Effects of water vapor on activated carbon load equalization of gas phase toluene

Experimental testing and numerical simulations were conducted to assess the effects of elevated water vapor concentrations on the ability of granular activated carbon (GAC) to achieve load equalization of dynamically varying gas-phase toluene concentrations. Columns packed with Calgon BPL 4 x 6 mesh GAC were subjected to intermittent (8 h/day) toluene loading in air streams containing up to 90% relative humidity. Influent toluene concentrations ranged from 100 to 1000 ppm(v), and GAC column empty bed residence times ranged from 1.5 to 10 s. In comparison to load equalization performance achieved with dry air, high relative humidity improved load attenuation at high influent toluene concentration (e.g., 1000 ppm(v)) but decreased the degree of load attenuation at low influent toluene concentration (e.g., 100 ppm(v)). Model simulations conducted using a pore and surface diffusion model were in good general agreement with experimental observations. Collectively, results demonstrate that GAC columns can be of practical benefit as passively-operated load equalization devices even in the case of high relative humidity. Such systems may prove useful as a pre-treatment process for biofilters and other air pollution control devices that would otherwise be subjected to wide variation in contaminant loading.