Optimization Of Ti/SnO₂+Sb₂O₃Electrode And Effects Of Electrolytic Oxidation On Nanofiltration In Treating Dye Wastewater

Dye wastewater, which heavily pollutes the environment, is a kind of effluentwith high colority, high content of organic matters, and it is of great quantity and hardto degrade. The electrolytic oxidation can decolorize the dye wastewater rapidly, but itis appropriate for only little amount of wastewater because of the low currentefficiency. Nanofiltration is of high rejection, no secondary contamination, and easy tooperate in treating dye wastewater. However, the concentration polarization andmembrane fouling cut the flux and the membrane lifetime down. In our article, wecombined the two methods to achieve coupling, the dye was congregated by themembrane, and the electrolytic oxidation played the role of controlling concentrationpolarization.The optimum preparation conditions of the Ti/SnO₂+Sb₂O₃catalytic electrodewere ascertained through the experiments, and the modification was carried out byadding yttrium. The catalytic electrode was used to degrade the simulated acid red73#wastewater, and the effects of process conditions on the colority and CODremoval were discussed.The final modified Ti/SnO₂+Sb₂O₃catalytic electrode was applied as anode andstainless steel mesh as cathode, and the D series nanofiltration membranes was usedin the coupling experiments. The promotion effects of electroosmosis, electrophoresisand electrocatalysis oxidation on nanofiltration were studied, and the effects of thecoupling conditions on the permeate flux were emphatically researched.The results showed that both the oxygen evolution overvoltage and the life of theelectrode increase remarkably after modification. In the degradation of the wastewaterby electrolytic oxidation, the higher current density and electrolyte concentration, thelower initial dye concentration and pH, all of these lead to higher colority and CODremoval. And we got better results when the electrolyte is NaCl than Na₂SO₄. Theincrease of the dye and electrolyte concentration and the decrease of the currentdensity and pH, were all conductive to the current efficiency enhancement.The electroosmosis flux increased linearly with electric field intensity in thecoupling experiments. The movement of the dye molecules under electrophoresis, tosome extent, inhibited the concentration polarization. The degradation of the organics near the membrane increased with the rise of the current density, and so we got higherpermeate flux. When the voltage reaches2.5V, the smaller molecules from dyeoxidation led to the membrane pore blocking, and so the permeate flux decreased.With the continuous increase of the voltage, the smaller molecules were furtheroxidized, so the permeate flux increased. The increase of the dye concentration,operating pressure and cross flow velocity was conductive to the increase of permeateflux. Besides, the rise of the temperature played an active role in the permeate fluxenforcement.In summary, the electrode properties were enhanced a lot after the modificationand the colority and COD removal were significantly affected by the processconditions. In the coupling of electrolytic oxidation and nanofiltration, theconcentration polarization was basically controlled by electrophoresis andelectrocatalysis oxidation. So the permeate flux was greatly improved.