Destruction of Methyl Bromide Sorbed to Activated Carbon by Thiosulfate or Electrolysis

Methyl bromide (CH₃Br) is widely used as a fumigant for postharvest and quarantine applications for agricultural products at port facilities due to the short treatment period required, but it is vented from fumigation chambers to the atmosphere after its use. Due to the potential contributions of CH₃Br to stratospheric ozone depletion, technologies for the capture and degradation of the CH₃Br are needed to enable its continued use. Although granular activated carbon (GAC) has been used for CH₃Br capture and thiosulfate has been used for destruction of CH₃Br in aqueous solution, this research explored techniques for direct destruction of CH₃Br sorbed to GAC. Submerging the GAC in an aqueous thiosulfate solution achieved debromination of CH₃Br while sorbed to the GAC, but it required molar concentrations of thiosulfate because of the high CH₃Br loading and produced substantial concentrations of methyl thiosulfate. Submergence of the GAC in water and use of the GAC as the cathode of an electrolysis unit also debrominated sorbed CH₃Br. The reaction appeared to involve a one-electron transfer, producing methyl radicals that incorporated into the GAC. Destruction rates increased with decreasing applied voltage down to ∼−1.2 V vs the standard hydrogen electrode. Cycling experiments conducted at −0.77 V indicated that >80% debromination of CH₃Br was achieved over ∼30 h with ∼100% Coulombic efficiency. Sorptive capacity and degradation efficiency were maintained over at least 3 cycles. Capture of CH₃Br fumes from fumigation chambers onto GAC, and electrolytic destruction of the sorbed CH₃Br could mitigate the negative impacts of CH₃Br usage pending the development of suitable replacement fumigants.