Product Description

State-of-the-art Digestion Plants for Biowaste and Kitchen Waste

Digestion plants for biowaste and kitchen waste are usually implemented on a large industrial scale. Biowaste is separately collected organic waste generated by households. The contents of organic waste collection bins, into which kitchen and garden waste from private households is placed, varies depending on the time of year. Kitchen waste mainly originates from restaurants, hotels, canteens and other facilities with commercial kitchens.


Customized solutions

Prior to the actual fermentation process, biowaste and kitchen waste must be pretreated. Removal of impurities, screening, grinding or chaffing and homogenization form an integral part of pretreatment. If your substrates contain impurities, we develop a customised process chain for processing your substrate. To achieve this we use wet or dry processing techniques. If hygienisation is required, this is usually carried out at a temperature of 70° C and for a duration of 1 hour. Input material with a high dry-matter content is diluted with process water in order to guarantee that there are no problems with the process technology. Depending on the quantity of kitchen waste within the biowaste, a two-stage digestion process may be required; i.e. the input material first goes into the hydrolysis tank and subsequently into the digester. The initial biological process is hydrolysis. With this type of acidification, the biogas produced is primarily made up of CO2 and does not contribute to energy generation. The actual production of biogas then takes place in the digester.

Digesters are built according to industrial standards and are made of concrete or coated steel, and they are sometimes agitated centrally from above, or sometimes laterally. These methods of mixing are intended to prevent the formation of any floating or sedimentation layers.

Gas engines are usually employed to utilize the resultant gases, and these may well have capacities in the MW range. The gas is normally stored temporarily in large gas tanks. The plant is equipped with an emergency flare to burn off the excess biogas. Other system components are: cooler, condensate shaft, desulphurization system, gas measuring device, etc.. Alternatively, the biogas can be processed to meet natural gas specifications and fed into the natural gas grid in the form of biomethane.

Following fermentation, the digestate is often dewatered. The solid part can be sold as compost to private households, tree nurseries, garden centers, wine-growing enterprises or landscape gardeners. The liquid part is pumped back to the start of the process, in order to liquefy the input material. One potential problem with this process water recirculation system is the fact that the liquid contains a lot of dissolved salts, and after several cycles high concentrations build up which may inhibit bacterial growth. Appropriate expertise and experience are essential for the process engineering design.

For a digestion plant to be able to operate effectively and efficiently, it is monitored by a comprehensive control system featuring a variety of measuring and control devices.

The fermentation of biowaste is relatively complex. The Krieg & Fischer engineers have many years of experience planning these kind of plants, and can therefore offer profound and competent expertise.

If you are interested, we can provide an energy calculation and a cost assessment for your individual and tailor-made biogas plant free of charge. Contact us directly at


Reference Projects

Huntstown Biogas Plant

  • Location: Ireland.
  • Input: Thermal pressurised brown bin and food waste.
  • Fermenter: Steel tanks, 4 x 4,900 m³.
  • Gas utilization: Gas engine 2 x 2,4 MWel.
  • Particularities: Grit removal, input material cooling, 2 buffer tanks, external gas holder.
  • For more information.


JCBE Derby Biogas Plant

  • Location: UK, Derby.
  • Input: Hydrolised Kitchen Cat. 2 (viscera)-, paper and cardboard waste (treated by TPH), water (recycled, rain, mains).
  • Fermenter: Concrete tank, 2 x 5,300 m³.
  • Gas utilization: Gas-upgrading system.
  • Particularities: Pretreament system: Thermal Pressure Hydrolysis (TPH) for input material, cooling tank with central agitator for reception of hot input material, substrate cooling system, two storage tanks, two digester and one secondary digester – all equipped with double membrane gas holder roof, biogas upgrading system.
  • For more information.




Biogas Plant im Brahm

  • Location: Germany.
  • Input: Pig manure, kitchen waste, horse dung.
  • Fermenter: Concrete Tank, 1,205 m3.
  • Gas utilization: Gas engine, 2 x 190 kWel + 2 x 190 kWel extensions.
  • Particularities: Digester mixed with side-mounted mixers, gas holders on top of all tanks, secondary digester, storage tanks, heat utilisation (pasteurisation kitchen waste, heating of buildings and the nearby Schlosshotel).
  • For more information.

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