Microbial Fuel Cells Turn Wastewater Into Electricity, Review Finds

Imagine a device that devours sewage, farm runoff and even toxic textile dyes, and spits out electricity. That is the promise of microbial fuel cells, a technology that has quietly matured over more than a century and is now the subject of a comprehensive review published in Discover Biotechnology. Neha Tarun Kuity and Seema Ajay Sambrani of Somaiya Vidyavihar University in Mumbai surveyed the state of bio-electrochemical energy recovery, tracing the field from its earliest experiments to modern pilot installations, and their assessment is both encouraging and sobering. The core idea is elegantly simple: certain bacteria can hand over the electrons they strip from organic matter to an electrode, generating a current that can be harvested. The waste that would otherwise pollute rivers becomes, in effect, a fuel.

The historical arc of the technology stretches back to 1911, when M.C. Potter first demonstrated that microbial metabolism could produce electricity using yeast and bacteria. B. Cohen advanced the concept in 1931 by building microbial half fuel cell stacks that generated measurable voltages. But the decisive turning point came late in the twentieth century with the discovery of electroactive bacteria such as Shewanella oneidensis and Geobacter sulfurreducens. These organisms shuttle electrons outside their cells without the need for synthetic mediators, a capability that transformed fuel cell design. Geobacter species, in particular, form conductive biofilms threaded with cytochrome-based nanowires, dramatically improving electron transfer and, with it, power output. Those early findings laid the groundwork for today’s materials research, including polypyrrole-coated anodes and nitrogen-doped carbon nanotubes that boost bacterial adhesion and electron transfer rates.

At its heart, a microbial fuel cell is a two-part electrochemical machine. In the anodic chamber, electroactive microorganisms oxidize organic or inorganic substrates, releasing protons and electrons as by-products of their metabolism. The electrons travel through an external circuit from anode to cathode, generating usable current, while protons migrate across a proton exchange membrane to the cathodic chamber. There, they combine with a terminal electron acceptor, most often oxygen, completing the circuit. Oxygen is the ideal acceptor because it leaves no toxic residue, and platinum is commonly used to catalyze the cathode reaction. But platinum is expensive, which undermines the economics of the whole system. Researchers are therefore testing cheaper alternatives, including manganese dioxide and iron- and cobalt-based catalysts, as well as biocathodes in which microorganisms themselves catalyze the electron transfer, reducing reliance on noble metals.

The microbiology inside the anode is where the real chemistry happens. Substrates such as glucose and acetate are broken down through glycolysis, the tricarboxylic acid cycle and respiratory electron transport chains, producing the reduced cofactors NADH and FADH2 that ultimately donate electrons to the anode. The efficiency of this process is measured as Coulombic efficiency, the fraction of electrons from the oxidized substrate that are captured as electrical current, and losses occur whenever microbes divert electrons toward biomass growth, methanogenesis or competing respiratory pathways. Extracellular electron transfer, the defining trait of electrogenic microbes, occurs through direct contact, through soluble mediators, or through conductive nanowires. Acetate, with its simple molecular structure, remains the benchmark substrate, delivering some of the highest electron recovery rates observed.

Design choices matter enormously. Dual-chambered fuel cells separate oxidation and reduction into distinct compartments divided by a proton exchange membrane, maximizing stability and electron transfer efficiency, but the membrane adds cost and operational complexity. Single-chambered designs merge the anode and cathode into one vessel, cutting internal resistance and simplifying construction, often using an air cathode that draws oxygen passively from the atmosphere. The trade-off is that oxygen can leak into the anodic chamber, disrupting the anaerobic metabolism the electroactive bacteria depend on. Temperature is another critical variable: performance peaks between 20 and 40 degrees Celsius and falls off outside that window as microbial activity slows or proteins denature, a serious concern for outdoor deployments subject to seasonal swings.

What sets microbial fuel cells apart from other renewable technologies is the extraordinary range of waste streams they can consume. Carbohydrates from wastewater and biomass are the most widely used substrates, prized for their biodegradability, though complex sugars require enzymatic hydrolysis and can cause biofouling. Organic acids, particularly acetate, feed directly into microbial electron transport and avoid the fouling problems of sugars. Alcohols such as ethanol from bioethanol production waste can be oxidized to acetate by acetogenic bacteria, while inorganic compounds like ammonia, hydrogen and sulfate extend the technology’s reach into nitrogen removal and sulfur cycling. Power outputs vary widely depending on the feedstock, ranging from roughly 1 to 3600 milliwatts per square meter, with most systems falling between 10 and 1000.

