German researchers to convert wood waste into biohydrogen

GERMAN engineers have developed a biotechnological process to convert old wood waste into biohydrogen which can be used to power local industry.

Researchers from two of the Fraunhofer Society’s 72 institutes, the Institute for Interfacial Engineering and Biotechnology, and the Institute for Manufacturing Engineering and Automation, have collaborated with the University of Stuttgart on the process which uses sugar from the wood waste to produce hydrogen using bacteria.

The German Federal Ministry of Education and Research is investing €12m (US$12.7m) into the project, which the Fraunhofer Society expect to feed into demand for green hydrogen in the Black Forest region of southwest Germany.

Making biohydrogen

Wood waste such as pallets, old garden fences, and furniture offcuts are typically used in the process.

Under a pressure of up to 200°C, the wood is broken down in a mixture of ethanol and water to separate the wood fibres from its chemical contaminants, including lignin, adhesives, and paints.

Cellulose remains in the wood fibre after boiling and is further broken down into individual sugar, including glucose and xylose, becoming food for hydrogen-producing anaerobic microorganisms.

Two hydrogen solutions

With the process wood, researchers have developed two interlinked fermentation processes using bacteria and microalgae to produce biohydrogen.

The glucose from the cellulose can be put into a fermenter as a carbon source for bacteria, which grows to produce hydrogen and CO2.

The CO2 is separated from the hydrogen and transferred into an algae reactor, specifically a photobioreactor, where it is used as a carbon source for microalgae to multiply.

The microalgae are then transferred to another reactor, releasing hydrogen via direct photolysis.

The researchers have found that around 1 kg of wood waste can produce 0.2 kg of glucose, subsequently producing 50 l of hydrogen. In parallel, around 2 kg of CO2 can produce 1 kg of microalgae biomass, 50% of which is starch that can be used to make plastic products.

Commercial prospects

The Fraunhofer Institute for Interfacial Engineering and Biotechnology is working with the University of Stuttgart’s Institute of Industrial Manufacturing and Management to implement the process in the Black Forest region.

The H2Wood – BlackForest project began in 2021 with the objective to develop wood waste from the region as a local hydrogen resource.

Researchers from the institutes have developed a hydrogen roadmap to match waste wood quantity to the local demand around the region for green hydrogen in industry, transport, household, and building sectors.

Vladimir Jelschow, a research scientist at Fraunhofer IPA, said: “The study shows that the Black Forest region has a significant potential to produce hydrogen from local resources, but this potential can only be fully exploited by further developing the technologies and expanding the infrastructure.”

The Fraunhofer Society says a modular expandable pilot plant with three bioreactors is currently under construction and a biorefinery is set to begin operation next year on Campus Schwarzwald, a research centre dedicated to the Black Forest region and a key partner in the H2Wood project.