The degradation of EDTA by the bimetallic Fe–Cu/O2 system

• The Fe–Cu/O2 process exhibited higher removal rate of EDTA than that of ZEA process.
• It would not cause heavy new metal pollution in initial acidic condition.
• Cu0 may improve the generation of OH in acidic condition.
• The degradation of EDTA may be attributed to OH in acidic condition.
• It may be attributed to a mixture of OH and ferryl ion in alkalinity condition.

The bimetallic Fe–Cu/O2 process exhibited significantly higher reactivity than did the Fe/O2 process for the degradation of ethylenediaminetetraacetic acid (EDTA). With the analysis of the soluble Cu2+ in the solution and decomposition of H2O2 catalyzed by Cu0, possible enhanced-pathways at different pHs were suggested. The degradation efficiency of EDTA increased with decreasing initial pH ranging 3–9, however, the reactions proceeded at a weakly-basic to basic condition in most of the reaction time. POD inhibition test showed that in situ generation of H2O2 played a pivotal role in the EDTA degradation, however, the instant concentration analyzed by DPD–POD method was less than 4.5 μM due to rapid subsequent Fenton reaction. Furthermore, DMPO–ESR spectroscopy and BA-trapping experiments detected the in situ generation of OH. The mechanism of EDTA oxidative degraded by the bimetallic Fe–Cu/O2 process was verified using control experiments of absorption, stripping, and coagulation sedimentation of EDTA in the system, analysis of solid residue, oxidation of O2 and H2O2, as well as detection of H2O2 and OH.