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Driving cars with biogas produced from biological waste

The ETAMAX research project brings together partners from research, the energy sector and industry and is aimed at using a combined, modular process to produce biogas from low-lignocellulosic waste such as supermarket waste and micro-algal biomass, at the same time as closing all substance cycles. The regenerative biomethane will be used to fuel a small fleet of gas-driven vehicles.

Easily fermented supermarket waste such as salad, fruit and vegetables will be transformed into biomethane using a new method. © Fraunhofer IGB

Renewable energy is a sustainable alternative to fossil fuels aimed at reducing our dependence on dwindling oil resources and reducing carbon dioxide emissions. Plant biomass plays a prominent role alongside water, wind and the sun in the production of bioenergy for creating electricity, heat or fuel. Due to its high net energy yield, biogas is the most important bioenergy carrier. Biogas is a mixture of methane and carbon dioxide that is produced during the anaerobic fermentation of organic mass. In combination with the power-heat coupling of a block heat and power plant, the production of biogas is seen as a technique with huge potential to prevent the production of CO2. 

Nevertheless, the potential of biomass for the production of biogas on the basis of energetically usable methane gas is far from being exploited to its fullest in terms of car fuel. The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart now hopes to change this situation through its work with partners from research, the energy sector, and the car and plant engineering industries. The objective is to fully exploit easily fermentable, wet biomass - in particular inexpensive biowaste and algal biomass - for maximum energy recovery. "Regenerative methane is the key product in this process and can be produced and used regionally," explained Professor Walter Trösch, deputy director and head of the Department of Environmental Biotechnology and Bioprocess Engineering of the Fraunhofer IGB. "Biomethane can be transported along the existing network just like natural gas, whose main component is methane. It can also be used to drive CNG vehicles (compressed natural gas), which is something we are doing as part of our pilot project.

Recycling of waste biomass

The researchers are mainly focusing on recycling wet waste biomass that can be easily and quickly fermented and that does not compete with food production: waste from the food industry which contains a high proportion of water, for example. In addition, kitchen waste from private households, canteen kitchens and student restaurants or supermarket waste which usually ends up in composting facilities, and whose energy is lost as heat. Due to its low lignin and lignocellulose content (the wood components of the biomass that are normally difficult to degrade in the absence of atmospheric oxygen) these waste products are excellently suited for fermentation. Following high-load fermentation, a process developed by the Fraunhofer IGB several years ago and technically used for the fermentation of sewage sludge, the solid substances of these biowaste fractions are converted almost completely into biogas in just a few days.

Additional biomass through the culture of algae

Biomass, and waste biomass in particular, is not an inexhaustible resource. The Fraunhofer IGB therefore also intends to use wet low-lignocellulosic biomass in the form of algal biomass for multi-substrate high-load fermentation. The production of energy from algal biomass has become a very efficient process thanks to a photobioreactor platform developed at the Fraunhofer IGB. In this bioreactor, the algae reach a high cell density with sunlight as the only source of energy, carbon dioxide as carbon source along with inorganic nitrogen and phosphate.

ETAMAX is aiming to close the carbon cycle by using the carbon dioxide that accumulates as co-product during fermentation and the combustion of biogas as carbon dioxide source for the cultivation of algae. The researchers need to find robust algae that can grow in the presence of this waste gas and that take into account the seasonally fluctuating light and temperature conditions in Central Europe.

Biomethane as regenerative fuel

These processes are being carried out and tested on the technical scale in a pilot plant on the premises of the EnBW co-generation power station in Stuttgart Gaisburg. It is envisaged that a future large-scale plant will be able to produce 300,000 cubic metres of methane gas per year from the municipal biowaste produced in the city of Stuttgart. After purification, the methane produced can then be used to fuel a small fleet of refuse collection vehicles with natural gas engines. The use of methane will also have benefits for air quality. In addition to closing the carbon cycle, the optimisation of biogas fuel quality will be further advanced in collaboration with EnBW Energie Baden-Württemberg AG and the use of methane as car fuel will be further advanced in collaboration with Daimler AG.

ETAMAX involves numerous partners from Baden-Württemberg

The project, which started in June 2009, will be funded for a period of five years with a total of 6 million euros from the German Federal Ministry of Education and Research (BMBF) as part of the "BioEnergie 2021" programme. In addition to the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, further research partners include the Karlsruhe Institute of Technology (KIT) and the Swiss Paul Scherrer Institute PSI. Industrial partners of the collaborative projects are the companies Daimler AG, EnBW Energie Baden-Württemberg AG, FairEnergie GmbH, Netzsch Mohnopumpen GmbH, Stulz Wasser- und Prozesstechnik GmbH and Subitec GmbH. The city of Stuttgart is also part of the ETAMAX "Mehr Biogas aus lignocellulosearmen Abfall- und Mikroalgenreststoffen durch kombinierte Bio-/ Hydrothermalvergasung" (More biogas from low-lignocellulosic waste and micro-algal residues via combined bio/hydrothermal gasification) project.

Contacts for further information:

Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB
Nobelstraße 12
70569 Stuttgart

Prof. Dr. Walter Trösch
Deputy Director and Head of the Department of Environmental Biotechnology and Bioprocess Engineering 
Tel.: +49 711 970-4220
Fax: +49 711 970-4200
E-mail: walter.troesch(at)igb.fraunhofer.de

Ursula Schließmann
Bioenergy
Department of Environmental Biotechnology and Bioprocess Engineering 
Tel.: +49 711 970-4122
Fax: +49 711 970-4200
E-mail: ursula.schliessmann(at)igb.fraunhofer.de

Website address: https://www.biooekonomie-bw.de/en/articles/pm/driving-cars-with-biogas-produced-from-biological-waste