## Permeate
### Membrane-Based MFCs and Membrane bioreactor-Microbial Fuel Cells  
Several studies were conducted where MFCs were integrated with different types of bioreactors to improve the quality of the wastewater (Figure 3). One such method was the traditional activated sludge process integrated with an MFC [29]. The aeration tank was utilized as the cathodic compartment, and the catalyst was the developing aerobic biofilm. The biofilm is an inexpensive alternative for the catalyst and helps in reducing the overall cost of operating this integrated system. The continuous flow process was maintained by a clarifier, which was tailed to the aeration tank. However, extra costs were incurred due to  
Figure 2: MFC-capacitive deionization (MFC-CDI) system. the installation of the clarifier and the sludge pumping. As this integrated system faced obstacles during industrial scale-up, another setup integrating the MFCs with a sequencing batch reactor (SBR) was introduced. This approach was explored to estimate COD removal and energy production. This setup consisted of a bioachode-equipped membrane-less MFC combined with an SBR. This helps in the retrieval of energy as electricity from the aeration, hence reducing the operating cost for SBR operation [30]. The MFC combined systems were used to examine different types of wastewaters. For example, a combined system of an up-flow anaerobic sludge blanket reactor, MFC, and biological aerated filter (UASB-MFC-BAF) was employed to treat molasses water [31]. In this arrangement, all three components complement each other by filling up the gaps where the others lack. Here, the UASB was used primarily for sulfate reduction and removal of COD. The resultant sulfide is oxidized by the use of the MFC, along with the production of energy. The phenolic compounds were decolorized and degraded in the BAF. The azo dye, Acid Orange 7 (AO-7), underwent decolorization in the MFC-integrated setup and was denatured into less poisonous complexes. The AO-7 was degraded by a reduction process in the MFC into the constituent aromatic amines [32]. Another system was devised for the degradation of Congo red, where the integration of the MFC and a catalytic oxygen reactor (COR) was used. In this system, Congo red was degraded with the help of oxidants in the existence of a catalyst [30]. One commercially available technology used for the treatment of wastewater is the MBR (membrane bioreactor), which can be combined with the MFC to reduce the cost of energy and develop the superiority of an effluent [33]. These advantages were the reason that many studies were conducted on the MFC-MBR system to check its efficiency and viability. The system born out of the assimilation of the advantages of the MFC and MBR was named a \"bioelectrochemical membrane reactor\" [20]. Although the scheme of this bioreactor was quite complicated, it was capable of reaching an extreme power density = of 4.35 W/m3. It has also demonstrated improved contaminant removal, which was credited to solid elimination and significant biomass retention [33]. Another setup was reported which had increased O\({}_{2}\) uptake in the aeration tank of the MFCs with the use of a bioachode. The MBR was mounted on the MFC, where sections of steel mesh membranes acted as both filtration units and cathode. These mesh membranes had the advantage of being simply stripped and washed without affecting the anode chamber [30]. A different  
Figure 3: Representation of a typical MFC-integrated MBR reactor. study came up with a similar combination but using commercial cathode membranes (stainless steel net altered using a polypyrrole film treated with 9,10-anthraquinone-2-sulfonic acid (AQS)). This added to fouling alleviation and the electrocatalytic denaturation of the pollutants via the bioelectricity that is generated [34]. Several sorts of MBRs (fluidized bed, hollow fiber, tubular) were combined with MFCs. An MFC-tubular MBR system was assembled by integrating a bioachode-equipped MFC with a tubular membrane.