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Resolve floating layers professionally


The problem

Floating layers are formed as a result of unfermented or unconverted substrate and are a frequent problem in biogas plants. This issue can occur not only in a fermenter, but also in secondary fermenters and post-fermenters. It is caused by many different factors – a fault in or failure of the agitator equipment due to problems with the biological process, quality differences when the substrate is replaced (e.g. new harvest), or when new substrate or substrates which are deemed to be difficult to break down (e.g. grass or whole crop silage) are employed.
In the fermentation vessels, floating layers lead to a major deterioration of the flow and agitation properties of the fermentation substrates. Mixing and degassing are also significantly impaired. Floating layers one metre thick or more can restrict plant operation, or even cause a complete standstill.


Dissolve floating layers organically using enzymes

Attempting to resolve the issue by dilution with additional water, external agitation or dredging usually results in the shutdown of parts of the plant and a drop in electricity generation.
On the other hand, the addition of tried-and-tested enzyme preparations is the only method that can resolve the floating layer issues without the need to shut down the affected fermenter. Breaking down these floating layers with effective enzyme preparations such as MethaPlus® or Axiase™ is a cost-effective and efficient approach, as their use is tailored individually to the specific situation. The enzyme product is selected on the basis of the composition of the respective substrate

The field-proven approach from DSM Biogas offers the following benefits:

  • All material in the floating layer is gradually converted into biogas
  • No need to shut down or restart the fermenters
  • The problem is resolved quickly without interrupting the electricity generation process
  • A cost-effective alternative to the elimination of floating layers



Biogas plant N., Czech Republic

  • BIOGEST Umwelttechnik GmbH 600 kW
  • Hectarage 2,700 m³; process temperature 42°C
  • Floating layer thickness 0.5 m,
  • Mainly unfermented grass silage
  • Time required to dissolve layer: 1 week

Agrargesellschaft mbH Siedenlangenbeck; Germany

  • Biogas plant 400 kW
  • Floating layer thickness 0.5 m,
  • Mainly unfermented grass silage
  • Time required to dissolve layer: 6 days

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