Abstract
As a step towards the diversification of electricity and heat sources, the EU countries suggest the use of biomass. The combustion of biomass poses the problem of the use of ash produced in the process. There are fluctuations in the properties of energetic biomass, which results in high variability of ash obtained by combustion, especially in terms of specific conductivity (EC) (8.1−9.7 mS·cm−1), the total content of components and their bioavailability. The combustion of biomass leads to large fluctuations in the total content of carbon in the ash (13.6%−28.6%). In this way, waste material with very different biological properties and cation exchange capacity is obtained. Ash from the combustion of biomass is an alkalizing material, rich in Ca, K and Mg carbonates (4.5%). The high average bioavailability of Pb (87.4%), Cd (63.1%) and Zn (46.9%) present in the ash is an environmental problem. The mobility of these heavy metals was reduced by half by the addition of bentonite during the process of ash granulation. With high doses of ash (4.4% of the mass of substrate), there is a significant bioaccumulation of Cd in the roots of Begonia semperflorens and Thuja occidentalis (1.0−3.8 mg·kg−1). Another disturbing issue is that during the cultivation of these plants, Cr is bioaccumulated in the roots (0.5−3.8 mg·kg−1).