Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2005
Publication Date: 2/19/2005
Citation: Chow, A.T., Guo, F., Gao, S., Breuer, R., Dahlgren, A. 2005. Filter pore size selection for characterizing dissolved organic carbon and trihalomethane precursors from soils.. Water Research. 39(2005) pp 1255-1264. Interpretive Summary: Dissolved organic carbon (DOC) reacts with chlorine to form a group of health hazardous compounds including trihalomethanes (THMs) during drinking water treatment processes. The relationship between the physical size of DOC and THM precursor is not well understood. This research investigated the propensity of organic carbon fractions to form THMs from soil extracts that passed through various pore-size filters. Soils studied are from the Sacramento-San Joaquin Delta, a source of drinking water for 22 million Californians. This study identified that the major contribution of soil organic carbon to water and to form THMs is from DOC passing through 0.1 micro-m. This leads to the conclusion that further identification and characterization of THM precursors should focus on the finer sized DOC rather than traditionally used size of 0.45 micro-m. The information is also valuable for water utilities to adopt effective water treatment technologies when removal of organic carbon in drinking water source is needed.
Technical Abstract: Filters with a pore size of 0.45 micro-m have been arbitrarily used for isolating dissolved organic carbon (DOC) in water. This operationally defined DOC fraction often contains heterogeneous organic carbon compounds that may lead to inconsistent results when evaluating trihalomethane formation potential (THMFP). A finer pore size filter provides more homogeneous properties and enables a better characterization of organic matter. In this study, we examined effects of filter pore size (1.2, 0.45, 0.1 and 0.025 'm) on characterizing total organic carbon, ultra-violet absorbance at 254 nm (UV254) and THMFP of water extracts from a mineral and organic soil in the Sacramento-San Joaquin Delta, California. Results showed that the majority of water extractable organic carbon (WEOC) from these soils was smaller than 0.025 micro-m, 85% and 57% in organic and mineral soils, respectively. A high proportion of colloidal organic carbon (COC) in mineral soil extracts caused water turbidity and resulted in abnormally high UV254 in 1.2 and 0.45 micro-m filtrates. The reactivity of organic carbon fractions in forming THM was similar for the two soils, except that COC from the mineral soil was about half that of others. To obtain a more homogeneous solution for characterizing THM precursors, we recommend a 0.1 micro-m or smaller pore-size filter, especially for samples with high colloid concentrations.