Enhanced removal of nitrate in an integrated electrochemical-adsorption system

The electrochemical (EC) method of removing pollutants in water is a widely used process in water and wastewater treatment. An EC-adsorption integrated system was investigated to test whether the simultaneous removal of nitrate by the two processes would be better than removal utilising the individual EC and adsorption methods. In the integrated system, an adsorbent (ion exchange resin - Dowex 21k XLT) was placed inside a stainless steel box that served as an anode with a Cu plate as cathode. In an experiment using 2 L nitrate solution containing 20 mg N/L and 2 g adsorbent the rate of nitrate removal in the integrated system was initially fast with 35% removed in 30 min, though slowing down later. The rate of removal increased with increasing current, voltage and pH up to 7 but decreased as the distance between the electrodes also increased. The optimum nitrate removal of 67% was obtained at pH 7, 1 A, and 31 V for a distance of 1 cm between the electrodes after 180 min. The amount of nitrate removed fell when sulphate was present in the integrated system due to sulphate competing with nitrate for adsorption. Concentration of ammonium produced by nitrate reduction in the EC system was reduced in the presence of adsorbent. Nitrate removal in the integrated system is approximately equal to the sum of the removals in the two individual processes.