Abstract
The sulfate-reducing bioprocess is a promising technology for the treatment of heavy metal-containing wastewater. This work was conducted to investigate the possibility of promoting heavy metal removal by the addition of citrate to mask Ni2+ toxicity to sulfate-reducing bacteria (SRB) in batch reactors. SRB growth was completely inhibited in Ni2+-containing medium (1 mM) when lactate served as the sole carbon resource, leading to no sulfate reduction and Ni2+ removal. However, after the addition of citrate, SRB grew well, and sulfate was quickly reduced to sulfide. Simultaneously, the Ni-citrate complex was biodegraded to Ni2+ and acetate. The NiS precipitate was then formed, and Ni2+ was completely removed from the solution. It was suggested that the addition of citrate greatly alleviates Ni2+ toxicity to SRB and improves the removal of Ni2+, which was confirmed by quantitative real-time PCR targeting dissimilatory sulfite reductase (dsrAB) genes. Analysis of the carbon metabolism indicated that lactate instead of acetate served as the electron donor for sulfate reduction. This study offers a potential approach to increase the removal of heavy metals from wastewater in the single stage SRB-based bioprocess.
Highlights
Heavy metals, often associated with mine waters and industrial wastewater contributions, have been reported as a cause of many human diseases, such as kidney or nervous system damages and cancers.Sulfate-reducing bioprocess for treating wastewaters from mining and mineral processing are becoming an alternative to conventional chemical treatment [1,2,3]
In anaerobic semi-continuous stirred tank reactors, when the heavy metal concentration is above the tolerable concentration of sulfate-reducing bacteria (SRB), the growth and sulfate-reducing activity of SRB were completely inhibited, and no metal was removed from the solutions [8]
Media, the predominant Ni-citrate complex constituted 45.58% and 74.92% and the Ni-lactate complex constituted 23.10% and 8.02%, respectively. These results indicated that the presence of citrate led to a great reduction of free Ni2+
Summary
Sulfate-reducing bioprocess for treating wastewaters from mining and mineral processing are becoming an alternative to conventional chemical treatment [1,2,3]. This anaerobic process is carried out by sulfate-reducing bacteria (SRB) that utilize sulfate as the final electron acceptor for the oxidation of organic compounds (electron donors), resulting in the production of hydrogen sulfide (H2S). The SRB-based bioprocess has been successfully applied by using single or separated unit processes to treat metal-containing wastewaters [4,5,6]. In anaerobic semi-continuous stirred tank reactors, when the heavy metal concentration is above the tolerable concentration of SRB, the growth and sulfate-reducing activity of SRB were completely inhibited, and no metal was removed from the solutions [8]
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