Modeling bio-protection and the gradient-resistance mechanism

We expand the biogeochemical program CCBATCH to describe transport processes in 1-D ground-water systems. We use the expanded CCBATCH with our biogeochemical framework for metal detoxification in sulfidic systems to study complex bio-protection scenarios. In particular, in our numerical experiments we expose a consortium of sulfate-reducing bacteria and fermenting bacteria to a toxic concentration of Zn²⁺ in a 1-D system with precipitation of zinc-sulfide solids turned off or on. Our results confirm the key role of sulfide precipitation in detoxification when coupled effects of transport and biological processes are considered. The potential of sulfide as a detoxifying agent in bio-protection is explained by its high mobility, its high affinity for metals, and its high rate of production in sulfidic systems. Thus, our numerical results offer important evidence for the gradient-resistance mechanism and validate that a metal-resistance criterion developed from an analytical solution is accurate for defining when bio-protection should succeed.