Bioclogging in Porous Media: Tracer Studies

Tracer studies show that the flow regime may transform from near uniform flow at the starting conditions to non-uniform flow under conditions with severe bioclogging. The mode of observation (flux averages or point measurements) thus becomes important. It is proposed that bioclogging may lead to changes in transport patterns as well. A first phase, where the dispersivity increases approximately linearly as the hydraulic conductivity decreases is explained as the result of an increase in the number of microcolonies located strategically in pore throats. A second phase follows, where the capacity for diffusion between the mobile water phase and the immobile biophase has increased, leading to significant tailing in solute breakthrough. A third phase may develop, where preferential flow paths results in fracture-like breakthrough. The results show that calculated changes in bulk hydraulic conductivity may be reproducible from experiment to experiment, while, in some cases, and especially those involving point injection of nutrients, the initial heterogeneous distribution of bacteria will affect the development of bioclogging patterns.