New and innovative digester design solutions
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GasTop™ is a new family of innovative digester design solutions including patented gas washer with flat roof digester construction.


Krüger, a Veolia Water Technologies subsidiary, has developed a new digester design with the main purpose of reducing operating costs and capital costs while improving digestion. 


  • Construction with a flat-roof and no gas space in the concrete part of the digester results in a reduction of the capital costs. The design simplifies the construction and reduces the risk of corrosion of the concrete surface in an acidic environment inside the digester.
  • Sludge in the GasTop flat roof digester literally touches the roof so there is no classic gas zone known from classic design. Gas volume in its design is only limited to the volume of biogas gathered in a gas washer called GasTop. Thanks to that, volume of biogas can be significantly reduced more than 15 times in comparison to classic design, which has a great impact on safety, ATEX zoning or explosion risk assessment. 
  • Integrated GasTop gas cooler improves the gas quality, reduces foam overflow, and acts as a flame arrester. 
  • Built-in cleaning and maintenance possibilities, i.e. cleaning of blocked pipes, removal of sand and grit during operation, safe maintenance of the mixer and no shutdown of the digester are all improvements that increase the operational reliability and reduce the costs related to operation and maintenance. 



  • Simplified operation and maintenance.
  • Removal of sand and floating sludge.
  • Reduced foam formation.
  • Reduced operating and capital costs.
  • Improved performance.
  • Improved biogas quality.
  • Reliable solution, incl. ATEX .
  • Safe working environment.

Enhanced biogas quality

  • Less moisture
    • For biogas at 38°C reduced from 6.4%w/w to as low as 1,6% w/w at 15°C.
    • For biogas at 55°C reduced from 14% w/w to as low as 1,6%  w/w at 15°C.
  • CH4 content increased due to water condensation.
  • Less H2S – up to 50% less.
  • Less CO2 – dilution in sprayed water.
  • No foam.
  • Higher calorific value.


Resources & Product range


Yeosu STP, South Korea :

  • 2 digesters x 1,500 m³.
  • Mesophilic operation, THP. 

Lynetten WWTP, Denmark:

  • 2 digesters x 6,000 m³. 
  • Thermophilic operation. 

Zhengzhou New Area sludge digestion, China:

  • 6 digesters x 12,700 m3.
  • Mesophilic operation. 

Limassol WWTP, Cyprus:

  • 2 digesters x 3,000 m3.
  • Mesophilic operation.

Ginestous WWTP, France:

  • 2 digesters x 6,000 m3. 
  • Mesophilic operation, THP.

(article from wave magazine - p.35)