Circular Challenge

BlueCity Circular Challenge 2020 – the recap


4 waste streams. 4 challenges. 1 winner! On November the 2nd, four teams of young professionals pitched their ideas for a new, circular product during the Grand Finale of the Circular Challenge. But there can only be one winner: team Provincie Zuid-Holland! With their prototype for a tile made of duckweed, the team aims to tackle multiple challenges at once.

The multidisciplinary team had six weeks to find a circular solution for a waste stream of duckweed provided by Provincie Zuid-Holland. The goal? Developing a new, scalable product with economic added value that can process the large quantities of duckweed that are being removed every year.

The challenge: finding a circular solution for duckweed

Duckweed is a water plant that 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 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 Amelung of Provincie Zuid-Holland says.

The solution: Flip the City

Well, leave it to Hidde Griek, Eliza Scholtens, Emma Raijmakers, Nina Rodenburg and Sophia Queckenberg, the young professionals making up team Provincie Zuid-Holland. The group of five did not only come up with a solution for the residual flow of duckweed; they also devised a solution for tackling water stress, heat stress and loss of biodiversity in cities.

“We boiled and compressed batches of duckweed in order to create fully biodegradable tiles with embedded flower and plant seeds.” the team explains during their pitch. These tiles could replace concrete ones, thereby increasing the biodiversity and benefiting water and heat relief.

The duckweed acts as a substrate on which the seeds can grow, and after approximately 2 to 3 months the tile decomposes, leaving lovely flower beds behind. “But we could also grow herbs, or maybe even vegetables!” the team adds. “It’s a very easy way of gardening, you can create a bed of flowers with just the flip of a tile!” 

Sounds good, right? But let’s add some math to that. The team estimates that they’ll need 6.5 m2 of duckweed to create one tile. To visualise that for you: by harvesting duckweed from the Heemraadssingel 118 times, they can make 50.000 tiles.

The competition

Although the panel of judges was immediately enthusiastic about this idea, it was a tough call for judges Wouter Veer, founder of Stichting ifund, Antoine Heideveld, managing director at Het Groene Brein and Maya van der Steenhoven, founder of Smart Distance Lab to pick a winner. It goes without saying that team Provincie Zuid-Holland faced strong competition.

The team working with a waste stream of fruit, provided by Voedselbank Rotterdam and Voedselbank Haaglanden, developed Fruitin Produce Life Extender: a spray made with extracted cutin from left over fruit that can be used by consumers to prolong the life of fruits and vegetables at home.

Also on behalf of the Voedselbank, the team working with a waste stream of vegetables developed Veggie Water: drinking water that is extracted from leftover vegetables, cleaned and then returned to society. Last but not least, the team working on behalf of Ludvig Svensson created a new, circular product with discarded climate screens.

Moving forward

Leaving the competition behind, #teamduckweed claimed first prize: 3 months of free work space in BlueCity and BlueCity Lab to develop their brand new circular business case into a real startup! Moving forward, the team hopes to collaborate with various stakeholders like the Provincie Zuid-Holland, Gemeente Rotterdam, Hoogheemraadschap van Rijnland and various biodiversity organisations to create their first pilot with 10.000 tiles. 

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Word of thanks

A special thanks to everyone who made this edition of the Circular Challenge possible: Provincie Zuid-Holland, Ludvig Svensson, Voedselbank Rotterdam, Voedselbank Haaglanden, Rabobank, BlueCity Lab, the host of the evening Rindert de Groot, the judges Wouter Veer, Antoine Heideveld and Maya van der Steenhoven, Wies van Lieshout, Eva Aarts, Emma van der Leest, Arjen van Klink, Jamie Hornes, Merlijn Boer, Dave de Held, Jan-Willem Vogels, Eveline Bal, Lisanne Addink, Rik Winsemius and Pieter De Stefano for guiding the teams throughout the challenge and everyone else who contributed in one way or another to one of the lectures or workshops!

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 that will start in February 2021 and turn your waste stream into a circular business case! Send an email to or give Niels Braamse a call on 06 82719180.