Abstract
Nitrate content in surface and underground water increased in some areas of the world caused by runoff from some industrial processes such as coking industry. Several degradation and separation techniques have been developed to eliminate nitrate efficiently from water. Electrodialysis (ED) represents a modern progressive electromembrane technology gaining an increasing attention in wastewater recovery. In this work, a bench-scale ED unit has been used to separate nitrate from synthetic solution and industrial wastewater collected from an Egyptian coke plant. Statistical design was applied to study the influence of different parameters (time, nitrate concentration and applied potential) those affecting the nitrate removal efficiency, and a mathematical model was generated. The results on synthetic solutions showed that all studied parameters are effective. The results have been collected at a 3-D cube that showed that at high levels of parameters (25 min, 15 V and 700 ppm) the nitrate removal efficiency was almost 100%, while a small nitrate removal efficiency of about 51% was obtained at the low levels (5 min, 5 V and 100 ppm). The wastewater sample was found to contain several inorganic and organic pollutants those could be separated together with nitrate. Only 2.5 hrs is sufficient to separate about 80% of nitrate at 15 V where longer time has no pronounce effect on nitrate separation. This is corresponding to about 15 ppm nitrate content in the output water, which is far less than the acceptable concentration of <= 44 ppm. After 5 hrs of ED operation, the removal efficiency of nitrate, sulphate, chloride, cyanide, ammonia phosphorus and phenol were 82, 99, 96, 99, 98, 60 and 40%, respectively. These results revealed that electrodialysis can efficiently separate nitrate and most pollutants from coking wastewater for possible re-use. Spherical particles (5-20 mu m) of mainly ammonium nitrate were obtained by evaporating the rejected water after ED operation.