Study On Degradation Of Printing And Dyeing Wastewater By Encapsulated Iron Compounds Activated Persulfate

Dyeing wastewater has become a difficult problem in water pollution control due to its complex and variable water quality and its difficulty in biodegradation.The industry often uses a combination of biological and physical processes to treat printing and dyeing wastewater,and the effect is not very substantial,and the investment is huge.In recent years,persulfate（PS）has received extensive attention as an emerging advanced oxidation technology.PS has higher oxidation activity and longer half-life than Fenton’s reagent.PS is stable at room temperature,Excessive metal iron is commonly used as an activator,but traditional iron-based activators are easily oxidized and cannot be recycled and reused,resulting in waste of resources.First,the activators CS@NZVI and CS@Fe₃O₄ were prepared by coating chitosan（CS）with nano-zero-valent iron（NZVI）/Fe₃O₄.The activator was characterized by SEM,XRD,FT-IR and XPS.Using Rhodamine B（RhB）as the target pollutant,the efficacy and mechanism of degradation of RhB by CS@NZVI-PS and CS@Fe₃O₄-PS activation systems were studied by activator dosage,temperature,initial pH and PS concentration.（1）In the CS@NZVI-PS activation system.The optimal degradation conditions were:initial concentration of RhB was 10 mg/L,PS was 3 g/L,CS@NZVI was 0.7 g/L,initial pH=2.5,temperature was 55°C,degradation rate was 91%at 1 h,and the reaction rate constant was 0.049 min^-1.Orthogonal experiments show that the primary and secondary relationships of various factors are:temperature>PS>time>CS@NZVI>pH.The activation degradation behavior is consistent with the first-order kinetic model.As the pH decreases,the temperature increases and the reaction rate constant increases.The activation system reduces the activation energy of the reaction from 20.45KJ/mol to 10.92KJ/mol,and CS@NZVI can be reused four times at a rate above 0.036min^-1.The free radical capture and capture experiments show that the CS@NZVI-PS system is mainly composed of SO₄^-·and?OH to attack RhB molecules,of which SO₄^-·is dominant.（2）In the CS@Fe₃O₄-PS activation system,the optimal degradation conditions are:initial concentration of RhB is 10mg/L,PS is 3g/L,CS@NZVI is 2g/L,initial pH=3.5,temperature is 55°C,30min The degradation rate was 100%,and the reaction rate constant was 0.0862 min^-1.Orthogonal experiments show that the primary and secondary relationships of various factors are:temperature>time>PS>pH>CS@Fe₃O₄.The activation degradation behavior was consistent with the first-order kinetic model,and the activation energy of the system decreased from 21.41 KJ/mol to 12.59 KJ/mol.The activator can be reused five times at a rate above 0.0453 min^-1.SO₄^-·plays a major role in the activation system,and?OH assists in oxidative degradation of RhB.Then,the effects of common components of printing and dyeing wastewater on the degradation of RhB by two activation systems were studied and compared with the PS system.Among them,NaH₂PO₄ and Na₂SO₄ deactivated the surface of the two activators,hindered the reaction,and decreased the decolorization rate of RhB.With the increase of concentration,the inhibition effect is more obvious;K₂Cr₂O₇ will accelerate the degradation rate of the two activation systems,and the degradation rate of RhB will be accelerated by PS system.It is speculated that the Cr⁶⁺-PS system produce R^-·which can attack RhB molecule;Na₂CO₃ and disodium EDTA will precipitate and sequester Fe²⁺in the two activation systems,resulting in a lower decolorization rate than the PS system.Studies have shown that with the progress of the reaction,the inorganic salt and the dyeing agent have little effect on the degradation of RhB by the two activation systems,and the faster decolorization rate is compared with the PS system.Finally,the degradation of printing and dyeing wastewater by CS@Fe₃O₄-CS@NZVI-PS combination system in continuous flow system was studied.The results showed that the effluent was stable after treatment of simulated printing and dyeing wastewater for 4 h,the decolorization rate was 100%,and the Fe²⁺was 10.2 mg/L.When the CS@NZVI-PS and CS@Fe₃O₄-PS systems were completely decolored,the effluent Fe²⁺was 9.2 mg/L and 11.9 mg/L.It is speculated that the combined system undergoes a cyclic reaction between Fe⁰ and Fe³⁺,thereby effectively utilizing Fe³⁺in the system.After 8 hours of treatment of the actual printing and dyeing wastewater,the effluent was basically stable,the decolorization rate was 98%,and the COD removal rate reached 64%.The practical application effect is considerable.