Impact of Acidic Conditions and High Sulfate Concentrations on Mtbe Mass Transport and Mass Transfer in Gac

Abstract

Sodium persulfate (SP) oxidation regeneration of granular activated carbon (GAC) is a developing technology. During SP regeneration of GAC, aggressive oxidative conditions lead to high acidity and the accumulation of sodium persulfate residuals in the GAC. In a previous investigation, this condition was attributed as the cause of a decline in MTBE sorption capacity by limiting MTBE diffusion onto GAC and by physical blockage of sorption sites after SP regeneration (Hutson et. al, 2012). This proposed conceptual model was evaluated in this study through MTBE desorption and diffusion experiments, on MTBE-pre-amended GAC. The accumulation of sulfate was primarily responsible for the blockage of sorption sites and hindered MTBE desorption (i.e. desorption + diffusion) in this study. Desorption decline was amplified equally under strong and weak acid condition, indicating pH played a less significant role in limiting MTBE desorption than sulfate pore blockage. Raising the pH in acid-amended reactors and washing with DIW resulted in the removal of residual sulfate and improved MTBE desorption from post-treatment GAC. This indicates the mechanisms responsible for limiting MTBE desorption are partially reversible. These results can be used to optimize future studies involving thermally-activated SP-regeneration of GAC.