Granular Activated Carbon Adsorption For Groundwater Decontamination

Adsorption is a process by which a solute, a liquid organic pollutant in this case, accumulates or concentrates on the internal and external surface of a solid, such as granular activated carbon.

Among all groundwater decontamination technologies available and feasible, granular activated carbon (GAC) adsorption is the second most popular process adopted by practicing environmental engineers. In the United States, GAC has been applied in 27% of the corrective actions requiring VOCs removal from contaminated groundwater [4].

GAC adsorbers are usually packed in similar manner to sand filters, except that GAC firms the media instead of sand.

In process operation, there are two types of applications. When the GAC adsorbers are used for groundwater treatment, they are "liquid phase GAC adsorbers." When the GAC adsorbers are used for air stream purification, they are "gas phase GAC adsorbers" [37,48-50].

The GAC adsorbers are very effective for VOCs and SVOCs reduction. Because GAC costs are high, GAC adsorbers are usually used for final polishing of either the water stream or air stream. Periodically, the spent GAC must be either disposed of properly, or regenerated for reuse. Regeneration of GAC for desorption of VOCs and SVOCs can be carried out either in situ, ex situ, onsite, or offsite. Without regeneration, the spent GAC, which contains VOCs and SVOCs, may be classified as hazardous waste.

The gas phase GAC adsorbers adsorption efficiency can be significantly increased if the humidity of the contaminated air stream can be reduced.

The most cost-effective and popular GAC regeneration process the is low-temperature thermal desorption process discussed earlier. The most efficient GAC regeneration process is high-temperature pyrolysis (in the absence of oxygen), discussed earlier. A complete onsite GAC regeneration process has been developed by Wangs et al. [37].

Purus, Inc., San Jose, CA, has developed a similar air stripping-adsorption system (Fig. 12) for groundwater decontamination. The difference between Wang's system [37] and the Purus system (Fig. 12) is that the former uses GAC, while the latter uses polymeric adsorbent. A detailed operational diagram of a polymeric adsorption system is shown in Fig. 13.

OEJUtMR TO STAC*

OEJUtMR TO STAC*

30Ö. VAPOR OHOUWOWATER INLET INLET

Figure 12 Combined air stripping and polymeric adsorption system for groundwater decontamination. (Courtesy of USEPA.)

30Ö. VAPOR OHOUWOWATER INLET INLET

Figure 12 Combined air stripping and polymeric adsorption system for groundwater decontamination. (Courtesy of USEPA.)

Adsorption Apparatus Image
Figure 13 Polymeric adsorption system for groundwater decontamination. (Courtesy of USEPA.)

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