| Summary: | 碩士 === 東海大學 === 環境科學系 === 89 === Humic acids (HA), which have been shown to be natural organic matters (NOMs), are recognized as one of the most important precursors to the formation of disinfection by-products (DBPs) during chlorination. Their complex and huge structures. result in the formation of DBPs while the functional groups react with chlorine. This study has been concentrated on three parts. First, XAD-8 resins are used to separated the Te-Chi Reservoir sample into the natural humic acids, fulvic acids and XAD-8 effluent. Then the separated samples are chlorinated with sodium hypochlorite respectively to study the influence of the various functional groups on the DBP formations. Second, commercially available humic acids are chlorinated to study the influence of reaction temperature and chlorine dosage on the formation of DBPs. Additionally, the profiles of DBP formation resulting from changes of the functional groups during chlorination are discussed. Third, pre-ozonation and post-chlorination are combined to investigate how the DBP formation can be reduced, based on the changes of functional groups.
Experimental results reveal that for Te-Chi sample, humic substance contributes 22~29% of the NOMs while the non-humic substance contributes 71~78% of the total isolated NOMs. Elemental analysis indicates that humic acids contained in Te-Chi Reservoir are coming from the degradation of pedogneic plants, and that humic acids contain less aromatic structure than fulvic acid. C=C and CºC are the main component of unsaturated structures. Ratios of THMFP/DOC, HAAFP/DOC and AOXFP/DOC are 25 mg/mg, 50 mg/mg and 79 mg Cl/mg, respectively for HA, are 37 mg/mg, 47 mg/mg and 168 mg Cl/mg, respectively for FA, and are 15 mg/mg, 22 mg/mg and 131 mg Cl/mg for XAD-8 effluent. For commercial humic acids, the chlorination reaction with NaOCl in originally active but becomes gentle after 48 hours. The formation of HAAFP is higher than THMFP. Considering the effect of different condition on the DBP formation, the chlorine dosage is founded to be more important than reaction temperature.
For commercial humic acids, pre-ozonation decreases 58% THMFP/DOC, 63% HAAFP/DOC and 66% AOXFP/DOC resulting from changes in the composition of functional groups. During the initial phase of ozonation aliphatic structures are observance to decrease at rapid ratio, and the aromatic structures decrease until the ORP exceeds 450 mV. The carbohydrate and the carboxylic groups decrease at the beginning of reaction, but their reductions are insignificant. This verifies that the decrease in DBPFP by pre-ozonation is caused by the decrease of aliphatic carbon and aromatic carbons.
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