Comparison of the forest fertilizer properties of ash fractions from two power plants of pulp and paper mills incinerating biomass-based fuels

In Finland, the new Decree on fertilizer products came into force on 13 September 2011. In this study, the forest fertilizer properties of bottom and fly ash fractions from two large-sized (246 MW and 296 MW) power plants of pulp and paper mills incinerating biomass-based fuels (i.e. peat, bark, woodchips and sawdust) were investigated. The concentrations of heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni and Zn) in the bottom ashes and fly ashes were clearly lower that their current Finnish limit values, and therefore, these residues are potential forest fertilizers. However, the Ca concentration in the bottom ash from a 246 MW power plant and the sum of phosphorous and potassium concentrations (P + K) in all ash fractions did not meet the requirements of the current limit values. In this study, we present the current and previous Finnish limit values for ash used as a forest fertilizer. We also present the literature values of nutrient and heavy metal concentrations in the Finnish biomass-based ashes reported by the Finnish Food Safety Authority Evira, which registers and controls power plants that produce ash for use as fertilizer.