Cities experiment with closing the waste loop

Circular agriculture

WUR is focusing on the reuse of organic waste, such as grass, pruning waste and leaves from urban parks in Apeldoorn. Photo: Shutterstock

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Is it possible for a city to reuse all of its own organic waste and construction waste? European researchers, urban policymakers and companies are considering that question in the CityLoops project. Seven cities across Europe, from Finland to Spain, are taking part. The Netherlands is involved too with Apeldoorn, where scientists from Wageningen University & Research are collaborating with the municipality on five specific applications. “You really need to get the entire city on board.”

Making paper from the grass cuttings from the city park. Using fibres from Japanese knotweed to produce a new part for your coffee machine on your home 3D printer. Or converting the collected leaf waste into a soil improver for local use. These are just a few of the examples of how you can reuse organic materials that are now seen as waste to make something new. With the ultimate goal of a climate-neutral society, cities in the European Union are working on making their waste and production chains more sustainable. The circular economy – in which raw materials are constantly reused and there is no such thing as waste – is a key concept in this endeavour. In the European CityLoops project, seven medium-sized cities in Europe will work on new circular-economy applications over the next few years. One of those cities is Apeldoorn in the Netherlands.

We want to pick out the truly promising solutions by examining the options through a scientific lens

The fibres of the stubborn Japanese knotweed could potentially be used in filaments to make objects using a 3D printer. Photo: Shutterstock

CityLoops aims to investigate how European municipalities can be more ‘circular’ in the way they deal with organic and building waste. Municipalities often manage these two waste streams directly, which makes it easier for them to influence what happens. The idea is that all the waste produced by a particular city is reused by that city. At the same time, a network of circular-economy cities was established, in order to learn from and with one another. Various public authorities and scientific organisations in Europe are involved in addition to Wageningen Research (see inset). “In the Netherlands, the circular economy mainly operates on a larger scale: the region or province”, explains project manager Edwin Keijsers, a chemical process engineer at Wageningen University & Research (WUR). “In this project, we look at whether you can also reuse raw materials at the scale of a single city. Is that a good idea or do you need larger areas to make it an efficient exercise?”

The bigger picture

In CityLoops, the Wageningen team is focusing mainly on the reuse of organic waste (or bio-waste). That includes the grass, pruning waste and leaves collected from urban parks, as well as organic waste from households and restaurants. Keijsers: “What products can you make from organic material? That is where our expertise lies at Wageningen Food & Biobased Research.” What is more, the Wageningen team is accustomed to taking a broad approach. “Perhaps it would be sensible from a circular economy perspective to alter the choice of greenery in parks because some plants are more useful. But such decisions also affect the habitat for animals and consequently biodiversity. In short, the question is: what is the ultimate impact of your policy choices? We see that bigger picture here in Wageningen.”

Researchers in Apeldoorn are experimenting with bokashi, an alternative to compost. Photo: Edwin Keijsers

In Apeldoorn, WUR researchers are carrying out various ‘demonstrations’ – practical try-outs. “We are experimenting with bokashi, for example, an alternative to compost. Can you make bokashi from autumn leaves and use that to fertilise the city’s parks and verges? We also want to produce filaments made from Japanese knotweed, a persistent weed, using a 3D printer. And we will be turning park waste into biochar, a soil improver.” In all these experiments, the researchers both want to show that it is possible and at the same time investigate whether the approach is feasible from the technical, ecological and social perspectives. “That means we take a pragmatic view”, says Keijsers. “Can we really make this object using 3D printing in a factory? And if we want to use bokashi as a fertiliser, what specific arrangements do we need to make?”

Seven European cities pilot solutions to be more circular via the EU-funded CityLoops project.

Success factors

In their quest, the Wageningen experts are not just looking at the technical solutions. “The societal and spatial aspects are also important when considering such issues”, explains Carmen Aalbers, a senior researcher at Wageningen Environmental Research who is also involved in CityLoops as an advisor. “Closing the loop in a city is a huge challenge and you won’t achieve it just with a group of municipal officials. You really need to get the entire city on board.” That is why local customs, culture and support for such measures are key factors determining the success, she says. “It is all very well thinking up a system to recycle organic waste, but perhaps residents in some places are already used to composting their peelings themselves. If so, this initiative is pointless. Anyway, a city faces very different organic waste challenges than a municipality that consists of a collection of small villages.”

Other things need to be taken into account too when turning science into policy. “You need to investigate whether a solution ties in with the themes that the municipality is currently working on,” says Aalbers. “We check whether the knowledge tools are a good fit with administrators’ working practices. The form you choose for conveying your message also matters: you will have different discussions with a sustainability expert than with a policymaker.

We might find that recycling leaves is all very well but you need to focus on food waste for real impact

In the CityLoops project park waste is turned into biochar, a soil improver. Photo: Shutterstock

Furthermore, adds Edwin Keijsers, you should always critically assess whether a circular-economy solution is worthwhile. “Sustainability is in but not all initiatives have sufficient impact. We want to pick out the truly promising solutions by examining the options through a scientific lens.”


CityLoops lets Dutch scientists and policy-makers learn from the expertise of their counterparts in other European cities. “That is incredibly valuable for a city like Apeldoorn”, says Aalbers. “After all, you are at the cutting edge of developments with a project like this. CityLoops is a great opportunity for both us in Wageningen and our European partners to share knowledge between countries.” That cross-fertilisation spreads out too: researchers at Wageningen Research use the experience they gain in CityLoops as input for other WUR projects and with external partners. Aalbers: “For example, if colleagues elsewhere on campus are doing another study with bokashi, we will say, ‘Why not take a look at the lessons learned with bokashi in Apeldoorn?’ What is more, we draw on the insights we got as a research group when we talk to other Dutch municipalities.”

Closed-loop tenders

The CityLoops project has been going for three years now and will end in 2023. In addition to the experiments in the individual cities, the team is also examining exactly what organic waste streams look like in cities and consequently where you can have the biggest impact. Keijsers: “For example, we might conclude that recycling leaves is all very well but you really need to focus on food waste to make a genuine impact.” The participants are also looking at how a municipality can best set up tendering procedures for a closed loop. And they are using key indicators to calculate the extent to which the various experiments actually make a city more ‘circular’. Ultimately, they want to share all this knowledge with other cities in Europe. “We hope the network of circular-economy cities will grow bigger and bigger.”

European research context

CityLoops addresses the following European policy challenge: Developing a circular-economy waste policy in cities

Wageningen University & Research groups involved: Wageningen Food & Biobased Research, Wageningen Environmental Research Countries involved in Europe: Denmark, Finland, the Netherlands, Norway, Portugal and Spain

Duration 2019 – 2023

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