Modeling Of MCDI Adsorption And Desorption And Study On Removal Of Inorganic Ions From Landfill Leachate

Capacitive deionization(CDI)is a water treatment technology which removes ions and regenerates its electrosorption capacity through a cyclic charge and discharge process.Membrane capactive deionization(MCDI)covers the ion exchange membrane(IEM)on surface of electrode on the basis of CDI,and the adsorption efficiency is improved by suppressing the adsorption of ions which have the same polarity as the electrode.Compared with traditional technology,MCDI has the advantages of lower energy consumption,better regeneration performance and hardly production of by-products.The presence of high concentrations of ammonia nitrogen and humus is a major obstacle to apply MCDI to desalting landfill leachate.Exploring the mechanism and application feasibility of MCDI technology not only has important theoretical significance,but also plays an important guiding role in the practical application of MCDI in landfill leachate desalination.In this paper,a PE ion exchange membrane was used as a membrane material,and an activated woven carbon cloth(ACC)was used as an adsorption material to assemble a MCDI device.This experiment uses a quasi-first-order kinetic model to fit the dynamic changes of salt concentration during the adsorption and desorption of MCDI,and explores the accuracy and optimal circulation of the model by changing the initial salt concentration and circulation flow of the system.The pseudo-first-order kinetic model was found to describe the adsorption process of MCDI well according to graphical analyses of fitting results,but it cannot accurately describe the desorption process.And 40 ml/min and 60 ml/min are the optimal flow rates for adsorption and desorption,respectively.The ACC electrode consists of a large number of filamentary fibers of the same thickness and intertwined,and the pores of electrode are mainly mesopores,with large pore volume,specific surface area and specific capacitance,which are beneficial to the adsorption of ions.In addition,the simulated landfill leachate containing ammonia nitrogen and humic acid with different concentration gradients was subjected to adsorption desalination experiments.The results show that the increase of ammonia nitrogen concentration will increase the adsorption amount of ammonia nitrogen in MCDI,but the adsorption amount of other ions will decrease,and the adsorption amount of TDS is basically stable at about 13 mg/g.The high concentration of ammonia nitrogen has no pollution effect on ACC electrode.The specific surface area,pore volume and total specific capacitance of the electrode material are only slightly reduced or not reduced,and can be recycled many times.The TDS removal rate of the landfill leachate containing ammonia nitrogen by MCDI can be increased by increasing the residence time.After the time reaches 31.25 min,the TDS removal rate can reach 59.45%,which has a good removal effect.The increase of humic acid concentration will lead to a decrease in the amount of TDS adsorption(up to 45.86%),and the adsorption amount of SO42-,NO3-and Na+ is greatly attenuated.After multiple cycles,a large amount of humic acid will remain on the electrode during the second and third adsorption cycles and cannot be desorbed,resulting in a decrease in specific surface area,total specific capacitance and impedance of the electrode material,reversibility and stability of the electrode.Significantly worse,the adsorption amount of inorganic ions is significantly reduced.To remove desalting of landfill leachate by MCDI technology,it must be pretreated by Fenton technology,MBR technology and other pre-processes to reduce the content of organic pollutants.