ARS | Publication request: TRIHALOMETHANE FORMATION POTENTIAL OF FILTER ISOLATES OF ELECTROLYTE-EXTRACTABLE SOIL ORGANIC CARBON

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 10, 2004
Publication Date: October 12, 2005
Citation: Chow, A.T., Guo, F., Gao, S., Breuer, R.S. 2005. Trihalomethane formation potential of filter isolates of electrolyte-extractable soil organic carbon. Journal of Environmental Quality, 34:1992-1997.

Interpretive Summary: Trihalomethanes (THMs) are the largest group of disinfection by-products that are formed in drinking water from natural organic matter by reacting with chlorine during the chlorination process. This has been a continuous concern in Sacramento-San Joaquin Delta water sources due to elevated organic carbon concentrations where Delta organic peat soils are one of the main contributors. Identification and isolation of reactive organic carbons to form THMs has been a great challenge due to the complexity of organic matter. This research examined peat soil extracts of various strength of sodium- and calcium- based electrolytes that simulate field seasonal salinity changes and cause organic carbon leaching. These extracts were isolated into different size groups of organic carbon using a series of filtration processes. The quantity and reactivity of these extracts and isolates to form THMs were determined. Results clearly showed the effect of strength and the type of electrolytes on organic carbon production from soils and their reactivity to form THMs. The information provides information about factors that affect organic carbon production from Delta peat soils that contribute to Delta waters and thus helps scientists and water facility managers determine strategies that improve drinking water quality from the Delta.

Technical Abstract: Certain organic C moieties of soil origin in drinking source waters of Sacramento–San Joaquin Delta (Delta) can react with chlorine to form trihalomethanes (THMs) during the disinfection process. Isolation and characterization of them and quantitation of their THM formation potential (THMFP) is necessary for developing effective strategies to reduce their influxes in Delta waters and for removing them during drinking water treatment. In this study, organic C from two Delta soils was extracted using deionized H2O and four Na- or Ca-based electrolytes of varying electrical conductivity values. Extracts were filtered into particulate, colloidal, fine colloidal, and soluble organic C for quantitation and THMFP determination. Results suggested that <1.5% of soil organic C was electrolyte-extractable. The soluble organic C fraction from both soils dominated in quantity and THMFP. Electrolyte effects were cation dependent. Sodium-based electrolytes at either conductivity level did not significantly decrease extractable organic C (EOC) or THMFP compared with deionized H2O. In contrast, Ca-based electrolytes reduced EOC and THMFP by >50% even at 1 dS m'1. Further increase in Ca concentration did not significantly decrease EOC or THMFP. Most reduction in EOC and THMFP by Ca-based electrolytes occurred with the fractions other than the soluble organic C. Results suggested that under natural soil leaching and runoff conditions, the majority of THMFP are associated with organic C of <0.025 µm in diameter. Further molecular characterization of the fractions with high THMFP may help understand the nature of chlorine-reactive organic C from Delta soils.