Study On The Degradation Of Polyvinyl Alcohol In Desizing Wastewater By Peroxymonosulfate Catalyzed By Loaded Biochar From Printing And Dyeing Sludge

Polyvinyl alcohol（PVA）-containing desizing wastewater is a complex,high-COD,and difficult-to-biodegradable wastewater produced in the printing and dyeing desizing process,which will have a greater adverse effect on subsequent biological treatment and receiving water bodies;among them,PVA is a high-molecular polymer that is difficult to biodegrade,so it is necessary to find an effective method for treating desizing wastewater and degrading PVA.In recent years,persulfate advanced oxidation has been extensively studied due to its higher redox potential.With the rapid development of the printing and dyeing industry,the output of sludge is increasing day by day.The preparation of sludge biochar for advanced oxidation catalysis has become an effective way to turn sludge into resources.In this paper,printing and dyeing biochemical surplus sludge was used as a carrier to prepare supported printing and dyeing sludge biochar（MSDBC）through activation and impregnation calcination,which was used to catalyze peroxymonosulfate（PMS）in order to degrade simulate PVA solution,optimize the preparation conditions and explore the kinetics and reaction mechanism.And we used the coagulation+MSDBC/PMS system to treat the actual desizing wastewater to explore the possibility of practical application.（1）First we prepared activated modified biochar.The experiment determined that the best activator was Na OH,the best activation temperature was 450℃,the best activation time was 2h,and the best activator concentration was 2 mol/L.The adsorption and degradation rates of PVA for 2 hours of biochar reaction were 17.8%and 63%.On the basis of the optimal activated modified biochar,the loaded manganese copper bimetal was impregnated.The single factor experiment determined that the optimal condition is:the calcination temperature was 450℃,calcination time was 2 h,metal loading was 5 mmol/g,manganese copper impregnation loading ratio was 2:1.Under certain reaction conditions,the degradation rate of PVA within 2 h reached96.5%.Orthogonal experiment analysis showed that the actual degree of influence was sorted as calcination time>metal impregnation>calcination time>manganese-copper ratio,and the optimal preparation conditions obtained were consistent with the results of the single factor experiment.The obtained biochar successfully loaded the active components Fe₃O_4,Cu O and Mn O₂,and had rich functional groups、good pore structure and magnetic properties.（2）Single factor experiment determined the optimal reaction conditions:PMS dosage was6 mmol/L,MSDBC dosage was 5 g/L,the initial p H of wastewater was 7,and the degradation rate of PVA in 2 h was 96.5%.The reaction process conformed to the secondary reaction kinetics.Orthogonal experiment analysis showed that the optimal reaction conditions were that the dosage of MSDBC is 5 g/L,the dosage of PMS was 7 mmol/L,and the p H was 8;under this condition,the degradation rate in 2 h was better than that under the optimal conditions of single factor experiment.The degradation rate was 98.7%,and it has good reusability and low metal leaching,which has application potential.（3）Mechanism analysis proved that SO₄^-·,·OH,O₂^-·and ¹O₂ were the active species in the MSDBC/PMS system under optimal reaction conditions,of which ¹O₂and·OH played a major role;after MSDBC/PMS catalytic oxidation,the molecular weight in the PVA solution was reduced,and organic substances such as small molecules of aldonic acid,which are easily degraded,were produced.The degradation mechanisms presumed to be that Fe₃O₄,Mn O₂,and Cu O catalyzed the production of SO₄^-·,·OH through valence conversion and simultaneously produced SO₅^-·,·OH,and then SO₄^-·,·OH reacted to produce O₂^-·,and SO₅^-·and PMS produced ¹O₂ under the catalysis of the surface groups of carbon materials and Cu O,which then attacked the PVA long chain to produce small molecular organics,and eventually degraded completely.（4）The experimental results of coagulant screening and dosage showed that the best dosage of PAC was 1450 mg/L,and the removal rate of COD and PVA for desizing wastewater were 36.3%and 14.4%respectively,and the precipitation effect was good.The MSDBC/PMS system was used to treat the coagulation effluent.When the dosage of MSDBC was 22.5 g/L,the dosage of PMS was 30 mmol/L,and the reaction time was 2.5 h,the removal rates of PVA and COD reached 98.6%and 38.1%respectively,and its biodegradability had also been improved.The degradation rate of PVA and COD was still 85.4%and 29.7%after four repeated use,and had certain application prospects.By introducing the wastewater effluent from printing and dyeing,the degradation effect was guaranteed and the total amount of wastewater was not increased,while the dosage of chemicals was reduced,which provided a way of thinking for the engineering application of coagulation+heterogeneous PMS system to treat desizing wastewater.