Remediation of actual groundwater polluted with nitrate by the catalytic reduction over copper–palladium supported on active carbon

Abstract

Catalytic reduction of nitrate (NO 3 −) in groundwater over a Cu–Pd catalyst supported on active carbon was investigated in a gas–liquid co-current flow system at 298 K. Although Cu–Pd/active carbon, in which the Cu/Pd molar ratio was more than 0.66, showed high activity, high selectivity for the formation of N 2 and N 2O (98%), and high durability for the reduction of 100 ppm NO 3 − in distilled water, the catalytic performance decreased during the reduction of NO 3 − in groundwater. The catalyst also irreversibly deactivated during the reaction in groundwater. The organic species in the groundwater caused the decrease in the catalytic performance and the irreversible catalyst deactivation. Ozone-treatment of the groundwater to remove the organic species substantially helped to maintain the catalytic activity and to halt the irreversible deactivation of the catalyst. Chloride ion (Cl −) in the groundwater also caused the decrease in the activity and selectivity, but the effects of Cl − were reversible. Sulfate ion (SO 4 2−) and cations, including Mg 2+, Ca 2+ and K +, had little or no effect on the catalytic performance of Cu–Pd/active carbon, though they were present in the groundwater sample. More than an allowable level of NH 3 (NH 4 +) was formed during the catalytic reduction of NO 3 − in the groundwater, but was completely removed by the cation-exchange process using Na-mordenite.