Dehalogenation of trihalomethanes in drinking water on Pd-Fe bimetallic surface

Trihalomethanes (THMs), water disinfection-byproducts, in potable water are of public health concern. Degradation of THMs by palladium-treated iron granules (Pd-Fedegrees) has been studied in a flowthrough column system. Laboratory-scale columns of approximately 628 cm(2) were loaded with Torpedo and Silica sands plus anthracite mixed with Pd-Fedegrees at a 10:1 ratio (w/w). The column setup in regard to composition and flow rate was aimed at simulating real rapid-sand filtration conditions. A single passage of THM samples with concentration range 50-200 ppb through the column resulted in greater than 90% disappearance of parent THMs with one or more bromine atoms (CHCl2Br, CHClBr2, CHBr3), but the degradation of CHCl3 occurred much more slowly. Only 4-11% of the degradation of THMs resulted in the formation of dihalogenated products, indicating that they are degraded to form products other than dihalomethanes. The dehalogenation of brominated THMs decreased by less than 6% when the column temperature was lowered from 23degrees to 4degreesC. Within the pH range of 4.0-6.5, there was little change in the dehalogenation, however the substantial decrease in the degradation occurred at pH 10. The Pd-Fedegrees also contributed significantly to the degradation of other halogenated and some nonhalogenated volatile compounds. Dehalogenation efficiency of the column was decreased by about 38% following 3 weeks of daily operation but could be regenerated with simple acid washing. No measurable Pd and iron concentrations (<300 ppb) were detected in the column effluents over a period of 3-4 weeks, indicating that the Pd-Feo is fairly stable in the column. (C) 2003 Society of Chemical Industry.