| Summary: | 碩士 === 淡江大學 === 水資源及環境工程學系碩士班 === 97 === Phorate and terbufos are organophosphorus pesticides. Using the synthetic raw waters containing 100 μg/L of phorate or terbufos, the purposes of this study are (1) to investigate the removals of phorate and terbufos by the Fenton coagulation process, and (2) to compare the removals of phorate and terbufos among iron salts (Fe2+/Fe3+) coagulation, the Fenton((Fe2+/H2O2) coagulation and the Fenton-like (Fe3+/H2O2) coagulation processes. The operational variables studied include pH, type of iron salts, hydrogen peroxide (H2O2) dosage and coexisting organics of humic acid. All experiments are conducted by the Jar test.
The results show that the optimum pH for the removal of phorate and terbufos was at 4.0. The mechanism for the removal of phorate and terbufos was mainly by adsorption and precipitation. The removal of phorate and terbufos by ferric coagulation was better than that by ferrous coagulation. Furthermore, the removals of both phorate and terbufos by peroxidation and iron salts coagulation were less than 55%. The optimum pH for the removal of phorate and terbufos by the Fenton coagulation and Fenton-like coagulation was at 4.0 and the residuals of phorate and terbufos were less than 5%. The removal of phorate and terbufos was mainly by hydroxyl radical oxidation. Comparing the removals of phorate and terbufos among different processes at pH 4, the sequence of the removals of phorate and terbufos were Fenton coagulation＞Fenton-like coagulation＞ferric coagulation＞Ferrous coagulation＞peroxidation. The increase of phorate removal was not affected significantly by increasing H2O2 dosage.
As the synthetic raw water contained coexisting organics of humic acid of 1.0~5.0 mg/L as NPDOC, the residuals of phorate and terbufos increased and reached to 90% for ferric coagulation and ferrous coagulation processes. This was due to the competition of adsorption sites on coagulants between humic acid and organophosphorus pesticides. Therefore, coexisting of organics of humic acid affected the removals of phorate and terbufos by iron salts coagulation. In contract, in the presence of humic acid, the removals of phorate and terbufos decreased slightly 2-10%.It implied that the effect of the removals of phorate and terbufos on coexisting humic acid was not significant for the Fenton coagulation and Fenton-like coagulation. It is concluded that H2O2 could enhance the phorate removal by iron salts coagulation and was less affected by coexisting of humic acid.
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