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Simultaneous reduction of perchlorate and nitrate using fast-settling anoxic sludge

Nathan Stein¹, Aditi Podder², Jennifer Lee Weidhaas¹

¹Department of Civil and Environmental Engineering, University of Utah, Salt Lake City, UT, 84112, USA.

|August 10, 2021

Summary

This study demonstrates effective simultaneous removal of perchlorate and nitrate using fast-settling, anoxic sludge in an anaerobic sequencing batch reactor (AnSBR). Microbial activity and gene expression confirmed efficient contaminant reduction, with shifts in microbial communities observed under varying operational conditions.

Area of Science:

Environmental Microbiology
Water Treatment Technologies
Bioremediation

Background:

Perchlorate and nitrate are common water contaminants.
Simultaneous removal is challenging due to competing electron acceptors.
Anaerobic bioreactors offer a potential solution for contaminant reduction.

Purpose of the Study:

To evaluate the efficacy of fast-settling, anoxic sludge (FAS) for simultaneous perchlorate and nitrate reduction.
To investigate the impact of hydraulic retention time (HRT) and loading rates on removal efficiencies.
To analyze microbial gene expression and community shifts during the bioremediation process.

Main Methods:

Cultivation of FAS in an anaerobic sequencing batch reactor (AnSBR).
Long-term operation (>500 days) with controlled perchlorate and nitrate loading rates.
Batch activity tests to assess substrate utilization and inhibition.
mRNA-based gene expression analysis of key reductase and dismutase enzymes.
16S rRNA gene sequencing to track microbial community dynamics.

Main Results:

Achieved high removal efficiencies (>96% for perchlorate, >99% for nitrate) under tested loading rates.
Observed preferential nitrate utilization over perchlorate, causing inhibition under carbon-limiting conditions.
Demonstrated increased specific reduction rates with decreased HRT and increased loading rates.
Confirmed simultaneous heterotrophic denitrification and perchlorate reduction via gene expression.
Detected nitrous oxide (N2O) production due to incomplete denitrification, highest at elevated nitrate loads.
Observed a shift in microbial dominance from Thauera to Dechloromonas species as HRT decreased.

Conclusions:

FAS in an AnSBR is effective for simultaneous perchlorate and nitrate removal.
Nitrate competition impacts perchlorate reduction efficiency.
Optimizing HRT and loading rates enhances bioremediation performance.
Microbial community structure adapts to operational changes, influencing contaminant degradation pathways.

Keywords:

Dechloromonas Heterotrophic denitrification Nitrate reduction Perchlorate reduction Thauera

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