AWWA WQTC69286

This paper describes research into S₂O₃^2- oxidation bychlorine. Free chlorine was used as a pretreatment method to remove S₂O₃^2- from groundwater in Redlands, California. Chlorination in the form of hypochlorous acid(HOCl) and hypochlorite ion (OCl^-) was used to oxidize S₂O₃^2- to sulfate prior totreatment with tailored granular activated carbon (TGAC). Thiosulfate, RSS, was seen tocompete with ClO₄^- for adsorption sites on the TGAC. Experiments were first conductedsynthetically using deionized distilled (DI) water spiked with different concentration ofClO₄^-, S₂O₃^2- and chlorine depicting a variety of treatment conditions. Conditions includeconcentrations of 1 and 0.5 mg/L ClO₄^- and 1, 0.5 and 0.1 mg/L of S₂O₃^2-. Theseexperiments were carried out as pseudo reactions where free chlorine was in excess.Redlands groundwater was also spiked with S₂O₃^2-, the same concentration asbackground ClO₄^- concentration that is found in the groundwater. Results showed that DIwater spiked with only 1 mg/L ClO₄^- broke through at 15,000 bed volumes, while DIwater spiked with both 1 mg/L S₂O₃^2- and 1 mg/L ClO₄^- broke through at 8,000 bedvolumes, representing a 47% capacity reduction. Moreover, deionized distilled water thatwas spiked with 1 mg/L ClO₄^- and just a mere 0.1 mg/L S₂O₃^2- 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/LClO₄^- and 0.1 mg/L S₂O₃^2-; and in this case, ClO₄^- broke through at 12,000 bed volumes.This indicates that chlorine oxidation of S₂O₃^2- increased the TGAC capacity to removeClO₄^- from 63% to over 80%. As follow-up, Redlands groundwater that contained30 µg/L ClO₄^- was spiked with 40 µg/L S₂O₃^2-, plus the 0.25 mg/L of HOCl. This RSSCTexhibited no difference for ClO₄^- breakthrough between the RSSCT that was spiked,30,000 bed volumes, and the RSSCT that had no S₂O₃^2- present, 31,000 bed volumes.Significant difference in bed volumes to breakthrough was however observed whenS₂O₃^2- was more than 10 times greater than the ClO₄^- concentration. The TGAC capacityto remove ClO₄^- decreased to 17% and 50% when S₂O₃^2- concentration was 250µg/L and1mg/L respectively. Results to date suggest that S₂O<sub>3<

Product Details

Edition:

Vol. - No.

Published:

11/01/2008

Number of Pages:

15

File Size:

1 file , 810 KB