The production of biomethane from kitchen waste offers an as yet untapped potential for the energy transition. So far, only a small portion has been used for this purpose.
Of 85 kilograms of kitchen waste generated in private households per person and year, only about 21 kilograms is collected via the organic waste garbage can so far and used for further recycling into biogas and compost. "In order to generate biogas from kitchen waste, the waste must be properly separated. A large part of kitchen waste mistakenly ends up in residual waste and is thus incinerated and lost for high-quality energy and material recycling," explains Steffen Walk. He is part of the Bioresource Management (BIEM) research group at the Institute of Wastewater Management and Water Pollution Control at the Hamburg University of Technology, which has set itself the goal of recycling biowaste with a project. Up to now, in many places, biogas has not yet been obtained from the portion that goes into the organic waste garbage can, but only compost is produced. Ideally, there should be a process cascade of biogas production followed by composting of the so-called fermentation residue for efficient energy and material use of the biowaste. Biogas contains mainly methane and carbon dioxide. By removing the carbon dioxide, the biogas can be upgraded to biomethane, which has a similar calorific value to fossil natural gas. "Only about 15 percent of Germany's 120 or so municipal biogas plants operate according to this principle and feed biomethane into the natural gas grid, while the others directly convert it into electricity. So there's still room for improvement," Walk said.
Covering gas consumption for a year
If the biowaste potential of all 83 million inhabitants in Germany were used to produce biomethane, the gas consumption of 2.8 million people could be covered for a year. We can all contribute to this by separating kitchen waste better. The use of small containers with lids is recommended for separating organic waste in the kitchen. Compared to plastic or paper bags, this saves resources and is easy on the wallet. The more that is collected, the greater the incentive for new construction and upgrading of compost and biogas plants for biomethane production. Steffen Walk demands: "Politicians should also demand kitchen waste separation more consistently. Separation rates of 65 percent, equivalent to 55 kilograms per person, are definitely possible." A start here would be the consistent installation of organic garbage cans for all households. So far, only just under 60 percent of German households have an organic waste garbage can.
Project Circular Economy
In order to give people a practical understanding of waste separation and recycling, Steffen Walk founded the "BioCycle" project. "BioCycle" describes the interrelationships of a cycle in which food becomes waste and then becomes new products, such as biogas or compost and soil fertilizer. The idea is that not all waste is avoidable. "You have to throw away a banana peel, but, disposed of properly, it can close the biocycle" explains Walk. In times of scarce energy and degradation of soils due to their over-intensive use, this problem can be counteracted with a circular economy. Biocycle is conceived as a learning opportunity, designed in six stages to show the cycle of food.
The project is also integrated into the "mudflat walks" organized by the Hamburg Open Online University (HOOU). The concept includes hiking or "driving" through places in Hamburg where renewable energies are produced.
More Information
www.tuhh.de/aww
www.hoou.de/projects/biocycle/preview
wattwanderungen.hoou.tuhh.de
