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Understanding and presenting simple closed-form expressions for enhanced dispersivity in aquifers colonized by biofilms
  • Xavier Sanchez-Vila,
  • Paula Rodriguez-Escales
Xavier Sanchez-Vila
Hydrogeology Group(GHS, UPC-CSIC), Universitat Politecnica de Catalunya

Corresponding Author:[email protected]

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Paula Rodriguez-Escales
Hydrogeology Group(GHS, UPC-CSIC), Universitat Polit├Ęcnica de Catalunya
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The growth of bioflm in porous media causes disruption in the groundwater flow patterns. In conservative tracer tests performed in columns, this translates in significant changes in the observed breakthrough curves (BTCs) in bio-ammended as compared to biofilm-free porous media, then translated to bioclogging-dependent interpreted hydraulic parameters. While the impact upon reduction in saturated hydraulic conductivity values has been widely explained and modeled, this has not been the case for the reported significant increase in apparent dispersivity values. We present here simple, yet practical, expressions for the evaluation of enhanced effective dispersivity coefficients in bio-ammended saturated porous media, based on the modification of the BTCs (in terms of temporal moments) with respect to the biofilm-free porous media and for a number of proposed models with slightly different underlying hypotheses. The advantage of the expressions provided is that they are written in terms of observables that are relatively easy to measure in the lab or the field, contrarily to existing expressions that relate the effect to channelization caused by pore constriction assuming a simple geometry for the biofilm. One model is then used to interpret nine column experiments from the literature, allowing to use data of measured dispersivity, porosities, and flow rate to provide a lumped parameter that incorporates accessibility of solutes to biofilm by a mass transfer term between the biofilm and the flowing water.