Recovery of Metals from Sewage Sludges and Incineration Ashes by Means of Hyperaccumulating Plants

Austria and many other countries have to import up to 90% of the material inputs of metals from abroad. These primary resources are becoming more expensive as they become more scarce and remaining deposits more difficult to mine, which is a serious concern for industrialized nations. Basic economic and strategic reasoning demands an increase in recycling activities and waste minimization. Technologies to recover metals in a reasonable and economically relevantmanner from very diffuse sources are practically non-existent or require large amounts of energy,complex equipment and chemicals with potentially high environmentall risks. Agriculture uses large volumes of mineral fertilizers, which are often sourced from mines aswell, and are also subject to the principle of finiteness and potential shortages. These assimilated biological nutrients through the food chain and human consumption end up in sewage systemsand wastewater treatment plants in great quantities. In Austria, they mostly do not return to agriculture, but due to contamination with heavy metals are diverted to be used as construction aggregates or are thermally treated and end up rather uselessly in landfills.