Polycyclic Aromatic Hydrocarbons and Other Organic Compounds in Ashes from Biomass Combustion

Power generation from biomass is a substantial source of ashes, the extent of which depends on the type of biomass fuel and technology of combustion being used. The current study focuses on comparison of ashes with a special emphasis on hazardous organic compounds, particularly the polycyclic aromatic hydrocarbons (PAHs) fraction, present in ash. The reason is that ashes from combustion of wood or straw are considered as fertilizers in agricultural soils. Ash samples were therefore collected from power plants in the Czech Republic coming from combustion of wood chips, sawdust, bark and straw. The organic fraction was separated by extraction, the final determination of PAHs was performed by GC-UV. The total concentration of PAHs was found to be in the range 15-733 μg/kg. These compounds are formed during the pyrolysis stage of the combustion process by the secondary aromatization reactions in char at temperatures above 400 °C. The created PAHs are bound in the porous unburned carbon. For a more detailed qualitative analysis of other organic compounds the GC-MS was used. Higher and branched aliphatic hydrocarbons, ketones, amides and phthalates in the sample with the highest unburned carbon content were found.