Special Features of Photodegradation of Organic Compounds upon Exposure to Excilamp Light

The use of gas discharge sources of modern spontaneous radiation – excilamps – for photodegradation of organic compounds is discussed. The process of photodegradation upon exposure to excilamp light is considered on an example of degradation of a widespread herbicide – 2,4-dichlorophenoxyacetic acid (2,4-D) – in a continuous-flow photoreactor upon exposure to light of Xe₂ (λ _rad ~ 172 nm), KrCl (λ _rad ~ 222 nm), and XeBr (λ _rad ~ 283 nm) excilamps. It is found that the degradation of 2,4-D after exposure to Xe₂ excilamp light occurs much more effective than upon exposure to other radiation sources. However, the dechlorination process accompanying the photodegradation of 2,4-D in an aqueous solution upon exposure to the KrCl excilamp is more intensive than that upon exposure to Xe₂ lamp. The dynamics of changing the toxicant concentration in the solution during UV irradiation is established. The toxicity of 2,4-D aqueous solutions and photolysis products after irradiation are estimated. It is found that the initial bioluminescence index increases upon exposure to XeBr excilamp light, thereby reducing the toxicity in comparison with the Xe₂ and KrCl excilamps. The solutions become most toxic under excitation by the Xe₂ excilamp. We have succeeded in reducing the toxicity and increasing the efficiency of the photoreactor with the KrCl excilamp by addition of hydrogen peroxide. In this case, the complete 2,4-D decay has been achieved.