| This study investigated complete reductive dechlorination of chlorinated aliphatic hydrocarbons (CAHs) over a broad range of concentrations. Tetrabutoxysilane (TBOS), as a slow-release anaerobic substrate, was studied for enhanced reductive dechlorination of tetrachloroethylene (PCE) present as a dense non-aqueous liquid (DNAPL). Four different site-mixed cultures were used in the study: Site-300 Lawrence Livermore National Laboratory, CA (LLNL), Point Mugu, CA (PM), the Evanite site in Corvallis, OR (EV), and a binary mixed culture of the PM and EV cultures (BM). Batch studies showed that one mol of TBOS abiotically and slowly hydrolyzed to 4 mol of 1-butanol, which fermented to butyrate and/or acetate, producing H2 during fermentation. The produced H 2 as a direct electron donor was shown to effectively promote the reductive dechlorination of PCE and trichloroethylene (TCE).; A simple kinetic method was developed for determining maximum utilization rates (kmax) and half-velocity coefficients ( KS) that well characterize the dechlorinating microorganisms. Batch inhibition studies indicated that the more chlorinated ethylenes inhibited dechlorination of the less chlorinated ethylenes. Competitive inhibition models simulated well the inhibition experimental data. Inhibition constants of chlorinated ethylenes, KCI (muM), were comparable to their respective half-velocity coefficients, KS (muM).; Two kinetic models fitted the sequential transformation experimental data over a wide range of PCE and TCE concentrations (∼PCE 1000 muM and TCE 4000 muM): one that included competitive inhibition kinetics and the other that included both competitive and Haldane inhibitions. Both kinetic models captured the data well with up to PCE concentrations of 300--400 muM. The kinetic model with competitive and Haldane inhibitions better fit the higher PCE and TCE concentration tests. The PM culture had Haldane inhibition constants of 900, 6000, and 7000 muM for TCE, cis-1,2-dichoroethylene (c-DCE), and vinyl chloride (VC), respectively, indicating slight Haldane inhibition for c-DCE and VC. The EV culture showed significant Haldane inhibition for TCE, c-DCE, and VC (Haldane inhibition constants of 900, 750, and 750 muM, respectively). The BM culture showed better dechlorination ability over a broad range of PCE and TCE concentrations, and more complete dechlorination for remediating PCE DNAPL with TBOS than either of the single mixed cultures. |
