## Permeate
### Integration of Microbial Fuel Cells with Microalgae  
The concept of microalgae MFC is dependent on substantial MFC and microalgae research. A combination of algae and MFCs will be a unique technology that converts solar energy to electric energy through the metabolic processes of photosynthetic microbes (Figure 7) [92]. Likewise, MFCs are used in algal bioreactors, and the bases of microbial-fuel-cell-combined algal bioreactors are solar energy; hence, the existence of algal biomass turns solar energy into chemical energy. Furthermore, the accessible algae transform chemical energy into electrical energy. Photosynthetic fuel cells or solar cells are MFCs that have been integrated into algal bioreactors. Microbes oxidize organics at the anodic compartment, and algae release oxygen at the cathode to meet the need for aeration in the alternative arrangement of algal MFCs. As a result, it is regarded as passive aeration from algae, which provides an oxidant to the cathode for the anode's reaction accomplishment [12]. \begin{table}
\begin{tabular}{c c c c} \hline
**Type of Integrated MFCs-CW** & **Power Density** & **COD Removal Rate** & **References** \\ \hline Vertical flow MFCs-CW & 531.04 mW/m\({}^{3}\) & 72.17\% & [88] \\ \hline Up-flow\({}_{-}\) & 50.268 mW/m\({}^{3}\) & 81\% & [89] \\ \hline Horizontal subsurface flow, continuous & 36 mW/m\({}^{2}\) & 71\% & [83] \\ \hline Horizontal flow bed-CW & - & 60–70\% & [90] \\ \hline Vertical CW & 53,714.08 mW/m\({}^{2}\) & 82.32\% & [91] \\ \hline \end{tabular}
\end{table} 
Table 3: Microbial-fuel-cell-integrated constructed wetlands. In the case of a microalgae photobioreactor (PHB), microbes use incoming light to convert CO\({}_{2}\) to biomass and O\({}_{2}\)[3]. Furthermore, the oxygen generated by _Chlorella vulgaris_ during photosynthesis in the cathodic chamber of MFCs could act as the terminal electron acceptor. Therefore, the integrated system can be used to sequester carbon dioxide, produce oxygen, and remove nitrogen from contaminated water [93]. In another technique, dead microalgae were employed as the substrate in the anode compartment of MFCs, while viable algae were introduced in the cathode chamber. When the conductive cathode was fixed with multiple strains of algae, such as _C. vulgaris_, _Dunaliella tertiolecta_, and _Synechocystis_ sp., the energy production of single-chambered photosynthetic MFCs was detected. When irradiated with 10 W/m\({}^{2}\) of white light, an MFC containing _Synechococcus_ sp. had a maximum energy output of 10.3 mW/m\({}^{2}\). A serial arrangement of four MFCs can produce enough energy to run a commonly available tiny digital clock (currently around 10 mA and a potential of 2 V) [94,95]. An anoxic MFC was generated using dissolved CO\({}_{2}\) as an electron acceptor and a photobiocathode that was activated. The MFC achieved an energy output of 750 mW/m\({}^{2}\) after this bioachode efficiently fixed CO\({}_{2}\)[96]. The MFC was used in conjunction with a tubular PHB as the cathode chamber, which was colonized with _C. vulgaris_. The amount of oxygen produced by _C. vulgaris_ and the amount of power produced by the MFC were both light-dependent. Under inconsistent illumination, an MFC with an algal biocathode attained the highest energy output of 24.4 mW/m\({}^{2}\), which was 2.8 times greater than the MFC with an abiotic cathode [97]. During the anaerobic digestion of Taihu blue algae, biohydrogen employing migrating ammonia as a nitrogen supply and biogas upgrading using hydrogen collected at the bio-cathode in an integrated bioelectrochemical system (BES) were examined by [PERSON] et al. [98]. The use of an integrated BES allowed for simultaneous ammonia reduction and biogas upgrading. It was observed that under a 0.4 V applied voltage, ammonia utilization and hydrogen production achieved 73.67% and 202.87 mL, respectively. As a result, performing ammonia mitigation, hydrogen production, and biogas upgrading all at the same time with BES appears to be an effective approach.