Every time somebody flushes a toilet in Mannheim, they contribute to ecological shipping. Since March 2025, the German city’s wastewater treatment plant has been feeding an experiment of global relevance: Transforming sewage gases into green methanol, a cleaner, nearly-carbon-neutral alternative to heavy fuel oil. The pilot, known as Mannheim 001, is the first full case study of how human waste can be captured, processed and converted into fuel powerful enough to propel cargo ships across oceans. “It’s the first time the entire value chain — from sewage to finished methanol — has been demonstrated,” says David Strittmatter, co-founder of Icodos, the start-up behind the project.  At first glance, the pathway from toilet to tanker might seem implausible. But the chemistry is straightforward. Wastewater plants produce sludge — the thickened residue left after sewage is treated and cleaned. Mannheim’s plant ferments this sludge in oxygen-free tanks, yielding biogas rich in methane and carbon dioxide, which is usually burned for heat or flared off. Icodos’ innovation is to clean and upgrade that gas. “The sewage gas is dried, desulfurized, and then the carbon dioxide is separated from the rest,” Strittmatter explains. Using renewable electricity, the captured carbon dioxide is then combined with hydrogen through a catalytic process to form methanol — a liquid fuel that can run ship engines with only minor modifications. The Mannheim 001 process. As a nearly-climate-neutral alternative to heavy fuel oil, e-Methanol is being hailed as central to the sustainable transformation of the shipping industry. Image courtesy of Icodos. “Wastewater exists everywhere,” says Strittmatter, gesturing to a model plant pinned on his office wall. “The sludge contains up to three times more energy than the treatment process needs. We just usually waste it. Why not use it as fuel?” International shipping, which carries about 90 percent of world trade, is responsible for approximately three percent of global greenhouse gas emissions — more than the entire country of Germany. Cargo ships also spew sulfur oxides and particulates, contributing to air pollution along coastlines and in port cities. For decades, the sector has resisted cleaner alternatives, arguing that no scalable, affordable fuels existed. But that defense is crumbling. Regulators, customers and climate urgency are pushing the industry to look for replacements. Methanol is emerging as one of the most promising. Weighed down by negative news? Our smart, bright, weekly newsletter is the uplift you’ve been looking for. [contact-form-7] It is energy-dense, can be stored and transported in liquid form, and — crucially — many ship engines can be converted to run on it. Global giants like Maersk and CMA CGM are already operating methanol-powered container vessels. The International Maritime Organization has set a target to reach net-zero greenhouse gas emissions from global shipping by 2050, making green fuels essential. “Shipping companies have very strong ambitions to reduce their footprint,” says Strittmatter. “IKEA, Amazon and other big retailers increasingly want green supply chains. If the transport is dirty, the whole brand suffers.” Built at a cost of nearly €4 million ($4.6 million), with funding from the Karlsruhe Institute of Technology, the European Commission and Mannheim’s own Climate Fund, Mannheim 001 currently produces about 15,000 liters of methanol per year — enough to fuel smaller workboats or local needs, but nowhere near enough for a large container ship, which consumes tens of millions of liters annually. “A ship needs about as much fuel as 100,000 cars,” says Strittmatter, who has already secured an industrial area near Paris in France for the next upscaled plant, partly funded with a grant from the European Union. Mannheim 001’s anaerobic digester. At the wastewater treatment plant, biogas is converted into methanol using electricity and hydrogen. Photo courtesy of Icodos. The vision extends beyond shipping. Methanol is also a feedstock for plastics, solvents and other chemicals. A wastewater-to-methanol system could, in theory, help decarbonize multiple industries. But shipping is the most urgent target. “It’s literally waste that’s flushed away every day,” says Strittmatter. “We’re turning a liability into a resource.” Wastewater is a massive, underused resource. Each day, humanity produces about 900 million kilograms of feces and nearly 10 billion liters of urine. Harnessing even a fraction could help decarbonize industries, fertilize fields and power communities. Globally, less than 20 percent of sewage is treated before release, according to the UN. Even in highly regulated countries like Germany, where treatment rates exceed 96 percent, sewage plants consume enormous amounts of energy. Some municipalities spend up to 60 percent of their annual budgets running them, according to the German magazine brand eins. What if instead of burning energy to destroy sludge, we flipped the equation and mined its hidden power? Sewage is rich in carbon, nitrogen and phosphorus — the building blocks of fuel, fertilizer and food. A new wave of innovators is showing how to turn waste into wealth. One of the most striking efforts comes from another German startup: Shit2Power. The company has designed modular, shipping-container-sized units that sit directly beside wastewater plants. Inside, a thermochemical gasification process transforms sewage sludge into green hydrogen. Shit2Power works locally and is particularly useful for small municipalities. A small town of 30,000 residents could cover up to a third of its own electricity needs, explains co-founder and CEO Nina Heine. For many municipalities, that would amount to a small-scale energy transition right on their doorstep — and a relief for their waste balance sheets. This year, the Berlin startup plans to build its first facility; so far, the technology has only been tested in the lab. Wait, you're not a member yet? Join the Reasons to be Cheerful community by supporting our nonprofit publication and giving what you can. Join Cancel anytime “The potential of our technology is nothing less than redefining the entire sewage sludge treatment system,” says Heine. “We’re turning an expensive waste product into a resource that simultaneously generates energy and keeps essential nutrients in circulation. And what applies to sewage sludge can also be extended to other types of biomass.” Governments have taken notice. In 2023, Germany’s Federal Ministry for Economic Affairs awarded Shit2Power the German Founders Prize. The European Union and regional utilities are also backing pilots, including those led by Shit2Power. For rural communities, the technology could be a lifeline, cutting waste disposal costs while generating homegrown renewable power. What a large-scale investment looks like can be seen in southern Denmark. Publicly inaugurated in May 2025, the Kassø e-methanol facility is the world’s first commercial-scale plant of its kind, producing 53 million liters annually with biogenic carbon dioxide from a local biogas plant.  “The interest is huge,” says Icodos’ Strittmatter. “[…] With methanol, you avoid sulfur emissions and dramatically cut particulates. The climate and air quality benefits are real.” According to Icodos, scaling sewage-to-methanol worldwide could cover the entire fuel demand of the global shipping sector. Credit: MartinLueke/Shutterstock. Yet the future of poop power isn’t without obstacles. Regulations are a major hurdle. Wastewater laws were written to protect waterways, not to harvest energy and nutrients. Many treatment plants lack legal frameworks for selling byproducts as fuel or fertilizer. “Once you think of wastewater not as a liability but as an asset, the possibilities multiply,” says Strittmater. “You can make fuel, fertilizer, clean water, even building materials.” Indeed, innovators are experimenting with sewage-derived bricks, plastics and biochemicals. The combined potential is staggering: According to Icodos, scaling sewage-to-methanol worldwide could cover the entire fuel demand of the global shipping sector. Shit2Power estimates its modular units could cut energy costs for thousands of small municipalities.  In a warming world, pragmatism may matter more than aesthetics. “Progress doesn’t have to be pretty,” Strittmatter says. “It just has to work.” The post The City That Turns Human Waste into Clean Fuel appeared first on Reasons to be Cheerful.