Fermentation technologies

There are numerous technological solutions for biogas production, out of which the most applicable one shoud be chosen after complex assessment of all technical and economical aspects.

Applied biogas technologies can be divided into different kinds of categories. According to operation temperatures, we can talk about 3 types:

  • Psychrophilic         10-25 °C
  • Mesophilic              36-38 °C
  • Thermophilic             54-55 °C

According to the dry substance content of processed feedstocks, 3 groups can be differentiated as well:

  • up to 12% dry substance content:  vertical cylindrical, mechanically agitated bioreactors,
  • up to 19% dry substance content: horizontal, plug-flow bioreactors,
  • dry fermentation (over 30% dry substance content).

Vertical cylindrical, mechanically agitated bioreactor features:

  • Size: up to 6000 m3 digester size,
  • Design: steel or concrete, situated over or under ground level, or partly/fully in the ground,
  • Recommended: for processing feedstocks easily mixed, with low or medium dry material content.
  • Advantages:
    • specific costs of investment are favourable,
    • different operation forms (storage tank, flow-through) are possible
    • technological elements can be repaired without digester drainage,
    • biological desulfurization in the gas dome can be realized.
  • Disadvantages:
    • in big digesters it is not easy to ensure effective mixing and safe saeling
    • in case of "short-circuit" current flow, part of the feedstock leaves the bioreactor within a shorter time than is needed for decomposition,
    • risk of crust-formation and settlement.

Plug-flow bioreactor features:

  • Size: 200 -  800m3,
  • Design: horizontal cylindrical (tube digester) made of steel, or horizontal cuboid made of concrete,
  • Recommended: for processing feedstocks with high dry material content (e.g. energy plants),
  • Advantages:
    • efficient volume use,
    • different phases of the decomposition process are separated in the plug flow,
    • crust-formation and settlement can more easily be prevented,
    • shorter retention time,
    • efficient heating and mixing.
  • Disadvantages
    • only economical in the specified size,
    • in case of mixing apparatus breakdown, the digester needs to be drained,
    • specific costs of investment are high.

Dry fermentation features:

  • Size: due to the modular design there is no specified size,
  • Design: cuboid chambers, containers, boxes built of steel or concrete,
  • Recommended: for processing feedstocks easily manageable and with high dry substance content,
  • Advantages:
    • low energy demand, because there are only few moving apparatus,
    • low service and handling costs,
    • heating of feedstock is not necessary.
  • Disadvantages:
    • immature technology, only few successful references,
    • intermittent biogas production,
    • feedstock is not decomposed completely due to the lack of mixing
    • explosive storage and removal require an effective security sytem.

According to the planned biogas plant’s feedstocks and other relevant aspects, the First Hungarian Biogas Ltd. chooses the most effective and economical technical solutions for its partners.