Isolation Of Sulfate Reducing Bacteria From Sewage Sludge And Determination Of Its Heavy-metal-removal Mechanism

Treatment of acid mine drainage(AMD), characterized by low pH and high concentrations of heavy metal ions and sulfates, has been focused on biological approach, especially sulfate reducing bacteria(SRB) method. This method was widely investigated mainly due to its effectiveness and low process cost and no further pollution. So it is a very promising technology. However, the classification and identification of SRB has been incomplete. The study on the purification and identification of SRB is benefit to establish a scientific and complete classification identification system. On the other hand, many studies have focused on the removal mechanism of heavy metal ions based on SRB. However, the results are not satisfied at present. The research on the removal mechanism of heavy metal ions is very important for the development of efficient treatment of AMD based on the use of SRB.In this paper, a strain of sulfate reducing bacteria was isolated from sewage sludge by the use of repeat dish sandwich. The physiological and biochemical characteristics of SRB and removal mechanism of heavy metal ions(Fe2+, Zn2+, Cu2+) were also studied.Phylogenetic analysis based on 16 S r DNA gene sequence of strain SST1 revealed that the isolate designated strain SST1 was a member of the genus Desulfovibrio,family Desulfovibrionaceae in δ-Proteobacteria, with “Desulfovibrio marrakechensis”being its closed relative(sequence similarity of 99.87%). Cells of strain SST1 were rod-shaped with non-spore forming, non-motile, and strained Gram-negative. Strain SST1 grew optimally at 35 oC, p H 6.27, and 0.59 % Na Cl in a medium with 20mmol/L ethanol as carbon source. The removal efficiency of sulfate was declined gradually with the increase of metal ions concentration. The maximum tolerance concentration of Fe2+, Zn2+, Cu2+ of SST1 were 300, 55, 14 mg/L respectively.Determination of heavy metal removal mechanism by SST1 was studied withheavy metal ion concentrations of Fe2+ 55 mg/L、Zn2+ 32 mg/L and Cu2+ 10 mg/L, in which the removal efficiency of sulfate was higher. The removal efficiency of heavy metal ions was Fe2+ 98.53% and Zn2+ 99.88%. Cu2+ was not detected which means it has been removed completely. Combined with biological control tests, X-ray diffraction(XRD) and scanning electron microscopy(SEM), the mechanism of heavy mental ions was demonstrated that Fe2+ was removed mostly as sulfide precipitate(Fe3S4) while Zn2+ was removed in the form of sulfide precipitate(Zn S) and Cu2+ was removed in the form of cell adsorption.