Optimisation de la réduction des nitrates par voie électrochimique

Abstract

The purpose of the present investigations was to model and optimize the performance of nitrate electroreduction in aqueous media in terms of yield and energy consumption. In reliminary attempts, stainless steel turned out to be the best material for electrodes, as compared to aluminum and graphite which were prone to severe corrosion and erosion. The individual effects and interactions were evaluated on 316L stainless steel electrodes for several parameters selected from preliminary experiments and literature review. The distance between the electrodes, the electric potential (voltage) applied, pH and reaction time are the main parameters considered for modeling and optimization. An 34 factorial design of experiments and measurements was used to model both the yield and energy consumed during the nitration electroreduction process. In optimal operating conditions, the nitrate reduction yield increased up to 80 %. When correlated to a minimum energy consumption of 0.8·10-3 kWh/g-N, the yield was of 67 %. For a volume of 300 mL, the concentration of nitrate decreased from an initial value of 200 to 40 mg-N/L after 120 minutes of processing. The individual effects and interactions of the distance between the electrodes, electric potential were the predominant factor in the mathematical model obtained. Accurate measurements generated high model adequacy, and the calculation data correlated well with the experimental results. Comparison of the calculated and measured amounts of OH ions was discussed in terms of undesirable side-chain reactions that affect nitrate reduction. The best electroreduction performance was obtained for distances between the electrodes around 10 millimeters, an electric potential of 6.0 V and a reaction time of 120 minutes. Regardless to the pollution level, the results obtained provide herein promising prospects to develop a low-cost and very affordable electroreduction technology for nitrate removal.

Date	16 Sept 2010
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Frédéric Monette (Supervisor) & Abdelkrim Azzouz (Co-supervisor)