Recapturing and decomposing methyl bromide in fumigation effluents

Abstract

Methyl bromide (CH 3Br) is an important fumigant for treating agricultural produce and structures, but emissions during fumigation may contribute to stratospheric ozone depletion and impose hazardous effects on human health. A method is described that uses activated carbon to recover CH 3Br from air streams, and sodium thiosulfate (Na 2S 2O 3) to degrade the recovered CH 3Br to relatively nontoxic Br −. Degradation of carbon-adsorbed CH 3Br in Na 2S 2O 3 solution was completed in less than 9 h at room temperature (20°C). In simulated pilot experiments, two coconut-based activated carbons trapped CH 3Br up to 15% of the weight of carbon, while an excessive molar amount of Na 2S 2O 3 in solution completely converted the CH 3Br to Brovernight. The reaction products, Br − and sodium methylthiosulfate (NaCH 3S 2O 3), are freely soluble in water, non-corrosive, non-volatile and low in toxicity. Solutions containing 1% of these products may be disposed of directly into the drain according to current environmental regulations, which allows the spent carbon to be regenerated simply by rinsing in water and drying at a moderate temperature. Carbons recycled in this manner showed similar capacities in adsorbing CH 3Br as the unused carbons. The reported approach is environmentally-compatible and low in cost, and is especially suitable for on-site application.