**11. Conclusions**

To summarize, the development of MEC technology has shown positive results, primarily by lowering the total cost of wastewater treatment and energy generation. Simultaneously, it delivers a significant advantage via the creation of value-added fuels such as hydrogen. Furthermore, MEC technology is still in its early stage, since it faces several obstacles such as mass transfer restrictions, energy loss, and other issues that must be thoroughly investigated on a pilot and industrial scale utilizing real-world wastewaters. However, when it comes to the actual applications of MEC technology, it should be noted that establishing unique configurations in both anode and cathode structural

design, as well as membrane structural design, should be given top priority to maximize the technology's cost-effectiveness. However, in recent years, reports have emerged that the technology's prospects are promising, as seen by the successful construction of many pilot-scale MEC reactors, indicating that the first commercial encounter with the technology is on the way. There is a significant gap between the literature results and the reality of scalable research, and the real challenge today is now to study the credibility of pilot-scale studies. Moreover, there is no comparative analysis of the cost estimation with respect to conventional technologies and MEC, which could help in the commercialization. The obstacles to bringing this technology forward from TRL 5 are not only technological but are also connected to innovation policy incentives. The stringent regulatory efficiency restrictions and the profitability of water utilities do not support developments in systems that are unlikely to satisfy these standards immediately.

Biofuels and bioenergy are being developed using this approach, which has been proposed as a means of transforming electrical energy from renewable energy sources such as solar and wind into biofuels and bioenergy. As a result, the development of integrated MECs with hydrolysis has the potential to increase the rate of breakdown of nonbiodegradable complex organics and, as a result, improve the overall efficiency of production.

**Author Contributions:** Conceptualization, P.D. and P.S.; software, P.D.; validation, P.S., S.K., M.K., S.P., Y.-H.Y. and S.K.B.; writing—original draft preparation, P.D. and P.S.; writing—review and editing, P.S., D.J., and P.K.G.; supervision, P.S., S.K., S.P. and S.K.B. All authors read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the Research Program to solve social issues of the National Research Foundation of Korea (NRF)s funded by the Ministry of Science and ICT (grant number 2021R1F1A1050325). This study was also performed with the support of the R&D Program of MOTIE/KEIT [grant number 20014350 and 20009508].

**Institutional Review Board Statement:** Not Applicable.

**Informed Consent Statement:** Not Applicable.

**Acknowledgments:** The authors would like to acknowledge the KU Research Professor Program of Konkuk University, Seoul, South Korea. The authors would like to acknowledge the Sharda University Seed gran<sup>t</sup> for research, India.

**Conflicts of Interest:** The authors declare no conflict of interest.
