Electrochemical techniques for evaluating short-chain fatty acid utilization by bioanodes

Area of Science:

• Biotechnology and Bioengineering
• Environmental Science
• Electrochemistry

Background:

• Short-chain fatty acids (SCFAs) are key substrates in microbial electrolysis cells (MECs).
• Understanding SCFA utilization is crucial for optimizing MEC performance and energy recovery.

Purpose of the Study:

• To investigate the utilization of propionic, n-butyric, and isobutyric acids in MECs.
• To determine the role of acetic acid as a byproduct and co-substrate.
• To evaluate the influence of applied potential and substrate concentration on current generation and efficiency.

Main Methods:

• Monitoring individual SCFA concentrations.
• Employing electrochemical techniques: linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS).
• Analyzing coulombic efficiency and electric current dependence on substrate concentration.

Main Results:

• Acetic acid was consistently produced and utilized when n-butyric or isobutyric acid was the sole substrate.
• Applied potential controlled current for isobutyric acid, with high coulombic efficiency (90%).
• Lower coulombic efficiency (30-60%) was observed for n-butyric acid.
• Electric current magnitude was more dependent on acetic acid concentration than other SCFAs.
• Exchange current in EIS was a better indicator of substrate favorability than charge transfer resistance.

Conclusions:

• Exoelectrogenic bacteria can directly utilize isobutyric acid with high efficiency in MECs.
• N-butyric acid utilization is less efficient, potentially due to byproduct formation and utilization dynamics.
• Acetic acid plays a significant role as both a byproduct and a preferred substrate in SCFA-driven MECs.
• Electrochemical impedance spectroscopy, specifically exchange current, offers valuable insights into substrate utilization in MECs.