Granulated biofuel ash as a sustainable source of plant nutrients

Recovery of nutrients from biomass combustion ash is of great importance for sustainable bioenergy waste use. In this work, granulated fertilizer materials were engineered from biofuel bottom ash, lime kiln dust and water, analysed for their chemical complexity and tested in pot experiments (2017-2018) for their propensity to release nutrients. The results obtained in this work showed that spring barley yield was observed to be the highest for granulated biomass ash with 30% of ash in the granule. The yield increased 3.99 t ha^-1 per 100 kg ha^-1 potassium oxide (K₂O) in 2017 and 1.23 t ha^-1 per 100 kg ha^-1 K₂O in 2018. Straw yield varied between 1.39-5.08 t ha^-1/100 kg ha^-1 in 2017 and 0.36-1.23 t ha^-1/100 kg ha^-1 in 2018. Calcium concentration significantly increased in soil. No significant changes in soil mobile phosphorus (P) were obtained as well as for the heavy metal concentrations in soil. This suggests that biofuel ash can be a significant source of certain major nutrients for crops that can also beneficially affect soil pH. The results of this work can provide policy-makers with the information needed to diversify existing and enable new biomass bottom ash utilization routes which currently vary significantly between the countries.