Challenges and Future Directions:
Low Power Output:
The power output of individual MFCs is currently low, limiting their practical applications.
Material and Cost Issues:
Research is ongoing to improve electrode materials, membranes, and overall system design to reduce costs and improve efficiency.
Scaling Up:
Scaling up MFC technology to meet large-scale energy demands is a significant challenge.

Thank you for this clearly written, yet detailed explanation and justification.