## 1 Introduction  
Microbial fuel cell (MFC) can be operated based on the oxidation of biodegradable waste at an anode and oxygen reduction at a cathode [1, 2]. Over the last few years, MFCshave received great interest in treating contaminated water; however, most of them are only used in the laboratory. An MFC technique provides treatment of contaminated water and electricity generation simultaneously [3]. The issues related to the power output of an MFC have been improved through a number of research studies. Nevertheless, at the pilot scale, the application of an MFC appears to be restricted, and power outputs appear to have plateaued; consequently, it failed to replace the existing wastewater treatment tools as a stand-alone technology. As a result, some MFC-based integrated techniques have evolved in recent years [4]. Upscaling studies of an MFC as a single unit have not yet been completed, although it has been achieved by many studies using stacked MFCs. Upscaling and practical applicability of MFCs are difficult due to their numerous disadvantages, as mentioned in further sections. The main disadvantage of an MFC is at the cathode region, where there is a shortage of terminal electron acceptor (TEA), which is considered a rate-limiting factor [5; 6; 7]. The majority of an MFC's efficiency depends on oxygen available at the cathode as a terminal electron acceptor and its efficient reduction on the cathode surface. Several studies have utilized a platinum catalyst at the cathode to improve efficiency and eliminate cathode issues. However, employing Pt is expensive and, in most situations, unsuitable for use in MFCs due to possibilities of poisoning. The size of an MFC is the second issue. The internal resistance of systems develops as the size of MFCs rises, which in turn reduces energy density. The other issue is maintaining electrode fouling in MFCs when they are applied on an industrial scale [8]. MFCs have been amalgamated with other existing technologies to overcome their limitations, as mentioned above [9]. In this context, numerous interesting hybrid MFC-based sewage treatment methods have been developed in recent decades, some of which show tremendous potential for future applications [10; 11]. Hybrid approaches (i.e., combining two or more processes to establish a novel method that integrates the particular qualities of the original techniques) have been emerging. These integrated techniques provide a versatile environment for tackling some difficult challenges, and they often outperform a stand-alone technology [12]. This paper discusses various categories of integrated MFC systems, including integration with capacitive deionization technology, forward osmosis technology, anaerobic digester, constructed wetland technology, microbial desalination cells, and so forth. The integrated CDI-MFC system starts with the electrostatic segregation of ions from water, which is followed by the adsorption of the ions or other pollutants in the electrode-solution interface. This process is used to overcome the disadvantage of stand-alone MFCs of limited ion removal. On the other hand, an MFC integrated with dark fermentation (DF) is used for extensive H\({}_{2}\) generation via an anaerobic hydrogen production process. An MFC-integrated MBR is used to reduce the cost of energy produced in the process, whereas integration of an MFC with an FO membrane aids in the cost-effective treatment of salty water on an industrial scale with simultaneous production of energy. Not only would such MFC-integrated systems lower overall costs, but they would also increase the combined system's sewage treatment efficacy and sustainability. Micropollutants and new pollutants, such as dyes, which are often not absorbed or decomposed by traditional procedures, can also be effectively removed by combining MFCs with other technologies. As a result, such integration of BESs with existing technologies is vitally needed to address the cost-related issues of BESs while also improving the degree of treatment received by sewage.