Electricity-Generating Bacteria Could Reclaim Energy and Nutrients from the 359 Billion Cubic Meters of Wastewater Produced Each Year

Every year, the world produces approximately 359 billion cubic meters of wastewater - enough to fill Lake Geneva four times over. About half of that is simply discarded without treatment. The other half is treated at substantial energy and financial cost, and the resources it contains - organic carbon, nitrogen, phosphorus - are largely lost in the process.

A review published in Frontiers in Science by an international research team makes the case that this framing inverts the actual economics. Wastewater is not primarily a problem requiring disposal. It is a resource stream that existing technology is already capable of mining, at a scale that could supply meaningful fractions of global energy and agricultural nutrient demand.

"Globally, our wastewater contains over 800,000 GWh of chemical energy - equivalent to the annual output of 100 nuclear power plants. It's also rich in nutrients used in agricultural fertilizers which, if reclaimed, could supply 11% of global demand for ammonia and about 7% for phosphate," said lead author Professor Uwe Schroder at the University of Greifswald, Germany.

Microbial electrochemical technologies

The review centers on microbial electrochemical technologies (METs), a class of systems that use a specific group of bacteria - called electrogenic or electroactive bacteria - to process wastewater while generating electrical current. These organisms transfer electrons to their surroundings as part of their metabolism, and when connected to electrodes, they produce a measurable electrical current in the manner of a biological fuel cell.

Conventional anaerobic digestion - the most widely used form of microbial wastewater treatment - converts about 28 percent of wastewater's chemical energy into usable biogas. METs, in laboratory conditions, have demonstrated conversion efficiencies of up to 35 percent to direct electricity. The authors note that METs could be integrated into existing anaerobic digestion infrastructure, potentially improving both energy recovery and treatment quality rather than replacing proven systems outright.

Beyond energy, the same bacterial processes that consume organic matter can be configured to extract phosphate and nitrogen from the treated water. These compounds would otherwise require energy-intensive industrial production - the Haber-Bosch process for ammonia, for instance, accounts for about 1 to 2 percent of global energy consumption. Recovering them from wastewater would simultaneously reduce nutrient pollution (which causes algal blooms and oxygen depletion in waterways) and substitute for a portion of industrially produced fertilizer.

From Glastonbury to Uganda

The technology has moved beyond laboratory settings in targeted deployments. A urine-powered MET system called Pee Power was trialed at the Glastonbury Festival in 2015 - one of the world's largest outdoor music events, handling waste from hundreds of thousands of attendees. The system converted urine to electricity and used that electricity to power lighting around the toilet facilities. It has subsequently run in longer-term field trials in Uganda, Kenya, and South Africa, providing lighting in areas without reliable electrical grid access.

These deployments demonstrate that METs can function under real-world conditions, at scale, outside of laboratory settings. They also illustrate the technology's particular appeal in contexts where grid infrastructure is absent and sanitation capacity is limited. About 3.5 billion people globally lack access to managed sanitation - a number that bears directly on both public health and the viability of wastewater resource recovery at a meaningful scale.

What is blocking wider deployment

The review is forthright about the barriers. Regulatory frameworks in many countries are not designed for circular economy approaches that treat waste streams as inputs. In a specific and illustrative example, urine-derived fertilizer cannot legally be applied to food crops or animal feed in numerous jurisdictions - regardless of its chemical composition or safety profile. Regulations designed to prevent pathogen contamination were not written with resource recovery systems in mind, and updating them requires both political will and technical standardization work.

Engineering challenges also remain. Maintaining the performance of electrode materials under continuous operation - rather than in laboratory batch conditions - proves more demanding than initial tests suggest. Scaling up from bench to industrial-scale systems involves fabrication challenges and cost pressures that have not yet been fully solved.

"While it would be a stretch to imagine powering our homes with wastewater, microbial electrochemical technologies could enhance existing water treatment processes. Rolling METs out widely would be especially beneficial for heavy loaded types of wastewater or in places where existing treatment is too expensive or doesn't reach everyone," said co-author Professor Falk Harnisch from the Helmholtz Centre for Environmental Research, Germany.

The water sector currently accounts for around 4 percent of global energy use. A technology that could make that sector partially self-powering while also recovering materials of agricultural value would represent a significant shift in the resource economics of water management.