| Manganese-oxidizing microorganisms have been found in fresh water, deep sea, soil and sediment. This kind of bacterium envolved the ability to oxidize soluble Mn(Ⅱ) into insoluble manganese oxides, which were recoganized as highly reactive minerals with high sorption and oxidation capacities for a wide variety of metal ions, and play an important role in the cycles of mineral nutrients and heavy metals in the nature environment. Aesenic (As) is a very toxic metalloid pollutant in the environment, As(Ⅲ) is more toxic than As(Ⅴ) and As(Ⅴ) ios negative changed which is much easier to be removed from solution than the As(Ⅲ). Thus the pre-oxidation of As(Ⅲ) to As(V) is generally required.in the arsenic-containing wastewater treatment technologies. Overall, study on As(Ⅲ)-contaminated wastewater treatment using the produced biogenic manganese oxides is with practical significance. It’s usefull for knowledge enrichment, not only in Mn(Ⅱ) oxidation mechanisms and interaction of inorganic arsenic with biogenic manganese oxides, but also in application of biogenic manganese oxides in the biogeochemical cycles and cleaning of wastewaterMarinobacter flavimaris MnI7-9 and Lysinibacillus sp. Mn44 were isolated from the sediment of deep-sea Mn nodules in India ocean and Pacific ocean, respectively, and both of them showed high Mn(Ⅱ)-oxidizing capability after strain adaptation. In this study, characteristics of growth and heavy metal resistance of stain MnI7-9 and strain Mn44 were investigated. The manganese oxidation mechanism and influence factors of Mn(Ⅱ) oxidation progress were studied as well. Besides, As(Ⅲ) oxidation and removal capability of biogenic manganese oxides were detected, by co-culture experiments and post-culture experiments compared with commercial manganese oxides.The results indicated that both strain MnI7-9 and strain Mn44 had high Mn(Ⅱ) oxidation and removing ability. In a certain concentration range of Mn(Ⅱ) (strain MnI7-9:0-14 mmol/L; strain Mn44:0-2 mmol/L), strain MnI7-9 was able to remove 95% of Mn(Ⅱ) in a 5-day period, while strain Mn44 removed nearly 100%. These Mn(Ⅱ) oxidation progress were greatly effected by addition of Fe(Ⅱ) and Cu(Ⅱ), and Mn(Ⅱ) oxidation rates varied with the concentration of Mn(Ⅱ), Fe(Ⅱ) and Cu(Ⅱ). Under the optimal conditions with initially 10 mmol/L Mn(Ⅱ),0.2-0.3 mmol/L Fe(Ⅱ) and 0.04 mmol/L Cu(Ⅱ), strain MnI7-9 reached the highest oxidation efficiency, oxidizing 80.82% of Mn(Ⅱ); the optimal conditions for strain Mn44 to oxidize Mn(Ⅱ) were the cultivation with initially 2 mmol/L Mn(Ⅱ) and 0.2 mmol/L Fe(Ⅱ) concentrations.The structures of Mn oxides were observed using SEM (scan electron microscope) and XRD (X-ray diffraction) analyses. Resultes showed that biogenic Mn oxides adhere to the cell surface of strain MnI7-9 were regularly layer-forming, containing two typical crystal structures of y-MnOOH and 8-MnO2. These biogenic Mn oxides were highly reactive minerals that owned high capability in treating As(Ⅲ)-polluted water. In a co-cultivation system, almost 70% of As(Ⅲ) was removed. Through the entire proceeding, no As(Ⅴ) was detected in the supernatant, thus, we considered that As(Ⅲ) was first converted into As(Ⅴ) and then absorbed by the biogenic Mn oxides. In a post-culture system, concentration of As(Ⅲ) decreased from 55.02μmol/L to 5.55μmol/L. Thereinto,90% As(Ⅲ) was oxidized into As(Ⅴ) so that detoxification was achieved although most generated As(Ⅴ) was still existed in the supernatant.This study is valuable for the application of manganese-oxidizing bacteria in bioremediation of As(Ⅲ)-polluted wastewater and for the basic understanding of the maganese oxidation mechanisms. |
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