MFC-cascade stacks maximise COD reduction and avoid voltage reversal under adverse conditions

Area of Science:

• Environmental Science
• Electrochemistry
• Microbiology

Background:

• Microbial Fuel Cells (MFCs) offer a sustainable approach to wastewater treatment and energy generation.
• Optimizing MFC configurations is crucial for improving performance and scalability.

Purpose of the Study:

• To evaluate the performance of a vertical cascade of six continuous-flow MFCs under different electrical connections.
• To assess the impact of substrate imbalances and starvation on MFC stack operation.
• To compare the efficiency of stacked MFCs against single large units.

Main Methods:

• Six continuous-flow MFCs were configured in a vertical cascade.
• MFCs were tested under parallel and series electrical connections.
• System performance was monitored during stable operation, substrate imbalances, and starvation periods (up to 15 days).
• Chemical Oxygen Demand (COD) reduction was measured.

Main Results:

• Parallel MFC configuration showed stable operation with higher power and current densities than individual MFCs.
• Cascading achieved over 95% COD reduction in 5.7 hours (7.97 kg COD m(-3) d(-1)).
• Series configuration performance improved significantly after proper insulation, outperforming individual units.
• The 6-MFC system exhibited no significant performance degradation during 15-day starvation periods.
• Substrate imbalances and starvation did not lead to cell-voltage reversal.

Conclusions:

• Cascade-stacking of small MFC units enhances electricity production and treatment rates compared to single large units.
• This approach offers a cost-effective solution without expensive catalysts.
• MFC stacks demonstrate resilience to operational challenges like substrate variability and starvation.