Green fibre from grass clippings as peat substitute in potting soil
Grass clippings from roadsides and lawns are today processed through composting. This is a cost to society borne by local authorities, and therefore taxpayers.
In this project, Releaf aims to demonstrate the development of an innovative circular model where grass clippings are processed into fibres that we can blend into potting soil, replacing peat. In this way, we also save on peat, a non-renewable resource.
In each step of this circular chain, we work together with partners. The City of Ghent and ILvA provide us with clippings that we process into fibres thanks to an innovative technology. Next, those fibres go to Agaris, a Flemish company (with production site in Ghent) and one of the most prominent players on the European potting soil market. Finally, the City of Ghent demonstrates the potting soils in flower boxes in the city centre. At these planters there is also information to inform passers-by about the issue and our research.
Our goal is to eventually set up a sustainable and future-proof processing process for grass clippings.
We compared different mowings based on four quality parameters. From natural grass and sports field cuttings, we selected test fibres that were evaluated by Agaris. The cuttings from sports fields were retained.
We optimised the release process of the cuttings based on the desired properties for the fibre in potting soil. Thus, we succeeded in producing an adequate green fibre that can serve as a peat substitute in potting soil.
Agaris formulated two potting soil recipes based on the green fibre. In an evaluation trial, both were found to be similar to the control potting soil. That result was confirmed by a demonstrationtest with flower boxes on the Reep in Ghent.
We mapped the biogaspotential of the cuttings as a function of seasons and different characteristics.
MOST IMPORTANT LESSONS LEARNED
The type and origin of the grass clippings play an important role not only for the quality of the final fibre, but also for the ease of processing. For example, the presence of disturbances and waste in certain grass clippings complicated the process.
Thanks to our innovative processing process, we managed to produce a high-quality fibre that can act as a peat substitute in potting soil. However, we could not yet sufficiently stabilise the fibre, which mainly has undesirable logistical and visual consequences.
The financial analysis tells us that in the current climate, the fibre is not competitive enough for introduction into the potting soil industry. This is mainly due to the economies of scale specific to the sector, but also to the uncertain legal framework around renewable raw materials.
The biogas tests taught us that the course of the seasons and the dry matter content of the cuttings have a major influence on the biogas potential and the stability of the process.
5types of grass clippings evaluated
3.000kg of clippings processed
6process steps evaluated
WHAT DOES THE FUTURE HOLD?
In the future, we aim to further improve the current process of processing grass clippings.
Besides grass clippings, we are also looking at other green waste streams and their potential as peat substitutes in potting soil. Indeed, this project has given us a lot of knowledge about the needs within the potting soil industry and the development of a suitable fibre.