Plant waste, leftover food, sewage and other organic waste could be a valuable source of ‘green’ hydrogen for transport and industry, according to researchers.
Regionally produced green hydrogen could replace as much as 30% of fossil fuel energy in some regions within 10 years, the team from Fraunhofer IPA in Stuttgart, Germany, found.
Germany produces about 15m tonnes of organic waste each year, including plant waste and refuse from public parks, agriculture, food production, sewage by-products, and leftover food. Most of it is brought to composting plants, or is incinerated to generate heat and electricity, creating carbon dioxide (CO2) emissions.
“Organic waste is far too valuable to be used in this way,” said Johannes Full, head of the Sustainable Development of Biointelligent Technologies group at Fraunhofer IPA. “It would make more sense to use the material to generate hydrogen. The CO2 emitted during the process could then be separated, stored or used in industrial applications.”
Hydrogen is currently mostly produced from natural gas. A production process based on plant waste such as wood cuttings would be much more climate friendly, the Fraunhofer researchers said, in the same way as electrolysis with renewable electricity.
Treatment of plant waste – whether it is used in hydrogen production, composted, or incinerated – always releases CO2, but the researchers said it could be captured during the hydrogen production process and either used in the chemical industry or stored in abandoned natural gas fields.
In the new analysis, Full and his colleagues evaluated recently developed processes for converting biomass into hydrogen.
In a project with a company in the metal industry, the researchers took waste from local fruit farmers and winemakers, as well as cardboard, wood and canteen waste. The fruit and leftover food was first fermented by bacteria, before being converted to methane through another fermentation process at a conventional biogas plant. The methane was then converted into hydrogen and CO2. The wood and paper fibres were separately split into the two gases using a wood gasifier. The hydrogen was then directly used in metal processing.
Purple bacteria is particularly efficient at producing hydrogen from fruit and dairy waste, the researchers found. Researchers at the University of Stuttgart modified the bacterium so that it hardly requires light, meaning the hydrogen production process requires less energy. Together with Fraunhofer IPA, they are investigating financially viable methods of producing hydrogen with purple bacteria on a larger scale.
Another study by the researchers demonstrated that green hydrogen could cover some energy demands of selected industrial sectors and heavy goods traffic. They found that decentralised green hydrogen production and use is effective if the distribution centres are positioned as close as possible to consumers.
“Ideal locations are near busy roads with truck depots where hydrogen filling stations can be set up,” said Dr Jürgen Henke, scientist at Fraunhofer IPA.
Looking at the state of Baden-Württemberg, they found that 30% of fossil fuel energy could be replaced by green hydrogen within 10 years, using only hydrogen produced in the region.
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