Biogeochemical Controls on the Fate of Metal Contaminants in Environmental Systems

Providing cheap and sustainable energy, while not degrading environmental resources, is one of the world's largest challenges for the 21st century and will undoubtedly necessitate a portfolio of options.  Moreover, as energy demands continue to increase, the impact of mining, fuel transport, and industrial manufacturing on soil and water quality will be of upmost importance. The biogeochemical behavior of redox active metals and metalloids (U, Cr, Se, As etc.) in environmental settings, comprised of dissolved metals, organic ligands, native microbes, and mineralogical matrices is complex and in many cases poorly understood.  Two examples of environmental metal contaminants are uranium and chromium.  The potential for uranium transport in the subsurface decreases in anaerobic conditions as compared to aerobic conditions, through the formation of the sparingly soluble UO_2(s) phase, a process often facilitated by dissimilatory metal and sulfate reducing bacteria.  Additionally, uranium may adsorb on a variety of mineral surfaces decreasing its solution concentration; however, the presence of dissolved calcium has a profound impact on uranium redox cycling, both limiting U(VI) adsorption and reduction.  In engineered systems, treatment processes for metals in industrial stormwater can be cost prohibitive. Therefore, passive remediation strategies using natural materials and microbial processes have the potential to provide affordable solutions for removing metals from aqueous waste streams, which is important from regulatory and environmental quality perspectives. Here we explore key chemical, biological, and physical processes promoting removal of hexavalent chromium from an industrial stormwater treatment system by association with granular organic peat media.