Visual MODFLOW. While the groundwater flow is simulated with MODFLOW, the transport and attenuation of pollutants is computed with RT3D. The effect of location of infiltration region and oxygen content of infiltrated water on overall degradation rate of BTEX was analyzed. In addition, the effectiveness of injection of oxidant on enhancing the degradation rate was also looked into. The results show that BTEX degradation resulted from elevated oxygen level induced by infiltration is about 20% in the simulated gas stations leakage scenario. On the other hand, only about 5% of the total amount of BTEX in tank farm site has been degraded. Furthermore, the results showed that the infiltration near the point of leakage has resulted in most significant degradation of BTEX. In contrast, infiltration at the downstream of the point of leakage led to degradation of the leading front of the plume and effectively restrained the plume from moving further downstream. For a runoff coefficient, C, of 0.6 the infiltration in the source region led to fastest degradation, while the infiltration at downstream of source region caused most degradation when C = 0.75. Injection of oxidants into aquifer can lead to degradation 50 – 80% of BTEX within 90 days in the simulated gasoline station leakage case. On the other hand, only 20 – 30% of BTEX degraded in 180 days in the tank farm case.
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