Capture of methyl bromide emissions with activated carbon following the fumigation of a small building contaminated with a Bacillus anthracis spore simulant

Abstract

A wide-area Bacillus anthracis spore contamination incident will present immense challenges related to decontamination capacity. For this reason, fumigation with methyl bromide (MeBr) has been proposed as a potential remediation option. Although a few bench-scale laboratory studies have been conducted to evaluate activated carbon for the capture of MeBr, these studies were conducted at conditions replicating commodity fumigation using relatively low MeBr concentrations, temperatures, and/or relative humidity (RH) levels. The more rigorous MeBr fumigation requirements to fully inactivate B. anthracis spores are much more of a challenge for an activated carbon system (ACS) to capture MeBr, and warrant their own investigation. Further, while the aforementioned studies have shown activated carbon to be a possible option for the capture of MeBr in gas streams, these tests were conducted at laboratory bench scale, and thus lack operational perspective and data. Thus, we present for the first time the results of a full-scale study to evaluate an ACS employed for the capture of MeBr at conditions that would be used for decontaminating a building structure contaminated with B. anthracis spores. Airflow rate, temperature, RH, and MeBr levels were measured within the ACS during its operation. Despite the relatively high humidity, temperature, and MeBr levels, the MeBr capture efficiency of the ACS was demonstrated to be more than 99%. The concentration of MeBr exhausted from the structure was reduced from 41,000 to 136 ppmv in 3.5 hr, corresponding to an overall atmospheric emission rate of less than 2 kg. The practical adsorption rate of the ACS was determined to be 4.83 kg MeBr/100 kg carbon. The information and data presented here will facilitate future use of this technology when fumigating with MeBr.Implications: This investigation presents data to characterize the performance of a full-scale activated carbon system (ACS) for the capture of methyl bromide (MeBr) used for the decontamination (fumigation) of a small building contaminated with Bacillus anthracis spores. The data presented on the ACS operation and performance characteristics such as adsorption capacity, breakthrough times, and removal efficiency of MeBr will facilitate future use of this technology when fumigating with MeBr. Efficient capture of MeBr following fumigation (whether for anthrax inactivation or agricultural commodities) will reduce emissions to the atmosphere, thereby lowering potential human exposure as well as mitigating depletion of stratospheric ozone.