Clean fuel from excrement: Mannheim sewage treatment plant produces methanol

How excrement can be turned into "gold" has recently been demonstrated in Mannheim. The start-up ICODOS, the Karlsruhe Institute of Technology (KIT) and the city of Mannheim's urban drainage department have retrofitted the local sewage treatment plant and turned it into a production facility for green marine fuel. Methanol is produced from the wastewater and green hydrogen in the "Mannheim 001" demonstration plant – in a climate-neutral process, according to ICODOS.

The technology, which is housed in containers, uses CO₂ produced in the biogas plant at the municipal sewage treatment plant. In the two steel digestion towers, which rise into the sky like giant, silvery birds' eggs, bacteria transform the substances from the wastewater not only into biogas for heating, but also into CO₂, which has long been an undesirable waste product. "The technology we use to extract the carbon dioxide from the biogas mixture and convert it into methanol is at the heart of our new and patented process," says ICODOS founder David-Andre Strittmatter.

E-methanol from CO₂

The gas mixture is blown into a water-methanol mixture in which practically only the CO₂ dissolves. It is then released again using suitable temperature-pressure combinations "and can be converted into methanol at the same time as hydrogen," emphasizes the entrepreneur. This combination of process steps is unique to date. And there is another special feature. This is because the initial product is not pure methanol, but a methanol-water mixture. Only part of this is distilled in order to obtain pure methanol for ship operation. "The trick is that we feed the other part of the mixture back into the process as a solvent for CO₂ extraction. This hybrid system therefore continuously regenerates itself."

Until now, carbon dioxide for green methanol production has usually been separated using membranes or chemically bound in solutions with nitrogen compounds. Some research groups are also working with so-called metal-organic frameworks, or MOFs, which absorb and hold CO₂ molecules in molecular lattice cages. The start-up Aerleum from France, for example, recently reported on a new method of extracting the greenhouse gas from the air in sponge-like substances in order to produce e-methanol.

However, the ICODOS process would not work with air. The CO₂ content in it is not even a twentieth of a percent. "We can use gas mixtures with a CO₂ content of more than two percent," says Strittmatter. But there are also a number of other sources, such as biogas from agricultural waste or industrial wastewater treatment plants. Sludge from pulp production and waste gases from cement plants or waste incineration plants are also suitable, reports the entrepreneur. "However, our focus is currently on biogenic sources."

Limited supply of hydrogen

According to ICODOS, the demonstration plant in Mannheim can produce between 15,000 and 17,000 liters of e-methanol per year. "Of course, that's only enough for small ships," admits Strittmatter. For larger quantities, many such decentralized plants are needed. In future, container or cruise ships could also be supplied with green methanol from the sewage treatment plant. Methanol is an important chemical raw material, as a solvent or as a base material for polymers, resins and paints, for example.

Other plants in France, Spain and Scandinavia are helping the developers to ramp up green methanol production. The technology is basically infinitely scalable, says Strittmatter. However, the supply of gas mixtures for this is naturally limited, as is the supply of green hydrogen. Its production also consumes a lot of energy. "For a plant on a conventional scale, you would need your own wind farm of four to five gigawatts." Whether e-methanol production from sewage sludge catches on depends not least on its economic viability.

This article first appeared on t3n.de .

(mki)