Photochemical degradation of hydrophilic xenobiotics in the UV/H2O2 process: Influence of nitrate on the degradation rate of EDTA, 2-amino-1-naphthalenesulfonate, diphenyl-4-sulfonate and 4,4'-diaminostilbene-2,2'-disulfonate

Photochemical oxidation methods can be successfully used to eliminate hydrophilic xenobiotics in the water phase with a high efficiency. The influence of nitrate on the photochemical degradation kinetics of organic micropollutants in the presence of H2O2 proved to be different from its influence in the absence of H2O2. In the presence of H2O2, nitrate acts as an ''inner filter'' and reduces the UV light intensity in the photoreactor. As a consequence, the degradation rate of the micropollutants in the UV/H2O2 process decreased with increasing nitrate concentration. The degradation rate of the photolysis (UV irradiation only) was enhanced in the presence of nitrate. This could be explained by the formation of HO radicals during the nitrate photolysis. The influence of nitrate on the degradation rates in both UV processes was significantly more distinct for the irradiation of lambda(ir) = 222 nm compared to the degradation at lambda(ir) = 254 nm. This is mainly caused by a higher UV absorption of nitrate al the shorter wavelength. Problems with this technology can arise because nitrite and peroxynitrite were formed during UV irradiation of nitrate. (C) 1997 Elsevier Science Ltd.