Kinetics and scale up of oxygen reducing cathodic biofilms

Area of Science:

• Electrochemistry
• Microbial Ecology
• Bioelectrochemical Systems

Background:

• Cathodic biofilms catalyze oxygen reduction, a key process in bioelectrochemical systems.
• Scaling up these biofilms presents challenges due to factors like electrode surface area and medium conductivity.

Purpose of the Study:

• To investigate the kinetics of oxygen reduction in mixed-culture cathodic biofilms.
• To identify factors controlling the scale-up of these biofilms across various electrode sizes.
• To understand the role of microbial community structure in biofilm scale-up.

Main Methods:

• Enrichment of cathodic biofilms on electrodes of increasing surface area (14.5 cm² to 466 cm²).
• Electrochemical characterization including cyclic voltammetry and oxygen reduction kinetics analysis.
• Mathematical modeling using Michaelis-Menten and Butler-Volmer equations.
• Microbial community structure analysis using 16S rRNA gene sequencing.

Main Results:

• Biofilm enrichment shifted oxygen reduction potential, confirming catalytic activity.
• Oxygen reduction followed Michaelis-Menten kinetics, with maximum current density decreasing as electrode surface area increased.
• Scale-up limitations were attributed to ohmic resistance caused by low ionic conductivity in the wastewater medium.
• Microbial community structure showed low variability across different electrode sizes and regions, indicating it does not control scale-up.

Conclusions:

• Ohmic resistance, not microbial composition, is the primary limiting factor for scaling up oxygen-reducing cathodic biofilms.
• The findings provide insights into optimizing bioelectrochemical systems for larger-scale applications.
• Further research should focus on improving medium conductivity to enhance scale-up efficiency.