Treatment Of Electroplating Industries Wastewater By Electro-oxidation In A Higee Electrochemical Reactor With Rotating Mesh Disc Electrodes

Electroplating wastewater, which is a typical heavy metal wastewater, might render increasingly serious pollution to the environment for its huge emissions and serious toxicity. Compared to metal ions, which is easily removed from wastewater, metal complexes couldn’t be precipitated directly.In this paper, a higee electrochemical reactor with rotating mesh disc electrodes(RMDE-HEC) was designed under the foundation of high gravity(higee). In this reactor, the mass transfer was enhanced by rotating disc electrodes. The centrifugal force generated from the rotating electrodes which promoted the thin liquid film on the electrodes updating faster. Hence, the treatment efficiency and current efficiency of electro-oxidation was enhanced, much less special energy consumption could be obtained by improving the current efficiency and treatment efficiency. Instead of a non-uniform current density was exist in the common electrodes, the current density on the rotating disc electrodes was uniform.Electroplating wastewater with metal complexes of Cu, Ni and Cr was treated using the RMDE-HER. The effect of current density, rotation speed of rotating electrodes and the p H of solution to the treatment effective of RMDE-HER was investigated with focusing on destruction rate of metal complexes. The results shown that,the destruction ratio of metal complexes improved with the increasing of the current density. The lower current efficiency caused much more energy consumption when the current density over 10 m A·cm-2. The mass transfer coefficient in the reactor was first increased with the rotation of rotating electrodes increasing, and then remained unchanged during the rotation speed of rotating electrodes over 200 rpm. The efficiency of destruction of metal complexes was good in a wide range of p H from 3.0 to 12.6, and the efficiency on the condition of acidity or alkaline was higher than that on the condition of neutral. The acid solution could weaken the secondary reaction of O2 evolution; and more hydrogen peroxide and ·HO2 activity species would be generated in a alkaline solution. On the condition of p H=11.0, the reaction rate was the fastest, first-order rate constant of it was-0.0448 min-1. On the optimal condition of current density of 10 m A·cm-2, rotation speed of 200 rpm and p H=11.0, after 90 min electrolysis, the destruction ratio of Cu, Ni and Cr were 98.09%, 95.57% and 96.10%, respectively. The specific energy consumption of Cu, Ni and Cr metal complexes were 106.04 k W·h·kg-1, 518.29 k W·h·kg-1 and 938.12 k W·h·kg-1.In addition, the RMDE-HER was used to pretreat wastewater with refractory biodegradable organic to enhance the biodegradability of the wastewater. The effect of current density and rotation of rotating electrodes on CODCr and the value of B/C was studied. The results indicated that the effect of wastewater pretreatment by electro-oxidation was good. On the optimal condition of current density 10 m A·cm-2 and rotation speed 200 rpm, after 90 min electrolysis, the B/C value of the wastewater improved from 0.20 to 0.48; and the CODCr of it decreased at the same time.