Hybrid process for nitrates elimination in water

Abstract

Groundwater contamination with nitrates is a worldwide problem that needs a solution, because these compounds are harmful to health. There are several technologies to reduce the nitrate content in water to values accepted by the W.H.O. (10 mg L−1). Among them, one of the most advantageous is the catalytic reduction. This paper proposes the use of a combined process, using Pd-Sn catalysts supported on an anion exchange resin. First, nitrates are retained at the resin exchange sites, and then reduced over the metal sites in a regeneration stage. Different formulations were studied; the most active and selective catalyst was Pd 2%-Sn 0.5%, reaching conversions of 97%, with 66% selectivity to N2, when the regeneration was performed in H2 flow at room temperature and atmospheric pressure. This catalyst was also remarkably stable, maintaining conversions close to 90% in 28 successive cycles. The variables involved in the regeneration process were investigated. The addition of CO2 to the H2 stream did not improve either the conversion or the selectivity. The increase in temperature accelerated the process, but favored the catalyst deactivation. The regeneration time was optimized being possible to regenerate the catalyst in 12 h.