Ethylenediaminetetraacetic acid (EDTA), a common industrialagent for complexing metal ions in water, frequentlyinhibitsconventional metals-removal technologies used in watertreatment. This study investigated the use of TiO
2photocatalysis for the aqueous-phase oxidation of EDTA andseveral metal complexes of EDTA. Reactions wereperformedat 0.1 wt % loading of Degussa P-25 TiO
2, asoluteconcentration of 0.8 mM and at a constant pH. Thedifferentmetal-EDTA complexes exhibited widely different photocatalytic oxidation rates under equivalent conditions of pH= 4 ± 0.1 in an aerobic system: Cu(II)-EDTA >Pb(II)-EDTA >> EDTA > Ni(II)-EDTA
Cd(II)-EDTA
Zn(II)-EDTA >>> Cr(III)-EDTA. Photoefficiency based ontheCu(II)-EDTA initial rate is nearly 60%. The rates oftotalorganic carbon (TOC) removal and formaldehyde generationduring photocatalytic EDTA oxidation indicate similaritiestoelectrochemical oxidations of EDTA. Several meanswereexplored to enhance the oxidation of Ni(II)-EDTA,whosebehavior was taken to represent that of the slowlyoxidizingcomplexes. Continuous addition of H
2O
2solution during thephotocatalytic treatment increased the oxidation rate forNi(II)-EDTA as did the presence of homogeneousCu
2+.The presence of Cu
2+ led to rapid ligand exchangetransformingthe Ni(II)-EDTA into Cu(II)-EDTA, which is easilyoxidized.