from entering a facility through the ventilation system and to decontaminate a building after an attack. Carbon adsorbents and molecular sieves (zeolites) are conventional adsorbents; their effectiveness for specific contaminants must be determined and documented. Special adsorbents may need to be developed for hard-to-remove contaminants. Absorption techniques may be used for removing gaseous contaminants from air in conventional scrubbers/packed columns using appropriate solvents. Reactive packed-sorbent (reagent) beds may also be used for removing contaminants from water or air by chemical reaction/neutralization. A need exists to identify appropriate contaminant/sorbent combinations and possible interference factors, e.g., humidity. Some dissolved contaminants may be removed from water with selective membrane filtration; however, membranes require a concentration gradient that may not be available for rapidly dispersing dilute contaminants. Membrane techniques based on preferential diffusion of contaminants will thus be highly specialized for specific contaminants. Microporous membranes may, however, be combined with an appropriate reactive absorbent/adsorbent for the removal of contaminants by facilitated transport.8 In such an application the membrane simply provides a large surface area for effective and efficient removal of dilute contaminants.
Another area of need is for better methods to contain and neutralize clouds of airborne toxic materials such as ammonia, chlorine, hydrogen fluoride, hydrogen sulfide, and sulfur dioxide. Work to date has shown that large quantities of water must be sprayed in the air to “knock down” any significant portion of such airborne chemical clouds (Dandrieux et al., 2001; Petersen and Diener, 1990). The use of reactive foams in existing fire-suppression systems to counter chemical and biological agents should also be explored.
Recommendation 4.5: Universities, companies, and federal agencies should work together to improve existing technologies and develop new ones for removing chemical contaminants from air and water. Research is especially needed on filter systems capable of treating large volumes, novel media that can help prevent toxic materials from entering facilities through ventilation systems, and methods to contain and neutralize clouds of airborne toxic materials.
The problem of decontamination has been studied for many years at DOD, the national laboratories, and universities. While new approaches may be found in areas already being explored, it is possible that better solutions could lie in
A facilitated transport membrane contains a complexing agent that exhibits an affinity toward one species in a mixture. A reversible interaction between the two selectively enhances the solubility and transport rate of the one species relative to others that do not interact. This transport mechanism can achieve higher separation factors than simple (passive) transport, where species diffuse down a concentration gradient but have little or no interaction with the membrane.