Optimising and up-scaling residual grassland biomass use through sequential base-acid conditioning

The conversion of species-rich, structurally complex grassland biomass from landscape management into high-quality solid fuel and biogas poses significant environmental and technological challenges due to its high mineral content and low energy density. This study explores an advanced adaptation of the Integrated Generation of Solid Fuel and Biogas from Biomass (IFBB) process, incorporating a sequential base–acid treatment (IFBB-B/A) with sodium hydroxide and acetic acid, tailored for such feedstocks. Optimised through systematic lab-scale trials, the improved IFBB-B/A process demonstrated superior enrichment of energy-relevant constituents (cellulose +54 %, volatile matter +13 %, carbon +6.4 %) compared to conventional IFBB, enhancing higher heating value (+5.5 %) and significantly reducing ash content (−81 %). Upon scaling to industrial screw-press equipment, IFBB-B/A maintained robust performance, achieving high ash reduction (−71 %), improved thermochemical fuel quality, reduced slagging potential (slagging index reduced from 5.2 to 2.1), and increased sulphur-to‑chlorine ratio (from 1.9 to 13.5), thus minimising corrosion risk. Press fluid from industrial-scale IFBB-B/A yielded over 500 Ln CH₄/kgVS and methane concentrations above 85 vol%, underscoring the process's capability for efficient production of high-quality biogas and solid fuels from challenging biomass sources. The findings confirm the potential role of species-rich grassland biomass for decentralised provision of renewable energy. • Sequential base-acid treatment reduces ash by 81 % in grassland biomass. • Up to 98 % reduction of chlorine in treated biomass. • Slagging index of biomass reduced from 5.2 to 2.1. • Heating value of biomass increased by 5.5 %. • Biomethane potential of press fluid exceeds 500 Ln CH 4 /kg VS.