Odors from New York City's sewage treatment plants are controlled by activated carbon housed in 44 large towers, each holding about 11 tons of carbon. The carbons are impregnated with NaOH or with KOH, or are unimpregnated but continuously injected with ammonia gas.
A study is now under way in our laboratory to monitor the progressive exhaustion of these carbon beds and to predict their useful lifetimes. The monitoring tests include a measure of the residual breakthrough capacity of the carbon for hydrogen sulfide, and an estimate of the remaining capacity for physical adsorption of other gases. For the caustic-impregnated carbons, the tests include a measure of the actual life-extension that can be realized by the retrofit of ammonia injection without interrupting the operation of the carbon vessels. A procedure to predict the results of in situ regeneration is described.