1. Sludge is dewatered to 16-17% dry solids (DS) and led to a storage silo.
2. The dewatered sludge is fed into the pulper to be mixed and heated by recycled steam from
the reactor(s) and the flash tank.
3. Process gases are compressed and broken down biologically in the digesters (no odour).
4. Thermal hydrolysis takes place in reactor(s) at 165ºC for 20-30 minutes. The steam is gradually
released and sent back to the pulper.
5. The sterilized sludge is then passed rapidly into the flash tank, resulting in cell destruction from
the pressure drop. The sludge temperature is decreased to approximately 102º C by flashing
steam back to the pulper.
6. The sludge is then cooled to the required digestion temperature partly by adding dilution water
and partly in the heat exchangers.
7. The THP process is followed by anaerobic digestion, converting the organic matter (volatile solids)
to biogas, mainly consisting of approximately 65% methane (CH4) and 35% carbon dioxide (CO2).
8. The biogas can be utilised in a gas engine with generator producing electricity. Alternatively it is
cleaned (stripped) of CO2 and used to substitute natural gas in gas grid/vehicles.
9. Steam for thermal hydrolysis is mainly produced in a cogeneration waste-heat boiler
using exhaust gas and cooling water from the gas engine. Alternatively, biogas or other
fuel sources can be used.
10. The digested sludge is dewatered into a high-class biosolids product with 30 – 40% dry solids.
11. The resulting cake/biosolids is applied directly on agricultural land or dried and used as fuel or
Click here to see an Animation of the THP process.