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Abstract
The degradation of atrazine and parathion-methyl by UV-light in the presence of O2(UV/O2) and by a combination of UV-light and ozone in the presence of O2(UV/O2/O3) was studied at a pilot plant for drinking water treatment. The photolysis rate of parathion-methyl increased with UV/O2/O3 compared to the treatment with UV/O2 only, while the photodecomposition rate of atrazine was not enhanced by the UV/O2/O3 combination under the working conditions applied.
In field experiments with a large-scale plant the degradation of atrazine and desethylatrazine was studied at a drinking water supply. The applied ozone dose rates were smaller and the residence time of the liquid phase in the UV-reaction unit was shorter than in the pilot plant. The degradation rate of both atrazine and desethylatrazine increased with increasing ozone dose rates and increasing radiant power. At a continuous flow rate of 70 m3/h of contaminated raw water atrazine could be degraded below the threshold limit for pesticides (0.1[ugrave]g/L) at optimum operation conditions, whereas the resulting desethylatrazine concentration exceeded this limit. At a continuous flow rate of 30 m3/h desethylatrazine could be degraded below the threshold limit, too.
