**13. Conclusions and Future Direction**

The use of agricultural waste in MFC has been critical in the renewable energy industry, contributing significantly to the production of bioenergy. Similarly, the development of MFC technology has enabled the use of agricultural waste as a feedstock by various microbial communities in the anode compartment of the fuel cell. Due to the complex structure and crystallinity of agricultural biomass, biodegradation is limited. As a result, the agricultural waste's greater moisture content would assist in overcoming this barrier. By using a variety of wastewater resources, such as agricultural wastewater and fruit wastewater, the bacteria may easily break down the solid biomass. Conclusively, this review has demonstrated the use of various agricultural wastes for bioelectricity generation. Therefore, the use of different agricultural wastes and wastewater containing different industrial-by products for bioelectricity production in MFC seems to be a promising and alternative source of renewable energy generation. Moreover, it has been shown that different varieties of agricultural wastes and wastewater can be utilized using several different MFCs to enhance bioenergy production; thus, the conversion of agro-waste into bioenergy can be carried out by both biochemical and thermochemical MFC routes. Several papers report numerous experimental studies, whereby the use of various substrates from different agri-based industries and with different compositions for application in MFCs, has been demonstrated: most importantly, in terms of simultaneous wastewater treatment and energy recovery. Another attractive and fascinating trait of MFC technology development is the incorporation of wastewater treatment, which provides an alternative

solution to wastewater management, pollutant removal, and the maintenance of a safe and eco-friendly environment in addition to energy production. Overall, it has been noted that MFC technology offers significant advantages such as low input energy cost and a low level of residual biosolid production. In essence, improvement has been made in the total bioenergy production arena in using—concentrated wastewater derived from various agro-waste, indicating that various microbial consortia of different origins play an important role during the oxidation-reduction reactions for bioenergy production using different anodes and cathodes. Overall, an effective pretreatment approach has been made to solve problems associated with agri-waste mitigation even when such waste has a different particle size, calorific value, etc. There is also a need to promote environmental sustainability in agricultural activities and the standard management of agro-wastes that will reduce the volume of wastes released into the environment and provide a channel for bioenergy generation. To this end, local governments and regulatory agencies should explore ways of generating bioelectricity from various agro-waste as there is an urgent need to disabuse the general public's minds that agro-waste is useless.

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

**Funding:** This research received no external funding.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
