Granular Activated Carbon Sorption as a Load Equalization Mechanism in Operation of Air Pollution Control Devices

Abstract

Transient periods of unsteady loading pose a challenge in design and operation of bioreactors for air pollution control. As a potential means of overcoming some of these challenges, a systematic study of granular activated carbon (GAC) sorption was conducted to further evaluate its potential as a load equalization mechanism for unsteady loading of volatile organic carbons (VOCs). GAC columns were experimentally tested under dynamic loading conditions involving variations in contaminant concentrations, gas flow rates, and relative humidity. Toluene was used as model VOC, and BPL 4x6 mesh GAC was used as a model adsorbent. The research was divided into four tasks. These involved evaluation of GAC load equalization for transient loading conditions involving: (1) intermittent toluene loading with contaminant non-loading intervals occurring for relatively long periods of time (e.g., two to seven days); (2) intermittent toluene loading with high relative humidity gas streams; (3) loading condition characterized by a single concentration spike and a series of concentration spikes of various intensity and duration; and (4) intermittent loading with turndown of air flow rates during pollutant non-loading periods. Collectively, experimental testing and results from simulations performed using a pore and surface diffusion model (PSDM) demonstrated that GAC columns have the potential to serve as an effective strategy in management of a wide variety of transient loading conditions. GAC columns can provide a more even and attenuated loading concentration when dynamically varying concentration spikes in influent occur and provide supplemental feed during intervals when no contaminants would otherwise be supplied to the biofilter. Such performance proved to be viable even in conditions of high gas humidity and intermittently reduced flow rates. Overall, GAC sorption may prove practical application in alleviating adverse impacts of starvation conditions in bioreactors, dampening spikes in contaminant concentrations to prevent reduction in treatment efficiency, and in reducing costs due to reduced size requirement for the downstream air pollution control device.