Torwash Turns Sewage Sludge and Wet Waste into Biofuels

In principle, Torwash’s reactor can handle all waste streams, as long as they are biological. Preferably as wet and dirty as possible, because that’s where the most money can be made. The company’s slogan is therefore: Waste, too Good to Waste. The start-up aims to convert all organic waste into sustainable chemicals and fuels—circular products that can combat climate change both here and in developing countries.

Energy Carrier

Now that Minister Jetten has stopped subsidizing the burning of wood as biomass, Torwash’s biofuels could offer a sustainable alternative. Eneco will be the first customer to burn pellets made from sewage sludge in its biomass plant in Groningen. These will come from the first demo factory Torwash is building at a sewage treatment plant in Brabant. “What we make is an energy carrier,” say Torwash project leader Pavlina Nanou and general director Levien de Legé.

TNO Spin-Off

The inventor of the Torwash technology is TNO researcher Jan Pels. In 2004, he came up with a way to turn wet grass into fuel with the same quality as clean, dry wood pellets. Over the years, he developed the technology to work with almost any waste. From vegetable scraps to autumn leaves, sewage sludge, digestate (a residue from manure or plants after fermentation), beet tops, mushroom compost, slaughter waste, manure, straw, aquatic plants, or plastic—you name it, and Pels has tried it.

It’s almost always about wet waste and residual streams that companies have to pay to dispose of. Pels’s TNO colleagues, Pavlina Nanou and Levien de Legé, were equally enthusiastic about the promising technology. Normally, TNO licenses the technology to suitable companies for commercialization. But this time, the three decided to start a spin-off themselves. In 2020, they founded Torwash BV, with TNO owning a 25% stake.

Better Fuel

The technology uses hydrothermal conversion and is suitable for turning various wastes into useful applications and fuels. “It seems like an enormous variety of materials, but it’s all biological material. Our process does the same for all applications,” explains De Legé. “We cut the molecules in chains that contain oxygen. This happens in water, by heating it to high temperatures without boiling it. This takes place in a high-pressure reactor, a sort of pressure cooker. We use superheated water. By making that cut, the material partially breaks down, and oxygen is removed. That oxygen is released as CO₂, which is just enough to cause interesting chemical properties. For instance, it becomes much easier to remove water. The material becomes hydrophobic instead of holding water.

You also remove the oxygen and salts, making it a better fuel. So it doesn’t matter what you put in, as long as it’s wet and dirty. That type of waste is often the most expensive to process. We simply turn it into neat, clean pellets, just like the ones you buy for your stove.”

Sewage Sludge Incinerators Can Close

In principle, Torwash can process anything, but you have to start somewhere. That’s why the focus is on processing sewage sludge from the country’s water treatment plants. This contains a lot of water and is currently dried and burned in waste incinerators, such as those operated by HVC in Dordrecht and SNB in Moerdijk. Over 1.5 million tons of sludge are burned each year, at a cost of €150 million.

“What a waste,” thought Torwash, since sludge is not waste but a resource. “Sludge is very difficult to dewater, but it becomes hydrophobic in one go. After that, we can remove most of the water with a mechanical press. If this is applied on a large scale, the sludge incinerators in the Netherlands could eventually close,” says De Legé. “The existing dewatering methods produce sludge that still contains 80% water, which is then transported in tanker trucks to a sludge incinerator. Essentially, you’re burning water.”

Fully Circular

Torwash can remove the water and turn the sludge into combustible pellets or dry cakes. The extracted water is efficiently fermented into biogas, making the entire system energy-neutral. The phosphate in the sludge can also be recovered. The water is returned to the water treatment plant and eventually released into surface water. No waste is left behind, making the system fully circular.

Demo Plant Under Construction

The process has already been proven during an extensive test at the water treatment plant in Almere, in collaboration with the Zuiderzeeland Water Authority. The biofuel and biogas produced were found to be excellent for sustainable energy production. For this reason, Torwash chose to scale up further. Together with TNO and several water authorities, the start-up began constructing a demo plant twenty times larger at the water treatment facility of the Aa and Maas Water Authority in the Land van Cuijk.

“Here, we will prove the technology on a larger scale, processing 500 kilos of sludge per hour,” says Nanou. “We will process 10% of their sludge stream in our installation, a Torwash reactor, and a filter press. Soon, we will produce nice dry cakes, which can be shaped in any desired form. Eneco will use those blocks in its biomass plant for demolition wood in Delfzijl. But this is a limited amount. What we produce will be consumed there in just ten minutes.”

Ten Times Larger

The plant is half-funded by a DEI+ (Demonstration Energy and Climate Innovation) subsidy. This summer, the demo plant is expected to become operational. The next step is to scale the plant up tenfold, processing 5,000 kilos of sludge per hour. The modular design already accounts for this, allowing new reactors to be added to the existing installation. By 2027, Torwash reactors should be available for purchase. Initially, they will be targeted at small water treatment plants and later at all facilities.

Using Agricultural Waste Near the Equator

The technology is also applicable in agriculture, where many waste streams remain unused. Not in the Netherlands, where most agricultural waste is already reused, but near the equator. “So much food is grown there. All those by-products from coffee plantations, palm oil plantations, and sugarcane plantations are left to rot. With our process, you could perfectly convert that into combustible pellets for fuel. This way, you wouldn’t need to use wood for fuel,” says De Legé.

Torwash would, for example, like to set up near a sugar factory and process all its waste into pellets. An additional advantage: agricultural waste processed through the Torwash reactor becomes more suitable for fermentation into bioethanol, a future raw material for bioplastics.

“But it’s very difficult to get funding for these kinds of projects. That’s why it’s not our priority, and we’re focusing on developing the sludge business case,” he adds.

Recycling Dirty Plastics

Plastic waste can also be processed in the Torwash reactor. Currently, most plastics in the Netherlands are incinerated with household waste. What is recycled often finds low-value applications, such as traffic posts. “That option is just as interesting,” say Nanou and De Legé.

“The cut we make in the material also works with bioplastics, often biological polyesters. For instance, a biodegradable plastic like PLA is fully broken down into its building blocks again. This is true recycling. The advantage of our process is that the waste doesn’t need to be clean. Food residues, metal, and other plastics simply sink to the bottom.”

There is, however, a condition: a proper recycling system for biodegradable plastics must be in place. Currently, no one wants them. Composters reject them because they decompose too slowly, and sorting facilities don’t mix them with sturdier plastics.

Processing PLA in the Torwash reactor could kickstart a new collection and recycling system.

Green Chemistry Accelerator

Torwash has received support and guidance from the Green Chemistry Accelerator in recent months. This accelerator program, run by the platform Groene Chemie, Nieuwe Economie (GCNE), Invest-NL, and the Dutch Regional Development Agencies, helps green chemistry start-ups achieve key goals in 100 days.

The customized support has also enabled Torwash to accelerate financing for its pilots and demo plants. Torwash is one of five selected start-ups in the program, alongside ETB Global, Paques Biomaterials, Relement, and Susphos. All are promising game-changers for greening chemistry.

Step By Step

Torwash learned to focus on the short term during the program. Nanou says, “We had to set priorities to move forward and determine what we needed to work on in the next three months. This way, we discovered what we must do next to further develop our business model. The coaches and experts helped us immensely with this.”

By asking questions of other entrepreneurs who have already gone through this process, Torwash is taking steps forward.

This article originally appeared at Change Inc. as part of a campaign with Green Chemistry New Economy. Read the full series on our website or at Change Inc.