Robert Zona

Degradation of 2,4-dichlorophenoxyacetic acid by ionizing radiation: influence of oxygen concentration.

Ionizing radiation has been proved as a promising method for the degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The gamma-radiolytic decomposition and chloride formation follows an apparent first order kinetic, kde/kCl = 3. For complete removal of 500 microM 2,4-D, a dose of 4 kGy is required. Phenolic intermediates (2,4-dichlorophenol, the isomers 2-chloro-4-hydroxy- and 4-chloro-2-hydroxy phenoxyacetic acid and three hydroxylation products of 2,4-D) are formed. Using oxygen saturation during irradiation, they are removed again with a dose of 4 kGy. For the formation of the main organic product acetic acid a reaction mechanism is discussed. Oxygen concentration enhances strongly fragmentation and mineralization. A reduction of 36% TOC could be achieved.

Ozone, Electron Beam and Ozone-Electron Beam Degradation of Phenol. A Comparative Study

The efficacy of electron beam (EB), ozone (O3) and the combined EB/O3 treatment on the removal of phenol, as a prototype for aromatic pollutants in water, is compared on the base of degradation, chemical oxygen demand (COD), total organic carbon (TOC) and toxicity. Complete decomposition of phenol (47 mg/L, 500 µM) was obtained with 14 kGy. Applying simultaneously 27 mg O3/L a dose of 10.5 kGy was sufficient. By the same amount of only ozone a phenol concentration of 45% remained. A TOC reduction of more than 70% was attained with EB/O3 (21 kGy/54 mg O3/L), whereas the identical, separate conditions solely led to 24% (EB) and 14% (O3). The EB/O3 treatment showed also the best results in COD decrease (79%, 21 kGy/54 mg O3/L) and detoxification (7 kGy/18 mg O3/L).

Degradation of Aqueous 4-Chloroaniline by Ozonolysis and Combined γ-Rays-Ozone Processing

The decomposition of 4-chloroaniline (4-ClA), used as a model for water pollutants, was studied by ozonolysis as well as by γ-rays in the presence of ozone under comparable conditions. The degradation process was followed by absorption spectroscopy and by HPLC-method as well. Depending on the ozone concentration (mg O3/min) introduced into the aqueous solution the substrate is decomposed to a mixture of carboxylic acids, which can be entirely degradated by prolonged treatment. The combined processing of 4-ClA by γ-irradiation in the presence of ozone proved to lead even to more efficient degradation of the substrate. Some primary reaction steps are briefly discussed.