A primary digester cover that is effective when sludge levels vary significantly, it is also very effective in conditions where extreme foam occurs.  The ballast blocks are located in the attic space and are designed to set the operating pressure.  The attic space provides insulation so additional insulation is not necessary.

A truss design is more expensive than comparable beam covers and the attic space collects condensation which will need to be removed periodically.



  • No insulation is required and is achieved through the attic space
  • Allows variance in sludge volume
  • Depresses scum
  • Trusses are not subject to interior corrosive environment


  • The second most expensive cover design
  • Cannot store a significant amount of gas
  • Condensation must be removed periodically from the attic space


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