A Study On The Numerical Simulation Of The Mass Transfer Process Of Electrocoagulation

In recent years, heavy metal wastewater pollution incidents occur frequently, Electrocoagulation(EC) is one of important heavy metal wastewater treatment technology. It is also often used for the removal of refractory organics wastewater. EC consists of multiple processes include the electrochemical reaction, mass transfer, hydrolysis reaction and adsorption reaction, which formed the interaction and inter-coupled relationship with each other. Therefore, the complicated coupled relationships limit the further study of EC mechanism. EC is composed of three successive processes: flocs production, flocs transportation and flocs adsorption. The production and distribution of flocs will have a significant impact on pollutant removal efficiency. A coupled mass and momentum transfer model was established. The electrochemistry and hydrolysis reaction were considered in our model. The generation and migration of flocs in the continuous EC process were discussed.Simulation results showed that aluminum ions generated by electrolysis mainly distributed near the anode, hydroxyl ions located in the vicinity of the cathode, which were gradually reduce in the streamline direction. In the front of the electrolytic cell, the ion concentration polarization is weak, the hydrolysis reaction was the control step; in the middle and rear of the cell, ions concentration polarization was strong, mass transfer was the control step. With the increase in current density, aluminum ion and hydroxide ion concentration also increased; in the absence of hydrolysis conditions, ion concentration polarization was weak, the entire cell significantly alkaline. Hydrolyzate dissolved aluminum was mainly distributed in the vicinity of the two electrodes, while flocs of aluminum were mainly distributed in the intermediate position of the two electrodes, while the floc aluminum was dominant in the entire cell. Along the flow direction, the percentage of the aluminum floc in the total aluminum gradually increased, the percentage of the dissolved aluminum in total aluminum decreased.The results also showed that flocs mainly distributed in the middle position of the latter-half of electrodes in the cell and the amount of flocs near to the cathode was trend to zero under the mass transfer of electro-migration and convection. At the streamline direction, the amount of flocs increases with the increment of current density and residence time, while the flocs’ amount was almost invariant in initial pH range of 5-7. The residence time, the current density and initial pH had no effect on the distribution of flocs perpendicular to the direction of electrode in the channel.