Analyse multivariée et optimisation par la méthode des surfaces de réponses (MSR) de l’électro-conversion de l’azote ammoniacal en condition saline

Abstract

High concentrations of ammoniacal nitrogen in the natural area related to human activities adversely affect the physical and biological quality of the environment. The physical, biological and geochemical treatment techniques for this pollutant are operational, economic and sometimes environmental. The electrochemical method is increasingly being explored in a context of process improvement for a better environmental and economic impact. The objective of this study is to evaluate the performance of a combination of the monopolar electrochemical device with chabazite in a saline environment for the electro-conversion of ammoniacal nitrogen. After the preliminary tests which made it possible to select the salts MgCl2 6H2O and NaCl, the electrochemical tests at 3 V give a superior performance in the presence of 3 g Cl-/L of NaCl 49.6% of yield and less than 1% of nitrate and nitrite. The analysis of the electrochemical and chemical parameters and the Principal Component Analysis (PCA) highlighted the negative effects of pH variation and of acidification and complexation reactions in the presence of the salt MgCl2 6H2O on the electro-conversion efficiency of N-NH4+. PCA identified salinity and energy as the primary factors in this electro-conversion. On this basis, the factor analysis with the rotation method by VARIMAX made it possible to select the Electrical Voltage (TE), the Chloride Ion Concentration (CC) and the Final Hydrogen Ion Concentration (HF) for the construction of the Electro-conversion yield model of N-NH4+ (RE). The analysis of variances (ANOVA) subsequently showed that the final concentration of hydrogen ions (HF) is not significant to the model response. This optimization model using the Response Surfaces Method (MSR) was therefore constructed using a three-level factor-by-factor design with the variables Electrical Voltage (TE) and Chloride Ion Concentration (CC). The electro-conversion efficiency model of N-NH4+ obtained with 94% determination coefficient indicates a yield of 68 % in optimal conditions of 12 V and 4 g Cl-/L. The economic analysis estimated a cost of $5.6/kg of N-NH4+ processed. This cost can be reduced by assessing the conditions for reuse of the regeneration solution and zeolite, and electrode replacement.

Date	28 Feb 2020
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Frédéric Monette (Supervisor)