Abstract: Ethylenediaminetetraacetic acid (EDTA) is chemically stable, and EDTA wastewater is difficult to meet direct discharge standards. During the remediation of a chemical-contaminated site inspected by the Central Environmental Protection Inspector, remediation agents containing EDTA were used, generating leachate containing EDTA that required treatment to achieve a chemical oxygen demand (COD) ≤ 50 mg/L. For low, medium, and high concentrations of EDTA wastewater with COD of 100,502,1503 mg/L respectively, the effectiveness of electrochemical oxidation and Fenton oxidation in COD removal was studied. The results showed that the COD removal rate by electrochemical oxidation was essentially the same for different initial concentrations. Controlling the wastewater at pH=3 throughout the process achieved a COD removal rate of 43.6%, which was 7.8 percentage points higher than thatofwithout pH control. The optimal parameters for electrochemical oxidation were a current density of 15 mA/cm², maintaining wastewater pH=3 throughout the process, and a reaction time of 120 minutes. Fenton oxidation achieved a COD removal rate of over 60% for medium and high concentrations but only 6% for low-concentration wastewater. The optimal parameters for Fenton oxidation were pH=3, the mass ratio of Fe²⁺，H₂O₂ and COD substances of 1:6:2 , and a reaction time of 90 minutes. By integrating the characteristics of the two advanced oxidation processes for EDTA removal, a combined process of "Fenton oxidation+ electrochemical oxidation+ flocculation sedimentation" was determined. The effluent COD of the combined process could meet the national direct-discharge standards with a COD removal rate of 84.6% for real EDTA leachate, and further improved the electrochemical oxidation efficiency to 49.8%.

Key words: ethylenediaminetetraacetic acid, chemical-contaminated site remediation, leachate, electrochemical oxidation, Fenton oxidation, combined process