Treatment of Groundwater Containing Perchlorate Using Biological Fluidized Bed Reactors with GAC or Sand Media

Summary

Ammonium perchlorate has been used by NASA and the U.S. military as a component of solid rocket fuels. The formulation has a limited shelf life and replenishment is done by high pressure water flushing of old fuel followed by replacement with fresh supply as part of regularly scheduled maintenance activities. Past practice allowed the spent flush water to be discharged to the ground. As such, large volumes of ammonium perchlorate have been disposed in Nevada, California, Utah and likely other states since the 1950s.¹ Ammonium perchlorate is very soluble in water (i.e., 20 g dL⁻¹ at 25 °C) and dissociates completely to ammonium and perchlorate ions. The perchlorate ion is mobile in aqueous systems and can persist for decades under typical groundwater and surface water conditions due to its lack of reactivity with other compounds.¹

Some concentrations of perchlorate are believed to be detrimental to human health. At relatively high doses, perchlorate has been found to interfere with the thyroid's ability to produce hormones and regulate metabolism. Biochemical treatment is the technology that offers the most promise for economical cleanup of perchlorate contaminated waters and wastewaters. A laboratory pilot plant study was conducted to compare the perchlorate degradation performance of biological fluidized bed reactors (FBRs) containing either granular activated carbon (GAC) or sand as the fluid bed media. The performance of alternative electron donors (i.e., ethanol, methanol and a mixture of the two alcohols) was also evaluated. Results from the study showed GAC and sand based FBRs using ethanol as the electron donor both achieved significant perchlorate reduction with GAC media exhibiting superior stability. It was also found that methanol was not as effective as ethanol in promoting perchlorate reduction. However, an ethanol-methanol mixture was found to be as effective an electron donor as ethanol alone for perchlorate removal. FBR perchlorate removal technology has been demonstrated on a full-scale basis in two 4.27 m diameter GAC based FBRs with ethanol added as the electron donor.

This work was presented at the 218th national meeting of the American Chemical Society as part of the Environmental Division symposium Perchlorate in the Environment, held August 22–24, 1999, in New Orleans, Louisiana.