The Process Study Of Wastewater Containing Chromium Treatment By Electrocoagulation-activated Carbon Technique

Currently electrocoagulation technology is finding increasing application in treatingcontaminated wastewater. Most researchers only concentrated on the removal efficiency butcould not get a better understanding of the removal mechanism. This paper focuses on theremoval mechanism of chromium by electrocoagulation technology.The effect of several factors, such as different initial pH, current density and electrodematerials etc., on the removal mechanism was investigated and the ratio of Cr/Fe (Cr/M) offlocs that could be used to evaluate the utilization ratio of flocs was proposed. It was foundthat when the solution was under acidic conditions, the removal mechanism mainlypresented as electrolytic reduction and subsequent precipitation; when the solution wasunder neutral conditions, the adsorption of flocs dominated in the removal process and theutilization ratio of flocs was the maximum； when the solution was under alkalineconditions，both of the two function were weak and the removal efficiency was much lower.The electrocoagulation process with Fe/Al electrode allowed the Al cathode dissolving andthis made the amount of flocs increased and the coexistence of Fe and Al flocs. Therefore,the electrocoagulation process with Fe/Al electrode has higher removal efficiency but theutilization ratio of flocs was relatively lower.This paper investigated the mechanism of polarization and passivation from the viewof electrochemical mass transfer and diffusion mass transfer. The research showed thatwhen the frequency is lower, the passivation of the anode plate can not be effectivelyeliminated; when the frequency is higher, the pulse cycle can not meet the charge anddischarge time of the double layer. When the duty cycle was smaller, electrochemicalreaction was the speed control step; When the duty cycle was bigger, the diffusion of ionswas the speed control step.The adsorption of activated carbon was served as secondary treatment to meet thedischarge requirements for the effluent. The study found that the adsorption effect ofactivated carbon improved with increasing temperature. The kinetic model of the adsorptionon Cr(Ⅵ) could be described by the pseudo second-order equation and the adsorptionisotherm was more suitable to the Freundlich isotherm.