Evaluation of UVA, UVB and UVC photolysis and photocatalysis for the removal of atrazine from contaminated water

The removal of atrazine from water using direct photolysis by UVA (320-400 nm), UVB (280-320 nm) and UVC (253.7 nm) radiation was investigated. The effect of the presence of natural organic matter (NOM) on the photolysis of atrazine was evaluated both for NOM-free and NOM-rich waters for different initial atrazine concentrations. The presence of NOM had a negative impact on the removal of atrazine where 8% and 15% reduction in degradation was observed in the presence of NOM levels of 5 and 15 mg/L, respectively, for samples treated by UVC irradiation. For UVB irradiation reduced atrazine removal in the presence of NOM was also observed. This reduction may be attributed to the screening effect for UV radiation by NOM compounds. The use of UVA irradiation showed no significant removal of atrazine under all conditions tested, however the presence of NOM has a positive effect on atrazine removal by UVA irradiation due to the photosensitizer role played by NOM molecules. Atrazine removal has been determined also on the basis of UV doses. Applying the same UV dose showed that atrazine removal by UVC was higher than UVB and UVA irradiation both in the presence and absence of NOM. The presence of TiO 2 (25 mg/L) increased atrazine degradation for all UV wavelength ranges in NOM-free and NOM-rich water. For example, atrazine removal by UVB irradiation increased by 20%. Increased TiO 2 concentration (125 mg/L) has a negative impact on atrazine removal by UVC and UVB irradiation as the shielding effect of the catalyst particles reduced the photo- catalytic degradation of atrazine. The increased TiO 2 concentration led to a slight increase in atrazine removal by UVA irradiation as TiO 2 produces the highest level of OH ● radicals under UVA irradiation. UVC, UVB and UVA irradiation resulted in the formation of atrazine and NOM (when used) degradation products. Identification of the atrazine degradation products was not in the scope of this study. The results obtained show that complete removal of atrazine molecule was achieved. However measurements of TOC, BOD and COD concentrations during atrazine degradation by UVC, UVB and UVA irradiation suggest that the UV processes tested are insufficient for complete treatment. Therefore, further investigation into complete mineralization of atrazine, atrazine by-products and the NOM compounds is required. Nitrite formation occurred with atrazine removal for all UV ranges tested. Nitrite concentrations were markedly higher in NOM-rich water than NOM-free water, which indicates that nitrite formation was mainly due to the breakdown and/or mineralization of NOM molecules by UV radiation. The presence of TiO 2 increased the formation of nitrite for all UV ranges due to catalysis of the photooxidation process of atrazine and NOM