Production of biogenic manganese oxides coupled with methane oxidation in a bioreactor for removing metals from wastewater

Abstract

Biogenic manganese oxide (BioMnO_x) can efficiently adsorb various minor metals. The production of BioMnO_x in reactors to remove metals during wastewater treatment processes is a promising biotechnological method. However, it is difficult to preferentially enrich manganese-oxidizing bacteria (MnOB) to produce BioMnO_x during wastewater treatment processes. A unique method of cultivating MnOB using methane-oxidizing bacteria (MOB) to produce soluble microbial products is proposed here. MnOB were successfully enriched in a methane-fed reactor containing MOB. BioMnO_x production during the wastewater treatment process was confirmed. Long-term continual operation of the reactor allowed simultaneous removal of Mn(II), Co(II), and Ni(II). The Co(II)/Mn(II) and Ni(II)/Mn(II) removal ratios were 53% and 19%, respectively. The degree to which Mn(II) was removed indicated that the enriched MnOB used utilization-associated products and/or biomass-associated products. Microbial community analysis revealed that methanol-oxidizing bacteria belonging to the Hyphomicrobiaceae family played important roles in the oxidation of Mn(II) by using utilization-associated products. Methane-oxidizing bacteria were found to be inhibited by MnO₂, but the maximum Mn(II) removal rate was 0.49 kg m^-3 d^-1.

Keywords: Biological manganese oxidation; Biomass-associated products (BAPs); Downflow hanging sponge (DHS) reactor; Methane oxidation; Minor metal removal; Utilization-associated products (UAPs).