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United States Department of Agriculture

Agricultural Research Service

Title: Relationships Between Specific Uv Absorbance and Trihalomethane Precursors from Water Sources of the Sacramento-San Joaquin Delta, California.

Authors
item Chow, A - UC DAVIS
item Dahlgren, R - UC DAVIS
item Gao, Suduan
item Guo, F - CALIF DEPT WATER RES
item Breuer, R - CALIF DEPT WATER RES

Submitted to: Water Quality Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 17, 2004
Publication Date: November 14, 2004
Citation: Chow, A.T., Dahlgren, R.A., Gao, S., Guo, F., Breuer, R. 2004. Relationships Between Specific UV Absorbance and Trihalomethane Precursors From Water Sources of The Sacramento-San Joaquin Delta, California. Water Quality Symposium Proceedings.

Interpretive Summary: The UV absorbance at 254 nm (UVA254) or specific UVA254 (normalized by organic carbon concentration) has been widely used to predict natural dissolved organic carbon (DOC) in water or its reactivity in forming disinfection by-products (DBPs) (e.g. trihalomethanes, THMs) during chlorination process. However, presence of other compounds in water also contributes to this measurement. This study tested a hypothesis that the differences in UVAs or SUVAs before and after chlorination should be more closely correlated to THM formation of DOC than the absolute values before chlorination. This research found better correlations of parameters using the differences than the traditional UVA measurement. Also, similar parameters at 272 nm showed slightly better correlations with THM formation than those at 254 nm. Because of easy measurement, these parameters offer potentially simple and reliable methods to quantify the contribution of organic carbon in water to formation of DBPs during chlorination, which is important in water industry.

Technical Abstract: Aromatic carbon is considered one of the most reactive molecular moieties with respect to trihalomethanes (THM) formation during water chlorination. Studies have shown that ultra-violet absorbance at 254 nm (UVA254) is a good proxy for aromatic content in dissolved organic carbon (DOC). Thus, specific UVA254 (SUVA254), which is equal to carbon normalized UVA254, has been widely used as a measure for aromatic organic carbon content and trihalomethane formation potential. However, recent studies have questioned the reliability of using SUVA254 to predict THM formation because nitrate, bromide and non-reactive conjugated double bonds of organic carbon under chlorination also absorb UVA at 254 nm. The authors hypothesize that the difference in SUVA254 before and after chlorination ('SUVA254) should be proportional to the formation of THM if SUVA254 measures the amount of THM reactive sites in DOC. The authors examined DOC originating from agricultural soils in the Sacramento-San Joaquin Delta and from 35 river sites in the Sacramento-San Joaquin watershed. The relationships between SUVA254, 'UVA254/DOC and 'SUVA254 versus specific THM formation potential were evaluated. Results indicated that the correlation coefficients of 'UVA254/DOC-STHMFP and 'SUVA254-STHMFP are slightly better than SUVA-STHMFP. Also, all these parameters in terms of UVA at 272 nm provide slightly better correlation than UVA at 254 nm.

Last Modified: 8/1/2014
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