Study On Simultaneous Removal Of Chromium And Organic Pollutants By Fenton-like Technology Coupled With Flocculation

The large-scale production of industrial chromium-containing wastewater not only affects the water environment in my country,but also the continuous accumulation of Cr(VI)will threaten life in the entire ecosystem.Cr precipitation using flocculants results in difficulty in Cr recovery and increase of salinity.In addition,chromium-containing wastewater is generally accompanied by refractory organic pollutants.At the same time,the fate of organic pollutants that exist has received little attention.Therefore,this research aims to remove chromium and organic matter at the same time,and provides a low-cost and environmentally friendly strategy for the treatment of chromium-containing wastewater.The Fenton-like reaction based on Cr redox reaction(Cr-Fenton-like reaction)coupled with Cr flocculation gives the opportunity to realize simultaneous removal of Cr and organic matters.In the coupling system,Cr-Fenton-like reaction generated more OH-for Cr flocculation via the H2O2 decomposition,meanwhile,Cr flocculation provided heterogeneous catalytic regions for Cr-Fenton-like reaction.The formation of Cr flocs was the key to the coupling effect.They created partially alkaline regions,therefore Cr-Fenton-like reaction(reaction condition:pH>5)and Cr flocculation(reaction condition:pH>8)occurred in these heterogeneous regions,although the pH of the solutions was below 5.Besides,the Cr floes in the coupling system tended to adsorb Cr(III)which also contributed to the coupling effect.Although Cr-Fenton-like reaction generated Cr(VI)inevitably,the dissolved Cr(VI)didn’t accumulate due to the persistent acidic condition and the heterogeneous catalysis of Cr flocs in the coupling system.Simulated tannery wastewater with Cr and organic co-pollution was treated using the coupling effect.The simultaneous removal rates for Cr and total organic carbon were 81.2%and 41.34%respectively after an 8-hour running.The above coupling system had some limitations.Additional H2O2 had safety risks in the transportation and storage of hydrogen peroxide solution,and the reactions of coupling system were difficult to control.Therefore,on the basis of this coupling system,the electrochemistry was used to assist in situ reduction of oxygen to generate H2O2.The effects of different electrode materials,applied voltage and initial concentration on the treatment of chromium-containing wastewater by electro-Fenton-like were studied.It was found that the TiO2/C modified graphite electrode had a superior effect on chromium-containing wastewater,when the voltage of-0.4V was applied.This wastewater treatment showed superior performance,and the removal rate of chromium and TOC reached 92.4%and 63.6%,which was greatly improved compared to the Cr-Fenton-like and chromium flocculation coupling technology.Therefore,the role of TiO2/C in the electro-Fenton-like treatment was deeply studied.First,the cyclic voltammetry scan was performed to confirm that the material can catalyze oxygen reduction in an alkaline chromium sulfate electrolyte solution.EPR capture analysis found that H2O2 the product of oxygen reduction can be decomposed to produce·OH under the action of metal chromium ions,which can degrade organic pollutants while removing chromium.The working electrode modified with TiO2/C material cycles after the experiment.The cyclic voltammetry characteristics have changed.Compared with the electrode modified with graphite powder,it is proved that this change is due to the effect of TiO2.The EDS analysis proves that chromium is present in the electrode after working.XPS analysis was performed on the chromium present on the electrode surface after the experiment.It is found that the existence form of chromium is similar to the XPS result analysis of chromium flocculation in the coupled system,indicating that H2O2 can directly undergo Fenton-like decomposition on the electrode surface to generate OH and OH-,which makes chromium flocculate and more Cr(III)accumulated on the surface of the cathode,and Cr(VI)generated after Fenton-like occurs was directly reduced at the cathode and will not accumulate in the solution.