Treatment Of Aniline Wastewater By Electrodialysis

Aniline is an aromatic amine used as an intermediate in the manufacture of many pharmaceuticals and chemical feedstock for rubber making. It is known to be a toxic water pollutant and its presence in wastewater even of a very low concentration has been shown to be harmful to human life. Therefore, aniline should be removed from the wastewater before disposal. Many techniques, including activated carbon adsorption, solvent extraction, advanced oxidation and biodegradation, have been adopted for the removal of aniline from wastewater. However, these techniques are sometimes restricted because of economical or technical constraints. Activated carbon adsorption is limited by the regeneration costs. Traditional solvent extraction usually produces secondary liquid organic waste, which may cause environmental problems. Advanced oxidation is not suitable to be applied to the practice due to the high costs and the fact that the pollutants can not be completely degraded. Biodegradation is not suitable for the wastewater with high concentration of aniline. Therefore, there is a need to develop a new method, which can be used to remove aniline economically and successfully.Electrodialysis (ED) is a membrane separation process based on the selective migration of aqueous ions through ion-exchange membranes as a result of an electrical driving force. Electrodialysis technology is one of the most mature membrane separation technologies, qualified such merits as low energy consumption, simple equipment, easy operation and so on. Combined these features of electrodialysis, a novel method was proposed for the treatment of aniline wastewater by using two-compartment electrodialysis to remove the aniline ions formed in presence of hydrochloric acid (HCl).The effect of some influencing factors on the removal performance of aniline was syudied experimentally, namely, the amount of HCl added, initial concentration of aniline, the voltage applied, the flow rate, the volume of diluent compartment and soon. Considering the treatment efficiency and energy consumption, the optimal operating condition of the electrodialysis processes was chosen as follow, the operating voltage of 32 V, the flow rate of 60 L/h and the aniline and HCl at molar ratio of 1:5. Under the selected conditions, about 99% aniline removal was obtained within 120 min; and the aniline concentration can be reduced from 500 mg/L to 4 mg/L, which suggest the city standards of pollution discharge (namely,5 mg/L) can be met. With a cycling concentration process, C6H5NH2-HCl solution can be concentrated from 500 mg/L to 6390 mg/L by the electrodialysis apparatus.In addition, the limiting current density, the energy consumption of this technology and the concentration limit are also evaluated. Under the selected conditions, the limiting current intensity is 135.5 mA and the total energy consumption is 0.71 W-h/L for a 1000 mg/L aniline wastewater. According to the experimental results, under the operating conditions of 32V operating voltage,60L/h flow rate and 337mg/L initial feed concentration, the highest final concentration of aniline solution in concentrated chamber is 29944mg/L. Therefore, this method can efficiently concentrate aniline to 88.9 times. These studies have provided a firm theoretical basis for the treatment of aniline wastewater by electrodialysis.