Influence of ferrous iron and pH on carbon tetrachloride degradation by Methanosarcina thermophila

The influence of environmental conditions on the biological transformation of a contaminant must be well understood to optimize remediation processes. One factor that impacts tile biological transformation of carbon tetrachlo ride (CT) is elemental iron (Fe-0). Previous research has shown that Fe-0 i ncreases the methanogenic CT degradation rate by providing H-2 for cell gro wth and dechlorination. As Fe-0 oxidizes it also increases the pH and Fe2levels, which may also impact the biological transformation of CT. Experime nts were performed with Methanosarcina thermophila to investigate the influ ence of these factors on CT degradation. The transformation of CT and CF wa s greatly influenced by pH, with the rate of CT and CF degradation increasi ng with increasing pH. After 6 h, > 90% of the CT had been degraded in the treatments containing cells at a FH of 8.5, whereas only about 51% of the C T had been degraded in similar treatments at a pH of.5.5. Fe2+ did not sign ificantly influence the degradation of CT; however, 60% less CF was formed in systems containing cells + Fe2+ than in systems containing cells only. I n addition, Fe2+ prolnoted rapid transformation of CF when added to treatme nts containing cells. The product distribution after 9 days in all systems containing cells was very similar, with 98.04 +/- 5.46% (two-sided 95% conf idence interval) of the originally fed CT present as soluble products. Thes e results show that pH and Fe2+ influence the degradation of CT and CF, alt hough transiently. Because the residence time of contaminants in Fe-0 barri ers varies with the thickness of the barrier, it is likely that this influe nce will be important for some Bow-through systems. This implies that a com bined Fe-0/organism remediation system may have previously unrealized advan tages (due to pH and Fe2+ changes). (C) 2001 Elsevier Science Ltd. AII righ ts reserved.