The use of high-quality biomass ashes for fertilisation processes or for geotechnical and industrial purposes is advisable; however, there are several open questions for fostering different areas of application:

• If ash is to be used as fertiliser or fertiliser supplement on a large scale, it has to be turned into a marketable product in a cost-effective manner. Therefore, a standard product has to be developed, making it applicable on different sites with specific nutrient supply and pH regulation requirements (Table 1.1). Separation of high-quality and low-quality ashes at the incineration plant is highly desir­able. Combustion processes that do not blend the entire ash but provide fractions of bottom and fly ash are preferable.

Table 1.1 Important steps for development and assessment of a user-friendly and cost-effective fertiliser with ash admixture Product development and assessment Formulation of the product

Detailed assessment of the processing conditions (granulation, pelletising)

Production of prototypes Chemical assessment of prototypes

Analysis of effects of soil application regarding physicochemical and microbial parameters as well as plant productivity Optimisation of product and procedures Economic assessment and cost optimisation of product Development of marketing strategies Registration of product

Development of monitoring programmes (fertilisation effect, ecotoxicology)

• Ash applications to soils and the use of ash for geotechnical and industrial purposes have to be accompanied by quality controls to guarantee short-term and long-term harmlessness and the usefulness of these amendments/admixtures. International programmes have to be implemented to build up and merge knowledge on the recycling of biomass ashes and to work out general user guidelines, accompanied by standardised tests.

• Whereas wood ash application in forest ecosystems is commonly accepted in northern European countries, this is not so in other European countries. It is thus necessary to increase public awareness of the importance of sustainable forest management, including the recycling of wood ashes.

• On a national and European level, end-of-waste solutions for ashes should be envisaged, based on strict quality limits.

1.2 Conclusions

Biomass ash is the inorganic residue produced during incineration of biomass for heat and electricity production, containing valuable macronutrients and micronu­trients from the combusted biomass. Physical and chemical characteristics of biomass ashes depend strongly on the plant type (plant species, origin of plants, plant parts combusted) as well as the process parameters during incineration and the storage conditions of ashes; thus, the quality of different biomass ashes differs considerably, even within the same incineration facility.

Investigations on the suitability of biomass ash application to forests as well as agroecosystems are difficult to compare, as different types and amounts of ash have been tested in various environments, hindering the establishment of general guide­lines for ash amendments. Biomass ash applications have been shown to be beneficial to soil ecosystems, as long as ashes of good quality are used and care is taken not to accumulate heavy metals or organic pollutants as a consequence of high application doses or repeated applications. These positive effects have been confirmed in long-term experiments in forest ecosystems in northern European countries, where wood ash applications have a long tradition. Long-term investiga­tions aside from these forest ecosystems are, however, scarce as are clear regula­tions and guidelines for biomass ash recycling to soil. The same is true for the use of combustion residues for geotechnical and industrial purposes.

Research on the recycling of biomass ashes is a relevant and timely issue. More specific information and recent research outcomes on the recycling of biomass ashes as fertiliser or fertiliser supplement in forests and agroecosystems as well as for geotechnical and industrial applications are provided in other chapters of this book.

Acknowledgements We wish to thank the University of Innsbruck, Austrian Federal Ministry of Science and Research, Federal Ministry of Agriculture, Forestry, Environment and Water Man­agement, Land Tirol and Tiroler Zukunftsstiftung, Osterreichische Bodenkundliche Gesellschaft, Tiroler Wasserkraft AG, Vorarlberger Kraftwerke AG, Salzburg AG and Dettendorfer Wertstoff GmbH & Co. KG as well as all project partners of K-Regio BioTreaT (http://www. biotreat. eu) for supporting the conference “Recycling of Biomass Ashes”.