MeBr Recapture System Up and Running

Methyl bromide has been an extremely useful fumigant for disinfesting perishable and durable commodities prior to sale either in the domestic market or to other countries. For years, it was the backbone of the U.S. fight against the introduction of unwanted pests to U.S. shores or exporting unwanted pests to other countries on our commodities. The use of methyl bromide for quarantine and fumigation purposes has been largely responsible for our ability to export commodities to partner nations. It has also formed the basis for lifting export bans against quarantine insects in many countries around the globe. Methyl bromide will be taken off the market for use and production on January 1, 2005, in the United States, as set forth in the Montreal Protocol. However, commodities may be treated with methyl bromide as part of a quarantine or required fumigation of an importing country. It has been estimated that California alone would lose between $300 and $400 million in exports if methyl bromide is not available and without viable alternatives.

As a result, in 1995, James Leesch, Research Entomologist in the Agricultural Research Service (ARS) Horticultural Crops Research Laboratory in Fresno, California, began investigating the capture of methyl bromide on activated carbon, after commodity fumigation. Such an apparatus would greatly reduce the amount of methyl bromide released to the atmosphere. Research began in 1995 in collaboration with Gerhard F. Knapp of GFK Consulting, Ltd. in San Clemente, California, a private cooperator. Great Lakes Chemical Corporation, led by David McAllister, also entered the cooperative research and development agreement in order to transfer the technology into practical uses within the agricultural community. Using such a system, however, is contingent on being able to use methyl bromide. According to the Environmental Protection Agency, uses of methyl bromide for quarantine and preshipment applications are already exempt from control under Article 2H of the Montreal Protocol.

With the exemption allowed, reducing the emission of methyl bromide to the atmosphere was in order. Essentially, after a commodity has been fumigated in a sealed chamber, the air in the chamber is passed through a carbon filter which adsorbs much of the methyl bromide. The carbon filter is sealed and removed to a treatment facility which thermally removes the trapped methyl bromide. "The thermal processing eliminates secondary waste," says Knapp.

Research has identified the most favorable type of carbon for the adsorption of methyl bromide as well as the best conditions for the adsorption. Activated carbon derived from coconut shells has proven to sorb more methyl bromide than carbon derived from either peat or coal. The adsorption of methyl bromide has been found to be inversely proportional to both the temperature and humidity of the gas stream containing the methyl bromide. Typical loading of the carbon with methyl bromide runs from 5 to 10 pounds of carbon for each pound of methyl bromide injected into the commodity fumigation chamber.

Two facilities currently use the methyl bromide recapture system. In the spring of 1999, Great Lakes Chemical Corporation, GFK Consulting, Ltd., and USDA, in a joint venture, installed the new methyl bromide recapture system in place at the Dallas-Fort Worth International Airport (DFW) in Texas. A similar system has been operating at Well-Pict, Inc., in Watsonville, California, since May 2001.

The goal for authorities at DFW was to increase cargo traffic and attract South American import products such as cut flowers. Upon arrival in the United.States, commodities infested with quarantine pests must be fumigated with methyl bromide to prevent the entry of unwanted pests. However, local air regulations at DFW prohibit the release of more than 1.1 pound per hour of methyl bromide. The recapture system vastly reduces the amount of methyl bromide released to the atmosphere—95 percent of recoverable methyl bromide is captured by the carbon. "The unit has been in operation for 2 years and is working well," says McAllister. "In terms of cost, it adds about one-half cent per pound of commodity being fumigated."

At Well-Pict, strawberries and raspberries are fumigated before export to the Far East via air freight from San Francisco Bay Area airports. The Well-Pict facility has seven fumigation chambers. An official source test, designed to demonstrate the recapture efficiency of the methyl bromide recapture system, was carried out June 6, 2001. The new recapture system allowed an average of only 0.14 pound of methyl bromide emitted to the atmosphere for every 1 pound of methyl bromide injected into the fumigation chamber. "We estimate this to be an 80 percent reduction from current practice," says Knapp. "By using the recapture system, the maximum concentration emitted to the atmosphere was reduced from 10,000 parts per million (ppm) methyl bromide to less than 500 ppm." Testing of the unit took 6 weeks and approval was given by the Monterey Bay Unified Air Pollution Control District (MBUAPCD) and the Santa Cruz County Agricultural Commissioner for full operation in July 2001.

By using the recapture system, the control district is expected to allow Well-Pict to ventilate four fumigation chambers per hour with a corresponding increase in the amount of fruit that can be processed and shipped in any one day. Jerry Steele of the control district is "excited about the possibility. This unit defines the best feasible control technology available." Steele anticipates final certified approval of the recapture system pending final results from the June source test. According to Steele, the California Occupational Safety and Health Agency's permitted exposure limit is 0.025 ppm for 8 hours of voluntary exposure. "This unit, which has a stack concentration of 5 ppm, probably emits less than 0.025 ppm by the time it goes out of the stack and back down to the ground," explains Steele.

The methyl bromide recapture system is designed to recapture about 95 percent of the methyl bromide that would otherwise be released into the atmosphere after fumigation without interfering with the normal time cycle of the fumigation. At the end of the fumigation exposure time, the atmosphere in the chamber, containing up to 96 ounces of methyl bromide per 1,000 ft³, is removed by the recapture system at a rate of 750 ft³ per minute through a bed of activated carbon. The air stream from the carbon bed contains less than 2 ounces of methyl bromide per 1,000 ft³. The DFW system is designed to ventilate enclosures up to 4,500 ft³ in 30 minutes or less.

David Moeller, Santa Cruz County Agricultural Commissioner, thinks "the recapture system demonstrates a good stewardship of methyl bromide by using the least amount of material most efficiently, thus minimizing the effect on the environment, public, and workers by reducing the amount of exposure." As the methyl bromide ban becomes reality, it is imperative to reduce the amount of methyl bromide that escapes to the atmosphere. This unit seems to do a more than adequate job.

Last Updated: January 17, 2002