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Published on: October 15, 2015
The effect of electron competition on chromate reduction using methane as electron donor
Pan-Long Lv1, Liang Zhong1, Qiu-Yi Dong1
1College of Environmental and Resource Science, Zhejiang University, Hangzhou, China.
Electron competition impacts chromate (Cr(VI)) reduction in methane-based membrane biofilm reactors. Sulfate addition initially boosted Cr(VI) removal, but high levels and selenium (Se(VI)) hindered it, revealing microbial roles in contaminant reduction.
Area of Science:
- Environmental Science
- Microbiology
- Environmental Engineering
Background:
- Chromate (Cr(VI)) is a toxic environmental pollutant.
- Methane (CH4)-based membrane biofilm reactors (MBfRs) are used for contaminant remediation.
- Electron supply often limits the efficiency of Cr(VI) reduction in MBfRs.
Purpose of the Study:
- To investigate the effect of electron competition on Cr(VI) reduction in a CH4-based MBfR.
- To understand the role of sulfate (SO4^2-) and selenium (Se(VI)) as electron competitors.
- To identify microbial players involved in Cr(VI) and sulfate reduction.
Main Methods:
- Operated a methane-based membrane biofilm reactor (MBfR) with varying surface loadings of sulfate (SO4^2-).
- Introduced selenium (Se(VI)) to assess its impact on Cr(VI) removal.
- Analyzed microbial community composition using 16S rRNA gene sequencing.
- Correlated microbial abundances with contaminant removal efficiencies.
Main Results:
- Low SO4^2- loading (4.7 mg/m^2-d) promoted Cr(VI) reduction from 60% to 70%.
- Complete removal of SO4^2- led to a further increase in Cr(VI) removal to 90%, indicating retained sulfate-reducing bacteria (SRB) activity.
- High SO4^2- loading (26.6 mg/m^2-d) and the presence of Se(VI) (0.5 mg/L) significantly inhibited Cr(VI) reduction.
- Microbial community structure was significantly influenced by Cr(VI) and SO4^2- loadings.
- Methylocystis (a type II methanotroph) was identified as reducing both Cr(VI) and sulfate.
- Meiothermus was found to reduce only Cr(VI), while Ferruginibacter reduced only SO4^2-.
Conclusions:
- Electron competition between Cr(VI), SO4^2-, and Se(VI) plays a critical role in MBfR performance.
- Sulfate-reducing bacteria (SRB) can contribute to Cr(VI) removal, but high sulfate concentrations can lead to competition.
- Specific microbial taxa, including methanotrophs, are responsible for the reduction of different contaminants.
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