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Nitrate effects on chromate reduction in a methane-based biofilm
Liang Zhong1, Chun-Yu Lai2, Ling-Dong Shi1
1Department of Environmental Engineering, College of Environmental and Resource Science, Zhejiang University, Hangzhou, China.
Nitrate (NO3-) significantly inhibits chromate (Cr(VI)) reduction in methane-fed membrane biofilm reactors (MBfRs). This inhibition is long-term, impacting microbial communities and reducing Cr(VI) removal efficiency.
Area of Science:
- Environmental microbiology
- Bioremediation
- Water treatment
Background:
- Chromate (Cr(VI)) is a toxic heavy metal pollutant.
- Membrane biofilm reactors (MBfRs) are effective for Cr(VI) removal using methane as an electron donor.
- Nitrate (NO3-) is a common co-contaminant in wastewater.
Purpose of the Study:
- To investigate the impact of nitrate (NO3-) on chromate (Cr(VI)) reduction in a methane-fed MBfR.
- To understand the long-term effects and microbial community shifts caused by nitrate (NO3-).
Main Methods:
- Operation of a membrane biofilm reactor (MBfR) with methane as the sole electron donor.
- Controlled introduction and removal of nitrate (NO3-) at specific loading rates.
- Analysis of Cr(VI) removal efficiency.
- Microbial community analysis using Weighted Principal Coordinate Analysis (PCoA) and UniFrac.
- Gene prediction analysis using PICRUSt.
Main Results:
- High nitrate (NO3-) loading caused significant and irreversible inhibition of Cr(VI) reduction, lowering removal from 100% to <25%.
- Cr(VI) reduction only partially recovered (~70%) after nitrate (NO3-) removal, indicating long-term inhibition.
- Nitrate (NO3-) introduction drastically altered the microbial community structure, decreasing Cr(VI)-reducing genera like Meiothermus and enriching denitrifiers.
- Gene analysis predicted a decrease in chromate reduction genes and an increase in denitrification, methane oxidation, and fermentation genes.
Conclusions:
- Nitrate (NO3-) poses a significant challenge to effective Cr(VI) bioremediation in MBfRs.
- The inhibitory effect of nitrate (NO3-) is linked to substantial shifts in the microbial community and metabolic pathways.
- Further research is needed to understand the mechanisms of inhibition and develop strategies to mitigate nitrate's impact.
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