Treatment of wastewater containing EDTA-Cu(II) using the combined process of interior microelectrolysis and Fenton oxidation–coagulation

Wastewater containing EDTA-Cu(II) originating from the electroless copper-plating process was treated in a combined system of interior microelectrolysis (IM) and Fenton oxidation and coagulation (FOC). The intermittent operation of an IM reactor showed that the treatment efficiencies and Fe(II) yields were much higher under lower initial pH of the wastewater, and when the raw wastewater was treated by IM for 20 min, the Fe(II) yields and pH of the IM effluent were 336.1 mg/L and 4.6, respectively. The proper reaction conditions for the treatment of IM effluent by the FOC process were a [H2O2]/[COD] ratio of 2.0, [Fe(II)]/[H2O2] ratio of 0.2–0.3, initial pH of 2.0–5.0, and reaction time of 60–80 min; thus, the Fe(II)-rich effluent of IM was suitable for treatment during a subsequent Fenton oxidation (FO) process without Fe(II) addition or pH adjustment. Under the optimal operating parameters, 100% Cu(II) and 87.0% COD were removed by the IM–FOC process. The contributions of IM, FO and coagulation to Cu(II) removal were 97.5%, 0%, and 2.5%, respectively, and those to COD removal were 22.3%, 47.8%, and 10.9%, respectively. After treatment, the BOD5/COD ratio of wastewater was enhanced from 0 to 0.42, indicating that EDTA was effectively oxidized in the combined system.

► IM–FOC process is used for the treatment of wastewater containing EDTA-Cu(II).
► Treatment efficiencies and Fe(II) yields of IM were much higher at lower initial pH.
► IM provides Fe(II)-rich wastewater with proper pH for subsequent Fenton oxidation.
► The contributions of IM, FO and coagulation to COD removal are 22.3%, 47.8% and 10.9%.
► IM–FOC process completely removes Cu(II) and effectively oxidizes EDTA.