Effects of Natural Water Ions and Humic Acid on Catalytic Nitrate Reduction Kinetics Using an Alumina Supported Pd−Cu Catalyst

Catalytic nitrate reduction was evaluated for the purpose of drinking water treatment. Common anions present in natural waters and humic acid were evaluated for their effects on NO3 - hydrogenation over a bimetallic supported catalyst (Pd−Cu/γ-Al2O3). Groundwater samples, with and without powder activated carbon (PAC) pretreatment, were also evaluated. In the absence of inhibitors the NO3 - reduction rate was 2.4 × 10-01 L/min g cat. However, the addition of constituents (SO4 2-, SO3 2-, HS-, Cl-, HCO3 -, OH-, and humic acid) on the order of representative concentrations for drinking water decreased the NO3 - reduction rate. Sulfite, sulfide, and elevated chloride decreased the NO3 - reduction rate by over 2 orders of magnitude. Preferential adsorption of Cl- inhibited NO3 - reduction to a greater extent than NO2 - reduction. Partial regeneration of catalysts exposed to SO3 2- was achieved by using a dilute hypochlorite solution, however Cu dissolution occurred. Dissolved constituents in the groundwater sample decreased the NO3 - reduction rate to 3.7 × 10-03 L/min g cat and increased ammonia production. Removal of dissolved organic matter from the groundwater using PAC increased the NO3 - reduction rate to 5.06 × 10-02 L/min g cat and decreased ammonia production. Elemental analyses of catalysts exposed to the natural groundwater suggest that mineral precipitation may also contribute to catalyst fouling.