Effects of the inoculum source, electron donor, and immobilization on the microbial community of sulfidogenic bioreactors

Abstract This study evaluated the biological treatment efficiency and microbial communities of eight anaerobic sequencing batch reactors treating sulfate-rich wastewater using inocula of sewage and industrial origin, immobilized or not, operated in two phases, first using lactate, and then ethanol as an electron donor. Regardless of the inoculum origin and immobilization, the maximum percentage of sulfate removal in the lactate phase was 80 ± 2%; the ethanol phase was 84 ± 3%. A lag phase in the sulfate removal was observed at the beginning of the reactor operation (lactate phase) for both types of sludge-inoculated reactors. The maximum chemical oxygen demand removal in the lactate phase was 70 ± 4%; the ethanol phase was 65 ± 5%. Pyrosequencing analysis demonstrated an increased abundance of sulfate-reducing bacteria. Only the reactors inoculated with industrial sludge presented methanogenic Archaea abundance of 3.44 and 4.15% in the lactate and ethanol phases, respectively. The genus Desulfovibrio was found in an abundance of 25.21 and 34.06% with ethanol as a carbon source in the reactors with the immobilized inocula of industrial origin, demonstrating the ability of the microbial consortium to adapt to the substrate and microenvironment. Understanding the potential for the effects of electron donors, inoculum origin, and its immobilization in the sulfate reduction and development of the microbial community can facilitate the establishment of strategies for the bioremediation of acid mine drainage.