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This paper describes research into Ssub2/subOsub3/subsup2-/sup oxidation bychlorine. Free chlorine was used as a pretreatment method to remove Ssub2/subOsub3/subsup2-/sup from groundwater in Redlands, California. Chlorination in the form of hypochlorous acid(HOCl) and hypochlorite ion (OClsup-/sup) was used to oxidize Ssub2/subOsub3/subsup2-/sup to sulfate prior totreatment with tailored granular activated carbon (TGAC). Thiosulfate, RSS, was seen tocompete with ClOsub4/subsup-/sup for adsorption sites on the TGAC. Experiments were first conductedsynthetically using deionized distilled (DI) water spiked with different concentration ofClOsub4/subsup-/sup, Ssub2/subOsub3/subsup2-/sup and chlorine depicting a variety of treatment conditions. Conditions includeconcentrations of 1 and 0.5 mg/L ClOsub4/subsup-/sup and 1, 0.5 and 0.1 mg/L of Ssub2/subOsub3/subsup2-/sup. Theseexperiments were carried out as pseudo reactions where free chlorine was in excess.Redlands groundwater was also spiked with Ssub2/subOsub3/subsup2-/sup, the same concentration asbackground ClOsub4/subsup-/sup concentration that is found in the groundwater. Results showed that DIwater spiked with only 1 mg/L ClOsub4/subsup-/sup broke through at 15,000 bed volumes, while DIwater spiked with both 1 mg/L Ssub2/subOsub3/subsup2-/sup and 1 mg/L ClOsub4/subsup-/sup broke through at 8,000 bedvolumes, representing a 47% capacity reduction. Moreover, deionized distilled water thatwas spiked with 1 mg/L ClOsub4/subsup-/sup and just a mere 0.1 mg/L Ssub2/subOsub3/subsup2-/sup showed breakthrough at9,400 bed volumes, representing a 37% reduction. Next, the authors also pre-chlorinatedDI water with 0.25mg/L of free chlorine as HOCl, while this water also contained 1 mg/LClOsub4/subsup-/sup and 0.1 mg/L Ssub2/subOsub3/subsup2-/sup; and in this case, ClOsub4/subsup-/sup broke through at 12,000 bed volumes.This indicates that chlorine oxidation of Ssub2/subOsub3/subsup2-/sup increased the TGAC capacity to removeClOsub4/subsup-/sup from 63% to over 80%. As follow-up, Redlands groundwater that contained30 g/L ClOsub4/subsup-/sup was spiked with 40 g/L Ssub2/subOsub3/subsup2-/sup, plus the 0.25 mg/L of HOCl. This RSSCTexhibited no difference for ClOsub4/subsup-/sup breakthrough between the RSSCT that was spiked,30,000 bed volumes, and the RSSCT that had no Ssub2/subOsub3/subsup2-/sup present, 31,000 bed volumes.Significant difference in bed volumes to breakthrough was however observed whenSsub2/subOsub3/subsup2-/sup was more than 10 times greater than the ClOsub4/subsup-/sup concentration. The TGAC capacityto remove ClOsub4/subsup-/sup decreased to 17% and 50% when Ssub2/subOsub3/subsup2-/sup concentration was 250g/L and1mg/L respectively. Results to date suggest that Ssub2/subOsub3

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Edition: Vol. - No. Published: 11/01/2008 Number of Pages: 15File Size: 1 file , 810 KB