Global wastewater production is estimated at around 359 billion cubic metres annually, a volume equivalent to four times that of Lake Geneva. Approximately half of this is discharged without treatment, while much of the remainder undergoes energy-intensive processing before reuse. The authors said that alternative treatment approaches could extract greater value from these flows while reducing environmental impacts.
Wastewater originates from domestic sewage, industrial and commercial processes, and food-related activities, and contains organic matter alongside nutrients such as nitrogen and phosphorus.
“Globally, our wastewater contains over 800,000GWh of chemical energy – equivalent to the annual output of 100 nuclear power plants. It’s also rich in nutrients used in agricultural fertilisers which, if reclaimed, could supply 11 per cent of global demand for ammonia and about seven per cent for phosphate,” lead author Prof Uwe Schröder at the University of Greifswald said in a statement.
Focus Point
The paper focused on microbial electrochemical technologies (METs), which employ electrogenic bacteria capable of transferring electrons to electrodes, generating an electrical current in a fuel cell.
Conventional anaerobic digestion systems convert around 28 per cent of wastewater’s chemical energy into electricity, but lab studies indicate that METs can achieve conversion rates of up to 35 per cent.
The authors suggested that such systems could be integrated into existing treatment infrastructure and, in principle, offset part of the energy demand of the water sector, which accounts for roughly four per cent of global energy use.
Beyond energy recovery, the same microbial processes can facilitate the extraction of nutrients for reuse.
“These are valuable chemicals that we cannot afford to throw away,” said co-author Dr Elizabeth Heidrich from Newcastle University. “After removal, the resulting water can be reused in many ways, like watering crops or industrial cooling. It could then be further treated to produce drinking water.”
Feasibility Studies
Pilot projects have demonstrated operational feasibility, such as with a urine-powered system called Pee Power at the Glastonbury Festival in 2015 and later tested in Uganda, Kenya and South Africa. The technology converts wastewater into electricity to power lighting near sanitation facilities, improving safety in areas without grid access.
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“The journey of METs over the last twenty years has moved us from understanding the ‘microbial black box’ to building modular, scalable systems capable of real-world impact. We are now at a stage where these technologies are technically feasible; the next step is ensuring they are economically competitive with traditional treatment methods,” said Dr Deepak Pant from the Flemish Institute for Technological Research. “By strategically integrating METs into our existing infrastructure, we can transform global wastewater management into a self-sustaining engine for resource recovery.”
The review linked these developments to the United Nations Sustainable Development Goal 6, which calls for universal access to safe water and sanitation.
“Globally, about 3.5 billion people cannot access managed sanitation. Expanding wastewater treatment could help improve living conditions for many of the world’s poorest people, as well as preventing ecological damage. Microbial electrochemical technologies could be a local solution to turn harmful sewage into a valuable resource,” said co-author Prof Ioannis Ieropoulos from Southampton University, who also serves as a director of MET-C, which is commercialising the microbial fuel cell technology.
Bottlenecks Ahead
Despite progress in laboratory and pilot settings, the authors highlighted regulatory and engineering constraints. In some jurisdictions, fertiliser derived from urine cannot be applied to food or animal feed production. Continuous operation at scale also presents materials and durability challenges.
“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 Prof Falk Harnisch, from the Helmholtz Centre for Environmental Research.
