Circular Economy: A multidimensional approach to valorise roadside grass clippings

Prof. Erik Meers, coordinator of the project, kicked-off the event, explaining the Grassification approach and briefly guiding the audience through the three different pillars on which the project is based.

Then he invited Marloes Arkesteijn from the Province of South-Holland to join the stage for an interview on the public-private approach to valorize greens from local landscape management. Marloes explained that the Province initiated a regional network in order to facilitate the interaction between key stakeholders actively contributing to the transition towards a more circular economy. The regional innovation network has the ambition to become a platform of reference where stakeholders can learn from each other’s experiences and translate bottlenecks into solutions. In this context, dialogue within the different parts of the supply value chain is proven to be the key asset to overcome challenges and create synergies aimed at valorizing green from local landscape.

After this inspiring start, Nathalie Devriendt from ProNatura introduced and moderated the first session on yielding raw material on roadside.

Nathalie interviewed Jo de Brauwer from Vandaele and Wim de Roo from the Province of West Flanders to discuss with them how to improve the quality of roadside grass clippings and enable their use as a feedstock.

As Vandaele developed the adapted mowing head used in the Grassification project, Jo illustrated the technical improvements they made and major requirements needed to get yield grass clippings of better quality. Mowing tests showed that the mowing height a minimum of 10 cm from the soil is the optimum to reducing  the dirt uptake, specifically sand content and litter. After discussing the technical part, Wim presented the procedure they developed for a joint public procurement. Wim explained they focused on three specific requirements that differ from standard mowing procurement process.  The first technical requirement is the minimum the limit of 10 cm, which has little impact on the sand content of the grass clippings and on the visual aspect of the roadside verge. Secondly, the award criteria are not anymore related to the price only but also to sustainability, shaving of the supply peak of grass clippings, and other criteria. And lastly, the Province of West Flanders focused on joint procurements between municipalities to boost economics of scale and have a large amount of mowing kilometers.

The debate showed that existing and improved mowing technologies combined with the joint public procurement procedures can help to facilitate the use of roadside grass clippings as renewable resource. However, a stronger involvement of all the actors of the value chain is needed to have a more efficient organisation, which cannot only enable the use of grass clippings as renewable sources, but also reduce significatively the costs of collecting them.

The session was then enriched by the presentation of Marcella Fernandes de Souza, project manager at UGent, who presented the anaerobic digestion of roadside grass clippings as a refining process. Marcella discussed the current obstacles hampering a viable anaerobic digestion process, such as the mowing season, the sand and litter content. In order to overcome these barriers Grassification investigated and adopted new solutions. Thanks to Vanheede, which designed a dry monodigester system, Grassification was able to produce biogas successfully. During the lifespan of the project, three batches were conducted, of which the second was able to get a biogas quality with a 50% methane content and produce 78.550 Nm3 gas. Despite the promising results, for the anaerobic digestion to be a really viable refining process not only energy can be taken out of grass but also fibers should be valorized as a product.

This led the audience to the second session of the day, which was moderated by Jappe de Best from Avans, who introduced the multiple ways of application adopted in the project that can be used both from the grass fibers and juice. From the anaerobic co-digestion to produce biogas, to the algae growth, to insect feed, to biofertilisers and biopolymers and infrastructures.

This latter was the focus of the session, which was opened by Willem Bottger from Avans, presenting the development of a 100% bio-based material that can be used outdoors to replace tropical hardwood and aluminum.  Avans produced a prototype samples, whose mechanical properties were tested. Accelerated weathering tests demonstrated a good life time expectance of the material. Currently, Avans redesigned the planks looking into two potential techniques, the pre-pregging and bulk moulding compound (BMC) and optimizing the use of the material. The end-result can be used for a 100% biobased demonstration nature path.  Check the video for more info

Following this presentation, Dries Vansteenkiste from Hogent showcased 4 different prototypes of biocomposite building materials they developed. The production of small grass clippings fiberboards, mineral building blocks and beams, needles punch geotextile and permeable roof or floor pressed grass-fibre tile were discussed.  Check the video for more info

The last speaker of the session, Harm Jan Thiewes from Millvision discussed the development of thermoplastic biocomposite compounds using grass fibers for landscape infrastructures. Millvision prototyped a 1.5 meters picnic set. Harm described the entire process, explaining that grass clippings were firstly transformed into grass pellets to be used as half-finished product for bio-composite production. This resulted in an increased grass storability, which ensured a higher availability and reduced transport costs. The functionality and the design of the picnic set were assessed and the picnic set was built and placed at Millvision’s premises to be tested under weather conditions.

The session was followed by a panel session, moderated by Erik Meers, in which speakers discussed the ‘market challenge’ for these new grass-based materials. Speakers agreed that to have a market pool, it is important to involve the whole value chain, get a good exposure and share market risks. More than this, it was also highlighted that the Grassification approach could be translated to other residual streams with a similar type of composition and, by combining these waste streams, products can be even improved further.

The last part of the event was dedicated to the assessment of the Grassification concept itself. This session was moderated by Ruben Guisson from VITO, who presented the mobilization strategies for roadside grass cuttings in 2 Seas Region. VITO developed a supply chain optimization service, called MooV to identify activities and processes including transport and logistics of all the steps alongside the supply chain. Roadside verges were calculated and mapped together with storage installation and end-processing and then turned into an optimal supply chain network. Different kinds of roadside, like highways, municipal roads, where taken into account as well as parameters like contamination, harvesting methodologies, which also have an impact on the quality of the grass. The MooV scenarios showed the grass availability is high enough to foreseen current practices like composting, digesting  but also incorporate future technologies, like the use of fibers for biocomposites. VITO also conducted a Techno-Economic Assessment to see to which extent these new technologies are economically feasible. Results, presented by Mohammed Nazeer-Khan, showed that the production of fibre for biocomposites from roadside grass has the potential to capture a major share of the natural fibre market. Storage still represents a major cost in the fiber production as well as the personnel and operational costs. However, fibers can be produced at around 300 euros per ton, which is much lower compared to the natural fibers available currently in the market.

But roadside grass clippings are still regarded as waste and thus also grass fibers. So what is needed to turn it into raw material? Nathalie Devriendt from ProNatura, interviewed by Ruben, explained to the audience her practical experience with the procedure to obtain material declaration for roadside grass products in Flanders. In the region, roadside grass clippings are still a waste, therefore their transport and use are strictly regulated. In order to allow the use of grass fibers in novel end-products, ProNatura applied for the Grondstof verklaring, which is part of the Material Decree in the Region. Nathalie described the specific conditions and requirements to obtain the material declaration and facilitate the local value chains in circular economy.

How to facilitate the local green initiatives was also at the core of the interview with Roos Marinissen from OZHZ.  Waste management laws can be strict and make difficult the transition towards a more circular economy. As law enforcer, the Province of South Holland is willing to create a bridge with the innovative companies and find a balance between law enforcement and innovation. Some grey areas and uncertainties still exist, but it is important to have clear standards for all both at regional and national level and be open to adapt laws in order to create valuable innovation pathways.

Again feeding the dialogue with innovators and involving the entire value chain are key aspects to create a supportive framework for the roadside grass clippings to become a renewable resource for different end -applications.

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