• AWWA WQTC69286

AWWA WQTC69286

Oxidation of Reduced Sulfur Specie (Thiosulfate) by Free Chlorine to Increase the Bed Life of Tailored GAC to Remove Perchlorate

American Water Works Association , 11/01/2008

Publisher: AWWA

File Format: PDF

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This paper describes research into S2O32- oxidation by chlorine. Free chlorine was used as a pretreatment method to remove S2O32- from groundwater in Redlands, California. Chlorination in the form of hypochlorous acid (HOCl) and hypochlorite ion (OCl-) was used to oxidize S2O32- to sulfate prior to treatment with tailored granular activated carbon (TGAC). Thiosulfate, RSS, was seen to compete with ClO4 - for adsorption sites on the TGAC. Experiments were first conducted synthetically using deionized distilled (DI) water spiked with different concentration of ClO4 -, S2O32- and chlorine depicting a variety of treatment conditions. Conditions include concentrations of 1 and 0.5 mg/L ClO4 - and 1, 0.5 and 0.1 mg/L of S2O32-. These experiments were carried out as pseudo reactions where free chlorine was in excess. Redlands groundwater was also spiked with S2O32-, the same concentration as background ClO4 - concentration that is found in the groundwater. Results showed that DI water spiked with only 1 mg/L ClO4 - broke through at 15,000 bed volumes, while DI water spiked with both 1 mg/L S2O32- and 1 mg/L ClO4 - broke through at 8,000 bed volumes, representing a 47% capacity reduction. Moreover, deionized distilled water that was spiked with 1 mg/L ClO4 - and just a mere 0.1 mg/L S2O32- showed breakthrough at 9,400 bed volumes, representing a 37% reduction. Next, the authors also pre-chlorinated DI water with 0.25mg/L of free chlorine as HOCl, while this water also contained 1 mg/L ClO4 - and 0.1 mg/L S2O32-; and in this case, ClO4 - broke through at 12,000 bed volumes. This indicates that chlorine oxidation of S2O32- increased the TGAC capacity to remove ClO4 - from 63% to over 80%. As follow-up, Redlands groundwater that contained 30 µg/L ClO4 - was spiked with 40 µg/L S2O32-, plus the 0.25 mg/L of HOCl. This RSSCT exhibited no difference for ClO4 - breakthrough between the RSSCT that was spiked, 30,000 bed volumes, and the RSSCT that had no S2O32- present, 31,000 bed volumes. Significant difference in bed volumes to breakthrough was however observed when S2O32- was more than 10 times greater than the ClO4 - concentration. The TGAC capacity to remove ClO4 - decreased to 17% and 50% when S2O32- concentration was 250µg/L and 1mg/L respectively. Results to date suggest that S2O3<

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