INHIBITION OF PERCHLORATE ADSORPTION ON TO TAILORED GRANULAR ACTIVATED CARBON BY REDUCED SULFUR SPECIES: THIOSULFATE

摘要

The present study was designed to evaluate the effects of reduced sulfur species on the adsorption of perchlorate on tailored granular activated carbon (TGAC); initial experiments focused on thiosulfate. Previous studies using Rapid Small Scale Column tests (RSSCT) showed that perchlorate broke through at 30,000-35,000 bed volumes (BV) when quaternary ammonium surfactants were preloaded onto activated carbon. These tests used groundwater, with 50-60 ppb perchlorate. However, when pilot tests were conducted, breakthrough occurred at 17,000-20,000 BV. It was hypothesized that intermediate-reduced sulfur species, found in the groundwater, were not fully oxidized before entering the treatment system; and they competed with perchlorate for adsorption sites on the TGAC. To test this hypothesis, experiments were conducted using RSSCTs. Deionized distilled water was spiked with 1,000 ppb perchlorate and 1,000 ppb thiosulfate. These experiments showed that thiosulfate caused a competition effect. The control experiment, which had 1,000 ppb of perchlorate but no thiosulfate, showed breakthrough starting at 15,300 BV. With the concentration of thiosulfate being the same as the perchlorate concentration, breakthrough started at 8,000 BV. These experiments reveal that thiosulfate competes with perchlorate for adsorption sites even at a 1:1 mass ratio.