The use of sulfate-reducing bacteria (SRB) in passive treatments of acidic effluents containing heavy metals has become an attractive alternative biotechnology. Treatment efficiency may be linked with the effluent conditions (pH and metal concentration) and also to the amount and nature of the organic substrate. Variations on organic substrate and sulfate ratios clearly interfere with the biological removal of this ion by mixed cultures of SRB. This study aimed to cultivate a mixed culture of SRB using different lactate concentrations at pH 7.0 in the presence of Ni, Mn and Cu. The highest sulfate removal efficiency obtained was 98 %, at a COD/sulfate ratio of 2.0. The organic acid analyses indicated an acetate accumulation as a consequence of lactate degradation. Different concentrations of metals were added to the system at neutral pH conditions. Cell proliferation and sulfate consumption in the presence of nickel (4, 20 and 50 mg l(-1)), manganese (1.5, 10 and 25 mg l(-1)) and copper (1.5, 10 and 25 mg l(-1)) were measured. The presence of metals interfered in the sulfate biological removal however the concentration of sulfide produced was high enough to remove over 90 % of the metals in the environment. The molecular characterization of the bacterial consortium based on dsrB gene sequencing indicated the presence of Desulfovibrio desulfuricans, Desulfomonas pigra and Desulfobulbus sp. The results here presented indicate that this SRB culture may be employed for mine effluent bioremediation due to its potential for removing sulfate and metals, simultaneously.

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.

Samples of vermicompost were used to decontaminate aqueous media containing Cd2+, Cu2+, Mn2+, Ni2+, Pb2+ and/or Zn2+ at concentration up to 10X higher than the limits of National Council of the Environment (Resolution 430/2011). For this purpose, 50.00 mL of synthetic solutions and wastewater from a chemical laboratory were stirred with dried vermicompost (~10.0000 g), in natura or with diameter ≤ 0.053 mm. Aqueous media were treated with vermicompost, either at rest (24, 48, 72, and/or 96 h) or under mechanical agitation (2, 4, 6, 8, and/or 10 h). All elements were spectrometrically determined in the different supernatants. In the synthetic solutions, except for Mn2+and Zn2+, all cations were undetectable (concentrations lower than the legal limits), when in natura vermicompost was used. After treating synthetic solutions with sieved vermicompost, Cd2+, Cu2+, Ni2+, Pb2+ e Zn2+ concentrations were undetectable, while Mn2+ concentrations were too close to the legal limits. In the wastewater, Cd2+and Pb2+ concentrations, which were 1.5 and 3.8X higher than the legal limits, respectively, were undetectable after treatment with vermicompost in natura. Besides its efficiency of retaining the evaluated metallic cations, vermicompost was able to increase the aqueous media pH from 0.9 to 6.0 ± 0.5.