Skip to main content

PONDUS® Thermal-Chemical Hydrolysis


The Task

Using and conserving resources

The waste activated sludge (WAS) from municipal sewage treatment plants has a low biogas yield. Thermal-chemical cell disintegration (hydrolysis) of the WAS increases its degradability in the digestion process, increasing the gas yield by up to 35%.
Economically, this results in further energy savings, ecologically in a higher yield of renewable energy and sustainably in higher utilisation (biogas).
For wastewater treatment plants, this means independence and a further step towards energy autonomy.

The Solution

That's how PONDUS® Hydrolysis works

A small amount of caustic soda is added to the thickened WAS. The sludge is heated to about 60 to 70 °C via a heat exchanger integrated into the reactor or an external heat exchanger. For example, 90 °C heating water or cooling water from a combined heat and power plant or steam can be used as the heat transfer medium. The sludge remains in the PONDUS® reactor for about two hours, the reactor is operated without pressure.

After digestion, the digested sludge leaves the reactor almost pH-neutral. The thermal energy still contained in the sludge can be used in subsequent process steps, for example in digestion. With the additional primary sludge flowing in, the total sludge flowing into the digestion is kept at a temperature just above the digestion temperature. In this way, practically no further heat energy is required for the thermal-chemical cell disintegration. The thermal energy required for digestion anyway can be used additionally for cell disintegration.

The Advantages

of the PONDUS® Hydrolysis

  • Reduced sludge quantity

  • Reduced viscosity ofthickened WAS up to 80%

  • Reduced anaerobic digestion volume up to 50%

  • Improved biosolids dewatering up to 5%

  • Increased biogas production up to 30%

  • Reduced polymer consumption at dewatering up to 20%

  • Reduced digester foaming


Gifhorn WWTP

Oldest PONDUS® Installation


PONDUS® Heat Exchanger

still without insulation


PONDUS® Caustic Soda Tank

Outdoor installation