From environmental invasive weeds to solid biofuels: assessing bioenergy potential through pelletisation and operational optimisation

Global moves towards net-zero emissions have led to rising demand for renewable solid bioenergy, including biomass pellets. Invasive environmental weeds (IEW) represent an underutilised biomass stream that can be diverted from landfills and repurposed as fuel. This study examines the potential of converting IEW into market-grade pellets. Fifteen weed species (woody and non-woody) were characterised for lignocellulosic composition, ash content, and elemental profiles. Pellets were produced under varied temperature (25–100 °C) and pressure (50–150  bar) conditions. Key indicators of quality (durability, unit density, ash content, and calorific value) were assessed against industry standards (ISO 17,225 and ENplus®). Non-woody species such as Brazilian Nightshade and Climbing Asparagus, containing about 24 % lignin, produced durable pellets (97–98 %) with high energy density (up to 3.9 GJ/m³) and low ash (<5.1 %). Some species (e.g., Singapore Daisy, Mexican Ruellia) had elevated ash and problematic elements (K, Na, S). Response surface modelling revealed optimal pelleting parameters, while principal component analysis underscored lignin content, ash chemistry, and particle size distribution as factors influencing pellet performance. Results show that, with suitable processing, IEW can be valorised for bioenergy. Future work should address ash-related challenges via co-pelleting or additives to facilitate large-scale uptake and contribute to net-zero targets.