Renewable energy potential of roadside grass cuttings

Roadside grass verges are an important part of transport corridors and have a critical role in ensuring road user safety. However, the verges require ongoing maintenance on a regular basis throughout the growth season and throughout the design life of the transport infrastructure. The collection of the verge cuttings, which are currently left in situ, may create environmental benefits such as economic and energy benefits from biogas production. This study focuses on Scotland where there are 56,000 km of verge potential and where the grassed verges commonly receive a 1.2 m swath cut two times per year. Our investigations revealed that the potential productive land along Scotland’s road network was of the order of 270x106 m2. Using comparative statistical analysis, we have estimated the potential average dry mass of cuttings per kilometer to be between 300 kg and 400 kg, yielding a biochemical methane potential of 0.271 m3 per kilogram of volatile solids added. The cautious estimate showed that potentially 18.2x106 m3 methane (CH4) could be produced, while, in the best-case scenario, up to 24.3x106 m3 CH4 may be produced through regular maintenance of the grass verge strips in Scotland. Cost-benefit analysis showed that considering the availability of cutting machinery and a potential increase in the swath cutting to 1.6 m would potentially yield between 24.3 x106 - 32,4 x106 m3 CH4. The sustainable treatment of cuttings arising can promote a healthy roadside verge environment and can reduce greenhouse gas emissions as Scotland looks to achieve their 80% emission target by 2050.