Bio-electricity can be produced from biomass. Typically, heat generated by burning solid biomass, biogas or biofuels can be converted into electricity by conventional means. Biogas can be used more directly in a gas motor that is linked to a generator for electricity production. Microbes are some time  capable to creat electricity while reducing or remediating organic wastes, and that these processes can be exploited using devices called Microbial Fuel Cells (MFCs). They also known as biological fuel cells.

MFCs are capable of converting energy, available in a bio-convertible substrate, directly into electricity with the help of bacteria; , that means directly converting biomass into electricity. These bacteria switch from the natural electron acceptor, such as oxygen (O2) or nitrate (NO3-), to an insoluble acceptor, such as the MFC anode.

This transfer can either occur by membrane-associated components, or by soluble electron shuttles. These electrons flow through a resistor to a cathode, at which the electron acceptor is reduced. In contrast to anaerobic digestion, a MFC creates electrical current and an off-gas containing mainly carbon dioxide (CO2) instead of an energy-rich gas such as methane (CH4) or hydrogen (H2). The concept of using microorganisms as catalysts in fuel cells was explored starting in the 1970s. Microbial fuel cells treating domestic wastewater were presented in 1991. However, now microbial fuel cells with an enhanced power output have been developed providing possible opportunities towards practical applications.

MFCs have both operational and functional advantages over the technologies currently used for generating energy from organic matter.

The direct conversion of substrate energy to electricity enables high conversion efficiency. MFCs operate efficiently at ambient, and even at low temperatures, distinguishing them from all current bio-energy processes. An MFC does not require gas treatment, as the off-gases of MFCs are enriched in carbon dioxide and have no useful energy content. In general, MFCs have potential for widespread application in locations lacking electrical infrastructures and have potential to expand the diversity of fuels we use to satisfy our energy requirements.

MFCs are being developed both for waste treatment as for bio-energy generation. Waste driven applications require mainly high removal of the waste substrate. Currently, when applying conventional aerobic treatment, approximately 1 kWh of energy is needed for oxidation per kilogram of carbohydrates present. For example, treatment of domestic wastewater represents an aeration energy cost of about 0.5 kWh per m3, amounting to an energy use of the order of 30 kWh per capita per year (about €3 energy cost per capita per year). MFCs can also be used to convert a substrate with positive market value, such as glucose, into electricity. The obtention of a high energetic efficiency is essential in this respect. Although the power density of the MFCs in comparison with for example methanol driven FCs is considerably lower, the versatility in terms of -safe- substrates is an important asset of this technology.

Overall, as a matter of reference, the capital expenditure (Capex) for energy recovery from biomass by means of high rate anaerobic digestion is of the order of 1 M€ per MW capacity installed. The latter value is also valid for energy production from fossil fuel by conventional combustion processes, by wind turbines and by chemical fuel cells. Hence, the processes are in a competitive area. Microbial fuel cells currently do not reach power outputs of this level. Loading rates of 0.1-10 kg COD per m3 reactor per day can be expected that can in practice provide a power output between 0.01-1.25 kW/m3. For a granular bed in a stacked MFC the capex cost based on materials as presented by Tsuchiya and Kobayashi, assuming a cost of €4000 per m3 of electrode compartment, and 1 kW power output per m3 anode, is at present estimated to be at a level 10 times that of the above mentioned energy producing processes. Taking into account a decrease in cost similar as expected for the chemical fuel cells in the future, microbial fuel cells still need important breakthroughs to become economically competitive. However, their overall applicability and potential to operate at ambient temperatures is still largely unexplored.