Oxidation of reduced sulfur specie (Thiosulfate) by free chlorine to increase the bed life of tailored GAC to remove perchlorate

Judodine Patterson, Robert Parette, Fred Cannon

Abstract

In a previous study it was observed that reduced sulfur specie (RSS) specifically thiosulfate (S2O32-), competes with perchlorate (ClO4-) for adsorption sites on tailored granular activated carbon (TGAC). This decreases the TGAC ability to removed ClO4- from groundwater effectively. Oxidation is one process that can be used to oxidize these RSS to sulfate, which has been proven to not affect ClO4- adsorption with concentration has high as 250mg/L. The present paper describes research into S2O 32- oxidation by chlorine. Free chlorine was used as a pretreatment method to remove S2O32- from Redlands groundwater in California. Chlorination in the form of hypochlorous acid (HOCl) and hypochlorite ion (OCl-) was used to oxidize S 2O32- 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-, S2O 32- and chlorine depicting a variety of treatment conditions. Conditions include concentrations of 1 and 0.5 mg/L ClO 4- and 1, 0.5 and 0.1 mg/L of S2O 32-. 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 ClO 4- 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 S2O 32- 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 ClO 4- and 0.1 mg/L S2032-; and in this case, ClO4- broke through at 12,000 bed volumes. This indicates that chlorine oxidation of S2O 32- increased the TGAC capacity to remove ClO 4- from 63% to over 80%. As follow-up, Redlands, CA 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 S 2O32- concentration was 250μg/L and 1mg/L respectively. Results to date suggest that S2O3 2- competes with ClO4- for adsorption sites and chlorination can be a useful pre-treatment method for removing this reduced competitive sulfur specie from groundwater before it enters the TGAC column.

Original languageEnglish (US)
Title of host publicationWater Quality Technology Conference and Exposition 2008
Pages573-586
Number of pages14
Publication statusPublished - Dec 1 2008
EventWater Quality Technology Conference and Exposition 2008 - Cincinnati, OH, United States
Duration: Nov 16 2008Nov 20 2008

Publication series

NameWater Quality Technology Conference and Exposition 2008

Other

OtherWater Quality Technology Conference and Exposition 2008
CountryUnited States
CityCincinnati, OH
Period11/16/0811/20/08

    Fingerprint

All Science Journal Classification (ASJC) codes

  • Safety, Risk, Reliability and Quality
  • Water Science and Technology
  • Geography, Planning and Development

Cite this

Patterson, J., Parette, R., & Cannon, F. (2008). Oxidation of reduced sulfur specie (Thiosulfate) by free chlorine to increase the bed life of tailored GAC to remove perchlorate. In Water Quality Technology Conference and Exposition 2008 (pp. 573-586). (Water Quality Technology Conference and Exposition 2008).