Generating fresh value from organic waste

January 2020
The BHS-Sonthofen Biogrinder is used to process and shred organic material.
The Association for Waste Management Kempten (Zweckverband für Abfallwirtschaft Kempten – ZAK) has been using their new biomass treatment plant since May 2019. Technology worth about €2.8 million in total now ensures that foreign matter is optimally removed from organic waste and green waste before fermentation. The plant-based elements have to be effectively decomposed in order to achieve the best result for the latter. That’s why a BHS-Sonthofen Biogrinder is now used to process and shred this material. Its low power consumption and exceptional shredding results, even for challenging input material, are what make it stand out.

The Association for Waste Management Kempten (ZAK) is a consortium made up of waste management bodies in the city of Kempten and the districts of Lindau and Oberallgäu in southern Germany. The waste of 312,000 residents is collected, recycled and disposed of in ZAK’s waste management plants. These include a fermentation plant for green waste and organic waste, a composting plant for green waste and a waste-to-energy plant in Kempten. About 25,000 tons of green waste and organic waste are processed in the fermentation plant each year. This is used to produce natural gas, with a total biogas yield of three million standard cubic meters per year. In order to achieve this, the plant manufacturer Komptech GmbH from Frohnleiten, Austria, was commissioned to plan and construct a new biomass treatment plant.

BHS-Sonthofen: A strong partner for decomposing organic waste

Komptech is a leading international technology company that provides machines and systems for the mechanical and biological treatment of waste material. Its core competences include composting, fermentation and biomass processing. This company got BHS-Sonthofen on board as a strong partner to help plan the new biomass treatment plant ordered by ZAK. The project posed a variety of challenges, including removing high volumes of foreign matter like plastic from organic waste and maximizing the gas yield. The issue of undesired components in organic waste was resolved by using more sophisticated separation technology. A screen, overhead magnets and a near-infrared sorter now separate organic waste from carelessly discarded plastic bags and metal parts.

BHS-Sonthofen contributed to more efficient biogas production. “The biogas is produced by microorganisms during fermentation. The more shredded the material, the more settlement areas the bacteria have,” explains Andreas Breuer, division head for Technology, Waste Management and New Energies at ZAK. “In the course of planning the plant with Komptech, we explicitly requested the BHS Biogrinder as a plant component, as we had already had good experiences with this machine in preliminary tests – it perfectly prepared our input material for decomposition.” The machine was also required to have a low power consumption and be maintenance friendly.

Finding the best solution for the customer

Each biomass processing step is unique, as the input material determines the process as well as the choice of suitable machine, equipment and settings. “We had carried out preliminary tests with the middle fraction of ZAK’s organic waste beforehand. This proved that the Biogrinder optimally prepares the material for the next process step in the fermenter,” says Tobias Steinhauser, Area Sales Manager for the Recycling & Environmental Technology division at BHS. The machine, which serves as the final component of the new plant, processes pre-shredded and sorted input material. The organic waste is separated into fine, medium and coarse fractions in the upstream process. While the coarse fraction is combusted, the fine and middle fractions are suitable for fermentation in the fermentation plant and thus also gas production. However, the middle fraction has to also be further broken down in the Biogrinder.

The material is fed into the center of the Biogrinder from above. Inside the machine is a rapidly turning, star-shaped rotor with a vertical shaft and massive crushing tools. “The feed material is centrifuged to fling it outwards and intensively process it through impact, shock and shearing forces,” explains Steinhauser. “This process is continuous – the decomposed material is then pushed downwards and outwards.” The Biogrinder of type RBG 08 with 90 kW was selected for this very specific range of tasks and the high material volume, as it can process up to six tons per hour in this application scenario.

Supplying electricity and heating for the region

After just a few weeks of use, Breuer from ZAK is already delighted with the new plant: “We have been able to increase our biogas yield by five percent. And this isn’t just a massive gain from an economic perspective – being able to recover as much value as possible from waste materials is also good for the environment.”

The biogas, which has a methane content of approx. 55 percent, is converted into electrical and thermal energy in three cogeneration units and supplies electricity to about 2,000 households and heat to approx. 200 households. “Thanks to our physical proximity to BHS-Sonthofen, maintenance technicians and spare parts arrive on site very quickly whenever we need them,” adds Breuer, noting a further advantage. “This also saves long transport and travel times, which is also beneficial to the environment.”