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Biotransformation of 4-Hydroxybenzoic Acid under Nitrate-Reducing Conditions in a MEC Bioanode
Siyuan Zhai1,2,3, Min Ji2,4, Yingxin Zhao2,4
1School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0512, United States.
Environmental Science & Technology
|January 12, 2021
Summary
This study shows that adding nitrate to microbial electrolysis cells (MECs) enables complete degradation of 4-hydroxybenzoic acid (HBA) for renewable hydrogen production. Nitrate reduction in the bioanode enhances exoelectrogenesis and biofuel waste valorization.
Area of Science:
- Biotechnology and Bioengineering
- Environmental Science
- Microbial Electrochemistry
Background:
- 4-Hydroxybenzoic acid (HBA) is a prevalent phenolic compound in lignocellulosic biomass conversion waste streams.
- Efficient valorization of HBA is crucial for sustainable biofuel production and waste stream management.
Purpose of the Study:
- To investigate the biotransformation of HBA in a microbial electrolysis cell (MEC) bioanode.
- To assess the potential for renewable hydrogen (H2) production from HBA using a denitrifying microbial community.
- To elucidate the role of nitrate in HBA degradation and exoelectrogenesis.
Main Methods:
- Enrichment of a mixed, denitrifying microbial culture with HBA as the sole electron donor.
- Operation of microbial electrolysis cells (MECs) under varying conditions (with and without nitrate).
- Analysis of electrochemical performance, H2 yield, HBA degradation pathways, and microbial community composition (including Magnetospirillum and Geobacter).
Main Results:
- In the absence of nitrate, HBA conversion to persistent phenol limited exoelectrogenesis.
- Under nitrate-reducing conditions, complete HBA degradation was achieved with minimal phenol accumulation.
- Active nitrate reduction in the MEC bioanode significantly enhanced exoelectrogenesis and cathodic H2 production.
Conclusions:
- Nitrate-dependent denitrification in the MEC bioanode is key to complete HBA degradation and efficient H2 generation.
- This study demonstrates a viable pathway for valorizing phenolic compounds from biomass waste streams.
- Mechanistic insights are provided for productive use of HBA and related aromatics in bioenergy applications.
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