Microbiologically Enhanced Mixing across Scales during <i>in-situ</i> Bioremediation of Uranium

Production of nuclear fuels for weapons and electric energy has resulted in groundwater uranium contamination at Department of Energy (DOE) sites. Reduction of uranium by dissimilatory metalreducing bacteria (DMRB) is an effective approach for in-situ bioremediation of these sites. In this process, an organic electron donor is typically delivered through a well into groundwater in order to promote the biological reduction of soluble and toxic U(VI) to insoluble and less toxic U(IV). A key challenge is mixing the organic electron donor with U(VI) in groundwater where laminar flow conditions prevail. A potential solution is to enhance reaction beyond the scale of physical mixing by promoting extracellular electron shuttling. Growing evidence suggests that extracellular electron shuttling can occur by either diffusion of aqueous phase electron shuttles (e.g., H2, quinones) between syntrophs and/or DMRB, or through direct electron transfer between cells through metallic-like appendage (i.e., nanowR. Al c A l d e i n McNa i r Sc h o l a r S re S e a r c h Jo u r N a l 2012 2 ires). In this project, we used pore scale, microfluidic experiments in order to elucidate cell-to-cell electron transport that can potentially enhance U(VI) reduction beyond the scale of physical mixing with an organic electron donor. Batch studies were performed to develop DMRB cultures, and to evaluate their growth with different electron acceptor and donor conditions. DMRB cultures from batch studies were used to inoculate pore scale, microfluidic reactors. The microfluidic experiments allowed direct imaging of microbial growth over various mixing length scales. Anaeromyxobacter dehalogenans Strain K and a mixed ground water culture were used, and we hypothesize that these organisms will enhance reaction beyond physical mixing scales by facilitated electron transfer.