Repurposing lignin rich biorefinery waste streams into the next generation of sustainable solid fuels

Value added lignin rich waste sludges from biorefinery processes are, as yet untapped valuable feedstocks that can be reformed into clean, high quality solid fuels. By water washing sludges produced from base hydrolyzed waste, a material stripped of water-soluble alkali and alkaline earth metals (ash) can be obtained. This work shows how leached bagasse, barley and wheat straw sludges can be valorised into clean, low ash solid biofuels that can be used to supplement global energy demands. Repurposed lignin rich sludges of 1.00–2.00 mm particle size feedstocks were found to exhibit calorific values +17.3 %, +16.8 % and +11.7 % for bagasse, wheat, and barley straw sludges, respectively higher than their untreated waste counterparts. Additionally, by employing densification in the absence of a binder, <0.25 mm particles of leached sludge feedstocks were found to experience 16.0 % (bagasse), 12.0 % (wheat) and 4.0 % (barley) increases to their calorific values.