Perchlorate removal via iron-preloaded GAC and borohydride regeneration

Tailored granular activated carbon (GAC) can reduce groundwater perchlorate levels from 60-80 μg/L to below detection. Specifically, rapid small-scale column tests, also called RSSCTs, showed that by preloading GAC with iron-oxalic acid, the GAC adsorption capacity could be improved up to 42%. When the preloaded GAC became saturated with perchlorate, 65-74% of the GAC's original adsorption capacity could be restored by chemically regenerating the GAC with sodium borohydride. This chemical regeneration could be achieved with the use of a small fraction of the water that had been processed during the water treatment cycle. The waste stream from chemical regeneration contained concentrated perchlorate levels as high as 7,000-15,000 μg/L. With this approach, the simulations described in this article indicated that when two tailored GAC beds were operated in series with a 40-min empty-bed contact time, they could provide water treatment service for 60-75 days during the first operations cycle; following chemical regeneration, the GAC beds could provide about an additional 30-40 days of water service for several successive treatment and regeneration cycles.