Enhanced bio-production from CO₂ by microbial electrosynthesis (MES) with continuous operational mode

Area of Science:

• Biotechnology and Bioengineering
• Environmental Science and Engineering
• Electrochemistry

Background:

• Growing need for greenhouse gas reduction and de-fossilization of chemical production.
• Microbial electrosynthesis (MES) shows promise for converting CO2 to feedstocks but suffers from low efficiency.
• Existing fed-batch systems lack optimal control for sustained high performance.

Purpose of the Study:

• To enhance the efficiency of microbial electrosynthesis (MES) for CO2 conversion.
• To investigate the impact of a continuous feeding regime on MES performance.
• To optimize operational parameters like hydraulic retention time (HRT) for improved product yield and diversity.

Main Methods:

• Implementation of a continuous feeding strategy for MES.
• Operation under a cathodic potential of -1.0 V Ag/AgCl with dissolved CO2.
• Systematic variation of hydraulic retention time (HRT) to assess its effects on pH, production rates, and coulombic efficiency.
• Analysis of microbial community composition in planktonic and biofilm states.

Main Results:

• Continuous feeding improved pH control and medium refreshment, leading to higher acetate production rates compared to fed-batch.
• An HRT of 3 days yielded the highest acetate production rate (651.8 ± 214.2 ppm/day) and coulombic efficiency (90%) at pH 5.2.
• An HRT of 7 days resulted in lower but stable acetate production (280 ppm/day) and coulombic efficiency (80%) at pH 4.5, with increased detection of diverse longer-chain products.
• Microbial analysis confirmed Acetobacterium as the dominant CO2-reducing bacteria in the biofilm across different feeding modes.

Conclusions:

• A continuous feeding regime is a simple yet effective strategy to enhance MES efficiency for CO2 conversion.
• Optimizing HRT is crucial for balancing acetate production rates, product diversity, and coulombic efficiency.
• Acetobacterium remains the key microorganism for acetate production via CO2 reduction in MES, even with operational mode shifts.