Institute for Chemical Engineering, University of Technology Graz, Inffeldgasse 25, A-8010 Graz, Austria, Europe
The energetic utilization of untreated biomass results in solid waste streams in the form of wood ash. Despite the fact that biomass utilization is environmentally advantageous, because of a steep decrease in the contribution to the greenhouse effect, the wood ash produced from biomass heating systems may well pose an environmental hazard. This is due to the fact that biomass concentrates some heavy metals like cadmium and lead, which result mostly from the utilization of fossil energy sources.
The content of heavy metals decides to a large extent the fate of the resulting waste streams. If the contamination reaches high levels, a recycling of the wood ash into agriculture is made impossible. This is disadvantageous for two reasons: first, the disposal of wood ash becomes cost intensive and further diminishes the chances of biomass utilization in economic terms; second, nutrient substances like calcium, potassium and phosphor, which are also contained in wood and which make this kind of material potentially valuable for fertilizing purposes, are lost and have to be replaced by virgin raw materials.
Substantial investigations in Austria have revealed that a large amount of the wood ash generated by energetic utilization can be recycled to agricultural use. The base of these investigations was a rigorous balance of the process of heat generation by biomass. This resulted in a clear picture of the ways heavy metals, especially cadmium, take through biomass heating systems. On the base of these findings, new technological solutions are envisaged that reduce the waste flow, increase the amount of wood ash utilized in agriculture, and decrease the overall hazard which biomass heating systems pose to the environment. A detailed review of these results will be given in the presentation.
wood ash, cadmium, lead, energetic biomass utilization
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.