WaterResearch39(2005)1639–1651 Biosorptionofprotonsandheavymetalsontoolivepomace: Modellingofcompetitioneffects FrancescaPagnanelli à ,SaraMainelli,SimonaDeAngelis,LuigiToro Department of Chemistry, University of Rome ‘‘La Sapienza’’, P.le A. Moro, 5, 00185 Rome, Italy Received5October2004;receivedinrevisedform25January2005;accepted27January2005 Availableonline14March2005 Abstract Heavy metal biosorption onto solid wastes from olive oil production plants, olive pomace, has been investigated. Acid–basepropertiesoftheactivesitesofolivepomaceweredeterminedbypotentiometrictitrationsandrepresented byacontinuousmodelaccountingfortwomainkindsofactivesites.Competitionamongprotonsandheavymetalsin solutionwasconsideredbyperformingbiosorptiontestsatdifferentequilibriumpHwithsingle(CuandCd)andbinary metalsystems(Cu–Cd).BothLangmuirextensionsandnon-idealcompetitiveadsorptionmodels(NICAmodels)can beusedtorepresentexperimentaldataofCuandCdbiosorptioninsinglemetalsystemsatdifferentequilibriumpH. Nevertheless only NICA models, accounting for site heterogeneity and non-ideal adsorption of the different species simultaneouslypresentinsolution,canadequatelysimulatethecompetitionamongCuandCdinbinarymetalsystems byusingtheparametersfittedtosinglesystemdata. r 2005ElsevierLtd.Allrightsreserved. Keywords: Biosorption;Heavymetals;Olivepomace;Equilibriummodelling;Binarysystems 1. Introduction Biosorptionofheavymetalsisanalternativetechnol- ogyinwatertreatmentusingdifferentkindsofwastesas sorbentmaterials(Veglio` andBeolchini,1997; Volesky, 2001). The main challenges related to an industrial application of this emerging technology are the identi- fication of abundant, selective and effective wastes (product development) and the design of continuous processes according to conventional and innovative configurations(processdevelopment)(Volesky,2001). Researchabouttheinteractionsamongthesebiologi- calmatricesandionicspeciesinsolution(heavymetals, protons, alkaline and alkaline earth metals) is a fundamental step to improve the adsorption perfor- mancesandtooptimizetheoperatingconditions.Inthis ambit equilibrium models are valuable mathematical toolstoinvestigatecompetitionmechanismsincomplex media typical of real waste waters and to identify optimumsorptionconditions.Inparticularcompetition fortheactivesitesofthebiosorbentmaterialamongthe ionicspeciesinsolutioncanberepresentedaccordingto modelling approaches characterized by different degree ofcomplexitysuchastheLangmuirextensions,mechan- istic models and non-ideal competitive adsorption models(NICAmodels). Langmuirextensionscanbederivedfromtheoriginal Langmuir isotherm (Eq. (A.1) in Appendix A) to describe both site heterogeneity and competition ARTICLE IN PRESS www.elsevier.com/locate/watres 0043-1354/$-seefrontmatter r 2005ElsevierLtd.Allrightsreserved. doi:10.1016/j.watres.2005.01.019 à Correspondingauthor.Tel.:+390649913333; fax:+3906490631. E-mail addresses: francesca.pagnanelli@uniroma1.it (F.Pagnanelli),sara.mainelli@uniroma1.it(S.Mainelli), luigi.toro@uniroma1.it(L.Toro).