Abstract
This work aims to present different electroreduction and electrocatalytic processes configurations to treat nitrate contaminated water. The parameters tested were: current density, cell potential, electrode potential, pH values, cell type and catalyst use. It was found that the nitrite ion is present in all process variations used, being the resulting nitrite concentration higher in an alkaline pH. The increase in current density on galvanostatic operation mode provides a greater reduction of nitrate (64%, 1.4 mA cm-2) if compared to the potentiostatic (20%) and constant cell potential (37%) configurations. In a dual-chamber cell the nitrate reduction with current density of 1.4 mA cm-2 was tested and obtained as a NO3- reduction of 85%. The use of single chamber cell presented 32 ± 3% of nitrate reduction, indicating that in this cell type the nitrate reduction is smaller than in dual-chamber cell (64%). The presence of a Pd catalyst with 3.1% wt. decreased the nitrite (1.0 N-mg L-1) and increased the gaseous compounds (9.4 N-mg L-1) formation. The best configuration showed that, by fixing the current density, the highest nitrate reduction is obtained and the pH presents a significant influence during the tests. The use of the catalyst decreased the nitrite and enhanced the gaseous compounds formation.
Highlights
Nitrate (NOÀ3(aq)) is an ion present in surface and groundwater and its presence in these systems can cause damage to the environment (Smith & Schindler 2009; Wang et al 2021) and to human health (Cameron et al 2013; Wang et al 2021)
To minimize the effect of membrane polarization, the current density applied in the electroreduction tests was 1.2 mA cmÀ2, which corresponded to the 85% of the limiting current density value obtained in the Current–voltage curves (CVC)
This work shows that the electrochemical process to nitrate reduction has the potential to be used as a way of treating wastewater with high and low nitrate concentrations
Summary
Nitrate (NOÀ3(aq)) is an ion present in surface and groundwater and its presence in these systems can cause damage to the environment (Smith & Schindler 2009; Wang et al 2021) and to human health (Cameron et al 2013; Wang et al 2021). Among different methods used for the treatment of water contaminated with nitrate, the membrane separation processes (MSP) stand out. Other options for the treatment of water contaminated with nitrates are the electroreduction and the catalytic processes, in which the nitrate ion (NOÀ3(aq)) can be reduced to nitrogen gas (N2(g)). To use the electroreduction process on an industrial scale it is necessary to study the different operational parameters that can influence the system, as each operational characteristic may have an effect on the ion removal efficiency and on the different products that can be formed, such as ammonium (NHþ4(aq)), nitrite (NOÀ2(aq)) and gaseous compounds (ideally nitrogen gas) (Beltrame et al 2018).
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