EFFECT OF SULFATE ON THE PROGRESS OF DECHLORINATION THROUGH ANAEROBIC BIOTRANSFORMATION

摘要

The collective literature on dechlorination performance in the presence of sulfate can be interpreted to suggest that dechlorination at sites with elevated sulfate concentrations may be incomplete. Previous work comparing laboratory and field data concluded that the presence of sulfate in sites contaminated with trichloroethylene (TCE) might delay dechlorination but not preclude its completion. To further reconcile these conflicting reports, this work studied quantitatively the effect of sulfate on TCE biotransformation with the aid of a series of laboratory batch experiments, some up to one year-long. Specifically, the aim of the study was three-fold: to confirm whether indeed complete dechlorination is possible under sulfate-reducing conditions, to quantify the delay of dechlorination with suitable metrics, and to investigate whether this delay can be reduced by increasing the quantity of the supplied electron donor. In experiments with initial sulfate concentrations of 1.56 mM (150 mg/L) and 4.16 mM (400 mg/L) and donor supply of 3 mM butyric acid, 0.5 mM (65.7 mg/L) TCE were completely dechlorinated to ethene in about 170 and 300 days, respectively, compared to less than a week, in the absence of sulfate. Accordingly, the rate of vinyl chloride reduction, assuming first-order decay, decreased from 3.13 day~(-1), in the absence of sulfate, to 0.03 day~(-1) and 0.01 day~(-1). The results also showed that under electron-donor limiting conditions, increasing electron donor supply improved dechlorination performance. But, addition of electron donor in excess was unable to speed up dechlorination completion.