*2.1. Materials*

SSA investigated originates from a sewage sludge mono-combustion plant that was kindly provided by "Wirbelschichtfeuerungsanlage Elverlingsen GmbH", 58791 Werdohl-Elverlingsen, Germany. All chemicals were supplied by Merck KGaA, Darmstadt, Germany. Reactants used were HCl, reagen<sup>t</sup> grade 36.5% (used 493.2 g and diluted to 1 L in a volumetric flask with distilled water to prepare 5.0 M) and NH4Cl. Epo-TEK by Epoxy Technology Inc., Billerica, MA, USA was supplied by Logitech Ltd., Glasgow, UK.
