Ultrasonic treatment of liquid waste containing EDTA

The presence of EDTA in decontamination wastes can cause complexation of the radioactive cations resulting in interferences in their removal by various treatment processes such as chemical precipitation, ion exchange etc. Further, it might also impart elevated leachability and higher mobility to cationic contaminants from the conditioned wastes i.e. waste immobilized in cement or other matrices and can adversely influence the quality of the final form of waste. Advanced Oxidation Processes (AOP) using ozone, H2O2, ultrasound (US), ultraviolet radiation (UV), Fenton’s reagent (FeII + H2O2) alone or in combination is considered as possible methods of clean and ecologically safe remedial treatment for the degradation of organics. In the present study, kinetics of sonochemical degradation of EDTA (20,000 mg/l) utilizing combination of processes viz., ultrasound + Fenton’s reagent and ultrasound + H2O2 at lower and higher frequencies of 40 and 130 KHz.was investigated. This was compared with the chemical degradation using H2O2 and Fenton’s reagent. Both chemical and sonochemical oxidation yielded complete degradation of EDTA at different rates. The sonochemical reaction was found to follow first order kinetics, the reaction being faster at high frequencies. From the observed pH changes during the oxidation processes, it could be concluded that there was loss of chelating ability of EDTA. Formation of amides in the sonochemical degradation using Fenton’s reagent and formation of acidic intermediates during the sonochemical degradation using H2O2 and chemical oxidation using Fenton’s reagent alone was confirmed.