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/gamma-Al2O3). Groundwater samples, with and without powder activated carbon (PAC) pretreatment, were also evaluated. In the absence of inhibitors the No-3(-) reduction rate was 2.4 x 10(-01) L/min g cat. However, the addition of constituents (SO42-, SO32-, 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 So(3)(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 x 10(-03) L/min g cat and increased ammonia production. Removal of dissolved organic matter from the groundwater using PAC increased the No-3(-) reduction rate to 5.06 x 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.