Chapter 12
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Disinfection By-Product Formation Reactivities of Natural Organic Matter Fractions of a Low-Humic Water Cordelia J. Hwang, Michael J. Sclimenti, and Stuart W. Krasner Metropolitan Water District of Southern California, 700 Moreno Avenue, L a Verne, CA 91750-3399
Colorado River water (CRW), a low-humic water (specific ultra violet absorbance of 1.0 to 1.6 L/mg•m), was fractionated and isolated into five natural organic matter (NOM) fractions—hydro phobic, transphilic, hydrophilic acid plus neutral (A+N), hydrophilic bases, and colloids—and then chlorinated or chloraminated. The disinfection by-product (DBP) yields of the major NOM fractions in CRW (on the basis of µmol DBP/μmol dissolved organic carbon) contrasted strongly with those of high -humicwaters. The highest yield of trihalomethanes came from the hydrophilic A+N, not the hydrophobic ΝΟΜ. Production of dihaloacetic acids (DXAAs) was significantly higher than that of trihaloacetic acids (TXAAs) after both chlorination and chloramination, whereas TXAAs are typically higher than DXAAs in high-humic waters after chlorination. The greatest decrease in haloacetic acid yield after ozonation was in the hydrophilic A+N fraction. The haloacetonitrile yields were highest for the hydrophilic A+N and hydrophilic base fractions, which were highest in nitrogen content. In a water low in humic NOM, the more polar fractions can impactDBPtype and level almost as much as the hydrophobic ΝΟΜ. Thus, treatments to minimize DBP formation inCRWshould address removal of the hydrophilic A+N fraction.
Natural organic matter (NOM) in drinking-water sources typically consists of humic (hydrophobic) substances, such as humic and fulvic acids, and nonhumic (hydrophilic) material, which is often of biological origin. These materials include precursors for disinfection by-products (DBPs), which form upon reaction with disinfectants such as chlorine and chloramines. Some of these DBPs are of health concern. Stage 1 of the Disinfectants/DBP Rule lowers the allowable level of trihalo methanes (THMs) and adds regulations for haloacetic acids (HAAs) and bromate (/). © 2000 American Chemical Society
In Natural Organic Matter and Disinfection By-Products; Barrett, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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174 In addition, most surface-water utilities are required to remove D B P precursors—as measured by total organic carbon (TOC)—by enhanced coagulation (I). T O C or dissolved organic carbon (DOC), ultraviolet (UV) absorbance at 254 nm, and specific U V absorbance ( S U V A ) — U V (m'^/DOC (mg/L)—have been used as indicators of the DBP-forming capability of a source water. In U.S. surface waters, typical ranges for T O C are 2 to 20 mg/L and for S U V A are 1.4 to 5.5 L/mg-m (2). Typically, S U V A at
