## 1 Introduction  
Over the decades, many wastewater treatment technologies have been employed to address the wastewater environmental menace. Wastewater treatment technologies, which consist of trickling filters, activated sludge, reverse osmosis, and membrane filters, are currently being used to treat all types of organic and toxic wastewater from industrial and municipal sources. However, they are not very productive, with regards to the cost and energy demand required in their operation [1]. It is projected that USD 2 trillion will be required in the U.S.A over the next 20 years to construct, operate, and maintain wastewater and drinking water facilities [2]. In addition to the current annual costs of USD 25 billion, around USD 45 billion is expected for wastewater infrastructure upgrades, with over half of operating expenditures aimed at aeration of wastewater. Power production measured here only for aeration could provide much-needed energy in the U.S.A from industrial wastewater alone [3]. According to [PERSON] (2015), some of these conventional wastewater treatment systems require 0.3-0.6 kW-h-m\({}^{-3}\) for treatment, whereas inherent in the same wastewater is energy that is equivalent to 10 times that needed for treatment [4]. Hence, the concept of generating electrical energy from the inherent chemical energy (organic matter) in wastewater during the treatment process will help offset the financial burden of treatment and provide access to clean water throughout the world, which would be highly recognized as sustainable [5,6]. In 1911, [PERSON] experimented and put forward the first microbial electrochemical technology (MET) and bio-electrochemical system (BES), established as microbial fuel cells (MFC), as a sustainable biotechnology [7,8]. A microbial fuel cell is an innovative wastewater treatment technology that uses electrochemical active bacteria (EAB) as a biocatalyst to transform the chemical energy inherent in sewage directly into electrical production without any environmental footprint [1,8]. MFCs use wastewater as a feed substrate for EABs to produce bio-electricity, while concurrently treating waste [1]. According to, [PERSON] et al. [1], MFC as a technology holds great potential for a clean and green energy environment. Constructed wetlands (CWs), on the other hand, are bio-physically assembled systems designed and built to take advantage of natural processes and interactions between wetland flora, soils, and associated microbial species to help regenerate wastewater [9,10]. Wastewater from a wide variety of sources, such as municipal, agricultural, or industrial wastewater, are treated by CWs [11]. They are easy to maintain and operate and can remediate many of the persistent pollutants that occur in conventional wastewaters into harmless by-products [12]. As a result, they have emerged as a substitute to traditional intensified systems for wastewater treatment [13,14]. A decade ago, researchers discovered that the embedded redox gradients, which naturally exist in wetlands, are highly compatible with the settings in microbial fuel cells, i.e., anaerobic zone in the inner-lower region and aerobic region at the air-water interface [15]. This connection makes their incorporation very plausible by creating a synergy between these two technologies for enhanced wastewater regeneration and bioenergy generation [16]. In the operation and utilization of this newly emerged technology, several factors are recognized to influence the system's efficiency, such as the appropriate selection of substrate media, microbial or electrogenic activities, hydraulic retention time, electrode material, and wetland plant type. Constructed wetland-microbial fuel cells (CWMCs) for wastewater treatment and bioenergy generation can be categorized into free-floating, floating leave, rooted emergent, and submerged macrophtye systems, according to the dominant plant species [17].