- 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 tetrachioroethylene (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 H₂ as a direct electron donor was shown to effectively promote the reductive dechlorination of PCE and
A simple kinetic method was developed for determining maximum utilization
rates (kmax) and half-velocity coefficients (Ks) that well characterize the
dechiorinating 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, Kcl (μM), were comparable to their
respective half-velocity coefficients, Ks (μM).
Two kinetic models fitted the sequential transformation experimental data
over a wide range of PCE and TCE concentrations (~ PCE 1000 μM and TCE 4000
μM): 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 μM. 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 μM
for TCE, cis-1,2-dichloroethylene (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 μM, 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.