Food waste will produce the energy of tomorrow

Category: Products and machines

In Germany alone, about 12 million tonnes of food go to waste each year. This is made up of expired food from the retail food industry, goods with damaged packaging or expired promotional goods. From a pure energy point of view, this food waste is very valuable, as biowaste can be made into sustainable energy in biogas plants and then fed into our electricity and district heating grids. Biowaste is also converted into compost. In order for this transformation from biowaste to bioenergy and compost to work, packaging and other foreign matter must be removed. This article shows how such biowaste can be optimally recycled today with the help of state-of-the-art grinding and separation technologies and how it promotes biowaste as a source of renewable energy.

Conserving resources by recycling packaged and unpackaged food waste

Today, the energy produced from biomass primarily comes from crops that already make a significant contribution to reducing CO2. Biowaste can also be used as a natural resource for CO2-neutral energy production. Doing so simply requires freeing the organic mass in the waste from the foreign matter and making it available.

It all depends on separating the materials

The reliable separation of biowaste from foreign materials and contaminants (i.e. packaging as well as objects that have wrongly landed in the recycling bin) is crucial to recovering energy and recycling biowaste. The crushed and mixed organic mass is utilised for energy and materials in accordance with the fundamental idea of closed-loop recycling: Biogas is produced in fermentation plants, and the fermentation residue is recycled into compost in composting plants. Farmers use this compost to improve plant growth, which allows them to dispense with chemical fertilisers. The optimum closed loop of biowaste recycling. The foreign matter separated by the DRM system is thermally recycled.

Optimum use of resources with the DRM separation mill

In contrast to conventional processing methods, the DRM system allows the organic materials to be precisely separated from the inorganic materials right from the start of the process. Conventional plant configurations for the treatment of biowaste and the separation of foreign matter require a number of process steps. Generally speaking, a wide variety of screening systems, usually downstream, are used at different stations. With the DRM separation mill, the biowaste is crushed while the foreign materials and contaminants are simultaneously discharged. This means that a DRM plant configuration can eliminate steps such as hand sorting, regrinding and various other screening techniques.

With its DRM separation mill, Tietjen achieves an unprecedented level of purity in the organic and inorganic fractions at a high rate of throughput. Designed for reliably separating biogenic content from foreign matter, the DRM separation mill ensures the purity of the substrate from the very beginning of the process. Its special design enables high separation performance with minimum energy consumption. This makes the DRM separation mill technically and economically valuable. Due to its compact design, the DRM separation mill can be integrated into almost any plant design where there may be mechanical-biological waste treatment processes (MBT processes).

Lean plant design for the treatment of food waste

The DRM separation mill is at the heart of our biomass plants. It is the centrepiece for crushing and separating foreign matter and contaminants. Upstream and downstream systems depend on the processing capacity and separation quality achieved by the DRM separation mill. The process is as follows:


The receiving container
A receiving container and screw conveyor transport the input material to the grinding chamber of the DRM double rotor mill. The DRM separation mill is engineered to reliably separate the biogenic content from foreign matter or contaminants from various waste streams. It is designed for processes with larger quantities of waste.

Crushing and separation
The crushing occurs via the rotors equipped with beaters that press the organic mass through sieves and eject foreign matter due to its specific weight. In addition to separating out contaminants, the DRM increases the surface area of the organic matter, thus increasing the specific gas yield of a subsequent fermentation line. At the same time, the homogenisation of the matter also reduces the viscosity of the biomass and significantly reduces energy consumption in subsequent processing stages. Easier precipitation of silicates (sand) has the following advantages:

  • Less wear,
  • a reduction in floating layers in the fermenter and
  • minimised pump and agitator loads.

This creates better conditions to fully utilise the biogas potential.

Due to the adjustable speeds and variable motor power (55/75 kW) of the rotors, it is possible to optimally adjust the DRM separation mill to various biowaste properties. The DRM separation mill is used in both liquid and dry fermentation. Generally, it is not necessary to add fluids to process packaged foods. Only in the case of very dry biowaste can adding a liquid improve the separation performance.

Press screw

The press screw prepares the foreign matter (plastic packaging) separated and crushed by the DRM separation mill for thermal recycling.

Customer-specific plant design with the DRM separation mill at the centre of the plant

Design and maintenance of the DRM separation mill

The DRM 800 is made of solid stainless steel, so it can withstand even coarse foreign matter. Its built-in hydraulics make it easy for operators to open housing halves for maintenance or to quickly remove any solid contaminants. Essential spare parts, which usually have to be replaced after a few years, have been intentionally designed to be screw mounted to achieve a very long machine life with little maintenance.

Would you like to find out more about plant design? We offer our customers dry grinding plant engineering and wet grinding plant engineering services. Feel free to contact us.

  • Author:
    Thomas Runde

  • Images:
    Title image: shutterstock 1309525609 // lovelyday12, plant in compost: shutterstock 755382610 // lovelyday12, Tietjen

  • Tags:
    Biogas, Biomass, compost, DRM separation mill, dry grinding plant engineering, electricity streams, energy production, food waste, renewable energy, separation, waste streams, wet grinding plant engineering

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