In recent years, there has been a significant accumulation of waste in the environment, and it is expected that this accumulation may increase in the years to come. Waste disposal has massive effects on the environment and can cause serious environmental problems. Thus, the development of a waste treatment system is of major importance. Agro-industrial wastewater and waste residues are mainly rich in organic substances, lignocellulose, hemicellulose, lignin, and they have a relatively high amount of energy. As a result, an effective agro-waste treatment system has several benefits, including energy recovery and waste stabilization. To reduce the impact of the consumption of fossil energy sources on our planet, the exploitation of renewable sources has been relaunched. All over the world, efforts have been made to recover energy from agricultural waste, considering global energy security as the final goal. To attain this objective, several technologies and recovery methods have been developed in recent years. The microbial fuel cell (MFC) is one of them. This review describes the power generation using various types of agro-industrial wastewaters and agricultural residues utilizing MFC. It also highlights the techno-economics and lifecycle assessment of MFC, its commercialization, along with challenges.

Carbon constraints, as well as the growing hazard of greenhouse gas emissions, have accelerated research into all possible renewable energy and fuel sources. Microbial electrolysis cells (MECs), a novel technology able to convert soluble organic matter into energy such as hydrogen gas, represent the most recent breakthrough. While research into energy recovery from wastewater using microbial electrolysis cells is fascinating and a carbon-neutral technology that is still mostly limited to lab-scale applications, much more work on improving the function of microbial electrolysis cells would be required to expand their use in many of these applications. The present limiting issues for effective scaling up of the manufacturing process include the high manufacturing costs of microbial electrolysis cells, their high internal resistance and methanogenesis, and membrane/cathode biofouling. This paper examines the evolution of microbial electrolysis cell technology in terms of hydrogen yield, operational aspects that impact total hydrogen output in optimization studies, and important information on the efficiency of the processes. Moreover, life-cycle assessment of MEC technology in comparison to other technologies has been discussed. According to the results, MEC is at technology readiness level (TRL) 5, which means that it is ready for industrial development, and, according to the techno-economics, it may be commercialized soon due to its carbon-neutral qualities.

Microbial fuel cells (MFC) are a promising system to simultaneously accomplish the goal of energy production and wastewater treatment. In the MFC, the cathode plays an important role in achieving high power density and thereby improving the cell performance. In the cathode, an allotrope of carbon [activated carbon, graphite, multi-walled carbon nanotubes (MWCNTs)] is commonly used as a support material for catalysts, such as Pt. Here we show the improved performance of single-chambered MFC (sMFC) using hydrothermally synthesized α-manganese dioxide nanotubes (MnO₂-NTs) as the catalyst and graphene as the support in the cathode. With a fixed MnO₂-NTs loading, a maximum volumetric power density of 4.68 W m⁻³ was achieved from the sMFC with MnO₂-NTs/graphene, which is higher than that of MnO₂-NTs/MWCNTs (3.94 W m⁻³) and MnO₂-NTs/Vulcan XC (2.2 W m⁻³) composite cathodes, but marginally lower than that of the benchmark Pt/C cathode (5.67 W m⁻³). The MnO₂-NTs/graphene composite also showed a higher oxygen reduction reaction (ORR) activity than the MnO₂-NTs/MWCNTs and MnO₂-NTs/Vulcan XC composites implying that the former is a better catalyst than the later two. This study demonstrates the high ORR activity and high power generation ability of the cost-effective MnO₂-NTs/graphene composite and makes it a potential cathode material for the replacement of expensive Pt in constructing large-scale MFC for wastewater treatment and bioelectricity production.