In-situ bioremediation of groundwater polluted with Cr(VI) under anaerobic conditions

The natural capacity of several microbes to reduce Cr(VI) to Cr(III) has been considered of much interest in order to remediate soil and groundwater polluted with Cr(VI). The objective of this work is to evaluate the enhancement of the activity of indigenous Cr(VI) reducing bacteria by the addition of carbon source and to investigate the synergistic effect of abiotic and biotic Cr(VI) reduction in the presence of iron reducing bacteria. In order to simulate in-situ bioremediation field conditions, microcosm experiments were conducted under anaerobic conditions and at hexavalent chromium (Cr(VI)) groundwater concentrations in the 0–2000 μg/L range. The groundwater and the soil used in the experiments were collected from the deep aquifer in the Oinofyta region. Two carbon (molasses and EVO) and an iron source (FeSO4) were used as ways to stimulate the metabolism and proliferation of bacterial Cr(VI) reducers in-situ. To quantitatively describe the degradation kinetics of Cr(VI), pseudo first-order kinetics were adopted. The results indicate that an anaerobic system dosed with simple (molasses) or complex (emulsified vegetable oil) external organic carbon sources can lead to practically complete Cr(VI) reduction to Cr(III) and the addition of Fe+2 can increase Cr(VI) removal rate significantly.