Use of a two-step process to denitrification of synthetic brines: electroreduction in a dual-chamber cell and catalytic reduction

BELTRAME, T. F.; ZOPPAS, F. M.; MARDER,L.; MARCHESINI, F. A.; MIRÓ, E. E.; BERNARDES, A. M.

ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2020 vol. 27 p. 1956 - 1968

0944-1344

Membrane Separation Processes are being currently applied to produce drinking waterfrom water contaminated with nitrate. The overall process generates a brine with highnitrate/nitrite concentration, that is usually send back to a conventional wastewatertreatment plant. Catalytic processes to nitrate reduction are being studied, but the maingoal of achieving a high selectivity to nitrogen production is still a matter of research. Inthis work, a two-step process was evaluated, aiming to verify the best combination ofoperational parameters to efficiently reduce nitrate to nitrogen. In the first step, thenitrate was reduced to nitrite by electroreduction, applying a copper electrode anddifferent cell potentials. A second step of the process was carried out by reducing thegenerated nitrite with a catalytic process by hydrogenation. The results showed that thehighest nitrate reduction (89%) occurred when a cell potential of 11 V was applied. Inthis condition, the nitrite ion was generated with all experimental conditions evaluated.Then, to reduce the nitrite ion formed by catalytic reduction, activated carbon fibers(ACF) and powder γ-alumina (γ-Al 2 O 3 ) were tested as supports for palladium(Pd). With the both catalysts the total nitrite conversion was obtained, being theselectivity to gaseous compounds 94% and 97% for Pd/Al 2 O 3 and Pd/ACF,respectively. Considering the results obtained, a two-stage treatment set-up to brinedenitrification may be proposed. With electrochemistry an operating condition wasachieved in which ammonium production can be controlled to very low values, but thereduction is predominant to nitrite. With the second step, all nitrite is converted tonitrogen gas and just 3% of ammonium is produced with the most selective catalyst.The main novelty of this work is associated to the use of a two-stage process enabling89% of nitrate reduction and 100% of nitrite reduction.