survey of DOC and UV measurement practices with implications for SUVA determination

摘要

Natural organic matter (NOM) in dissolved, colloidal, and particulate forms is ubiquitous in surface water and groundwater. The dissolved and colloidal forms are the most problematic and undesirable types of NOM with regard to water treatment and supply. A major concern for water utilities is the formation of disinfection by-products (DBPs) resulting from reactions between dissolved organic material (DOM) fractions and chlorine (Cl_2) or other disinfectants/oxi-dants. Because of the potential risk to public health posed by DBPs, the US Environmental Protection Agency (USEPA) imposes stringent standards under the Disinfectants/Disinfection By-products Rule (D/DBPR) (USEPA, 1998). Therefore, DOM must be assessed to effectively predict its removal from water as well as predict the potential for DBP formation during treatment. Four parameters―total organic carbon (TOC), dissolved organic carbon (DOC), ultraviolet (UV) absorbance, and specific ultraviolet absorbance (SUVA)―are commonly used for this assessment. TOC quantifies all organic materials in water and is the sum of two major components: particulate organic carbon (POC) and DOC. DOC is operationally defined as the organic carbon in water that has passed through a 0.45-μm filter. For many freshwaters, it has been reported that DOC represents 83 to 98% of the TOC (Owen et al, 1993). However, for waters high in POC (e.g., rivers after runoff events), DOC may represent only a smaller portion of the TOC. It is generally accepted that the absorbance of natural waters at UV wavelengths around 250 nm is caused primarily by aromatic structures (Korshin et al,1997). SUVA_λ, is the ratio of ultraviolet light absorbance of wavelengthλ (usually 254 nm) to the concentration of DOC in the water, i.e., UV(m~(-1))/DOC(mg/L).