Technology ▼ Solutions

Removing methyl bromide from shipping operationsThe deadline for the 1987 Mon treal Protocol’s phaseout by developed countries of methyl bromide (MeBr), a pesticide that depletes strato-spheric ozone, came and went in 2005. Although some countries have achieved a 100% phaseout, others, including the U.S., received exemp-tions for certain applications for which they claimed that no ef-fective or affordable replace-ment existed for the pesticide.

The focus of most of the ac-tions taken so far has been on the protocol’s targeted applica-tion of MeBr as a soil fumigant to kill insects and pathogens in agricultural fields. But the proto-col does not cover the pesticide’s uses for sterilizing structures and disinfecting goods before shipping. Such quarantine and pre-shipment applications ac-count for ~25% of the >45,000 t of MeBr consumed globally in 2000, ac-cording to the UN Environment Pro-gramme’s Methyl Bromide Technical Options Committee.

“There’s no limit as far as what can be emitted” by these shipping and quarantining operations, says Laurence Miller, an oceanographer and chemist at the U.S. Geological Survey. Miller and his colleagues ad-dressed this problem by developing a bioreactor to target these emis-sions, and they received a U.S. pat-ent on their design this spring.

They first described the bioreac-tor in a paper published in this jour-nal (Environ. Sci. Technol. 2003, 37, 1698–1704). The technology harness-es methylotrophic bacteria, which oxidize MeBr to get energy. The sys-tem is designed to recapture the pesticide from the waste-gas stream created after fumigation. The proof-of-concept, 10-L bioreactor success-fully removed 100% of the MeBr from an air stream.

“Here we have an ideal system,” Miller says. The bacteria “are gob-bling up and thriving on this thing that you want to get rid of.”

The global background levels of MeBr hover near 10 ppt, much low-er than the hundreds of parts per million pumped into shipping con-tainers for fumigation, according

to Miller. After ~36 h, the operators open a vent, start a fan, and blow the gas out into the atmosphere. Miller’s system calls for this gas to be passed through the bioreactor instead. Just one pass is required, he says.

The bioreactor is a tower contain-ing a liquid phosphate medium with cells of a bacterial strain called IMB-1, which Miller and his colleagues discovered in agricultural soils dur-ing past research. The tempera-ture is kept at 28 °C, and the waste stream is diluted with air to keep MeBr levels at <500 ppm, because the cells die at higher temperatures and concentrations. As the gas bub-bles up through the media, the bac-teria oxidize MeBr, creating CO2, hydrobromic acid, and water. Dur-ing the process, sodium hydroxide is added to the medium to neutral-ize the acid, and in the end, you get a “soup that has nutrients, sodium bromide, and live cells,” Miller says. “You can sterilize this with heat or

bleach, and it can go into a sanitary waste stream.”

Miller’s calculations show that re-moving MeBr from the fumigation exhaust of a standard shipping con-tainer in half an hour would require a 10,000-L bioreactor, which he envi-sions as a stainless-steel vat 12 ft tall and ~4 ft in diam.

Kelly Goodwin, a U.S. National Oceanographic and Atmospher-ic Administration researcher who has studied the biogeochemistry of

MeBr, points out that Miller’s system offers advantages over activated charcoal adsorption. The pesticide can be adsorbed on the charcoal and recovered, but the technique still creates emissions. Moreover, recycled MeBr does not have a market in the U.S., because it is not regis-tered as a fumigant.

Despite these advantages, Miller says that commercial in-terest in building a pilot system has been scant because of the lack of regulations for shipping

and quarantining uses of MeBr.That will change, according to an

official of the European Commis-sion’s Ozone Layer Protection Team. He explains that the parties to the Montreal Protocol focused on con-trolling emissions from soil fumiga-tion, which they deemed a critical use of MeBr, for two reasons. It was the biggest application area, forming ~75% of the pesticide’s consumption, and was easier to tackle, because countries with shipping fumigation operations would need to agree on alternatives, which include heat-ing, cooling, or irradiating the con-tainer. “But as critical-use phaseout is quite advanced, we should and will put more focus on [the shipping and quarantining] area and evaluate more possibilities to phase out [use of MeBr],” he says.

Meanwhile, at least two EU mem-bers have completely replaced MeBr for shipping uses. —PRACHI PATEL-PREDD

No regulations govern the use of methyl bromide for disinfecting goods in shipping containers.

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© 2006 American Chemical Society4540 ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / AUGUST 1, 2006