Getting the value out of roadside grass Many of Europe’s roads and river banks are lined with grass, which can be used to develop high-value products such as biomethane, a sustainable source of energy. Auke Smet and his colleagues in the GR4SS project are developing a demonstration plant to convert roadside grass into valuable products, contributing to the wider goal of building a more sustainable, circular economy. The roads and river banks of Europe are commonly lined with grass, much of which is currently composted after it’s been cut, destined to be used as fertiliser on agricultural land or in gardens. However, roadside grass can also be processed in other ways which lead to the development of higher value products than compost, a topic central to Auke Smet’s work in the EU-backed GR4SS project. “We’re developing a multi-feedstock fermentation plant to convert, among others, grass into high-value products. A multi-feedstock plant essentially keeps the bacteria happy, and we need to feed liquid material, such as beet molasses, organic glycerin or food products past their due date, or water to ensure the mixture is pumpable,” he outlines. The project consortium brings together four partners in this work, which alongside providing a renewable source of valuable products like fertiliser, biomethane and peat substitute, will also help reduce the greenhouse gas emissions associated with composting grass. “When you compost grass you produce CO2 , which is emitted into the air, rather than being captured in a digester,” explains Smet.
Fermentation plant As project developer in the GR4SS project, Smet is now working to develop a demonstration plant to essentially digest grass gathered from roadsides and convert it into valuable products. A first step is to pretreat the grass and remove any impurities,
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such as rubber, cardboard packaging and cans, before it can then go into a digester to be converted. “The biomass consists of a lot of water, which mainly goes to the digestate. Between 90-95 percent of the biomass that goes into a typical digester comes out in the form of digestate, and the other 5-10 percent is biogas, a mixture of CO2 and methane. In the installation we have a biomethane production that reaches as far as 95% of the biomethane potential of the biomass feedstock,” outlines Smet.
release of CO2 . Peat is essentially a layer of organic material, which forms when partially decomposed plant material accumulates in waterlogged, low-oxygen environments called peatlands. “Peat can be thought of as a very early stage of the fossil fuel production process,” says Smet. A lot of peat has been extracted over time across different parts of Europe, leading to significant CO2 emissions. Now Smet and his colleagues aim to provide an alternative. , which he says could have a major impact. “Currently almost all potting
“We produce biomethane with a negative carbon intensity (CI) score, because of the CO2 liquefaction and utilisation. We are essentially storing CO2, while also producing sustainable gas and replacing peat with sustainable alternatives.” The biogas can then be separated and purified to produce biomethane, reaching the same quality as natural gas, while Smet says the digestate is also a highly valuable resource. “The digestate is essentially a nutrient-rich slurry, which is separated into thick (solid) and thin (liquid) fractions. There is typically a certain quantity of nitrogen in the thin fraction, while there are Nitrogen, Potasium and Phosphates (NPK) and stable organic matter in the thick fraction,” he explains. “The thick fraction serves as a peat replacement, while it can also be used to produce organic fertiliser.” This work holds important implications in terms of providing an alternative to peat extraction, a process which leads to the
soil comes from peat, and so providing an alternative has great potential in terms of reducing peat usage,” he stresses. “The novel aspect of our project is that by applying these pre-treatment and aftertreatment technologies, we can produce this peat replacement, which can then provide a medium for growth, like soil,” he outlines. “We are also producing biomethane which we sell to offtakers across Europe, a contribution towards the EU target of producing 35 billion cubic metres (bcm) of biomethane annually by 2030. This biomethane comes with guarantees of origin (GOs), which is the proof of sustainability of the biomethane. Currently a lot of the GOs go abroad to foreign markets. We expect
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we will be able to sell these GOs in the Netherlands in future, adding value to our domestic market and helping to meet the targets set out in the EU ‘fit for 55’ package.” The plant itself is designed to deal with 60,000 tonnes of feedstock, but the size of any further plants developed in future could be modified to suit local circumstances and the availability of resources. This is likely to mean a combination of small and large plants, believes Smet. “We envision developing multiple plants of a certain size and density,” he says. The project team are also considering the way these products would be used; with gas, the idea is to inject it into the grid locally, so developing multiple plants would limit the need to transport it over large distances. “The gas grid in the Netherlands is like a tree, with a big branch going through the country. It then branches off from a high-pressure to a low-pressure network in smaller and smaller branches,” continues Smet. “Injecting gas locally is the most energy-efficient approach. Having lots of smaller plants would mean that gas could be fed into the grid from smaller locations throughout the year, without any gas grid congestion.”
