Influence of Transient Flow on Contaminant Biodegradation
Influence of Transient Flow on Contaminant Biodegradation
复制标题
瞬态流对污染物生物降解的影响
作者：
M. Schirmer;G. Durrant;J. Molson;E. Frind
受污染含水层的生物降解速率在很大程度上取决于分散的混合过程，这种过程现在被普遍认为是由速度场的空间变化造成的。然而，瞬态流场也有助于分散混合。瞬态流动对生物降解污染物的影响尤为重要，因为它可以增强与电子受体的混合，进一步促进反应过程。通过数值模拟，本文评估了瞬态流动对可生物降解污染物行为的影响，既考虑了明显大的水平横向分散的发展，也考虑了底物（电子供体）和电子受体之间增强的混合。模拟使用了BIO3D数值模型，该模型解决了在电子受体存在下底物的顺流色散传输与Monod型生物降解耦合。该模型应用于考虑单一基底的二维平面视图模式。发现瞬态流场产生较大的表观横向色散，因为纵向色散也横向作用于平均流动方向。在反应过程中，瞬态流场增加了底物与氧的混合，从而提高了生物降解的总体速度。结果表明，在流动方向适度变化的情况下，可以证明稳态流场是合理的，从而避免了完全瞬态模拟的较高计算成本。在这些条件下，在稳定流场中使用较高的横向水平色散可以充分预测羽流的发展。
The rate of biodegradation in contaminated aquifers depends to a large extent on dispersive mixing processes that are now generally accepted to result from spatial variations in the velocity field. It has been shown, however, that transient flow fields can also contribute to dispersive mixing. The influence of transient flow on biodegrading contaminants is particularly important since it can enhance mixing with electron acceptors, further promoting the reactive process. Using numerical simulations, the effect of transient flow on the behavior of a biodegradable contaminant is evaluated here both with respect to the development of apparently large horizontal transverse dispersion and also with respect to enhanced mixing between the substrate (electron donor) and electron acceptor. The numerical model BIO3D, which solves for advective‐dispersive transport coupled with Monod‐type biodegradation of substrates in the presence of an electron acceptor, was used for the simulations. The model was applied in a two‐dimensional plan view mode considering a single substrate. Transient flow fields were found to yield larger apparent transverse dispersion because the longitudinal dispersivity also acts transverse to the mean flow direction. In the reactive case, the transient flow field increases substrate‐oxygen mixing, which in turn enhances the overall rate of biodegradation. The results suggest that in the case of moderate changes of flow directions, a steady‐state flow field can be justified, thereby avoiding the higher computational costs of a fully transient simulation. The use of a higher transverse horizontal dispersivity in a steady flow field can, under these conditions, adequately forecast plume development.