BlueCity: The circular economy in a tropical swimming pool

Right on the Nieuwe Maas River embankment in Rotterdam lies BlueCity, a circular economy incubator located in an unmistakable glass-domed building topped with a “Tropicana” sign. Today this former tropical swimming pool is the home base for dozens of projects investigating how to put the principles of the circular economy into practice.

BlueCity: The circular economy in a tropical swimming pool

Text: Valérie Záhonová • Translation: Elizabeth Spáčilová • Photo: Jacqueline Fuijkschot

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The tropical-style swimming pool was built in the late 1980s, with the construction of the 12,000 m2 building completed in just one year. The pool switched owners three times and by 2010, the once popular pool was shut down because it was too costly to operate. “Afterwards there was a discotheque here, and then a squat. Now we’re sitting at the bar, which has been preserved from back then,” says designer Emma van der Leest, my guide at BlueCity.

There are plenty of relics of the building’s “tropical” past. The floor tiles near the entrance bear evidence of where the turnstiles once stood; the murals along the stairwell “pull” visitors into the jungle. Particularly striking are the unconnected tube slides and the enormous quantity of rocks which once separated individual swimming and wading pools. It’s strange to see a place like this without water. “The architect of the building imported the rocks all the way from Italy!” Emma explains. I’m amused by the whimsy of the monumental architectural design; the current philosophy towards the building, its overhaul and function, stand in stark contrast.

The BlueCity circular incubator is located inside a former indoor swimming pool on Rotterdam’s Maasboulevard. The “Tropicana” sign on the roof still harks back to this past. Photo: Sophie de Vos

Three years after the Tropicana closed, the founders of BlueCity, Mark Slegers and Siemen Cox, came up with an original idea for putting the building to new use. The pair were inspired by Gunter Pauli’s book The Blue Economy,1 which presents an alternative economic model based on local resources and the conversion of waste into value. In the blue economy, all production is modelled on the way in which nature builds complex systems. There is no waste or energy loss; a use can be found for everything, and in this way the blue economy resembles the circular economy.

Mark and Siemen decided to apply the principles in Pauli’s book in practice. Their new company, RotterZwam set up shop in the Tropicana building and started to cultivate oyster mushrooms in the former beauty salon. Spent coffee grounds, which coffee shops produced in abundance and threw away every day, were used as the substrate. This effort to convert coffee shop waste into something of value quickly grew into an idea for putting the building to new use, and soon new entrepreneurs intrigued by the idea of an alternative production model moved into the building.

In 2015 BlueCity received support from the ifund foundation, which purchased the run-down building for €1,7 million. Repairs needed to be made and the interiors adapted to the needs of incoming tenants, launching a new chapter in the life of the Tropicana. But sometimes its past comes knocking. “Even though we’ve been in the building for some time now, every once in a while some tourists come by and ring the bell because they’d like to go for a swim,”  Emma laughs.

The founders of RotterZwam started at BlueCity by growing oyster mushrooms in coffee ground substrate. Now they process seven thousand kilos of spent coffee grounds a month.2 Photo: Sophie de Vos

Superuse Studioswhich has more than twenty years of experience finding uses for waste materials in architecture, took part in completely revamping the building. As a result, most of the materials and fittings at BlueCity is steeped in history. The key idea of the blue economy is to work with what’s available. For example, without any clear plan, Superuse had more than sixty wooden windows from demolished buildings in southern Holland brought to BlueCity. The idea of what to do with the reclaimed windows came later. They were installed in the upper section of the building, where they act as office dividers between individual companies. The ingenious arrangement of the windows make them a dominant visual feature of the space.

The space below the glass dome represents a major challenge for future remodelling work. “In summer the temperature gets up to fifty degrees Celsius. What’s more, water leaks through the windows,” Emma adds. On our way to the lower section of BlueCity towards BlueCity Lab we pass by a poster summarising the amounts of material and emissions that have been saved. By using second-hand materials, 112 tonnes of CO2 were saved during renovation of BlueCity Lab and the Food Hub. To illustrate, that’s equal to more than six hundred fifty car rides from Rotterdam to Paris and back.3 But new uses for old materials aren’t always possible or practical. Emma cites the building’s ventilation and heating as an example. Brand new systems had to be purchased for the building.

The office space in the upper section of the building was designed by Studio Superuse. They used window frames from demolished buildings in southern Holland to divide the rooms, giving them a new lease of life. Photo: Wijnand van Til

BlueCity Lab is based in the former changing rooms and service rooms of the Tropicana. My guide is the founder of the lab, which is a space for experiments, production, and knowledge sharing. It contains laboratories, workshops, studios, and production areas for individual projects. In the mushroom lab, Emma introduces me to a man in a white coat. Nick van Biezen is a fermentation expert. He has thirty years of experience growing mushrooms in industrial conditions. As part of the Fabulous Fungi project, he’s at BlueCity to investigate options for using mushrooms as textile dye. Nick shows us his setup and samples, and enthusiastically tells us about his most recent experience. When he came to the lab this morning, he discovered that the mushrooms had concocted a new colour. “We can even do orange now!” he exclaims.

