Abstract
Natural attenuation of Mn(II) was observed inside the metal refinery wastewater pipeline, accompanying dark brown-colored mineralization (mostly MnIVO2 with some MnIII2O3 and Fe2O3) on the inner pipe surface. The Mn-deposit hosted the bacterial community comprised of Hyphomicrobium sp. (22.1%), Magnetospirillum sp. (3.2%), Geobacter sp. (0.3%), Bacillus sp. (0.18%), Pseudomonas sp. (0.03%), and non-metal-metabolizing bacteria (74.2%). Culture enrichment of the Mn-deposit led to the isolation of a new heterotrophic Mn(II)-oxidizer Pseudomonas sp. SK3, with its closest relative Ps. resinovorans (with 98.4% 16S rRNA gene sequence identity), which was previously unknown as an Mn(II)-oxidizer. Oxidation of up to 100 mg/L Mn(II) was readily initiated and completed by isolate SK3, even in the presence of high contents of MgSO4 (a typical solute in metal refinery wastewaters). Additional Cu(II) facilitated Mn(II) oxidation by isolate SK3 (implying the involvement of multicopper oxidase enzyme), allowing a 2-fold greater Mn removal rate, compared to the well-studied Mn(II)-oxidizer Ps. putida MnB1. Poorly crystalline biogenic birnessite was formed by isolate SK3 via one-electron transfer oxidation, gradually raising the Mn AOS (average oxidation state) to 3.80 in 72 h. Together with its efficient in vitro Mn(II) oxidation behavior, a high Mn AOS level of 3.75 was observed with the pipeline Mn-deposit sample collected in situ. The overall results, including the microbial community structure analysis of the pipeline sample, suggest that the natural Mn(II) attenuation phenomenon was characterized by robust in situ activity of Mn(II) oxidizers (including strain SK3) for continuous generation of Mn(IV). This likely synergistically facilitated chemical Mn(II)/Mn(IV) synproportionation for effective Mn removal in the complex ecosystem established in this artificial pipeline structure. The potential utility of isolate SK3 is illustrated for further industrial application in metal refinery wastewater treatment processes.
Highlights
Soluble Mn(II) ions persist in a wide pH range and, their removal from mining-impacted waters is a challenging task
Biogenic Mn-precipitates were periodically collected by centrifugation during Mn(II) oxidation by isolate SK3
Biogenic Mn-precipitates were collected during Mn(II) oxidation by isolate SK3
Summary
Soluble Mn(II) ions persist in a wide pH range and, their removal from mining-impacted waters is a challenging task. The majority of naturally occurring Mn-oxides in these environments are considered to originate directly from microbial Mn(II) oxidation or from the subsequent alteration of biogenic Mn-oxides [3] This indicates the ubiquitous and robust nature of these Mn(II)-oxidizing bacteria, resulting in an extensive impact on the Mn geochemistry of the earth’s crust. Based on the pH and ORP values of the wastewater, this phenomenon appeared to involve biological intervention, rather than spontaneous chemical Mn(II) oxidations The mechanism of this natural Mn(II) attenuation could be reconstituted as a bioprocess to be introduced in wastewater treatment facilities. The bioprocess could be potentially installed as a post-treatment following the neutralization step, in order to reduce the vast cost for alkaline agents For this aim, it was necessary to find an isolate which withstands high Mn(II) concentrations and displays robust Mn(II) oxidation, especially in the presence of MgSO4 as a typical major component in refinery wastewaters. Attenuation phenomena in the metal refinery wastewater pipeline, and isolation and characterization of a new Mn(II)-oxidizing bacterium with a robust Mn(II)-oxidizing capability
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