Nanosized iron oxides in microbial BTEX oxidation: a novel concept for groundwater remediation

Microbial reduction of ferric iron is a major biogeochemical process in groundwater ecosystems and often associated with the degradation of organic contaminants, as bacteria couple iron reduction to the oxidation of organic molecules like e.g. BTEX. Yet the high crystallinity and low solubility of iron oxides limits reduction rates. However, environmental nanosized iron(oxy)hydroxide minerals seem to have an unequally enhanced reactiveity potential compared to their bulk and highly crystalline parent materials of the same mineral. Therefore, we examined the reactivity of nanosized, synthetic and environmental colloidal iron oxides in microbial iron reduction in static batch incubations and column experiments. Results Colloidial particles showed an enhancement of reaction rates of up to 2 orders of magnitude higher reaction rates than bulk phases, independent of the kind of mineral phase and or surface area. Furthermore, soil column experiments demonstrated the high persistence of nanosized iron oxides under simulated environmental conditions, opening the perspective for their technological application as electron acceptors in the remediation of BTEX and putatively PAH contaminated sites. First studies on the feasibility of this technology showed a 5x-fold enhancement of toluene oxidation after application of nanosized iron oxide particles to microbial incubations, as well as the possibility of custom-tailoring the subsurface mobility of these particles after injection into a contaminant plume. Our results suggest that the injection of ferric iron nanoparticles as electron acceptors for microbial contaminant degradation in contaminated aquifers might develop into a novel bioremediation strategy creating in situ reactive barriers.