Patented Auto De-gritting Technology

The Fre-energy digester system is unique because it is the only system in the world that can continuously remove grit, sand, ash, soil, glass, metal and any other inorganic contaminants from the tank. In an ideal world these materials would not be allowed to enter the process but in the real world they inevitably do. Chicken litter, from both broiler and laying birds, is an extremely good feed for AD, but because it has a high level of grit content no other AD manufacturers claim to be able to digest it.

The patented de-gritting sytem The de-gritting trap
The Fre-energy patented de-gritting system (left), showing the de-gritting trap (right) and the de-gritting arm (below)


This patented system combines de-gritting with the well established low energy technique of Sequential Unconfined Gas Mixing. The de-gritting mechanism allows the continuous extraction of grit and silt from the digester, thereby removing the need to periodically empty the tank. By preventing the gradual accumulation of silt in the digester, the full volume of the digester is sustained for optimum operation.  



Traditional crop digester                                               Fre-energy waste digester

 Diagram of Fre-energy waste digester; Can handle any feedstocks and does'nt silt up.Diagram of a Traditional Crop Digrester; No silt or grit extraction
















The de-gritting and gas agitation system is designed such that all the serviceable parts are external to the digester. The drive system and bearings are located on the digester roof and can be disassembled without breaking the gas seal


Image of de-gritting arm stationary.


This ability to extract grit and silt extends the range of material that can be digested to include; root crops, food waste, chicken litter, slurry from cattle bedded on ash, sand and other high grit inputs.

The amount of grit collected will be dictated by the inputs. The output from the grit trap is usually pumpable and as such can be removed from the digester using the standard unloading pump. If a Fre-energy belt separator is used, the majority of the grit will be in the dry material.




Key Points:

  • AD patented automatic de-gritting system is available in all sizes
  • Never any need to stop the digester to empty it
  • Feed gritty feedstocks, such as slurry from cows bedded on sand/ash, unwashed sugar beet, chicken litter etc.
  • Highly efficient mixing system uses less than 1W/m3 to mix the feedstock.

Top of page