AWWA JAW57269

Granular activated carbon (GAC), although relatively expensive, is used extensively to treat drinking water in both the United States and the United Kingdom. However, GAC has a finite capacity to adsorb pollutants. Once this capacity is reached, it must be replaced with new GAC or the GAC must be recovered by thermal regeneration in a furnace and reused. This paper summarizes the most common GAC regeneration processes and the consequences of using these processes, including the likely cause of many phenomena observed by utility managers in water treated by regenerated GAC, e.g., high aluminum, high pH, and sulfide tastes and odors. Inorganic salts adsorbed during treatment catalyze oxidation reactions when the GAC is regenerated and lead to deterioration of its adsorbent properties. The authors found that acid-washing spent GAC adsorbents before thermal regeneration removes accumulated metals, particularly calcium, and significantly improves the GAC's adsorbent properties over thermal regeneration alone. This article should help water utility managers modify their GAC regeneration practices to combat the problems caused by adsorbed inorganic compounds. Includes 57 references, table, figure.