Business model This represents a new approach to using roadside grass, and while some companies may be ready to embrace innovative ideas, others may be more hesitant. This is an issue of which the project team are well aware, so Smet and his colleagues are developing a new business model to demonstrate the effectiveness of the plant and encourage the shift towards a circular economy. “We are in contact with the authorities in the province of Friesland and the surrounding municipalities to supply roadside grass,” he says. The aim with the demonstration plant is not just to showcase the technology, but also prove its economic viability, and Smet says there have already been expressions of interest. “Several companies have
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reached out to us and other consortium partners, even though the plant has not yet been demonstrated on a large scale,” he continues. “A pilot scale digester was operated between April-December 2024, where we demonstrated that the digestate can be separated into a thin fraction and a thick one, which can be used to produce a peat replacement.” With the conclusion of the pilot phase, the project team are now working to prove the effectiveness of the plant as a large-scale installation, and highlight its wider benefits. “We intend to process 60,000 tonnes of biomass to biomethane and digestate per year. In the end we expect to produce around 9.000.000 Nm3 of biomethane per year which is the equivalent of the annual gas consumption of 9.000 households. We also expect to produce around 9,000 tonnes of peat alternative,” says Smet. Alongside producing biomethane, peat substitute and fertiliser, Smet says residual CO2 coming from the biogas upgrading system – where CO2 and methane are separated – can also be utilised. “CO2 can actually be liquified and utilised as a fertiliser in greenhouses, so they don’t need to use natural gas-fired Combined Heat and Power (CHP) systems during the Summer months, when the plants are growing and the sun is shining,” he outlines. “By utilizing our green CO2 , we can replace fossil CO2 from natural gas-fired CHP systems.” There are also other potential ways in which CO2 could be utilised, further underlining the potential of the project’s work. “It can also be used by soda companies who produce fizzy drinks, or in making dry ice for example, while some companies are interested in storing CO2 in concrete,” says Smet. “We produce biomethane with a negative carbon intensity (CI) score, because of the CO2 liquefaction and utilisation. We are essentially storing CO2 , while also producing sustainable gas and replacing peat with sustainable alternatives.”
GR4SS Grass Refinery for Sustainability & Shared value
Project Objectives
The GR4SS project pioneers the first commercial multi-feedstock fermentation plant, converting roadside and natural grass into biomethane, peat substitutes, biogenic CO2, and organic fertilizer. Combining innovative and proven technologies, it reduces emissions, supports circular and climate-neutral economies, restores ecosystems, and strengthens biodiversity, while establishing a robust business model for sustainable grass processing.
Project Funding
The GR4SS project is co-funded by the European Union under the LIFE Programme – Grant Agreement No. 101074660.
Project Partners
• HOST BIOGAS BV https://host-group.com/ • D4 BV https://d4.nl/ • KEKKILA-BVB DE LIER BV https://www.kekkila-bvb.com/nl/
Contact Details
SPV Bermgras ECL B.V. Stationsplein 32 3511 ED Utrecht, the Netherlands T: +31 6 21 54 13 61 E: a.smet@host-group.com W: https://gr4ss.nl/
Auke Smet
Auke Smet, MSc in Sustainable Energy Technology, works as a Project Developer within the HoSt Group, driving innovative bioenergy projects and advancing sustainable solutions that accelerate the energy transition for a cleaner and fossilfree future.
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