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Jesús Carrera
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Conceptual challenges to model biochemical processes in aquifers
Pollution is arguably the worst environmental global challenge faced by society. While pollution problems are local in nature, current policies (e.g., spill it rivers the outflow of wastewater treatment plants, WWTPs) favor the broad spread of pollutants, to the point that many of them are becoming global threats (e.g., antimicrobial resistance, endocrine disruptors, microplastics). While this error is widely acknowledged by the scientific community, a misunderstood precautionary principle prevents the use of soil aquifer treatment to remove these pollutants from WWTP effluents. In this presentation, I will expand on the importance of pollution as a global challenge, on why regulations concerns are unfounded, and especially on the processes that govern pollutants removal. These processes rely on the fact that porous media display large specific surface areas. These surfaces host biofilms that tend to absorb many organic pollutants (specifically those that are toxic by accumulation), precisely in the locations hosting the microbial communities that degrade those pollutants (we conjecture that this is the result of natural selection). Retention and degradation processes are improved by the addition of a reactive layer, as it favors the growth of biofilms, ad the adsorption of ionic compounds. Research challenges of these processes are significant. Degradation occur at the sub-pore scale in biofilms, which host the vast majority of microorganisms that catalyze them. Therefore, solute transport and reactions become controlled by diffusive processes. But aquifer scale transport is controlled by dispersive processes and heterogeneity. The issue is further complicated by biofilm growth, which changes porosity and permeability and large-scale heterogeneity, as well as localized residence and reaction times in different portion of the medium. Addressing these pore scale processes, while acknowledging their impact on aquifer scale heterogeneity is challenging, but needed to understand how these “new” pollutants are removed during soil passage, in turn needed to help convince regulators.
