Summary
This experimental study investigates the co-pyrolysis of softwood with wood ash as an additive, examining interactions between ash concentration, temperature, and residence time on biochar production and properties. Adding 9 wt% ash to softwood feedstock increased biochar yield by 26% and carbon-conversion efficiency by 36%, with linear yield gains up to this concentration; higher ash concentrations showed diminishing returns. The resulting biochar remained safe for soil application (contaminant levels below thresholds) and demonstrated enhanced potassium availability and nutrient recycling potential, though some physical properties (micropore area, thermal stability) were reduced.
UK applicability
The findings are relevant to UK agricultural systems and biochar production initiatives, particularly in regions with softwood processing industries and ash residues available for co-valorisation. UK soil conditions and regulatory frameworks would require site-specific assessment of biochar safety and efficacy, though the demonstrated safety margins for contaminants suggest applicability within UK quality standards.
Key measures
Biochar yield (dry and ash-free basis); carbon-conversion efficiency; polycyclic aromatic hydrocarbon content; polychlorinated organic pollutant content; electron exchange capacity; micropore specific surface area; thermal stability; potassium content; sunflower biomass growth
Outcomes reported
The study measured biochar yield, carbon-conversion efficiency, pollutant content, electron exchange capacity, surface area, thermal stability, and agronomic performance (sunflower growth) in relation to wood ash addition at varying pyrolysis temperatures and residence times. Wood ash addition at 9 wt% increased dry biochar yield by 26% and carbon-conversion efficiency by 36%, with improvements in potassium content and electron exchange capacity, though micropore surface area and thermal stability decreased.
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