## 2 Configuration of CWMFC  
CWMFC is a hybrid system that seeks to integrate MFCs into built wetlands by leveraging the triple interaction of substrates, the plant and microorganisms' physical, chemical, and biotic elements for wastewater treatment and electricity production [25; 26; 27]. This hybrid system syndicates the advantage of two systems in a way that is proficient in attaining high levels of wastewater reuse and bioenergy [26]. On the basis of researchers identifying a variation of dissolved oxygen (DO) along the vertical profile of CW's natural environment, this integration was conceived to be plausible, which creates a naturally prevailing stratified redox gradient similar to that of MFC in its two-chambered cell, as shown in Figure 1[16; 28; 29].  
A typical CWMFC is, therefore, built similar to a traditional MFC with two major compartments--the lower anaerobic chamber and the upper aerobic chamber [27; 28; 29; 30; 31]--with an anode electrode deeply buried within the anaerobic chamber and cathode electrode positioned at the air-water interface around the root zone of the plant, also called the aerobic or cathodic section [23]. These electrodes are then connected using titanium wires with an applied external resistance crucial for electricity generation. By positioning the anode at the lower anaerobic zone and inserting the cathode at the air-water interface, CW-MFC takes good advantage of the existing redox condition [31]. The optimization of this redox gradient or potential difference established betwix the anode and the cathode is pivotal for power generation and contaminant removal in CWMFC [32]. Since the onset of this hybrid technology, carbon, and graphite materials have been widely used as electrodes, owing to their suitable surface microbial attachment and growth, high electrical conductivity, non-oxidative nature, and riveing characteristics for biofilm formation [14; 33].  
A CWMFC reactor configuration comparable to a built wetland often has its lower anaerobic region filled with a layer of soil, gravel or some other recent substrates, such as activated carbon, zeolite, or alum sludge, as a supporting matrix for the anode electrode. This support matrix also creates the desired environment for the oxidation reaction by microorganisms for contaminant removal and electrons transfer processes [14; 16; 26; 33]. All these components, as mentioned earlier, are essential in the configuration of CW-MFC bioelectrochemical systems. However, to maintain a highly aerobic upper cathodic chamber and increase the removal of pollutants, macrophytes that resource dissolved oxygen to the cathode through plant root respiration are planted in the upper cathode compartment, which contributes significantly to the reduction reaction. Aside from the maintenance  
Figure 1: A graphical illustration of constructed wetland coupled MFC.  
of appropriate operating conditions, such as pH, temperature, organic loading rate flow regime, and hydraulic retention rate, the system's physical and biological components' performance is essential for the overall system efficiency [21]. The macrophte components are recognized to play a pivotal role, as they interact with and influence the performance of all other required components, such as the substrate (filtration media), microorganisms, and electrode materials in CWMFC (see Figure 2). They also influence both the oxidation and reduction reactions. They act as biological filters and accumulators in the treatment process and as oxygenators to the cathode for electricity generation [15]. According to [PERSON] et al. [34], the plants' presence promotes the cathode's oxygen concentration through their photosynthetic activities. In a study by [PERSON] et al. [34], a CWMFC with plants produced an average voltage output of about 15% higher than an unplanted CW-MFC [35; 36; 37; 38].