## Permeate
### Sediment Microbial Fuel Cells  
MFCs can be integrated into a variety of technologies, including sediment microbial fuel cells, which have the same arrangement as a conventional MFC. The anode (anaerobic) can be immersed in the sediment, and the cathode (aerobic) can be found at the top part of the SMFC, where oxygen acts as a terminal electron acceptor (Figure 4). More intriguingly, it was not discovered until 2001 that bacteria can donate their electrons exogenously. By embedding an MFC in an oceanic sediment, [PERSON] et al. [60] investigated the feasibility of extracellular electron transmission. They explored exoelectrogenic electron transport by inserting an electrode in a marine sediment and harvesting energy from it. The anode component of SMFCs was inserted into the sediment (anaerobic) region of the ocean, while the cathode was placed at the water surface. Exoelectrogenic microbes are already active in the sediment, according to [PERSON] et al., and can give electrons to the electrode inanerobic environments. The electrons from the sediment can be transmitted to the cathode, which already contains dissolved oxygen from the surface water and can act as a terminal electron acceptor. From the initial SMFCs, they were able to attain an energy output of 50 mW/m\({}^{2}\). The aerobic and anaerobic portions of all categories of SMFCs were configured based on the surface and sediment, respectively. [PERSON] et al. [61] studied the feasibility of rotating a cathode electrode to generate more oxygen in river sediments and reached an energy output of 49 mW/m\({}^{2}\), compared with 29 mW/m\({}^{2}\) for a nonrotating cathode. The rotating cathode provided more oxygen at the cathode in this example, which improved the efficiency of electron transport from the anode. In the nonrotating cathode, on the other hand, it was discovered that the number of terminal electron acceptors at the cathode was limited. Another experiment investigated three laboratory-scale two-chambered MFCs with sea sand as the anode and saltwater as the cathode, and a mean energy output of 0.016 W was achieved. They discovered that Geobacteraceae uses electrodes as an electron acceptor under anaerobic environments [62]. Different types of sediment MFCs, such as benthic MFCs (BMFCs), floating-macrophyte-dependent MFCs (FMFCs), and soil-based MFCs (SL-MFCs), were developed with time [30]. BMFCs are also an advanced use of SMFCs in an aquatic environment, especially for bioremediation of contaminants, such as sulfur and organic matter in the sediments. The contaminants in the BMFC sediment aid as a source of energy for bacteria, and the oxidation of contaminants in the sediment and the decrease in oxygen at the surface produce power [63; 64]. As previously stated, constant monitoring of produced voltage and retention of power from BMFCs can also be used as a monitoring system in the sea [65]. The system design of FMFCs is also influenced by those of sediment MFCs and plant MFCs (PMFCs). Plants release rhizodeposits (organics and nutrients) in the sediment of PMFCs. The microorganisms use secretory rhizodeposits as a fuel in the sediment and oxygen as a reductant at the surfaces and subsequently generate energy. [PERSON] et al. [66] introduced FMFCs to remove excessive volatile fatty acids (VFAs) and residual organic matter from an H\({}_{2}\) bioreactor's outflow. COD elimination was around 86.67%, and VFA removal was around 72.32%, respectively. The power production was shown to accelerate as COD increased, reaching 224.93 mA/m\({}^{2}\) in some cases. [PERSON] et al. [67] estimated the use of an SL-MFC for anaerobic phenol decomposition. In a closed circuit, they removed 90.1% of the phenol with a maximum energy output of 29.45 mW/m\({}^{2}\). Further research used SL-MFC to remove organic pesticides, including hexachlorobenzene from the environment. This research discovered an elimination rate of 71.15% and an energy yield of 77.5 mW/m\({}^{2}\). The researchers found that the existence of  
Figure 4: A typical integrated sediment MFC.