TNO has developed a patented technology called TORWASH®. This year, a 50-L/h pilot plant has been commissioned and is operational at the wastewater treatment plant of Almere, The Netherlands. The goal is to reduce the volume of the sewage sludge waste stream, produce biogas from the liquid effluent and potentially recover phosphorus. This project is realized together with partners Paques, STOWA and Waterschap Zuiderzeeland.

For more information about the TORWASH Technology

Please contact Pavlina Nanou


The advantages of TORWASH®

Each year, roughly one and a half million tonnes of sludge end up in waste incineration plants, costing around 100 million euros. TORWASH® makes it possible to reduce the total amount by as much as 85%, resulting in enormous savings. Additionally, what is left over after the treatment is a substance that is much drier and can be used as a fuel.

These advantages were discussed during a symposium organized by TNO where water authorities were called to action to participate in the scale-up of the technology.

TORWASH® technology

TORWASH® is a high temperature treatment of wet biomass streams. This treatment: (1) enables efficient mechanical dewatering of the biomass, (2) enables efficient removal of salts, (3) allows for sufficient biogas production from the effluent because of the mild conditions used, (4) facilitates the recovery of phosphorus and (5) makes the use of additives redundant.

TORWASH® at Almere, The Netherlands (in Dutch)

Pilot testing in Almere, The Netherlands

In 2018, a mobile pilot plant for the thermal processing of sewage sludge was built at a scale of 50 L/h. The whole route from basic engineering to construction and functional testing took place in Petten at TNO’s facilities. This pilot was transported to the wastewater treatment plant of Almere, The Netherlands in July 2018. There we aim to prove that by thermally treating sewage sludge with our TORWASH® technology we can reduce this waste stream by a factor 10, produce biogas and recover phosphorus. This means that the treatment of wastewater can become cheaper for citizens, and that wastewater treatment plants can become more sustainable by generating their own bio-based energy and materials.

Pilot testing at Almere, The Netherlands

First pilot results

Tests were realized with sewage sludge, containing 3-6 wt.% dry matter. The produced slurry was dewatered on pilot scale using a filter press and the treated sludge could be pressed into a solid cake containing 50 wt.% dry matter.

The produced effluent is treated in an IC(X) pilot installation where biogas is produced (COD conversion of 70-80%) and phosphorus is recovered. All testing occurs on site at the wastewater treatment facility of Almere and the first pilot results are in agreement with previously obtained results in our lab.