22 06 2021

Roadside cuttings, the raw material of the future?

What if we consider the grass clippings as a raw material and not as a waste stream?

Mowing roadsides is an important part of the maintenance of the infrastructure for every road authority. Currently, roadsides are mowed mainly to ensure the safety of the road user. However, there is a lot of life to be found in our roadsides. To protect this biodiversity, we can mow at specific times and remove the clippings. In Belgium, the grass cuttings can be taken to composting plants and a few fermentation plants that are authorized to process grass cuttings.

This logistical operation of mowing, removing and processing involves a considerable cost for the roadside manager. This cost increases even more as more invasive plants such as Japanese knotweed occur on the verge. Then other management measures are needed, because mowing the verge is not an option. This again creates an additional challenge and an additional cost.

But what if we consider the grass clippings as a raw material and not as a waste stream?

From grass clippings to material

By composting grass clippings, you turn them into a soil-improving agent. However, the yield of compost is very low. A more interesting choice both technologically and economically is the fermentation of roadside clippings, especially a dry fermentation where it is mixed with GFT waste. In this process, produced biogas is converted into electricity and heat or even green gas. The digestate – the remaining part of the fermented input stream – can in turn be applied as a soil-improving agent. Next to the intermunicipal IGEAN that has been running a dry fermentation for years, now also IOK, Ecowerf and Verko are working on this, a positive evolution!

On to more: innovation

Can we dream of roadside mowing applications with a higher value than energy or soil improvement? A question to which Pro Natura started looking for answers four years ago within the project of Grassification.



This question led to an intense collaboration with a number of innovative material producers. Together with Pro Natura, they took up the challenge of testing fibers from roadside clippings in new materials. A challenge that led to beautiful results: decorative furniture panels, sound baffles, finishing layers for furniture and other design interior elements.

The first prototypes are currently being tested at end customers. For example, all new stores of Bio Planet (Colruyt Group) will produce their interior finishes with the materials of Circular Matters. The first store is already there (Eigenbrakel, PHOTO). Also the Circuit concept store of Kringwinkel in Antwerp will contain design elements with these materials.

And these are just a few examples of material applications. The blending of grass cuttings into paper and cardboard and into insulation boards (to replace glass wool) also appears to be technically possible.


Circular Matters: Bowls designed by Filip Janssens, based on roadside grass clippings and coffee grounds


Furniture piece by NNOF based on grass marble by Circular Matters and top layer by Touch of Nature.


Circular Matters: Grass panel or biocomposite incorporating grass fibers, display at BioPlanet.

From research to practice: the challenges

Making materials from roadside clippings, it is technically possible. And yet we must be patient in converting it to practice. The biggest challenge is to supply quality fibers (without contamination, with the right fiber size, dryness…) at a competitive price and consistent quality. This is difficult since not all roadside plants are exactly the same. In addition, fiber varies in proportion to the time of mowing, and grass clippings are currently released in spikes, requiring rapid pressing and/or drying before they rot.

The challenges!

  • Quality:

– Material producers have requirements by fiber size, dry matter content….

– Supplied raw materials must not contain plastics and other contaminants.

– There should not be a large percentage of dust or sand present because they cause problems when making the materials in the machines.

  • Logistics:

– Mowing is done seasonally, but the material producers would like to produce a whole year.

– Roadside clippings are not a stable product. When stored unchecked, it decays and loses a lot of good properties in a short time.

– The instability of the raw product combined with the large quantities released in spikes makes it logistically challenging to manage.

  • Cost:

– Solutions exist for many of the above challenges, but each additional operation comes with an additional cost. This cost translates into a higher cost to the fiber.


Within the Grassification project, Pro Natura worked with partners to find solutions to some of these challenges.


Solution 1: Get rid of impurities with the ecological mowing head

A few years ago, the company Herder introduced an ecological rotary mower to the market. It sucks up the clippings with reduced suction, which means that fewer insects and worms, as well as soil particles and waste are sucked in. This is an added value both ecologically and for the quality of the clippings: a win-win situation. However, practice has taught us that this ecological mowing head comes with two major disadvantages: a limited mowing speed and greater sensitivity to breakage.

Within the Grassification project, Vandaele developed an adapted mowing head: this flail mower cuts the verge a little higher and also has less suction, which results in a better quality of cut and a more attractive mowing pattern. However, this mowing head is less fast and maneuverable.

Litter in the mower remains a difficult issue to this day. A clean up of litter before the mower comes along seems to be the best solution.



Flail mower left (Vandaele)

Solution 2: pressing, drying and size reduction

To prevent the clippings from rotting, they must be processed immediately. You can stabilize it by pressing and drying. Afterwards the clippings are reduced to size and sieved.

– PRESSING: The fresh clippings (containing 90% moisture) are pressed. In this way one obtains juice and fiber cake. A Dutch grass press was tested in June 2019. Meanwhile, the Flemish start-up Releaf has also purchased a press. A point of attention with this process step is the sensitive screw press to contamination: stones and debris must be manually removed from the clippings for the time being.

– DRYING: The fiber cake (which still contains 45% moisture) must be further dried to about 10% moisture content. Currently, Pro Natura does this in a natural and simple way in a greenhouse, and consequently on a very small scale. Pro Natura is looking for a solution to dry on a larger scale without using fossil fuels. Drying on residual heat and/or using solar energy are the most obvious options.


SIZE REDUCTION: The dried fiber cake is now ready to be reduced in a hammer mill and is further sieved into different fractions. 

The above steps provide an answer to a lot of challenges around quality but also around stabilization of the cuttings. The most difficult step, however, remains the contaminants in the grass clippings: the plastics are difficult to extract efficiently after collection of the clippings. In the Netherlands, they wash the clippings before using them: an efficient but also expensive and less sustainable solution that we also prefer to avoid due to the high water consumption.

Solution 3: Avoid peak times

Large quantities of clippings are currently released at peak times. In order to process these quantities immediately, the processing installations and storage capacity must be very large. That investment cost is difficult to recoup. In the GrasGoed project, a great deal of research has been done into different ways of silaging. Technically, good results were achieved, but because of the many operations, this also proved expensive.

Pro Natura is continuing to look for solutions to make the processing infrastructure profitable all year round:

– Verge management plans: When drawing up a verge management plan, approval can be requested to deviate from the general mowing dates when this is ecologically justified. More staggered mowing to give fauna and flora more opportunities also ensures a staggered delivery of the grass clippings. The other side of the coin, however, shows that mowing in that case may become more expensive, as the staggering requires more planning and organization from the mowing company. This additional cost could possibly be compensated by combining the mowing assignments of a number of municipalities. These hypotheses are being tested in practice in Halle and Herne in the Reusable Verge project, run by intercommunal Haviland.

– Multifunctional use of the infrastructure: in addition, Pro Natura wants to use the processing infrastructure for the grass for green flows such as reeds, Japanese knotweed, raspberry trimmings, tomato stems, bell pepper stems… in order to be able to run all year round.

An opportunity: will you join us?

The technology to turn grass into raw material is available. Whether these raw materials can compete with conventional ones depends on the cost price and the quality delivered.  The processing needs to improve so that the price-quality ratio can increase significantly.

Pro Natura strongly believes in this circular and bio-based economy, which also creates local employment for people with fewer opportunities on the regular labor market. The social economy organization is pleased to invite you to its demonstration events:

– June 24, 2021, online event: Demonstration of the ecological mowing head, screw press and hammer mill. Debate with experts.

– September 28, 2021, Leuven: Mini-exhibition of bio-based office furniture based on fibers from green waste.