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An overview of the Advanced Oxidation Processes (AOP) studied for the degradation of pesticides combined with the formation of by-products is presented. It was found that the degree of conversion of pesticides is about the same with the Fenton process and UV/H2O2 within the margin of practical application, but slightly different with ozone/H2O2. Bentazone is readily degraded by the latter process, but more persistent during water treatment with the Fenton process and UV/H2O2, whilst atrazine is difficult to convert with all of these processes. Although bromate formation cannot be avoided completely with ozone/H2O2, it can be realized with the Fenton process and UV/H2O2. Upon degradation of pesticides with UV/H2O2 nitrite is produced, the amount depending on the water quality with respect to the nitrate concentration. Based on the a-selective nature of the hydroxyl radical AOC is formed out of DOC, which indicates that ozone/H2O2, the Fenton process as well as UV/H2O2 should be applicable for the development of biological GAC filtration.

Fenton process, known as Advanced Oxidation Process for the degradation of organic pollutants in waste and drinking water, was studied for the combination of iron removal and pesticide control in anaerobic groundwater. The combined effect of aeration and rapid sand filtration, which are commonly applied in groundwater treatment, was studied in a pilot plant. Pesticide degradation was performed on laboratory scale. It was found that addition of 2 mg/L H2O2 prior to aeration improved the removal of iron without hindering the filtration processes of manganese removal and nitrification. Under these conditions, the laboratory-scale tests showed pesticide degradations of up to 80% (influent concentration 1.6-2.5 μg/L). Dosing 8.5 mg/L H2O2 all selected pesticides were converted more than 80%. However, this dose appeared to have an adverse effect on the removal of iron and manganese and the nitrification process. This is attributed to the presence of relatively high concentrations H2O2 in the water entering the rapid sand filter. By filtration AOC, formed during oxidation with the low H2O2 dose, was reduced from about 70 μg/L to about 15-20 μg Acetate-C/L. Bromate formation did not occur. Residual H2O2 varied from 0.1-0.2 mg/L (2 mg/L H2O2 dose) to 0.2-0.4 mg/L (8.5 mg/L H2O2 dose) which is higher than the proposed guideline of 0.019 mg/L.

A low-pressure (LP-UV) and medium-pressure UV lamp (MP-UV) were compared for the formation of nitrite, assimilable organic carbon (AOC), and genotoxicity using pretreated surface water in a bench UV unit. The results have been compared with the by-products formed in pretreated surface water using a pilot unit equipped with four mediumpressure lamps identical to the one used in the bench unit. It was found that although significant nitrite formation occurred in the MP-UV bench tests, it remained well below the European standard (0.1 mg/L NO − 2 ) in the pilot unit. The LP-UV gave no or very low amounts of nitrite (bench unit). The AOC and genotoxicity increase with LP-UV was negligible. The AOC content and genotoxicity after MP-UV irradiation in the bench unit was significant as well, whereas AOC was formed limitedly in the pilot unit. Genotoxicity was elevated but not significant. Résumé :Une lampe UV à basse pression (LP-UV) et une lampe UV à pression moyenne (MP-UV) ont été comparées quant à la formation de nitrite, de COA (carbone organique assimilable) et pour la génotoxicité en utilisant de l'eau de surface prétraitée dans une unité UV de laboratoire. Les résultats ont été comparés aux sous-produits formés dans l'eau de surface prétraitée en utilisant une unité pilote équipée de 4 lampes à pression moyenne, identiques à celle utilisée dans l'unité de laboratoire. Bien que des quantités importantes de nitrite aient été formées dans les essais MP-UV en laboratoire, il a été trouvé que le niveau demeurait bien en deçà de la norme européenne (0,1 mg/L NO − 2 ) dans l'unité pilote. La lampe LP-UV ne donnait pas de nitrite ou seulement en très faibles quantités (unité de laboratoire). L'augmentation de la teneur en COA et de la génotoxicité avec la lampe LP-UV était négligeable. Après une irradiation MP-UV dans l'unité de laboratoire, la teneur en COA et la génotoxicité étaient aussi significatives, alors que la formation de COA était limitée dans l'unité pilote. La génotoxicité était élevée mais pas significative.