Biological treatment of mining wastewaters by fixed-bed bioreactors at high organic loading.

Acid wastewaters contaminated with Fe - 1000 mg L(-1) and Cu - 100 mg L(-1) were remediated by microbial sulfate-reduction at high organic loading (theoretical TOC/SO4(2-) ratio 1.1) in a laboratory installation. The installation design includes a fixed-bed anaerobic bioreactor for sulfate-reduction, a chemical reactor, a settler and a three-sectional bioreactor for residual organic compounds and hydrogen sulfide removal. Sulfate-reducing bacteria are immobilized on saturated zeolite in the fixed-bed bioreactor. The source of carbon and energy for bacteria was concentrated solution, containing ethanol, glycerol, lactate and citrate. Heavy metals removal was achieved by produced H2S at sulfate loading rate 88 mg L(-1)h(-1). The effluent of the anaerobic bioreactor was characterized with high concentrations of acetate and ethanol. The design of the second bioreactor (presence of two aerobic and an anoxic zones) makes possible the occurrence of nitrification and denitrification as well as the efficiently removal of residual organic compounds and H2S.