## 2 Bioelectrochemical Systems' Configurations
MECs have demonstrated potential in both single- and two-chamber configurations. For instance, a single-chamber MEC with a carbon fiber brush anode and a carbon cloth cathode coated with platinum (Pt) achieved hydrogen production of 38 L H\({}_{2}\) m\({}^{-2}\) d\({}^{-1}\) and a COD removal efficiency of 44.92%. The system also reached a power density of 0.012 A at 0.9 V and a CE of 75.60% [42]. In a two-chamber MEC, a Pt-deposited carbon cathode and a carbon felt anode resulted in hydrogen production of 4.3 L H\({}_{2}\) d\({}^{-1}\), with a COD removal efficiency of 61.5% [43]. Other significant BES configurations include the following:
* Sediment Microbial Fuel Cells (SMFCs), also known as benthic MFCs, generate energy by reducing oxygen in the water column and oxidizing organic substrates in anoxic sediments. These systems typically feature a cathode placed in the oxygen-rich water above and an anode embedded in the anaerobic sediments below, such as those found in paddy soils and benthic environments. Detailed construction and operational guidelines are described in the literature [33; 44]. * Plant-Type Microbial Fuel Cells (PMFCs) feature an anode located in the soil, in contact with the plant rhizosphere, while the cathode is exposed to atmospheric oxygen in order to facilitate the reduction reactions [45]. * Microbial Desalination Cells (MDCs) utilize bioenergy from the oxidation of organic wastes to achieve desalination by integrating electrodialysis into MFCs. Unlike traditional electrodialysis, the desalination process in an MDC offers relevant energy benefits, as it does not require external energy input for ion separation [46]. MDCs have been investigated in both laboratory and pilot-scale setups. For example, a study using a carbon brush anode and carbon cathode demonstrated a notable desalination rate of 31.5 mg L\({}^{-1}\) h\({}^{-1}\), achieving a 90% removal of organic compounds and 75% removal of ammonium (NH\({}_{4}\)) [47]. In a pilot-scale study using a 10 L MDC, the system achieved a removal rate of 154 mg L\({}^{-1}\) h\({}^{-1}\), showcasing the scalability and effectiveness of MDC technology in real-world applications [48]. * Constructed Wetlands Microbial Fuel Cells (CWMFCs) combine constructed wetlands and MFC technology to control water pollution with coupled energy generation. The effect of the anode material on system performance has been studied. The results indicated an 18% COD retention and a power density of 1730 mW m\({}^{-2}\) (346 mW m\({}^{-3}\)), underscoring the importance of selecting appropriate anode materials to enhance the efficiency and output of CWMFC systems [49; 50; 51; 52; 53]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Type of BES** & **Function** & **Anodic Chamber** & **Catholic Chamber** & **Microorganism** & **Substrate** & **Electron Acceptor** & **Comments** \\ \hline MFCs (Microbial Fuel Cells) & Electricity generation, & Anaerobic oxidation of organic matter removal & Aerobic reduction & Skumello,Generator, activated sludge & Domestic/industrial wastewater with holographic organic & O\({}_{x}\), K\({}_{x}\)FeCN\({}_{x}\), NaoC1, other oxidizing & Maximum current density: 390 \(\mu\)/m\({}^{2}\), \\ \hline Microbial electrolysis cells (MFCs) & Allow electrolysis of water, synthesis of H\({}_{0}\)O\({}_{x}\), CH\({}_{x}\), NaoC1, structure & Anaerobic oxidation of organic matter & Anaerobic, hydrogen generation & Electrophoretic at the anode & Biodegradable wastewater & H\({}^{*}\), CO\({}_{x}\), organic organic & H\({}^{*}\), CO\({}_{x}\), oxygenides are critical  
From Table 1, it is possible to analyze the functional diversity, microbial communities, and electron transfer mechanisms of the different type of BESs. MFCs and MDCs primarily focus on electricity generation and wastewater treatment, while MFCs and MES are designed for the synthesis of valuable compounds, requiring external energy input. Systems like SMFCs, PMFCs, and CWMFCs integrate natural ecosystems for sustainable energy harvesting and bioremediation.