School of Civil and Environmental Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332-0355, United States.
Environ Sci Technol. 2015 Feb 3;49(3):1501-10. doi: 10.1021/es503086p. Epub 2015 Jan 15.
Vapor intrusion from volatile subsurface contaminants can be mitigated by aerobic biodegradation. Laboratory column studies with contaminant sources of chlorobenzene and a mixture of chlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene showed that contaminants were rapidly degraded in thin reactive zones with high biomass and low substrate concentrations in the vicinity of the capillary fringe. Such behavior was well characterized by a model that includes oxygen-, substrate-, and biomass-dependent biodegradation kinetics along with diffusive transport processes. An analytical solution was derived to provide theoretical support for the simplification of reaction kinetics and the approximation of reactive zone location and mass flux relationships at steady state. Results demonstrate the potential of aerobic natural attenuation in the capillary fringe for preventing contaminant migration in the unsaturated zone. The solution indicates that increasing contaminant mass flux into the column creates a thinner reactive zone and pushes it toward the oxygen boundary, resulting in a shorter distance to the oxygen source and a larger oxygen mass flux that balances the contaminant mass flux. As a consequence, the aerobic biodegradation can reduce high contaminant concentrations to low levels within the capillary fringe and unsaturated zone. The results are consistent with the observations of thin reactive layers at the interface in unsaturated zones. The model considers biomass while including biodegradation in the capillary fringe and unsaturated zone and clearly demonstrates that microbial communities capable of using the contaminants as electron donors may lead to instantaneous degradation kinetics in the capillary fringe and unsaturated zone.
挥发性地下污染物的蒸气侵入可以通过需氧生物降解来减轻。用氯苯和氯苯、1,2-二氯苯和 1,4-二氯苯的污染物源进行的实验室柱研究表明，在靠近毛管边缘的高生物量和低基质浓度的薄反应区中，污染物迅速降解。这种行为可以通过一个模型很好地描述，该模型包括氧、基质和生物量依赖的生物降解动力学以及扩散传输过程。推导出一个解析解，为简化反应动力学和稳态下反应区位置和质量通量关系的近似提供理论支持。结果表明，在毛管带中需氧自然衰减有防止非饱和带中污染物迁移的潜力。该解决方案表明，增加进入柱的污染物质量通量会创建一个更薄的反应区，并将其推向氧气边界，从而使到达氧气源的距离更短，氧气质量通量更大，与污染物质量通量平衡。因此，需氧生物降解可以将毛细管带和非饱和带内的高污染物浓度降低到低水平。结果与非饱和带界面处的薄反应层的观察结果一致。该模型考虑了生物量，同时包括了毛细管带和非饱和带中的生物降解，并清楚地表明，能够将污染物用作电子供体的微生物群落可能导致毛细管带和非饱和带中的瞬时降解动力学。
