Laboratório de Corrosão, Proteção e Reciclagem de Materiais (LACOR, UFRGS), Av. Bento Gonçalves, 9500, Porto Alegre, 91501-970, Brazil.
Instituto de Investigaciones en Catálisis y Petroquímica (FIQ, UNL-CONICET), Santiago del Estero, 2829, S3000, Santa Fe, Argentina.
Environ Sci Pollut Res Int. 2020 Jan;27(2):1956-1968. doi: 10.1007/s11356-019-06763-x. Epub 2019 Nov 25.
Membrane separation processes are being currently applied to produce drinking water from water contaminated with nitrate. The overall process generates a brine with high nitrate/nitrite concentration that is usually send back to a conventional wastewater treatment plant. Catalytic processes to nitrate reduction are being studied, but the main goal of achieving a high selectivity to nitrogen production is still a matter of research. In this work, a two-step process was evaluated, aiming to verify the best combination of operational parameters to efficiently reduce nitrate to nitrogen. In the first step, the nitrate was reduced to nitrite by electroreduction, applying a copper electrode and different cell potentials. A second step of the process was carried out by reducing the generated nitrite with a catalytic process by hydrogenation. The results showed that the highest nitrate reduction (89%) occurred when a cell potential of 11 V was applied. In this 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-AlO) were tested as supports for palladium (Pd). With both catalysts, the total nitrite conversion was obtained, being the selectivity to gaseous compounds 94% and 97% for Pd/AlO and Pd/ACF, respectively. Considering the results obtained, a two-stage treatment setup to brine denitrification may be proposed. With electrochemistry, an operating condition was achieved in which ammonium production can be controlled to very low values, but the reduction is predominant to nitrite. With the second step, all nitrite is converted to nitrogen 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 enabling 89% of nitrate reduction and 100% of nitrite reduction.
膜分离工艺目前正应用于从受硝酸盐污染的水中生产饮用水。整个过程产生的盐水具有高浓度的硝酸盐/亚硝酸盐，通常会被送回传统的废水处理厂。正在研究催化还原硝酸盐的工艺，但实现高氮选择性生产的主要目标仍然是研究的课题。在这项工作中，评估了两步法，旨在验证最佳操作参数组合，以有效地将硝酸盐还原为氮。在第一步中，通过电还原用铜电极和不同的电池电势将硝酸盐还原为亚硝酸盐。第二步的过程是通过用氢化催化过程还原生成的亚硝酸盐来进行的。结果表明，当应用 11 V 的电池电势时，硝酸盐的还原率最高（89%）。在这种条件下，用所有实验条件评估时，都生成了亚硝酸盐离子。然后，为了还原催化还原生成的亚硝酸盐离子，用活性炭纤维（ACF）和粉末γ-氧化铝（γ-AlO）作为钯（Pd）的载体进行了测试。用这两种催化剂都获得了总亚硝酸盐转化率，Pd/AlO 和 Pd/ACF 的气态化合物选择性分别为 94%和 97%。考虑到所获得的结果，可以提出一种用于盐水脱硝的两段式处理装置。通过电化学，可以实现一种操作条件，其中可以将铵的产生控制在非常低的值，但还原主要是亚硝酸盐。在第二步中，所有的亚硝酸盐都转化为氮气，用最具选择性的催化剂只产生 3%的铵。这项工作的主要新颖之处在于使用了两步法，可实现 89%的硝酸盐还原和 100%的亚硝酸盐还原。
