Bioreduction of Cr(VI) from acidic wastewaters in a sulfidogenic ABR

In the present study, the biotreatment of synthetic acidic wastewater containing Cr(VI) (35-200 mg L-1), Fe(III) (100 mg L-1) and sulfate (3500 mg L-1), was studied in an ethanol supplemented (2730 mg L-1 COD) anaerobic baffled reactor (ABR) at constant hydraulic retention time (HRT) of 1.0 day. Reactor performance was very high even at low pH (2.5-3.5) and high Cr(VI) concentration (200 mg L-1). Sulfate reduction and COD oxidation degrees exceeded 80% and 90%, respectively, in all cases. The alkalinity generated due to the sulfidogenic oxidation of ethanol increased wastewater pH to neutral values (7.3-8.0) and facilitated precipitation of Cr(III) compounds. Electron flow from ethanol oxidation to sulfate reduction averaged 85.4 +/- 13%.