WUR and Rotterzwam studying the effects of used coffee grounds on the soil

Published on
April 12, 2019

In the former Tropicana swimming pool in Rotterdam, known today as BlueCity, dozens of companies are working hard to facilitate the circular economy. One of these companies is Rotterzwam, who grow oyster mushrooms on discarded coffee grounds from various businesses. This is a sustainable operation in itself, but now they are studying what else they can do with used coffee grounds, and with the substrate that remains after the oyster mushrooms have been harvested. Project leader Jente de Vries explains how Rotterzwam was established, their plans for new applications of used coffee grounds, and the partnership with Wageningen University & Research.

Rotterzwam has spent the last six years developing methods to efficiently reuse coffee ground waste in high-quality products. De Vries:

Our aim is to put this rich organic material to the best possible use. We started off by growing oyster mushrooms on used coffee grounds. The problem we have encountered in our new nursery is that we can only process 6,000 kg of coffee grounds per month, while the city of Rotterdam alone incinerates 5 million kg of coffee grounds every year.

The used coffee grounds collected from the various businesses are processed to form a homogenous material. Rotterzwam ensures it is free of foreign matter such as plastic or other materials that have accidentally been mixed with the coffee grounds. But Rotterzwam is more than just another waste processing company. Businesses currently have to pay to have their coffee grounds collected and processed into a high-quality product. In return, they receive an environmental impact report and various other perks, such as a tour of the Rotterzwam nursery or bitterballen (small croquettes) made from oyster mushrooms that were grown on their used coffee grounds and which they can use to promote their sustainable image.

Other applications

De Vries says she wants to find out what else you can do with coffee grounds and with the substrate that remains after the oyster mushrooms have been harvested. This substrate comprises the used coffee grounds and the spores of the mushrooms. At the start of the project, the substrate was sometimes collected by people who wanted to use it on their gardens. It was also made available to urban farm projects and Rotterdam’s edible garden project to use as a soil improver. There is a reason for this: coffee grounds appear to be good for the soil.

However, both the coffee grounds and the spent substrate are still officially waste materials, and can't just be used in agricultural applications. WUR's Soil Physics and Land Management Chair Group became involved because Rotterzwam wants to study the influence of used coffee grounds on the soil and their suitability as a soil improver, possibly in combination with other substances. De Vries:

WUR is conducting scientific research on the influence of the coffee grounds and the spent substrate on the quality of the soil, soil organisms and soil biodiversity.

'Back to the soil'

The partnership with WUR was established in the autumn of 2018. Now that preparations are complete, Rotterzwam and WUR are ready to conduct the first pot trials as part of the 'Back to the soil' project at Unifarm. De Vries hopes to present the preliminary results before 1 July. If it proves that the coffee grounds are detrimental to the soil, or pose another risk, they will not be able to be used as a raw material for agriculture. If no risks are identified, De Vries expects to start testing on a farm that same month. De Vries:

We are testing three waste flows. We expect that the spent substrate will not pose a problem. As for the coffee grounds, we are particularly interested in how caffeine affects the soil and its acidity.

Partnership with WUR

Rotterzwam received a POP3 grant from the European Union with co-financing from the Province of South Holland. POP3 is a grant programme for agricultural development, sustainability and innovation in the Netherlands. A condition is that the project has to partner with a farmer who has a soil-bound farm (i.e. a farm that has productive land). According to De Vries, WUR is a logical partner for research in this field because WUR's Jan Willem van der Schans is a well-known expert in circular agriculture and he has been following the progress of Rotterzwam for some time now. Wageningen Economic Research is examining the legal and economic aspects of the application of these waste flows as soil improvers for arable crops.

De Vries says that Rotterzwam has regularly had to deal with legal issues that were more complex than they expected. Coffee grounds are classified as waste, which is why Rotterzwam wants to have the material reclassified, for example for 'continued use'.

'We are engaged in talks with relevant bodies such as DCMR Milieudienst Rijnmond (an environmental protection agency), the Omgevingsdienst Zuid-Holland Zuid (an environmental administration agency), the Netherlands Enterprise Agency, the Ministry of Agriculture, Nature and Food Quality and the Directorate-General for Public Works and Water Management. The main priority at the moment is to arrange a temporary exemption to be able to conduct our research. At the same time, we have to prepare for the next step; for if the results of the research are positive. In that case, it will probably require a lot of paperwork to get the status of these waste flows changed,' she says.


The Blue Economy

The two founders of Rotterzwam have backgrounds in financial services and the energy sector, but both also have a long interest in sustainability. They became inspired by The Blue Economy by the famous sustainable entrepreneur Gunter Pauli. His book describes a number of business cases, one of which is the cultivation of oyster mushrooms on used coffee grounds.

'Used coffee grounds are a rich organic material and it is a waste to incinerate this product, which is what happens at the present,' says De Vries. 'The book described how you could use coffee grounds as a substrate, but the founders of Rotterzwam discovered the rest on their own, including experimenting with mixing the coffee grounds with other materials and finding the best temperature and the ideal humidity.'

Kitchen farmers

Rotterzwam supplies grow kits so people can become 'kitchen farmers' and grow their own oyster mushrooms on their used coffee grounds. De Vries:

We noticed that many consumers were attracted to the idea behind Rotterzwam and thought they could just drop by with a container of used coffee grounds for us, however that wasn't practical, because dealing with consumers directly is labour intensive and there is also a higher risk of contaminations in the coffee grounds.

They were unable to grow oyster mushrooms for a period of two years following a fire in the nursery in the basement of BlueCity, so there has been little activity recently. However, in May a new and larger nursery will be opening and more companies will also be added to the list of suppliers of used coffee grounds.