Laboratory of Environmental Science and Engineering, School of Mining and Metallurgical Engineering, National Technical University of Athens (NTUA), 9 Heroon Polytechniou, 15780, Athens, Greece. artin@metal.ntua.gr. Department of Environmental Engineering and Water Technology, UNESCO-ΙΗΕ, Westvest 7, 2611-AX, Delft, The Netherlands. National University of Ireland Galway, University Road, Galway, H91 TK33, Ireland. Department of Civil, Architectural and Environmental Engineering, University of Napoli Federico II, Via Claudio 21, 80125, Naples, Italy.