Electrochemical removal of nitrate from high salinity waste stream in a continuous flow reactor

Abstract

Nitrate contamination of groundwater continues to be a major concern worldwide. Nitrate removal from groundwater by Donnan dialysis generates a purified water stream and a contaminated waste stream of high salinity NaCl or Na2SO4 containing only the anionic composition of the treated groundwater. The objective of this research was to study the electrochemical removal of nitrate from a high salinity Donnan dialysis waste stream in a continuous flow system using Cu-DSA electrodes. The difference between the two high saline solutions were manifested in the nitrate removal efficiencies and ammonia production. Nitrate removal from Donnan dialysis waste, at an optimal 90 min residence time, resulted in a maximum removal of 63 % in high salinity Na2SO4 and 44 % in high salinity NaCl. Ammonia formation was suppressed by NaCl while 70 % of the nitrogen was reduced to ammonia in the high salinity Na2SO4 solution. The anionic composition had no effect of nitrate removal in high salinity Na2SO4. Yet, in high salinity NaCl solution bicarbonate inhibited the nitrate reduction, and sulfate facilitated the removal of the nitrate. Periodic current reversal, applied to overcome cathodic deactivation, resulted in copper dissolution. Higher salinities led to less cathodic dissolution in both high saline solutions. The results of this study render support to the viability of nitrate removal from high salinity stream by a continuous flow electrochemical cell.