Modification Of Granular Activated Carbon And Treatment Of Wasterwater Containning EDTA In The Three-dimensional Electrode Reactor

Abstract:Ethylenediaminetetraacetic acid (EDTA) is a powerful complexing agent with high affinity for heavy metals, which is often used as a masking agent in many industrical processes. As EDTA is widely used in many fields, a large amount of EDTA is discharged into the environment. Although EDTA does not have biological toxicity, it exhibits poor biodegradability, non-volatility and excellent complexing ability to heavy metal ions, which could reacts with heavy metal ions to form soluble complexes, then promote the migration of heavy metals and cause serious environmental pollution.Electrocatalytic oxidation is effective to treat intractable organic pollutants. As one of the Electrocatalytic oxidation, three dimensional electrolysis has a wide prospect in application of refractory organic pollutants treatment because of its higher ratio of electrode surface’s area and volume, which improved the mass transfer and current efficiency.In this research, various catalysts with different active metals, i. e. Fe, Mn, Zn, Ni, Sn, Sb and Ce supported over granular activated carbon (GAC) were prepared by the incipient wetness impregnation, which were used as three dimensional particle electrodes.the electrocatalytic activity and stability of the supported particle electrodes towards the degradation of EDTA simulated wastewaterhave been investigated. Then, morphologies, element compositions and crystal phase compositions of particle electrodeshave been analyzed via scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) to interpret the differences of the particle electrodes. It is shown that the Sn-Sb-Ce/GAC particle electrode was found to have the highest electrocatalytic activity and stability for the degradation of EDTA.The adsorption properties of EDTA on the GAC and the Sn-Sb-Ce/GAC particle electrode have been studied. The calculation of thermodynamic parameters indicated that the adsorption of EDTA was a spontaneous (ΔG<0) process and the adsorption capacity increased with temperature rise gradually on these two particle electrode. While the amount of surface adsorption sites of these two particle electrode were similar, the force between the Sn-Sb-Ce/GAC particle electrode and EDTA was stronger.The isosteric heat of EDTA adsorption on the Sn-Sb-Ce/GAC particle electrode was higher than GAC, which was indicated that the existence of dentate exchange force between the Sn-Sb-Ce/GAC particle electrode and EDTA.The technological conditions of wastewater containing EDTA treated by Sn-Sb-Ce/GAC particle electrode have been optimized. When the molar ratio of the Ce, Sn in the impregnating solution was3:50, the Sn-Sb-Ce/GAC particle electrode exhibited highest electrocatalytic activity towards EDTA degradation, while the stability of the electrode was also very well. The removal efficiency of total organic carbon (TOC) was above75%at200mA of current intensity,1.5ms/cm of electric conductivity,120min of electrolysis time,25℃of temperature,150mL/min of influent flow rate, and pH6.0. By adding tert-butyl alcohol as·OH radicals scavenger, it is proved that·OH existed in the process of wastewater treatment.