| Recently,persulfate(PS)advanced oxidation activated using iron-base transition metal is a new technology for wastewater treatment with efficient and economical method.Ultrasonics cavitation can efficiently degrade pollutants in water,among which hydrodynamic cavitaion(HC)technology has the advantages of high energy conversion efficiency and scale application compared with ultrasonic cavitation.Rhodamine B(RhB)is a typical heterocyclic basic dye with annual emissions of nearly 10,000 tons and is a common refractory organic compound.Combing the HC,iron-based catalyst and persulfate oxidation technology,the decolorization effect of RhB in four systems including HC/PS,HC-Fe0/PS,PS/FeMn@AC and HC-PS/FeMn@AC were conducted.The main research contents and conclusions are as followed:(1)The effects of inlet pressure(0～0.7 MPa),initial pH(2～9),PS concentration(0～2.4mM)and RhB initial concentration(10-50 mg/L)on RhB decolorization HC were studied in HC/PS system,in which persulfate were activated by HC.The results shown that the decolorization rate of RhB were 96.29%in 30 minwhen the inlet pressure is 0.5 MPa and the PS concentration is 1.2 mM at 25±2℃.Moreover,pH has a great influence on the decolorization rate of RhB,and proper acidic conditions are more favored decolorization then in neutral and alkaline conditions,but too low pH(pH<2)reduced the is decolorization rate of RhB.(2)HC-Fe0/PS reaction system was constructed by using zero-valent iron as heterogeneous catalyst to enhence decolorization rate.The capacity of HC to strengthen the activation of PS was studied,and the effects of inlet pressure(0-0.7 MPa),initial pH(2～9),Fe0 addition amount(0-0.16 g/L)and PS concentration(0-2.8 mM)on RhB decolorization efficiency were investigated.The results showed that HC can effectively enhance the Fe0/PS reaction,and the decolorization rate constant of RhB increased from 0.1496 min-1 to 0.3284 min-1 with the HC operation.Theresults of EDS test showed that the oxygen atom content on the surface of zero-valent iron catalyst decreased from 13.32%to 8.07%with exert of HC,indicating that HC can effectively prevent zero-valent iron surface from scaling.In addition,with exert of HC,surface corrosion of Fe0 was accelerated and iron ions were dissolved rapidly,with the second cycle recovery rate of Fe0 only 6.42%.(3)To maintain high activity of the catalyst and effectively recover it,FeMn@AC composite catalyst was prepared by the full mixing method,and the influence of parameters such as initial pH(3-11),FeMn@AC dosage(0～0.45 g/L),and PS concentration(0～3mM)on RhB decolorization efficiency of PS/FeMn@AC system was investigated.In PS/FeMn@AC system,without the adjustment to the initial pH value,RhB can effective decolorization,at 25 mg/L of initial RhBconcentration of,1.0 mM of PS,and 0.25 g/L of FeMn@ACat 20 ℃,99.5%of RhB decolorization were reached in 30 min.Although the catalyst still had high catalytic activity after three cycles,the content of FeMn@AC on the surface of FeMn@AC decreases and the content of low-valent metal ions(Fe2+,Mn2+)were oxidized to high valence state(Fe3+,Mn3+).Adding 100 mMmethanol and 100 mM tert-butyl alcoholas as scavengers,the decolorization rate of RhB was suppresses 82.19%and decreased slightly,respectively,indicating that free radicals SO4·-were the main active species of PS/FeMn@AC system.(4)To further improve the decolorization efficiency of RhB and the efficiency of catalyst use,HC enhanced PS/FeMn@AC degradation of RhB was studied in this experiment.The experimental results showed that HC-PS/FeMn@AC had a wide range of pH adaptation(pH=2～11).In the system,HC can effectively promote metal dissolution and improve the activation efficiency of PS.In addition,HC can promote metal ion circulation(Fe2+→Fe3+→Fe2+)and improve the recovery rate of FeMn@AC.After increasing HC,the recovery rate of FeMn@AC increased from 32.8%to 38.3%.Under the system of active free radicals have OH,SO4·-and O2·-,of which SO4·-is the main active substance,and O2·-produce the phenomenon with a delay.In addition,·OH is mainly produced by HC action on HC-PS/FeMn@AC system,and HC can shorten the time of O2·-.generated on PS/FeMn@AC system.To sum up,HC/PS,HC-Fe0/PS,PS/FeMn@AC and HC-PS/FeMn@AC treatments all have good decolorization effect on RhB,in which HC promotes metal dissolution and metal ion circulation,and has good synergistic effect with transition metal activation persulfate oxidation technology.FeMn@AC not only has a high recycling rate,but also can effectively activate persulfate,so FeMn@AC composite can be an effective alternative to Fe0 catalyst. |
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