Mackinawite and cobalamin have been known as reactive natural reductant and electron transfer mediator in subsurface, respectively. We have demonstrated reductive dechlorination of PCE by nano-mackinawite (nFeS) combined with cyanocobalamin(III) (Cbl(III)) and investigated the effect of environmental factors (pH, reactant concentration, competing ions) on the reductive dechlorination kinetics. The dechlorination kinetic increased (0.0017 to 0.1003 hr-1) as its suspension pH increased (pH 5 to 12). Ninety percent of PCE was degraded by nFeS-Cbl(III) at pH 12 in 30hr, while the removal significantly decreased as the order of pH 5(13%), 7(23%), 9(39%), and 11(51%). The oxidation-reduction potential (ORP) of nFeS-Cbl(III) was measured by cyclic voltammetry and the highest value was observed at pH 12. The reduction of Cbl(III) into Cbl(I) at pH 12 was verified by measurement of Cbl species on the nFeS surface with UV-Vis spectrometer. Subsequent experiments were performed at pH 12 to investigate the effect environmental factors on the reductive dechlorination kinetics.  As nFeS content increased (0.05 to 0.5g), the dechlorination kinetic was accelerated from 0.0423 to 0.3557 hr-1. In case of Cbl(III) concentration, higher concentration (0.5mM) can obtain faster dechlorination kinetic (0.9870 hr-1) but the kinetic rate constant reached plateau after 0.5mM of Cbl(III). The effect of various ions found in natural groundwater such as Na+, K+, Mg2+Ca2+ ,CO32-, SO42-, NO3-, and HCO3- was studied. The dechlorination kinetic 3 to 18 times increased in the presence of the ions except HCO3-. In case of HCO3-, the dechlorination kinetic decreased by 5 times. The experimental results can provide basic knowledge of environmental factors' impact on reductive dechlorination of PCE by natural reductant at high pH.

Reductive dechlorination of PCE by nano-mackinawite with cobalamin at high pH

248th National Meeting (2014)

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