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 (CCl4) 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 x 104 to 3.7 x 106 cell/ml, respectively. The biotransformation rate of CCl4 increased progressively with the increase in the concentrations of the substrate and microorganisms. In the low biomass-amended system (3.7 x 104 cells/ml), 28-71% and 57-96% of CCl4 removals were exhibited when 10-100 mg/l of acetate or glucose was supplemented, respectively, whereas nearly complete degradation of CCl4 was observed in the heavily inoculated systems (3.7 x 106 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 CCl4. 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. (C) 2000 Elsevier Science Ltd.