|Li, Yuanging - Stanford University|
|Liu, Chong - Stanford University|
|Yi, Cui - Stanford University|
|Olver, Ryan - University Of California|
|Zilberman, David - University Of California|
|Mitch, William - Stanford University|
Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2016
Publication Date: 9/9/2016
Citation: Li, Y., Liu, C., Yi, C., Walse, S.S., Olver, R., Zilberman, D., Mitch, W. 2016. Development of an activated carbon-based electrode for the capture and rapid electrolytic reductive debromination of methyl bromide from post-harvest fumigations. Environmental Science and Technology. 50(20):11200-11208. doi: 10.1021/acs.est6b03489.
Interpretive Summary: Methyl bromide (MB) is a postharvest fumigant that is highly effective against insect and microorganism pests. MB is also an atmospheric source of reactive bromine gases, which deplete stratospheric ozone. Anthropogenic utilization of MB is regulated by international agreement under the Montreal Protocol. In instances where postharvest chamber fumigations are permitted, contribution(s) to ozone depletion can be minimized, or eliminated, by removing MB from the ventilation effluent via activated carbon sorbent. As part of a larger research project to optimize activated carbons for this use, we conducted experiments to determine how MB was destroyed by electrolysis when we used a novel cathode, comprised of small activated carbon particles coated onto a carbon cloth. The cathode achieved 99% reductive debromination of MB sorbed at 30% by weight to the carbon within 15 h at -1 V applied potential vs. standard hydrogen electrode, a timescale and efficiency suitable for the logistical and infrastructural demands of routinely conducting postharvest fumigations. The cathode exhibited stable performance over 50 MB capture and destruction cycles. Initial cost estimates indicate that this technique could treat MB fumes at $5/kg, roughly one-third the cost of current alternatives. Finding cost-effective techniques for eliminating emissions into the atmosphere, such as the one described in this study, may help ensure that the continued use of MB has minimal environmental impact.
Technical Abstract: Due to concerns surrounding its ozone depletion potential, there is a need for technologies to capture and destroy methyl bromide (CH3Br) emissions from post-harvest fumigations applied to control agricultural pests. Previously we described a system in which CH3Br fumes vented from fumigation chambers could be captured by granular activated carbon (GAC). The GAC was converted to a cathode by submergence in a high ionic strength solution and connection to the electrical grid, resulting in reductive debromination of the sorbed CH3Br. The GAC bed was drained and dried for reuse to capture and destroy CH3Br fumes from the next fumigation. However, the loose GAC particles and slow kinetics of this primitive electrode necessitated improvements. Here we report the development of a cathode containing a thin layer of small GAC particles coating carbon cloth as a current distributor. Combining the high sorption potential of GAC for CH3Br with the conductivity of the carbon cloth current distributor, the cathode significantly lowered the full-cell resistance and achieved 99% reductive debromination of CH3Br sorbed at 30% by weight to the GAC within 15 h at -1 V applied potential vs. standard hydrogen electrode, a timescale and efficiency suitable for postharvest fumigations. The cathode exhibited stable performance over 50 CH3Br capture and destruction cycles. Initial cost estimates indicate that this technique could treat CH3Br fumes at $5/kg, roughly one-third the cost of current alternatives.