Avaliação do potencial de comunidades microbianas sulfato redutoras para tratamento de drenagem ácida de mina em reatores sulfetogênicos em escala de bancada

Abstract

Acid Mine Drainage (AMD) is a serious environmental problem in mining industries because of the low pH, high levels of sulfate and dissolved metals present in this wastewater. Biological AMD treatment have been used instead of the traditional method, due to high efficiency obtained in these bioreactors, which promote the sulfate reduction into sulfide by sulfate reducing bacteria (SRB) in the presence of organic matter and anaerobic conditions. An alternative for the biological treatment of AMD consists on the bioremediation using autochthonous SRB that guarantees environmental safety, cost effective and better adaptability. This work studied the potential of autochthonous SRB to sulfate removal in batch anaerobic reactors comparing two inoculum sources. An autochthonous (AUT) biomass, derived from enrichment culture of AMD sediments and, a non-autochthonous (NON-AUT), from a pre-acclimated sludge from a stable sufidogenic reactor adapted with lactate as carbon source, were tested. The sulfate reduction using cost effective electron donors (ethanol and formate) and the acidity resistance of AUT inoculum was also verified. Results showed a maximum sulfate removal of 57% for AUT and 62% for NON-AUT. Phylogenetic study of SRB group using sequencing of dsrB DGGE excised bands revealed the presence of Desulfotomaculum-related bacteria in AUT community, while Desulfovibrio was the predominant genus found in NON-AUT-derived community. When ethanol was used as carbon source, a sulfate reduction of 46% was found and 35% for formate, indicating that at neutral conditions, ethanol is the most viable alternative as carbon source for the enrichment process. At low pH, sulfate reduction still occurred, indicating that these microorganisms were resistants to acidic conditions. However the removal efficiency was reduced when lactate (only 30% on pH close to 3) and ethanol (only 18% on pH close to 5) were used as electron donors. When formate was the carbon source, the sulfate removal efficiency was maintained closely to 38% with pH reduction to 3 and 4, showing that at these conditions, formate is the best carbon source for SRB enrichment. Thus, AUT culture could be used for local AMD decontamination in substitution of pre-acclimated sludge from sulfidogenic reactors.