Wood Ash as an Additive in Biomass Pyrolysis: Effects on Biochar Yield, Properties, and Agricultural Performance

Summary

This experimental study investigated the use of wood ash as an additive during biomass pyrolysis in an auger reactor, examining interactions between ash concentration, temperature, and residence time on biochar properties and agricultural performance. Adding 9 wt% ash to softwood increased biochar yield by 26% and carbon-conversion efficiency by 36%, with linear yield response up to that concentration; however, ash addition reduced micropore surface area and thermal stability whilst increasing electron exchange capacity. The resulting biochar was deemed safe for soil application, with ash-amended biochar promoting enhanced sunflower growth, suggesting promise for nutrient recycling and carbon sequestration in agricultural systems.

UK applicability

The findings are potentially applicable to UK biomass pyrolysis operations and regenerative farming practices seeking to optimise biochar production and nutrient cycling. However, the experimental conditions (laboratory auger reactor, softwood feedstock, sunflower as test crop) would require field validation under UK soil and climate conditions before informing land management recommendations.

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; sunflower growth response; potassium content

Outcomes reported

The study measured biochar yield, carbon-conversion efficiency, pollutant content, electron exchange capacity, micropore surface area, thermal stability, and plant growth response when wood ash was added at varying concentrations during pyrolysis at different temperatures and residence times. Effects on biochar safety for soil application and nutrient recycling potential were assessed.

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