Impact of Sharp Interfaces on Biofilm Growth: Insights from Mixing Processes in a Flow-Through Column Experiment.

Biofilms in porous media host microbial communities that play a central role in the degradation of nutrients and Contaminants of Emerging Concern. Their importance for promoting contaminants removal in the context of Natural Based Solutions is acknowledged, but we still lack a complete understanding and quantification of biofilm growth dynamics in porous media, and their impact on flow and transport behavior. In this context, we aim to investigate the effects of sharp interfaces on the spatial and temporal distribution of biofilms growth and their subsequent role in the evolution of flow and transport properties. For this purpose, we conduct flow-through experiments in sand-packed columns characterized by two homogeneous porous media separated by a sharp interface. We inject electron acceptor and electron donor solutions sequentially and multiple times. This creates multiple reactive mixing zones that flow and evolve through the system, depending on the porous medium. The high-resolution monitoring system enables the quantification of biofilm activity, as well as changes in hydraulic conductivity over time and at different sections of the column. Additionally, image analysis allows for the evaluation of the spatial distribution of biofilm growth over time, while breakthrough curve concentrations derived from several tracer tests provide further insights into overall transport parameter changes.