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Dry fermentation

Generating biogas with dry fermentation

3D model of a “waste-to-energy plant“
3D model of a “waste-to-energy plant“

To date, biogas technology has primarily focused on the classical “wet fermentation” of liquid manure in the agricultural sector or biological waste from the municipal area. The disadvantage here is that the renewable raw material can only be mixed with high dry substance contents (e.g. corn silage) or solid manure to a limited extent.

So-called “dry fermentation”, however, enables the quick and easy methanisation of stackable biomass (possibly including contaminating substances) both from agriculture and from municipal biological waste without elaborate processing. The materials for fermentation do not have to be converted to a pumpable, liquid substrate which means that the fermentation of biomasses can be achieved with up to a 50% dry substance mixture.

The BEKON dry fermentation process

Sieving compost
Sieving compost

The BEKON dry fermentation process allows for the utilisation of biomasses with a large quantity of dry substance. As already mentioned, the technology is characterised by exceptional resistance and a lack of susceptibility to contaminating substances such as sand, steel parts, stones, wood or fibrous components. An elaborate drainage of the fermented substrate is no longer necessary at the end of the fermentation phase.

The actual process is based on an inoculation with already fermented material, where the fermentation substrate is fed into the digester (fermentation container) with a wheeled loader. The biomass is anaerobically (absence of air) fermented in a sealed container. There is neither another stage of mixing nor is material added during the fermentation process (batch operation). BEKON has developed and optimised this batch principle into a one-step process.  This means that the different degradation reactions (hydrolysis, acid and methane formation) take place and are controlled together in a fermentation container. The biomass filled into the digester remains there until the end of the holding period of approx. 4-5 weeks. During the fermentation process, the fed-in fermentation substrate is solely tempered and percolated to enable ideal life conditions for the bacteria. Usually, the fermentation process takes place in the mesophilic temperature range at approx. 38 °C. At the end of the holding period, the fermentation container is completely emptied and refilled. The fermented substrate can then be subsequently sent for composting, which creates high-quality compost that can be sold as a valuable organic fertilizer. Existing composting plants thus retain their successful marketing channels.

The biogas obtained during the fermentation process can be used, after appropriate processing and cleaning, either in a cogeneration plant directly for the generation of heat and power or fed into the public gas system of the local energy provider.

Profitability and efficiency of the BEKON process

A key advantage of BEKON dry fermentation process is that there is no need for constant mixing of the material. No pumps or stirring tools are necessary to feed or remove the fermentation substrate. The fermentation material needs little or no pre-treatment. This results in much lower technical expenses than required for liquid fermentation plants. No moving parts are installed in the digesters, and this has a positive impact on operating costs. The wear and maintenance costs are low. Energy consumption and service costs for a BEKON plant are significantly lower than comparable liquid fermentation plants. The feeding process for dry fermentation permits the utilisation of biomass with a large quantity of dry substances and is not susceptible to contaminating substances such as foils, stones, steel parts and wood or fibrous components.

Main features of BEKON technology

Its low susceptibility to undesirable substances and the absence of preliminary treatment stages make the BEKON dry fermentation process ideal for the extremely efficient generation of energy.  There are also the following critical advantages for our customers:

  • very modern plant and control processes
  • sustained utilisation of hitherto unused materials for energy
  • sophisticated and robust technology
  • high profitability from additional cost advantages
  • low investment and maintenance costs
  • low operating and personnel costs
  • high gas yields
  • high gas quality
  • high safety and emission standards