Laboratory examination of microbial effects upon redox in a geological disposal site for radioactive waste

The laboratory experiments described here, were aimed at examining the interaction of microbes with mineralogical surfaces involved with groundwater flow. These experiments were designed to study simple systems and were aimed at identifying relevant reactions both chemical and biological. They contained groundwater with either sulphate reducing bacteria (SRB), iron reducing bacteria (IRB) or a mixture of both, together with control experiments without bacteria. The results of the chemical analyses of fluid phases showed evidence for dissolution of primary minerals. Microbial analysis showed both SRB and IRE appeared to be active albeit for a limited period due to exhaustion of nutrient and energy supplies. SRB seem to have a greater effect on groundwater chemistry than IRE with sulphide being produced. However, when the two types of bacteria are mixed together, the IRE appear to dominate the system. Further work is underway to give detailed mineralogical analysis of the solids in order to better understand the influence of microbial interaction on the redox reactions.