The review highlights striking demonstrations across agro-industrial waste. Cassava starch wastewater, laden with organic matter and cyanide precursors, was treated in a fuel cell system that removed 88 percent of the chemical oxygen demand within 120 hours while producing a maximum power density of 1771 milliwatts per square meter. Adjusting anode pH from 5.0 to 9.0 in a single-chambered system boosted power density to 22.19 watts per cubic meter, underscoring pH as a master variable. Cellulose-degrading consortia, chicken feathers processed by Pseudomonas aeruginosa at 1206.78 milliwatts per square meter, rice straw hydrolysate, brewery wastewater with over 91 percent COD removal, and slaughterhouse effluent at 578 milliwatts per square meter all confirm the breadth of usable feedstocks. Fish market wastewater achieved 85 percent COD removal at 350 milliwatts per square meter, and fish scales have even been repurposed as biocompatible anode material.

Household and xenobiotic wastes round out the portfolio. Food waste leachate in a dual-chamber system generated 482 milliwatts per square meter with 85 percent COD removal, while blackwater treatment achieved roughly 80 percent COD removal with stable voltage production. Azo dyes, the synthetic colorants behind much textile pollution, can serve as electron acceptors at the cathode, where the azo bond is reductively cleaved into aromatic amines while the anode simultaneously generates current. Studies with Klebsiella pneumoniae, Geobacter and Shewanella showed that replacing ferricyanide with azo dyes as the cathodic acceptor increased power output by 40 percent. Selenium-contaminated wastewater can be reduced to less toxic elemental selenium, and nitrate removal efficiencies of up to 95 percent have been reported, though high selenium concentrations above 50 milligrams per liter begin to inhibit microbial activity.

The economics remain the technology’s Achilles heel. Platinum catalysts can cost as much as 3000 dollars per kilogram, and Nafion proton exchange membranes run between 500 and 1000 dollars per square meter. Activated carbon electrodes and ceramic membranes offer cheaper alternatives without sacrificing performance. Operational costs are low because the fuel is waste that often carries a disposal charge, and the systems need little external energy, avoiding the aeration expenses of activated sludge treatment. Yet power densities generally remain below 2 watts per square meter, well short of solar panels exceeding 20 percent efficiency, and scaling from laboratory reactors exceeding 1000 watts per cubic meter at 20-milliliter volumes to a 500-milliliter reactor producing just 20 watts per cubic meter illustrates the persistent scale-up penalty.

Real-world evidence is nonetheless accumulating. A liter-scale, single-chamber air-cathode system operating on primary effluent at a municipal wastewater treatment plant ran continuously for more than 400 days, achieving regular COD removal of up to 70 percent and power densities of 150 to 200 milliwatts per square meter of cathode area, all without external aeration or chemical supplements. The exoelectrogenic communities, dominated by Geobacter and Shewanella, adapted to shifting influent conditions over the seasons. The authors of the review argue that the path forward lies in high-performance electrode materials such as metal-organic frameworks and carbon nanomaterials, engineered microbial strains with enhanced electron transfer, modular and stackable reactor designs, and hybrid systems coupling fuel cells with anaerobic digestion or constructed wetlands. For off-grid communities and developing regions, where low-cost electricity and sanitation are equally scarce, microbial fuel cells may find their first foothold, converting the world’s waste into a modest but meaningful current.

Subject of Research: Microbial fuel cell technology for bioelectricity generation and waste utilization

Article Title: Bio-electrochemical energy recovery: the role of microbial fuel cells in waste utilization

Article References: Kuity, N. T., & Sambrani, S. A. (2025). Bio-electrochemical energy recovery: the role of microbial fuel cells in waste utilization. Discover Biotechnology, 2(1), Article 17. https://doi.org/10.1007/s44340-025-00025-y

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00025-y

Keywords: microbial fuel cells, bioelectricity, wastewater treatment, electroactive bacteria, Geobacter sulfurreducens, Shewanella oneidensis, bioremediation, extracellular electron transfer, azo dyes, agro-waste, proton exchange membrane, sustainable energy