• chromium (VI);
  • electromagnetic field;
  • bioreduction;
  • batch system

In this study, the bioreduction of chromium (VI) and Chemical Oxygen Demand (COD) were obtained using a mixed culture of microorganisms originating from the tannery industry. The influence of an electromagnetic field on the reduction of chromium (VI), together with the removal of COD and total chromium, were evaluated. Batch reactors were used, one in the presence of an electromagnetic field and another without exposure to the field. The bioreduction was conducted with various initial concentrations of chromium (VI) (50, 100, 150, and 200 mg L−1) at different electromagnetic field frequencies (1, 2, 5, and 10 Hz) with different initial volumes of the effluent (300, 500, and 1000 mL). Using an initial concentration of chromium (VI) of 100 mg L−1 in 500 mL of effluent at a frequency of 5 Hz, the maximum chromium (VI) bioreduction was 100% after 8 h, but the total removal of chromium was 38%. Using the same conditions but with a volume of 1000 mL, the same reduction of chromium (VI) was achieved, but there was a need for a longer processing time, ∼14 h. When using concentrations above 100 mg L−1, the same efficiency for the bioreduction of chromium (VI) was not obtained relative to the experiments performed without the presence of an electromagnetic field. The concentration of cells in both reactors remained almost constant over time, except when a frequency higher than 5 Hz was used, where we could observe the occurrence of cell death. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 88–98, 2015