AWWA ACE93143

Thermal regenerations were conducted on a spent granular activated carbon (GAC) that had served in a water treatment plant for about four years, and contained 1.8 percent calcium. Oxidation was conducted in steam, CO2, or steam plus CO2 at 650-950C. As described in an earlier article, when both steam and CO2 were employed together, the regenerated product's pore structure maintained greater micropore volume at high temperatures (greater than 800C) than at low temperatures (less than 750C). The work herein has linked this distinction to differences in reaction rate limitations: at high temperatures, with both oxidants employed together, the water-gas shift reaction (H2O + CO = H2 + CO2) limited overall rate, whereas at low temperatures, the C(O) gasification step limited overall rate. The CO2 created by the water gas shift reaction served as the primary oxidant. Although steam served only as a secondary oxidant, its presence also facilitated more extensive oxidant transfer to the carbon surface.