Evaluation of normalized energy recovery (NER) in microbial fuel cells affected by reactor dimensions and substrates

• Energy recovery affected by dimensions and substrates in MFCs has been studied.
• Longer retention time and/or a lower organic loading rate benefits energy recovery.
• Increasing MFC size does not necessarily decrease energy recovery.
• MFCs should be evaluated by both energy recovery and treatment performance.

The objective of this study is to provide an initial evaluation of normalized energy recovery (NER – a new parameter for presenting energy performance) in microbial fuel cells (MFCs) through investigation of the effects of reactor dimensions and anode substrates. Although the larger-size MFCs generally have lower maximum power densities, their maximum NER is comparable to that of the smaller MFCs at the same anolyte flow rate. The mixed messages obtained from the MFC size tests suggest that MFCs can be further scaled up without decreasing energy recovery under certain conditions. The low-strength substrates seem to be more suitable for MFC treatment of wastewater, in terms of both energy recovery and organic removal. However, because the MFCs could not achieve the maximum NER and the maximum organic removal efficiency at the same time, one must determine a major goal for MFCs treating wastewater between energy recovery and contaminant removal.

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