At a PepsiCo bottling plant in Fresno, California, a shipping container packed with hundreds of car-battery-sized cells does something that sounds like science fiction: it feeds sugary industrial wastewater to bacteria, and the bacteria generate electricity as they eat. According to the company running the system, San Diego-based Aquacycl, the setup helps the facility cut wastewater treatment costs by 20 to 60 percent while eliminating tens of tons of greenhouse gas emissions a month. It’s one of the first commercially operating deployments of a technology researchers have chased for decades: the microbial fuel cell, a device that turns the metabolism of naturally electricity-generating bacteria directly into usable power.
The Scientific Foundation
The organisms doing the work are called electroactive bacteria, and the best-studied examples are Geobacter sulfurreducens and Shewanella oneidensis. Unlike most microbes, which shuttle electrons internally during metabolism, these species evolved to breathe by transferring electrons directly onto external solid surfaces — originally minerals in soil and sediment, in a microbial fuel cell an electrode instead. Derek Lovley, the University of Massachusetts Amherst microbiologist who discovered Geobacter in the mud of the Potomac River more than three decades ago, later found that the organism builds hair-like protein structures called nanowires that conduct electricity along their length, a discovery that turned a curiosity of anaerobic soil chemistry into an engineering platform.
Lovley’s lab, working with electrical engineer Jun Yao, took that discovery somewhere unexpected: in a 2020 Nature paper, they showed that thin films of these Geobacter-derived protein nanowires could generate a continuous, sustained electrical current — about 0.5 volts across a film just seven micrometers thick — purely from ambient atmospheric humidity, with no sunlight, wind, or organic fuel required at all. Since then, the lab has engineered E. coli to mass-produce the nanowires, addressing what had been a supply bottleneck for scaling the technology up.
The Cross-Domain Connection
The genuinely novel synthesis here is treating a niche of extremophile microbiology as an engineering substrate for two very different problems at once: distributed power generation and decentralized wastewater treatment. Microbial fuel cells work by housing electroactive bacteria in an anaerobic anode chamber where they oxidize organic waste and release electrons, which flow through an external circuit to a cathode, generating current while simultaneously breaking down the pollutants in the wastewater. It’s a technology that sits at the intersection of microbiology, materials science (electrode and membrane engineering), and environmental engineering, and it took real cross-disciplinary work to move from lab curiosity to functioning industrial hardware.
Aquacycl’s approach, engineered by CEO Orianna Bretschger’s team, solved a problem that had stalled the field for years: naive attempts to scale microbial fuel cells by simply building bigger tanks and bigger electrodes lost efficiency as they grew, because mass transport, proton transport, and electrical conductivity all degrade at larger scale. Instead, Aquacycl built small modular units that link together like building blocks, each one keeping the bacteria working at peak efficiency, sized up or down by adding or removing modules rather than building one enormous tank. At the PepsiCo plant, the system now treats a concentrated waste stream responsible for roughly 60 percent of the facility’s sewer bill despite being only about 3 percent of its wastewater volume, removing 800 to 1,600 kilograms of biochemical oxygen demand per day. Beyond food and beverage waste, the company has also validated the technology for hydrocarbon remediation, consistently bringing regulated chemicals like benzene and naphthalene below detection limits in wastewater from tank-storage company Vopak.
What Remains Undemonstrated
The honest caveat is that microbial fuel cells still don’t generate anywhere near grid-relevant power, and probably won’t for a long time, if ever. A 2022 pilot at the U.S. Army’s Tobyhanna Depot in Pennsylvania, described in a 2023 trade publication account, treated a 1,400-liter system that removed 70 percent of biochemical oxygen demand from wastewater but converted only 9 percent of the electrons the microbes produced into usable electricity — the treatment benefit was real, but the power output was marginal. Even Aquacycl’s commercial systems, by Bretschger’s own account, still consume more energy than they produce in most deployments, with net-zero energy treatment described as an aspiration rather than an achieved baseline. The Geobacter humidity-harvesting Air-gen device remains a laboratory demonstration producing microwatt-scale currents suitable for powering small sensors, not a source of meaningful grid power. City-scale electricity generation from microbial fuel cells, as one recent industry piece put it plainly, remains a distant goal.
Why It Matters
The realistic near-term value isn’t replacing power plants — it’s replacing energy-intensive wastewater infrastructure and enabling power in places the grid doesn’t reach. Conventional wastewater treatment is enormously energy-hungry: globally, water and wastewater treatment is estimated to account for more greenhouse gas emissions than the entire shipping industry, according to Aquacycl’s own accounting, largely from the electricity needed to run centralized treatment plants and haul away resulting sludge. A modular system that treats concentrated industrial waste onsite while offsetting some of its own energy needs, and that leaves comparatively little sludge, is a meaningful decarbonization lever even without power to spare. Sediment-based microbial fuel cells installed under riverbeds or lakebeds are also already being explored to power remote water-quality sensors without batteries or grid connections, a genuinely useful niche where even microwatt-scale, always-on power beats a battery that needs replacing.
The Human Dimension
There’s a kind of stubborn optimism in a technology that keeps getting rediscovered by researchers who insist that bacteria discovered in river mud might one day matter to how we power the world — and who, decades later, are watching a shipping container full of them quietly cut a soda company’s carbon footprint. It’s not the future its earliest boosters imagined, in which biology might replace power plants outright. It’s a smaller, stranger, and more plausible one: bacteria doing the unglamorous work of cleaning up after us, and getting a little electricity out of the bargain.
Sources:
1. Liu et al., “Power generation from ambient humidity using protein nanowires,” Nature, 2020 — https://www.nature.com/articles/s41586-020-2010-9
2. UMass Amherst / ScienceDaily, “New green technology generates electricity ‘out of thin air,’” 2020 — https://www.sciencedaily.com/releases/2020/02/200217112730.htm
3. Aquacycl case study, “Continuous flow, large-scale, microbial fuel cell system for the sustained treatment of swine waste” — https://aquacycl.com/resources/case-studies/whitepaper-continuous-flow-largescale-microbial-fuel-cell-system-for-the-sustained-treatment-of-swine-waste/
4. XiaoZhi Lim, “Are microbial fuel cells ready to power the world?” Chemistry & Industry (SCI), 2023 — https://www.soci.org/chemistry-and-industry/cni-data/2023/7-8/are-microbial-fuel-cells-ready-to-power-the-world
5. “This startup uses microbial fuel cells to clean up wastewater,” Fast Company, 2022 — https://www.fastcompany.com/90812005/this-startup-uses-microbial-fuel-cells-to-clean-up-wastewater
6. Babanova et al., “Bioelectrochemical Treatment Technology—The New Practical Approach for Wastewater Management and GHG Emissions Reduction,” Frontiers in Chemical Engineering, 2022 — https://www.frontiersin.org/journals/chemical-engineering/articles/10.3389/fceng.2022.832505/full
7. Garbini, Barra Caracciolo, Grenni, “Electroactive Bacteria in Natural Ecosystems and Their Applications in Microbial Fuel Cells for Bioremediation: A Review,” Microorganisms, 2023 — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10263229/
Idea originated at artificialideas.org. Article researched and written by Claude Sonnet 4.6. Published at artificialideas.org.
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