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While most spent activated carbon (SAC) used in POU/POE systems is disposed of, regeneration and reactivation are viable options for industrial facilities and municipalities looking to reduce their carbon footprints or to save money. The terms regeneration and reactivation are often used interchangeably, but in truth they are very different processes. Basically, regeneration involves removing contaminants from carbon without destroying them. In contrast, reactivation utilizes a high temperature process in a controlled environment to destroy all contaminants. The reactivation process effectively redevelops the pore structure within the carbon to enhance its ability to continue in operation.
According to Leo P. Zappa, industry manager – municipal for Calgon Carbon Corporation, reactivation is the only way to ensure that all the contaminants absorbed by the SAC have been completely destroyed. “Reactivation is a complete destruction and [an] adsorption capacity recovery process,” Zappa explains. “The optimization of pore structures during reactivation also yields a more usable reactivated carbon product.”
Robert Potwora, technical director for Carbon Resources LLC, also favors reactivation over regeneration. “Reactivation allows up to 95 percent of the virgin activated carbon capacity to be restored,” he says. “The activated carbon can almost be reactivated indefinitely.” And an obvious benefit, Potwora adds, is that reactivation prevents SAC from ending up in landfills.
Benefits of reactivation
Reactivation of SAC presents invaluable environmental benefits over regeneration or disposal. Reactivation eliminates a waste that could otherwise be a long-term environmental liability if it is disposed of in a landfill. Another benefit, according to Zappa, is that reactivation creates a usable product from a waste material. “The usable product is considered a ‘green’ product since reactivation produces about 20 percent of the greenhouse gases as making virgin activated carbon,” he explains.
Reactivation can also provide significant cost savings. For example, a process known as “custom reactivation” has been introduced in recent years. With custom reactivation, a municipality sends its SAC to a reactivation facility where it is reactivated, blended with a small amount of virgin carbon and returned for reinstallation and continued use. “In these cases,” Zappa says, “the custom reactivated product is returned to the original customer at a significant cost savings when compared to the costs of buying virgin activated carbon and disposing of the spent [carbon] in a landfill or incinerator.”
Additionally, some facilities that use reactivated carbon may qualify to receive environmental credits issued by regulatory agencies for waste minimization.
Unfortunately, a water treatment dealer that serves the residential and commercial markets would have to have a very high volume of SAC for reactivation to make sense economically. “We really don’t have a great recycling or reuse option at this point,” says Dennis Roberts, director North America for Filtrex Corporation. “Most of this stuff just ends up in the landfill.” However, there are options available for dealers who sell activated carbon but still want to go green.
The traditional charring method of activating virgin carbon, commonly known as the open pit method, involves the release of greenhouse gases (GHGs) — such as methane, CO2 and a wide range of organic vapors — into the atmosphere. In fact, one ton of granulated activated carbon produced by the open pit method emits more than 8,000 pounds of CO2.
According to Roberts, a new charring method has been developed that captures the GHGs before they are released into the environment. In this process, the gas is captured to fire a boiler, which creates steam for a kiln. The steam is then harnessed in a steam engine that creates electricity. “[The process] makes the plant self-sufficient from a power standpoint,” explains Roberts.