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FIG. 9.17.12 Optimum carbon contact time. (Reprinted from E.K. Nyer, 1992, Groundwater treatment technology, 2d ed., New York: Van Nostrand Reinhold.)

When the adsorption capacity of the carbon is exhausted, the spent carbon can either be disposed of at a disposal site, regenerated, or reactivated for reuse. Offsite disposal at a landfill or an incinerator is the preferred method when the amount of carbon is small. For disposal at a landfill, testing and classifying the spent carbon are necessary to ensure that all regulations for disposal are being met. Spent carbon may be considered hazardous waste and may need to be disposed of at a hazardous waste landfill or burned at an incinerator where both the carbon and the hazardous waste are destroyed.

If the amount of spent carbon is large or the user has access to an offsite, multiuser facility, regeneration or reactivation for reuse may be the preferred solution. Regeneration exposes the spent carbon to steam to desorb the contaminants. Reactivation is conducted in electrical or multiple-heart furnaces where the temperature is high enough (up to 1800°F) to thermally destroy the contaminants and reactivate the carbon. Regeneration and reactivation can incur a 10 to 20% material loss and can change the adsorptive properties of the virgin grade material.

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