TransitionHERO helped TORWASH design how their technology, that turns sewage sludge into biofuel, fits into an existing wastewater treatment plant, ready for the next scaling stage.
Sewage sludge as resource, not as waste
Every year, Dutch wastewater treatment plants produce around 1.3 million tonnes of sewage sludge. Currently, this sludge is treated as a waste stream. Most of it gets trucked off and burned in incinerators, at a cost of roughly 150 million euros a year. TORWASH, a spin-off from Dutch research institute TNO, proves that sludge belongs in a different category: not waste, but feedstock. Their sewage sludge to biofuel process is designed to turn that expenditure into a source of energy.
Meet TORWASH: engineers who started at TNO
TORWASH was founded by three former ECN (now TNO) researchers: Levien de Legé, Pavlina Nanou, and Jan Pels. Their patented hydrothermal sludge treatment process uses high heat and pressure, without chemical additives, to separate water from sludge far more effectively than conventional dewatering techniques. The result is a volume reduction of around 85%. The remaining 15% form a high calorific biofuel and the extracted water is converted into biogas, making the whole process energy-neutral. Also phosphate in sludge can be recovered as struvite. Essentially, sludge to biogas and biofuel from a single process.
“Sewage sludge isn’t a waste problem. It’s a valuable resource we haven’t used well enough.”
Levien de Legé, co-founder, TORWASH
From pilot to demonstration
TORWASH had already proven the concept works: first at a pilot in Almere, with the Zuiderzeeland Water Authority, then, after receiving funding in 2021, at a demonstration plant roughly 20 times larger at the Land van Cuijk wastewater treatment plant, part of the Aa en Maas water authority. The next step is scaling further, and integrating directly into an existing facility, a wastewater treatment plant in Vlaardingen. That is a different engineering challenge than building a new plant from scratch. Every pipe, tank, and piece of equipment already on site is either an asset to reuse or a constraint to design around.
TransitionHERO as engineering partner
TransitionHERO first did concept engineering, and now have moved on to basic engineering, designing the reactor skid.
“The biggest challenge was integrating the TORWASH design into an existing plant. We looked for every place we could reuse existing equipment to bring down CAPEX, and that also simplified the permit application.”
Rocio, TransitionHERO
A change in technology providers
Partway through the project, TORWASH had to switch one of their technology providers, which could have derailed the timeline. Instead, the team held onto the original schedule for commissioning and construction. They used the lessons learned from the pilot phase so the scaled-up design would be even more robust.
The result
The result was a modular, integrated scaled-up design, ready for commissioning and construction. The application of TORWASH’s technology would help on the sludge line to reduce the amount of sewage sludge to be disposed of. For TORWASH, it would be proof that their technology can be integrated into existing water infrastructure, not just built as a standalone demo plant.
The lesson for other greentech start-up projects
The most valuable engineering work for a start-up scaling up their technology is often not the core process, it is the integration. Reusing what is already on-site can cut CAPEX significantly and shorten permit timelines. It’s advisable to let the design account for it from day one, not as a fix once construction has already started. We’ve helped other greentech scale-ups make this same jump from pilot to plant, like Growy’s vertical farm energy system.
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