Highly efficient degradation of dimethyl phthalate from Cu(II) and dimethyl phthalate wastewater by EDTA enhanced ozonation: Performance, intermediates and mechanism

In this study, the presence of Cu(II) ions was found for the first time to severely inhibit +-dimethyl phthalate (DMP) degradation by ozone due to the formation of the stable complex Cu(II)-DMP. However, 100% DMP removal was rapidly reached when ethylenediamine tetraacetic acid (EDTA) was added with a Cu(II)/EDTA molar ratio of 3:1. Subsequent studies indicated that Cu(II)-DMP is sequestrated by EDTA, then DMP was degraded and Cu(II) was removed by precipitation. The freshly formed Cu-EDTA(2-) and organic nitrogen intermediates further decomposed O-3 into (OH)-O-center dot, which induced to the rapid degradation of DMP. The k(obs) of Cu-EDTA/O-3 were 9-10 times greater than the k(obs) of DMP removed by ozonation alone within 10 min. The reaction mechanism involved a (OH)-O-center dot generation was proposed. The (OH)-O-center dot and O-2(center dot)- are generated from the rapid reaction between ozone and EDTA. Acting as a more strongly negative species, the specific Cu(II) in Cu-EDTA complexes is more inclined to react with O-2(center dot)- to give Cu(I), accelerating the forward reaction to produce more (OH)-O-center dot. The synergistic removal of DMP and Cu(II) can be achieved after reaction. Therefore, this study provides an effective method to dispose metal ion and organic pollutant wastewater.