Sulfate reducing bacteria (SRB) can be used as an alternative biotechnology to promote passive treatment of industrial effluents. Treatment efficiency however depends on pH and metals content of the effluent and also on the quantity of organic matter available. As COD/sulfate ratio varies, sulfate consumption changes. It is commonly assumed that the ideal COD/sulfate ratio is around 0.67. The aim of this work was to optimize the growth and sulfate reduction capacity of mixed bacterial cultures. Samples were cultured using modified Postgate C medium. Metals (Cu, Mn and Ni) were added to the medium in order to study bacterial resistance. Maximum sulfate reducing (98%) was achieved for lactate containing medium, pH 7.0. However, with ethanol containing medium sulfate removal was of about 50%. Acetate production was observed in all cases. Results shown that lactate was more efficient than ethanol for sulfate biological reduction and pH neutralization.