Photodegradation of EDTA and NTA in the UV / H2O2 Process

Abstract

The influence of H2O2 on the UV degradation of the broadly used aminopolycarboxylates EDTA and NTA in aqueous solution was investigated. The photochemical degradation in the UV /H2O2 process was compared with classical oxidative treatment of potable water. The German drinking water regulation (Trinkwasserverordnung) was the orientation for all experiments. The Advanced Oxidation Process (AOP) turned out to be superior to the classical oxidation processes. The photochemical degradation of EDTA and NTA by UV irradiation could be significantly stimulated in the presence of H2O2. There was a strong increase in the degradation rate and a decrease in the quantum yield of the aminopolycarboxylates. Experiments with butyl chloride as radical scavenger proved the photolytically generated hydroxyl radicals to be responsible for the increase in the degradation rates. The effect of increasing the degradation rate at higher concentrations of H2O2 was limited, because the steady-state concentrations of the hydroxyl radicals as reactive species, did not increase at the same rate as the initial concentration of H2O2. Low amounts of iron dissolved from the high-grade steel photoreactor walls had a significant catalytic effect on the degradation.