Next to the mushroom laboratory are a microbiology lab and workshops with machinery. “Initially we had an €80,000 budget for all the equipment. We were able to find a lot of things second-hand. We’ve got decommissioned functional equipment from hospitals and machinery from art schools,” explains Emma. We pass by saws, sanders, 3D printers, presses, crushers, and driers until we reach the part of the lab where individual projects are based. We walk by a fragrant soap producer, Kusala. It’s difficult to believe that even soap can be made from waste. Meanwhile, BlueBlocks BlueBlocks creates materials from brown algae. Emma shows me samples and notes that unlike most boards, their material, SeaWood, does not contain formaldehyde.4 We meet up with Hugo de Boon, a designer and the co-founder of Fruitleather Rotterdam. Fruitleather is producing an alternative to animal leather that’s made of mango. Rotterdam is the largest port in Europe, importing huge quantities of fruits and vegetables daily – but a significant percentage doesn’t arrive in saleable condition. Fruitleather creates sheets of vegan leather from the mangoes that are discarded.

Fabulous Fungi textile colours are made in BlueCity Lab. Photo: Ilse Kremer

A few steps down is the Vet & Lazy brewery. But they aren’t brewing beer right now – we’d smell that! Water and energy consumption is not as efficient at small breweries as it is at large ones, but this brewery collects and purifies rainwater from the roof and the heat generated from beer brewing goes through pipes into the floors of the lab, heating it in winter. The beer travels on to the building’s Aloha Baru and to customers in Rotterdam and beyond.

More than sixty ventures are currently based at BlueCity, from individuals and small projects to large companies. Some use the offices, while others have production space at the Lab or use the laboratory and workshop facilities. To get work space at BlueCity, the venture must have a focus on working in the circular or blue economy. “Very close connections often form between the ventures,” says Emma. “One person’s waste might be another’s raw material. Especially at companies that produce something, we track how they fit into the entire ecosystem.” 

BlueBlocks, a project at BlueCity that is investigating the use of algae in panel and board materials. Photo: Jacqueline Fuijkschot

One way to get involved in creating circular solutions is the Circular Challenge, an intensive, six-week project. Multidisciplinary teams of students or recent graduates convert companies’ existing waste flows into economically viable and scalable circular products. After ten weeks, they present their proposals and product business models to a committee. Projects that are selected then receive BlueCity support to continue their work. I ask Emma for an example. “Like Waterweg,” she responds. “The winning project from 2018 is still running successfully to this day.”

Waterweg makes water-permeable floor tiles from river sediment. In the lowlands of the Netherlands, flooding is a daily occurrence – and water-permeable surfaces help resolve the problem. That’s why Waterweg is already quite popular in Rotterdam. “But sometimes the winners don’t want to continue the project,” Emma adds. “And then some companies offer waste that is hazardous or difficult to utilise, like asbestos or concrete. In those cases the solution is understandably complicated, and right now we have to turn them away.”

Waterweg’s production space at BlueCity Lab. Photo: Jacqueline Fuijkschot

Given its scale, BlueCity is a unique project that shines a light on alternative opportunities for production. It doesn’t merely try to seek out new solutions, but also investigate possible connections between the individual ventures and, on this basis, build a resource-efficient and eco-friendly ecosystem where every bit of waste represents a future value. However, this sort of interconnectedness has its limitations. When a venture expands or moves away from the space, everything connected to it is affected. Consequently, the system must be resourceful enough to withstand such “turbulence”.

If you’d like to take a look at BlueCity or find some inspiration at the site, it’s a good idea to schedule your visit in advance. The building is open to the public only when cultural events, lectures, workshops, or paid tours are held there.


Emma van der Leest (1991) is the founder of BlueCity Lab. She studied product design at Willem de Kooning Academy in Rotterdam. Over the years Emma has worked with a number of various materials produced by microbes. Her research and her book about biodesign are called Form Follows Organism: The Biological Computer. Emma is also involved in educational activities; in 2022 she was the curator of the Nature Loves Technology exhibition at the Floriade Expo in Almere.


1 Gunter Pauli is a Belgian scientist, an economist by training, and the founder of the ZERI network. Pauli is an advocate for sustainable business practices. For more information:
2 Today Rotterzwam only has offices for innovation work at BlueCity. Besides selling its own products, the company is also dedicated to education, holding training programmes that teach people how to cultivate mushrooms. For more information:
3 More than 650 trips from Rotterdam to Paris and back represents about 590,000 kilometres driven.
4 Formaldehyde resin is used as a binder in the production of chipboard. It is also contained in glue, lacquer, carpeting, and cosmetics. The World Health Organisation has classified formaldehyde as a carcinogen. It primarily enters the body through breathing, causing irritation to the upper respiratory tract and eyes.

19. 1. 2023 (07:00)



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