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Greenprint's Journey: overcoming challenges and celebrating successes

The latest Live Labs 2 blog comes from Chris Harris, South Gloucestershire Council’s lead officer for Greenprint, who shares the latest update on the project.

Greenprint is an innovative project led by South Gloucestershire Council and West Sussex County Council, focusing on reducing the carbon footprint of highway verge maintenance operations through increased efficiency, innovations and behaviour change. 

As part of the project, we are testing new mowing equipment and transport machinery, as well as trialling different verge maintenance regimes. We are innovating by converting grass cuttings into valuable resources, which can be used for energy generation, vehicle fuel and as additives in road surfacing materials. 

Traditionally, grass cuttings were left to mulch and compost on roadside verges. We’re changing that approach completely. Instead of leaving the grass cuttings on the roadside verges to slowly compost, we are collecting the grass cuttings: this approach has multiple benefits:

• Prevents CO2 and Nitrous Oxide (N2O) from composting being directly released into the atmosphere.
• Increases carbon capture in the soil. 
• Converts waste to value by transforming cuttings into biofuels, biomethane, and biochar for construction materials.
• Reduces maintenance and machinery usage.
• Creates conditions for more diverse plant life. In the long term, reducing the frequency of cutting lowers nutrient levels in the soil, encouraging a wider variety of plants to thrive, including wildflowers, which grow less vigorously than grass. 

Reflecting on our successes

To accurately measure the effects of collecting grass cuttings on the soil’s ability to capture carbon and improve wildflower diversity, the conservation charity, Plantlife, carried out surveys on verges around both South Gloucestershire and West Sussex during this year’s growing season.

We have recorded data from both the cut-and-collect and cut-and-leave activities at predetermined representative sites -this will help us accurately assess and compare the impact of different verge management practices.

In both areas, our verge management activities in urban environments have scaled up, with new machinery from different manufacturers allowing us to test processes at a realistic scale. In West Sussex, we have also successfully carried out smaller trials in rural environments.

We have worked with Proving Services to develop our carbon baselining report. In addition we have developed detailed carbon modelling, creating experimental profiles for both our cut-and-collect and cut-and-leave approaches that is helping to build a true picture of the carbon impacts of both approaches. With the 2024 cutting season now at an end, we are analysing all data collected to improve our processes for the 2025 cutting season. It has already become clear that intensive cut-and-collect activity is a challenge for the machinery and we are working with the manufacturers to make improvements. In West Sussex, the project team is working with the University of Nottingham and Invica Industries to produce biochar through two systems – hydrothermal carbonisation (HTC) and pyrolysis. Producing biochar traps the CO2 otherwise released during grass composting and can be used in construction materials, including road surfacing. 

This is a key element of our innovations, and initial tests have been promising, allowing us to plan for an in-situ trial in 2025 to test the materials in real-life situations on a road.

West Sussex has been working with a company called Ricardo, which has been given a government grant to produce biochar and bio-energy from woodchip co-mingled with grass, testing various feedstock mixtures to analyse the energy outputs. They produced some initial batches of biochar using pyrolysis technology, with further experiments planned to optimise the process. 

In South Gloucestershire, grass cuttings have been going to an energy-from-waste plant in Cannington, near Bridgwater, where they are converted into biogas via anaerobic digestion (AD).

We have developed a benefits and key performance indicator tracker and are working closely with project partner Amey to capture and compare operational costs. This data will be crucial for demonstrating the financial viability and benefits of our initiatives and developing our Greenprint ‘How-To’ guide for other local authorities.

Effective communication remains a priority for the project, and we are developing opportunities, including webinars, to share data and discuss our progress.

We have developed workgroups on materials and biochar production aimed at involving not only local authorities, but wider stakeholders in the development of solutions, with the objective of testing and adoption as soon as possible. 

Reflecting on our challenges

Despite our successes, we have encountered several challenges. One of the critical challenges we are currently facing is the pending Ofgem approval for our Biomass Technical Innovation initiative. 

South Gloucestershire Council’s food waste is currently disposed of via the GENeco AD plant in Avonmouth. Ofgem approval is required before a co-mingled food and grass feedstock is permitted to be disposed of at the plant. The approval process itself has significant financial implications for GENeco, as their payments from Ofgem are suspended until approval is granted.

To progress this, Professor Colin Snape, from the University of Nottingham who is leading the project innovation on biochar, has written to the Secretary of State. In the letter, he urges the government to review the regulations for waste, with the aim of removing barriers that currently limit the potential use of biochar and give a concerted value to carbon. 

We have also faced operational hurdles with the integration of new biomass processing technologies. Initial experiments with biochar production revealed difficulties in handling mixed raw materials, which need to be addressed to optimise the process.

Different mower brands have shown some limitations, especially in wet conditions and under intensive usage. We are working with the manufacturers to provide live feedback and identify possible solutions. While our cut-and-collect trials were substantial in urban areas, the rural trial in West Sussex was not of sufficient scale to collect meaningful data. The level of road litter and pollution is potentially an issue for AD and HTC. As a result, we have run the risk of transporting batches of ‘polluted’ grass rejected at processing plants, which could end up as compost or even sent to landfill. We are working with Keep Britain Tidy to carry out a litter survey ahead of the 2025 cutting season. 

Data collection and analysis have been areas of focus because, while we have made progress in collecting soil carbon data, the analysis has revealed significant variations - for example, carbon levels in soil samples of different depths. These variations need to be understood and accounted for in our environmental impact assessments.

Greenprint’s next steps

We have further experiments planned to optimise the biochar production process, particularly in handling mixed raw materials, to help plan for our road deployment test next summer. As part of this in-situ road test we will use materials we have developed containing biochar and monitor the performance.

Moving forward, we will continue to closely monitor and record our 'cut-and-leave' data for the entire 2025 season in areas like those where we cut and collect. This will build a more accurate dataset, making the comparison more robust. We will consolidate the year 2 data collected by monitoring all operations in year 3. This comprehensive data collection process will improve our understanding of the environmental and operational impacts of our changed management practices.

Communication and engagement with the parishes are key to this project, and we will continue to keep our stakeholders informed and engaged, particularly ahead of the start of the new cutting season in 2025.

We will also focus on our engagement with more local authorities to establish cooperation and adoption of our Greenprint guide, to encourage its adoption by other councils as business-as-usual beyond the project’s lifetime. 

Further information 

• To find out more about the Greenprint project, subscribe to Greenprint’s quarterly newsletter   
• You can also visit the two project websites: www.southglos.gov.uk/greenprint and www.westsussex.gov.uk/greenprint
• LinkedIn - West Sussex County Council

Author

• Chris Harris is the lead officer for Greenprint, South Gloucestershire Council’s green carbon laboratory project.