# Novel Microfluidic Septum to Optimize Energy Recovery in Single-Chamber Microbial Fuel Cells
## 5 Conclusions  
In this work, the effective role of an intermediate microfluidic septum (IMS) in a-SCMFCs was demonstrated. Indeed, the IMS played a pivotal role in mimicking the fluid flow distribution according to a drop-like shape, thus ensuring a better distribution of sodium acetate close to the anode surfaces. All the obtained results, moreover, allowed us to confirm that the IMS could act as a separator material, able to minimize oxygen cross-over on anode electrodes and, consequently, to positively affect biofilm formation on the anodic electrodes. Indeed, during the start-up phase, the output potential provided by the IMS was immediately comparable with that of the control cells, thus leading us to confirm the correct proliferation of biofilm on the anode electrodes. Moreover, it was possible to appreciate that the IMS achieved reproducible voltage peaks within the first electrolyte replenishment. In comparison, the control cells steadily reached the value of the first peak, but not until the third electrolyte replenishment. Cells featuring an IMS had enhanced energy recovery from an electrolyte solution containing sodium acetate as the carbon energy source. By reducing the concentration of sodium acetate in the electrolyte medium, it was possible to verify that such overperformance persisted even when a smaller carbon energy source became available. In addition, in the long term, cells containing the IMS provided a more stable potential output compared to the control cells, suggesting that the development of the anodic biofilm might have been more efficient. All these optimal results were achieved with the proposed new configuration of an IMS cell that showed an internal volume of 6.6 mL, which is lower than that reported in the literature. Also, a fed-batch mode was implemented to refill the entire volume with fresh electrolytes; commercial carbon-based materials were employed as electrodes; and anodic biofilm was formed, starting from a mixed consortium. All these underlined parameters and characteristics played a pivotal role in guaranteeing the direct applicability of these devices in the environment.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **MFC Designs** & **Performance Achieved** & **Ref.** \\ \hline \(\bullet\) & Dual-chamber MFC & \\ \(\bullet\) & Separator: Nafion 117 membrane & Maximum output voltage: \\ \(\bullet\) & Internal volume: 50 mL & 0.59 V, reached after 4 cycles. \\ \(\bullet\) & Sodium acetate concentration: 0.5 g/L & \\ \(\bullet\) & Air-cathode single-chamber MFC & Maximum open-circuit \\ \(\bullet\) & Internal volume: 50 mL & voltage: 791 mV. \\ \(\bullet\) & Inoculum from aerobic activated sludge & \\ \(\bullet\) & Miniaturized air-cathode & Maximum power density for both \\ \(\bullet\) & single-chamber MFC & configurations was strictly \\ \(\bullet\) & Two architectures: squared and & correlated with the flow rate: the \\ \(\bullet\) & drop-shaped & higher the flow rate, the higher \\ \(\bullet\) & Sodium acetate variable concentration. The & the power density output. \\ \(\bullet\) & cells were operated in continuous mode & Drop-like architecture showed the \\  & & largest power output. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Literature references for comparison with different MFC designs.  
**Author Contributions:** Conceptualization and methodology, M.Q., S.B., N.V. and G.M.; design and fabrication, V.B., G.S. and N.V.; experimental activity and data processing, G.S.; writing--original draft preparation, review and editing, G.S., G.M., M.Q. and S.B.; supervision and funding acquisition, F.C.P. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data is unavailable.  
**Conflicts of Interest:** The authors declare no conflict of interest.