Circular Challenge

Finding a circular solution for duckweed – The Circular Challenge of Provincie Zuid-Holland

Circulair Challenge Portret 2020 LOGO-7

Duckweed, also referred to as water lentils, is the smallest flowering plant in the world. It’s also one of the fastest growing plants, and this causes problems. That’s why it’s currently being removed in large numbers, leaving the stakeholders involved with piles of green. During the Circular Challenge, a team of young professionals will rack their brains trying to find a new purpose for this waste stream provided by Provincie Zuid-Holland.

Together with her colleague Marloes Arkesteijn and the support of Gemeente Rotterdam and Hoogheemraadschap van Rijnland, Justine Amelung, Stakeholder Manager at Provincie Zuid-Holland, guides the assigned team working on this challenge. We talked to Justine and the team members about the waste stream it’s difficulties ánd potential.

The waste stream: duckweed


“We’ve put a lot of effort in finding an original waste stream to bring into this challenge.” Justine says, “Our intention was to provide a waste stream for which there is not any existing recycling technique available yet.” The waste stream that eventually made the cut was duckweed.

Even though you may have never heard about duckweed, you’ve probably seen it before. This water plant floats freely on or just beneath the surface of still or slow-moving water like ditches and small ponds. It’s one of the fastest growing plants on Earth, especially during hot summer months it multiplies quickly: one hectare in the open air can produce up to 20 ton of dry matter per year. This is problematic because it cuts off the light and oxygen supply for life underwater. In addition, duckweed can stink which causes people living near water to complain.

That’s why it’s currently being removed, and then composted or incinerated. “Since these are very low-value types of reuse, we asked ourselves: how can we turn something that is perceived as waste into something of value?” Justine says, “We think there’s a lot to gain here.” she concludes. In theory, duckweed namely has a lot of potential. It’s rich with protein (it contains more protein than soybeans) and is therefore considered a potential food source for humans.

The challenge: turning duckweed into a scalable product

The team: Emma, Hidde, Eliza, Remy and Justine

Unfortunately though, there is one little problem with ‘just eating it’. “Duckweed is, to some extent, toxic or polluted,” Justine explains. “and also the composition of the duckweed differs per ditch, pond or canal.” Luckily, the Circular Challenge team assigned to Provincie Zuid-Holland was not taken aback by this challenge: “We immediately thought that duckweed is a super interesting waste stream to work with and were eager to research its possibilities.” the team says. 

“We’ve challenged the team to develop a new product with economic added value, but other than that they are completely free in choosing a direction.” Justine continues. “However, it would be a bonus if the final concept can be used or implemented by us, the municipality or Hoogheemraadschap Rijnland.” This means that the team does not have to pursue a food related solution. What else can they do with duckweed? 

Whatever it may be, their concept must be scalable in order to process the large quantities of duckweed that are being removed. “And also the seasonality of the waste stream should be taken into account,” Justine adds, “there’s only large batches of duckweed available during the summer which, of course, is determinative for the business model.”

Experimenting, experimenting and more experimenting!


Three weeks into the challenge, the team’s concept is still in its early stages. “We’ve started doing some experiments in BlueCity Lab and have found that exposing the duckweed to heat pressing could be worthwhile to pursue,” the team explains, “even under relatively low temperatures something interesting happens with the texture of the material.” they conclude.

However, this finding is not enough to build a concept on yet. The next step for the team is to gain more information about the material. “Even though we’ve found research showing that duckweed is only slightly toxic, we do need to find out how toxic the batches we’re working with exactly are.” the team says. “And of course we still need to do a lot more research on the properties of the material. Experimenting, experimenting and more experimenting!”

> Curious to see the final concept? You can stream the grand finale live on the 2nd of November via YouTube. Each team will pitch their end product and a jury will pick a winner!

About Provincie Zuid-Holland

The teams at the Circular Challenge kick-off

Apart from participating in the Circular Challenge, the Provincie Zuid-Holland is working on various other projects within the circular economy. “We focus on different themes,” Justine explains, “participating in the Circular Challenge is part of our green resources and food theme, but we also have projects concerning circular manufacturing, plastics and the built environment.”

The ambition of Provincie Zuid-Holland is the same as the goal set by the national government. “We have a dedicated team working on reaching the goal to become fully circular by 2050.” Justine says, “To realize that, we believe it’s important to go out and practice what you preach, instead of linger in theory. The Circular Challenge is perfect for that!”

BlueCity Circular Challenge

The BlueCity Circular Challenge offers established companies the opportunity to become acquainted with the circular economy by developing a scalable product from their own waste stream within six weeks. Participants are at the cradle of promising startups and innovations.

Does your organization have circular ambitions? Sign up for the next BlueCity Circular Challenge and turn your waste stream into a circular business case! Send an email to or give Niels Braamse a call on 06 82719180.