ELECTRICAL CONDUCTIVITY OF DISSIMILATORY METAL-REDUCING BACTERIA (DMRB) AT DIFFERENT LIFE PHASES INFLUENCED BY CHROMIUM(VI)

Our objective was to determine changes in electrical conductivity of dissimilatory metal-reducing bacteria (DMRB) during different phases of their life cycle. Common organic contaminants (i.e. tetrachloride, trichloroethylene (TCE), and trinitrotoluene (TNT)) and inorganic contaminants (i.e. Cr(VI), U(VI), Tc(VII)) can be reduced coupled with the reduction of Fe(III) to Fe(II) by dissimilatory iron-reducing bacteria. DMRB may be used in bioremediation reactive zones in the treatment of groundwater or soils containing the aforementioned contaminants. Understanding the influence of DMRB on conductivity may help in monitoring the remediation progress while treating contaminated ground water and soil.

For each reduction constituent and for each phase of the DMRB life cycle, we used a platinum-plated electrical conductivity probe to measure electrical conductivities. These measurements were made under both aerobic and anaerobic conditions. Of the aforementioned contaminants, we investigated the influences of Cr(VI) on our measurements in the form of potassium dichromate (K2Cr2O7) which is reduced to Cr(IV), an environmentally favorable form of chromium. The reduction constituent scenarios were: (1) PIPES-phosphate, (2) PIPES-phosphate and Fe(III)-citrate, (3) K2Cr2O7, (4) PIPES-phosphate and K2Cr2O7, (5) PIPES-phosphate, Fe(III)-citrate, and K2Cr2O7, (6) DMRB and PIPES-phosphate, (7) DMRB, PIPES-phosphate, and K2Cr2O7, (8) DMRB, PIPES- phosphate, and Fe(III)-citrate, and (9) DMRB, PIPES-phosphate, Fe(III)-citrate, and K2Cr2O7. The type of DMRB we worked with is an iron reducer called Shewanella putrefaciens CN32. We observed changes in electrical conductivity during the Fe(III) reduction process, which may be detectable using in situ electrical conductivity or resistivity tools.

This project was possible because of support provided by Prof. William Burgos, Department of Civil and Environmental Engineering, Pennsylvania State University and by Prof. Hartmut Spetzler, Cooperative Institute of Research in Environmental Sciences, University of Colorado, Boulder.