Study On The Modified Ferrous-activated Pesulfate Processes For Azo Dye Orange G Degradation

With the great development of printing and dyeing industries in our country,the need of dye increased sharply.Dye products have the characteristics of high chroma,strong biological toxicity and difficulty in being biodegraded.It will casues a serious damage to our ecosystem if the dye products are discharged into natural waters without any efficient treatments.Recently the sulfate radical based advanced oxidation processes have been applied in the water treatment processes more and more due to its high degradation efficieny of organics.Generally,sulfate radicals are gernerated from the activation of persulfate,and so far the ferrous activated persulfate(Fe2+/PS)process is the most popular method.However the Fe2+/PS system has some inherent drawbacks.Hence in this research,the oxidation degradation capacities of two kinds of modified Fe2+/PS system were studied.First,the research deals with the degradation of orange G(OG)in aqueous solutions by electrochemically activated persulfate(EC/PS)oxidation.These processes are based on the generation of sulfate radicals(SO4·-),which are strong oxidizing species.The effects of current intensity,PS dosage,initial OG concentrations,initial pH of solution and coexisting anions in solution were studied.The results show that EC/PS system can degrade OG more effectively than EC or PS alone.The degradation rate of OG increases with the increase of the current intensity and the dosage of PS;Low initial pH are favorable for OG degradation in the pH range of 3-10;the degradation rate of OG decreases with the increase of the initial OG concentrations.Coexisting anions exhibit different degrees of inhibition effects,the degree of inhibition abiding from strong to weak by the following order:PO43->CO32->Cl-.Furthermore,the OG degradation efficenies in both EC/PS and EC/PS system were compared and it was found that the degradation efficiency in EC/PS was much higher than that in Fe2+/PS system.This result was attributed to the fast Fe2+ consumption and some side reactions in the Fe2+/PS system wich would not occur in the EC/PS system.In the second part of the research,the natural green tea extracts EGCG was added into traditional Fe2+/PS system to help it degraded OG by accelerating the transformation from Fe3+ to Fe2+.The effects of PS dosage,initial OG concentrations,initial pH of solution,Fe2+ dosage,EGCG dosage and coexisting inorganic anions in solution were studied.The results show that the addition of Fe2+,EGCG or PS alone and the combination of EGCG/PS or Fe2+/EGCG cannot degrade OG efficiently.The introduction of EGCG into Fe2+/EGCG system improved the degradation efficiency significantly.The degradation efficiency of OG increased with the increasing PS and Fe2+ dosage while decreased when OG concentration increased;the degradation efficiency increased with the increase of EGCG dosage when EGCG concentration was in the range of 10-40 ?mol/L,while the further increase of EGCG dosage would led to a decrease of OG removal.When pH?3.0,the degradation efficiency decreased obviously with the decrease of pH,on the other hand,the degradation efficiency were roughly the same when pH = 4-7.Coexisting anions exhibited the degradation efficiency of OG and the inhibiting effect can be ranked from high to low in an order of PO43->CO32->Cl-.Moreover,the exiting of SO4·-and HO· in the above two systems is confirmed by adding scavengers methanol and tert-butanol respectively and SO4·-was the primary active radical.The OG degradation in the two systems exhibited a pseudo-first order kinetics pattern and the degradation rate constants(kobs)were affected by some factors to different degrees.