Electrochemical removal of nitrate using ZVI packed bed bipolar electrolytic cell

The present study investigates the performance of the zero valent iron (ZVI, Fe0) packed bed bipolar electrolytic cell for nitrate removal. The packing mixture consists of ZVI as electronically conducting material and silica sand as non-conducting material between main cathode and anode electrodes. In the continuous column experiments for the simulated groundwater (initial nitrate and electrical conductivity of about 30 mg L−1 as N and 300 μS cm−1, respectively), above 99% of nitrate was removed at the applied potential of 600 V with the main anode placed on the bottom of reactor. The influx nitrate was converted to ammonia (20% to maximum 60%) and nitrite (always less than 0.5 mg L−1 as N in the effluent). The optimum packing ratio (v/v) of silica sand to ZVI was found to be 1:1–2:1. Magnetite was observed on the surface of the used ZVI as corrosion product. The reduction at the lower part of the reactor in acidic condition and adsorption at the upper part of the reactor in alkaline condition are the major mechanism of nitrate removal.

► The packing ratio of 1:1 and 2:1 (sand:ZVI) showed better current efficiency.
► The feed flow rate of 30 mL min−1 showed optimum current efficiency.
► Effluent pH was proportional to nitrate influx concentration.
► The nitrate was converted to ammonia as final product of nitrate reduction.
► The magnetite was found on the surfaces as corrosion products of ZVI.