“In 2020, we hope to implement the roofs we are testing here at a large scale.” A tour of the BlueRoof testing facility


In 2017, Bas van der Leeden and Jelle Scharff won the first-ever Circular Challenge with BlueRoof: a sustainable substrate for green roofs, made out of sewage waste. Now, two years later, Bas is taking us on a press tour of their testing grounds at the wastewater treatment plant Kralingseveer in Capelle aan de IJssel, where they are conducting tests before launching their product.

Bas van BlueRoof staat voor zijn testinstallatie op het dak

Our tour of the sewage plant starts at a meeting room on site. Bas, an executive and a spokesperson for the sewage plant take turns talking about the project. Bas: “We started two years ago with a feasibility study on a laboratory scale. That’s a really small scale. Now we are moving on to our final tests and are planning to launch our first lifecycle roof in spring 2020.” 

Blue roofs are green roofs 

After the introduction, we move outside to start our tour of the treatment plant. We discover a wheely bin filled with waste filtered out of the sewage a few days ago. According to Agnes van Zoelen, a member of the water board that oversees the project, 80% of the waste we are looking at consists hygienic wipes, baby wipes and make-up remover wipes. The rest consists of tampons, sanitary towels and the occasional lost mobile phone.

Nationwide, we flush about 200 wipes per person down the loo. At a small plant like this one, that means that they filter out about 100.000 kilos of wet wipes and other waste out of the water on an annual basis. In the current situation, this waste is all incinerated at waste disposal companies. This, of course, contributes to the emission of greenhouse gasses. Aside from the annual reduction in greenhouse gases that green roofs provide, one square metre of BlueRoof’s surface can prevent the emission of up to 5 kilo’s of C02.  

Roostergoed. Babydoekjes, tampons en andere troep die bij de rioolwaterzuivering uit het water gevist wordt.

BlueRoof receives the material directly from the sewage. They clean it, shred it and then compress it into sheets, ready to cover roofs with. Bas: “The wasted wipes and sewage water contain a lot of nutrients, like phosphates, which plants need to grow.” The sheets look like something you would insulate your floors with and surprisingly, don’t smell at all. “When we put the sewage waste into our production installation, it stinks to high heaven,” says Bas, “But when it comes out of it, it’s virtually odour free. 

Plaat substraat materiaal van BlueRoof

Testing BlueRoofs

On the second half of our tour, we visit BlueRoofs test installation. In the last phase of testing, BlueRoof is measuring the amount of water being absorbed and released by their “roofs”. Currently, they are testing four different setups with different kinds of surface and plant combos and one setup with just the material. The amount of rain is measured by a weather station on-site and then compared to the amount of water that is (later) released by the individual setups.

Testopstelling van 5 bakken op het dak van de waterzuiveringsinstallatie

“In 2020, we hope to implement the roofs we are testing here at al large scale,” Bas tells us, “we already have a location for the first roof.”  That location, however, is being kept a secret, much to our disappointment. “It’s at a prominent location,”  is the only hint we get. We have no other option than keeping an eye out once spring arrives, as one lucky roof in Rotterdam is about to get greener. 

Apply for the next BlueCity Circular Challenge

Are you a student or a young professional and ready to join the next circular challenge? Or are you a company looking to submit your waste stream(s) as a case for the next Circular Challenge? Great! We are looking for you. All the information you need, can be found on the Circular Challenge website.


An interview with BlueRoof
>Recap of the 2018 Circular Challenge