Relationship between electron donor and microorganism on the dechlorination of carbon tetrachloride by an anaerobic enrichment culture

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An investigation involving the supplement of different concentrations of substrates and microorganisms was carried out under anaerobic condition to assess the feasibility of bioremediation of carbon tetrachloride (CCl 4) with the amendment of low concentrations of auxiliary substrate and microorganisms. The concentrations of substrate and microorganisms ranged from 10 to 100 mg/l and from 3.7 × 10 4 to 3.7 × 10 6 cell/ml, respectively. The biotransformation rate of CCl 4 increased progressively with the increase in the concentrations of the substrate and microorganisms. In the low biomass-amended system (3.7 × 10 4cells/ml), 28–71% and 57–96% of CCl 4 removals were exhibited when 10–100 mg/l of acetate or glucose was supplemented, respectively, whereas nearly complete degradation of CCl 4 was observed in the heavily inoculated systems (3.7 × 10 6 cells/ml). An addition of electron donor in the low microbial activity batches enhanced greater efficiency in dechlorination than in the high microbial activity batches. The second-order rate constants ranged from 0.0059 to 0.0092 l/mg/day in high biomass input system, while a two- to four-fold increase in rate constant was obtained in the low microbial activity system. This study indicates that biomass was the more important environmental parameter than substrate affecting the fate of CCl 4. The addition of auxiliary substrates was effective only in low biomass-amended batches (0.56 mg-VSS/l) and diminished inversely with the increase of microbial concentration.