# Novel Microfluidic Septum to Optimize Energy Recovery in Single-Chamber Microbial Fuel Cells
## 4 Discussion  
With the main purpose of enhancing the overall performance of asymmetric SCMFCs, this work proposes to optimize the electrolyte distribution by redesigning the inner volume of the reactors to give them a shape able to most effectively follow the spontaneous fluid flow field. The improved management of the electrolyte, ensured by the microfluidic septum, allows the energy conversion to be optimized, as demonstrated during all the phases, and as can be observed in Figures 2 and 3. Not only was the output voltage higher for the IMS cells, but the peaks were more stable and reproducible than the control cells. The improvement is further confirmed by the last phase of the experiment, during which, the carbon source concentration was changed over time. This result is particularly important since it shows that the IMS is able to optimize the inner environment of the cells in such a way to optimize the activity of the anodic biofilm. Indeed, the metabolic activity of electroactive bacteria is strictly correlated to the maximum output potential generated by MFCs and the concentration of the carbon energy source dissolved in the electrolyte [31, 43].  
These results show that, acting as a physical barrier interposed between the anode and the cathode, the IMS plays a crucial role in allowing for the optimization of the flow and then the cross-over of chemical species inside the reactor. Indeed, due to its aspect ratio shown in Figure 1A, the separator introduces mass transport limitations, also highlighted by Figure 7. One fundamental limitation is expected to involve oxygen: the IMS actually limits oxygen cross-over on the anode surface, thus minimizing the oxygen dissolved into the electrolyte in the proximity of biofilm growth onto anode electrodes. Nevertheless, the specific IMS design guarantees an appropriate electrolyte flow during cell refills and optimal replenishment with minimum perturbation of the internal environment. The experiments carried out in this study have clearly demonstrated that the beneficial effect of the biofilm protection against oxygen contamination is also the leading phenomenon, overcoming the barrier effect on other species, and thus ensuring better behavior than the control cells, especially for long-term applications, as shown in Figures 5 and 6. As  
Figure 7: EIS characterizations performed on two representative cells, (**A**) IMS and (**B**) control, throughout the experiment lifetime. Data acquired at 8, 10, and 12 months belong to the standard working phase, while the curve at 17 months corresponds with the conclusion of the perturbation phase.  
summarized in Table 1, it was possible to confirm the effective role of the IMS inside the a-SCMFCs, not only to mimic the drop-like shape typical of fluid flow distribution inside the devices, but also to minimize oxygen cross-over to the anode surface. Indeed, the presence of the IMS allowed good performances to be achieved in terms of voltage output and energy recovery. All these optimal results were obtained with IMS cells that presented an internal volume of 6.6 mL, which is lower than that reported in the literature. Also, fed-batch mode was implemented to refill the entire cells' volumes with fresh electrolytes. In addition, cells were fabricated without the introduction of ion exchange membranes and with a biofilm formed starting from a mixed consortium. All the underlined parameters and characteristics played a pivotal role in guaranteeing the potential future direct applicability of these devices in the environment.