Abstract
In order to remove pesticides from ground and surface waters, destructions of trace organophosphorus pesticides in water by ozonation, ultraviolet (UV) irradiation and a combination of both techniques were investigated using a model system. Seven organophosphorus pesticides (Bensulide, Butamifos, Chlorpyrifos, EPN, Fenitrothion, Isofenphos and Trichlorfon) were examined at concentration of 4mg/L of each compound in water.
Ozonation (0.74 mg/L/h) of thiono type (P=S) pesticides in water was shown to convert rapidly into their oxygen analogs (P=O type) having higher cholinesterase inhibiting activity, and these P=O compounds formed were comparatively stable in the water. Treatment with UV irradiation of the pesticides in water was resulted in slowly cleavage of the phosphorothioate linkage, in some cases, to yield phenolic compounds and dialkyl thiophosphoric acids. Oxydation of the peseticides in water is significantly farster with ozone in combination with UV irradiation than UV irradiation or ozonation alone. For the pesticide decompositions, the process is over all first order in the compounds. With a continuously sparged stirred tank reactor, times for the elimination of 50% of the compounds were within 20 min.
