Simultaneous removal of nitrate and its intermediates by use of bipolar electrochemistry

Abstract

Electrochemical removal of nitrate and its intermediates, ammonia and nitrite, by use of a bipolar electrode connection, was investigated under different experimental conditions (initial pH (4, 7, or 10) current density (5, 10, or 15 mA/cm2), nitrate concentration (25, 50, or 75 mg/L NO3 −-N), with or without NaCl as supporting electrolyte). The results showed that nitrate and intermediates were significantly removed in the presence of NaCl as supporting electrolyte; ammonia and nitrite were not removed in the absence of NaCl. Nitrate was reduced from 50 to 8.65 mg/L NO3 −-N in 150 min; under these conditions final ammonia and nitrite concentrations were 3.36 mg/L NH3 and 0.01 mg/L NO2 −-N, respectively. Denitrification times required to reduce nitrate concentration to the recommended standard for drinking water of 10 mg/L NO3 −-N were 180, 120, and 60 min at current densities of 5, 10, and 15 mA/cm2, respectively; initial nitrate concentration is 50 mg/L NO3 −-N. The rate of reduction of nitrate at pH 7 and 10 was greater than at pH 4. With increasing initial nitrate concentration the time required to achieve the recommended standard for drinking water was increased.