Comparative studies of photo- and radiation-induced degradation of aqueous EDTA. Synergistic effects of oxygen, ozone and TiO2 (acronym: CoPhoRaDe/EDTA)

Abstract The photolysis (λ=254 nm) of aqueous EDTA in the presence of oxygen, ozone and TiO 2 individually and in mixtures of them as well as by ozonation only was investigated. Very high EDTA degradation yields were obtained by the synergistic action of UV light (λ=254 nm) in the presence of ozone and TiO 2 . By adding of a 2.5 mg ml −1 TiO 2 suspension to an aqueous solution of 1×10 −3 mol dm −3 EDTA and passing through 1.9 mg dm −3 min −1 O 3 a G ph i (-EDTA)=12.0 and at 29.3 mg dm −3 min −1 O 3 a G ph i =25.2 was obtained. Comparative studies were performed with γ-irradiation under similar conditions. A somewhat higher yield of EDTA degradation, G i (-EDTA)=13.5 was observed upon γ-radiolysis of 1×10 −3 mol dm −3 EDTA in the presence of 1.9 mg dm −3 min −1 O 3 and 2.5 mg ml −1 TiO 2 . In both cases the EDTA degradation depended on the absorbed radiation dose (UV-light or γ-rays), on the O 3 -concentration, and on the amount of suspended TiO 2 . By increasing the O 3 concentration also the degradation yield was strongly increased. Analysis of products resulting from photolysis and radiolytic of EDTA in the presence of oxygen, performed by the GC/MS-method are also reported. Economic considerations concerning the pollutant degradation by combined photochemical methods in comparison to ionising radiation under similar conditions have been made.