Évaluation du potentiel de réutilisation successive de la chabazite et de la solution de régénération dans un processus d'électro-conversion de l'azote ammoniacal fixé sur un milieu zéolitique

Abstract

The continuous production of ammoniacal nitrogen by anthropogenic activities as well as the operational and economic limits of the current available treatment techniques generate nitrogen pollution in the environment with various consequences, including the toxicity of the receiving aqueous media and the eutrophication of water courses, water and lakes. This study addresses the process of electro-conversion of ammoniacal nitrogen present in water as an environmentally friendly alternative that is adaptable to industry. The general objective is to evaluate the successive regeneration of a zeolite (chabazite) as well as the reuse of the regeneration solution used in a hybrid process which combines both the fixation of ammoniacal nitrogen on a zeolite and its electrochemical treatment by electro-conversion. The present study also aims to clarify the effect of the electrical parameters and the composition of the regeneration solution on the ammoniacal nitrogen removal yields of the zeolite as well as on its transformation into different forms. Different electrodes or combinations of electrodes (mild steel, stainless steel, titanium, nickel-copper) and electrolytic solutions (based on NaCl, KCl, LiCl, CaCl2∙2H2O, MgCl2∙6H2O, NaOCl) were tested according to their electrical consumption, which made it possible to choose mild steel as an anode, stainless steel as cathode as well as NaCl and NaOCl as base products for electrolytic solutions. Zeolite regeneration tests carried out with different compositions of electrolytic solutions showed that the NaOCl-NaCl mixture in the regeneration solution degraded the electro-conversion yields. Drinking water and the NaCl solution (13 mg Cl- / L) with a current surface intensity of 3,68 mA/cm2 also led to respective rates of nitrogen removal from the zeolite of 29 % (of which 75 % transformed into N2) and 25 % (of which 61 % produced in solution). Successive zeolite regeneration tests (retaining the zeolite but renewing the regeneration solution) and reuse of the regeneration solution (retaining the regeneration solution but renewing the zeolite) were then carried out. The results showed that the successive reuse of chabazite does not interfere with the electro-conversion process and that the chabazite retains its ammoniacal nitrogen fixation capacity (nearly 98 %) after nine cycles. The successive reuse tests of the regeneration solution have shown an improvement in the electro-conversion process of ammoniacal nitrogen with respective yields of nearly 40 % and 35 % for tap water and the solution of NaCl (13 mg Cl-/L). The concentrations of ammoniacal nitrogen, nitrites and nitrates in the solution vary during the treatment cycles, without however exceeding the threshold values of 80 mg N- NH4+/L, 2,73 mg N-NO2-/L and 1,58 mg N-NO3-/L. The successive reuse of the NaCl regeneration solution makes it possible to improve the rate of nitrogen conversion until values ranging between 81 % to 92 % are reached, of which nearly 10 % would be evaporated in the air by stripping process. This loss could however be avoided by improving the circulation of the solution in the reactor so that the liquid phase and the gas phase remain separate.

Date	11 Dec 2020
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Frédéric Monette (Supervisor)