THP after anaerobic digestion

Thermal hydrolysis after anaerobic digestion 

  1. From the wastewater treatment plant's primary and secondary treatment units, raw sludge is fed into the digesters, as in a conventional process
  2. The digested sludge is then dewatered at 16%DS and fed into the pulper
  3. From the pulper, the warm sludge is fed continuously to the reactors, in a sequential process that ensures sealed batches of sludge in each reactor
  4. From the reactor, the now sterilised sludge is passed rapidly to the flash tank, which operates at atmospheric pressure. The sudden pressure drop leads to substantial cell destruction for the organic matter in the sewage sludge.
  5. Leaving the flash tank, the hydrolysed sludge is directly dewatered while being still at high temperature and then cooled down before discharging it from the system
  6. The centrate with highly concentrated biodegradable material is returned to the digester for additional biogas production


When applied after anaerobic digestion, thermal hydrolysis has the following benefits when compared with conventional anaerobic digestion:

  • Increases the performance of existing plants with existing digesters
  • The end product is a high dry solids sludge cake, sterilised, with no odour
  • Reduces the volume of sludge cake for disposal up to 50% - 60%, making it the  ideal solution for projects with high disposal cost and high value of energy
  • Typically achieves 40% DS in final biosolids
  • Typically increases biogas production by 25%-40%
  • VS reduction up to 75%