The authors wish to acknowledge the public company Gestió Ambiental i Abastament S.A. (WWTP of Reus, Spain) for its kind collab-oration during this project. Magdalena Olkiewicz also thanks the
Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) of the GeneralitatofCatalunya (Spain)forthepre-doctoralscholarship.Financialsupport for this researchwasprovided bythe Spanish Ministerio de Educación y Ciencia and the FEDER grant (CTM2011-23069).