## 3 Microalgae Microbial Fuel Cell (mMFC)
### Microalgae and MFC
Additionally, the microalgae species _Chlorella vulgaris_ produces oil that can be used as a byproduct in biodiesel production. To make this integrated system economically viable, it is essential to determine the necessary design specifications of PBR cathodes [37; 55; 118]. One of the earliest reports on mMFCs studied the biomass production of _Chlorella vulgaris_ as a biological electron acceptor at the cathode while reducing CO\({}_{2}\) to biomass using a mediator with low bioelectricity generation [84; 119]. Subsequently, the use of CO\({}_{2}\) in an aqueous system as an electron acceptor was investigated. Microalgae were inoculated at the cathode without mediators, resulting in the production of phospholipids and electricity comparable to that obtained by ferricyanide-based MFCs [120]. Given that mechanical aeration in MFCs constitutes about 50% of the total operating cost [77], utilizing microalgae for oxygen production emerges as a crucial approach in the application of mMFCs. The cathode significantly affects MFC performance due to the oxygen reduction reaction (ORR) influencing the onset potential (V) value [121]. However, photosynthesis is not a continuous process and depends on the photoperiod, limiting power production to the light phase reaction [122]. Despite this, the production of oxygen, which depends on the microalgae in the cathodic chamber, is generally sufficient even when variations in electricity production occur [62]. The mMFC technology still requires additional investigation, as the highest power reported for an MFC (5850 mW m\({}^{-2}\)) is three orders of magnitude lower than that produced by conventional abiotic fuel cells [123; 124]. While the main advantage of mMFCs over MFCs is that the replacement of external aeration for the cathodic reaction by microalgae produced oxygen [125], the integration of microalgae in the cathode chamber offers additional benefits such as production of lipids and biomass, which can be used to make biofuels and other chemicals with added value. Algae also aid in the oxygen production and the CO\({}_{2}\) capture, which enhances MFC efficiency and reduces greenhouse gas emissions [64; 65; 126]. Further research is necessary to improve the performance of MFC photosynthetic systems, particularly in terms of biological catalysts, reactors, and electrodes coupled with MFCs. A better understanding of this technology and the successful practical application of MFCs are required [86]. Using mMFCs as a platform for biofuel/biochemical production (extracted from cultivated microalgal cells) would be financially beneficial. The organics present in wastewater and the residue remaining after algal extraction can potentially be utilized as anodic feeds in MFCs. To evaluate the economic feasibility of using MFCs or individual microalgae units, a detailed techno-economic analysis that considers factors such as land and water usage and greenhouse gas emissions is crucial [62]. Another challenge is researching genetic engineering to obtain better microalgae strains with higher extracellular electron transfer abilities. This is important when considering the use of microalgae at the anode and cathode [127]. The most important parameters in mMFC research will be discussed in the next sections.