Electrochemical Preparation Of Ferrate And Its Experimental Study On The Removal Of Dissolved Organic Matter And Phosphorus From Secondary Effluent

As the second stable water source,urban wastewater reuse is of great significance to alleviate the urban water crisis.Due to the fact that the secondary effluent still contains a certain amount of dissolved organic matter and phosphorus,direct reuse is easy to cause great harm such as eutrophication and odor increase.Therefore,advanced treatment is needed to effectively reduce the content of dissolved organic matter and phosphorus in secondary effluent.Ferrate(Fe(VI))is a kind of green water treatment agent,which has strong oxidation and good flocculation effect.It has good removal effect on many pollutants in a wide range of p H value.In this paper,solid ferrate(Fe(VI)(S))and liquid ferrate(Fe(VI)(L))were prepared.The chemical and physical properties of Fe(VI)(S)were characterized by XRD,FTIR and SEM.Taking the secondary effluent of sewage station as the research object,two kinds of Fe(VI)were used to carry out the removal experiment of dissolved organic matter and phosphorus in the secondary effluent,and the experimental study on the removal of dissolved organic matter and phosphorus in the secondary effluent by the combination of Fe(II)and Fe(VI)was carried out.The main results are as follows:(1)Under the conditions of KOH concentration of 14 mol/L,electrolysis temperature of60?and anode current density of 1 m A/cm²,the current efficiency of Fe(VI)(S)prepared by electrolysis can reach 65.3%,and the purity of product can reach more than 90%after secondary purification.According to the XRD spectrum,it can be seen that the characteristic diffraction peaks appear at the positions of 2?of 17.08°,20.62°,23.02°,24.6°,25.64°,27.64°,28.3°,28.84°,30°,30.44°,34.62°,39.8°,42.04°,45.32°and 53.06°,which are basically consistent with the standard card No.25-0652 in JCPDS diffraction card,indicating that the product contains K₂Fe O₄.According to the FTIR spectrum,it can be seen that there is a strong diffraction peak at the wavelength of 807 cm^-1 and a shoulder peak at the wavelength of 781 cm^-1,which once again confirmed that the product contains K₂Fe O₄.According to the SEM spectrum,it can be seen that the prepared product is mainly long rod-like or flake-like crystal particles of 10-30 microns.(2)With the increase of Fe(VI)dosage,the removal rates of dissolved organic carbon(DOC)and UV₂₅₄ increased rapidly at first and then slowly.When the dosage of Fe(VI)was300?mol/L,the removal rates of DOC by Fe(VI)(S)and Fe(VI)(L)were 14.7%and 16.56%respectively,and the removal rates of UV₂₅₄ by Fe(VI)(S)and Fe(VI)(L)were 45.02%and44.31%respectively.(3)Under the condition of a certain total iron dosage,when the molar ratio of Fe(VI)(S)/Fe(II)and Fe(VI)(L)/Fe(II)is 3:1,the removal efficiency of DOC and UV₂₅₄ is the best.(4)Under the condition that the total iron dosage is 180?mol/L,the removal effects of Fe(VI)(S),Fe(VI)(L),Fe(VI)(S)/Fe(II),Fe(VI)(L)/Fe(II)and Fe(III)on DOC and UV₂₅₄ were compared.The size of the removal effect on DOC and UV₂₅₄ is:Fe(VI)(L)>Fe(VI)(S)>[Fe(VI)(L)/Fe(II)]=3:1>[Fe(VI)(S)/Fe(II)]=3:1>Fe(III),the removal effect of DOC and UV₂₅₄ under different molecular weight ranges also has similar rules.It was found that doc and UV₂₅₄ of less than 1KDa did not decrease effectively after treatment,while doc and UV₂₅₄ of 3K-10KDa and>30KDa decreased significantly.(5)With the increase of Fe(VI)dosage,the removal rates of TP increased rapidly at first and then slowly.When the dosage of Fe(VI)was 300?mol/L,the removal rates of TP by Fe(VI)(S)and Fe(VI)(L)were 86.49%and 93.25%,respectively.(6)Under the condition of a certain total iron dosage,Fe(VI)(S)/Fe(II)and Fe(VI)(L)/Fe(II)have the best TP removal effect when the molar ratio is 1:1.(7)Under the condition of total iron dosage of 180?mol/L,the removal effect of Fe(VI)(S),Fe(VI)(L),Fe(VI)(S)/Fe(II),Fe(VI)(L)/Fe(II)and Fe(III)on TP in secondary effluent was compared.The results show that the removal effect of TP is:[Fe(VI)(L)/Fe(II)]=1:1>[Fe(VI)(S)/Fe(II)]=1:1>Fe(VI)(L)>Fe(III)>Fe(VI)(S).It is obvious that Fe(VI)has a good removal effect on TP,and the removal effect of Fe(VI)(L)is better than that of Fe(VI)(S).The addition of Fe(II)improves the removal effect of Fe(VI)on TP on the basis of reducing the amount of Fe(VI).