Nano zero-valent iron: A pH buffer, electron donor and activator for chain elongation

Area of Science:

• Biotechnology and Bioengineering
• Environmental Microbiology
• Chemical Engineering

Background:

• Medium-chain carboxylates are vital precursors for pharmaceuticals, antimicrobials, and biofuels.
• Optimizing the production of these carboxylates, such as caproate, is crucial for industrial applications.

Purpose of the Study:

• To investigate the effect of nano zero-valent iron (NZVI) on caproate production.
• To elucidate the mechanisms by which NZVI influences caproate synthesis and microbial community structure.

Main Methods:

• Addition of varying concentrations of nano zero-valent iron (NZVI) to microbial cultures.
• Measurement of caproate concentration, ethanol oxidation, and byproduct formation (butyrate, butanol).
• Analysis of pH changes, electron balance, and microbial community composition via high-throughput sequencing.

Main Results:

• NZVI addition significantly enhanced caproate production, reaching 27.2 mmol/L (a 100% increase) at 5 g/L NZVI.
• NZVI promoted ethanol oxidation while decreasing butyrate and butanol levels.
• Mechanism studies indicated NZVI stabilized pH above 5.4 via displacement reactions and provided electrons for microbial metabolism.

Conclusions:

• Nano zero-valent iron is an effective additive for enhancing caproate production.
• NZVI reshapes microbial communities, favoring chain elongators like Oscillibacter Marseille-P3260 and iron-utilizing Corynebacterium.
• The findings offer a novel strategy for improving the production of valuable carboxylates for various industries.