A Combination of Ion Exchange and Electrochemical Reduction for Nitrate Removal from Drinking Water Part I: Nitrate Removal Using a Selective Anion Exchanger in the Bicarbonate Form with Reuse of the Regenerant Solution

摘要

The process of selective nitrate removal from drinking water by means of ion exchange was studied. A commercial strong base anion exchanger with triethylammonium (-N~+Et_3) functional groups was used in the bicarbonate (HCO_3~-) and carbonate (CO_3~(2-)) form. The aim of this study was to optimize ion-exchanger regeneration in view of the subsequent electrochemical reduction of nitrates in the spent regenerant solution. The effects of ion-exchanger form, concentration of regenerant solution, and presence of nitrates, chlorides, and sulphates in the regenerant solution were studied. The strong base anion exchanger in HCO_3~- form that was investigated was able to treat 270 bed volumes of model water solution containing 124 mg dm~(-3) nitrates. To achieve adequate regeneration of the saturated anion exchanger, it is necessary to use approximately 30 bed volumes of fresh 1-M sodium bicarbonate (NaHCO_3) regenerant solution. The presence of residual 50-mg dm~(-3) nitrates in the regenerant solution, treated by electrolysis, resulted in an increase in the dose of regenerant solution to 35 bed volumes and a decrease in the subsequent sorption run of approximately 13 percent. The volume of applied regenerant solution was high, but the consumption of NaHCO_3 for regeneration was low.