Effect Of Polyvinyl Alcohol On Advanced Oxidation Processes Of Printing And Dyeing Wastewater And Its Resource Utilization

Polyvinyl alcohol（PVA）is a typical water-soluble polymer,which is often used as sizing agent in textile industry.The consumption of PVA used in textile manufacturing in China is about 140,000 tons per year.Almost all of these PVA were discharged into the wastewater during the fabric desizing process,resulting in desizing wastewater containing 5～15 g/L PVA and their COD_Cr is usually above20000 mg/L.Although PVA is non-toxic to organisms,it is not easily degraded by microorganisms during biological treatment.The impact of residual PVA entering advanced treatment on typical advanced oxidative processes（AOPs）is rarely reported.PVA molecule contains a large number of hydroxyl groups,and a large number of intramolecular or intermolecular hydrogen bonds which can make it form a stable network structure,which may also have negative effects on the elimination of co-existing contaminants in addition to their own difficulties in degradation.On the other hand,PVA may form long-chain carboxylic acids in AOPs,whether it will play a positive role in the generation of free radicals in advanced treatment is unknown.Therefore,we investigate the effect of different factors on the textile pollutants degradation for typical advanced oxidation technology,and focus on the effect of PVA coexistence on the treatment efficiency and residual product composition of advanced oxidation of printing and dyeing wastewater,and propose a method that can be used for resource utilization of PVA in desizing wastewater.（1）Based on the optimization of typical advanced oxidation treatment technology,the effect of PVA on the degradation of dye pollutants was investigated.The results show that the ozone oxidation system has the highest treatment efficiency for printing and dyeing wastewater.The presence of PVA has almost no negative impact on the Fenton system and the Ozone system,and the types of residue are simple.PVA will be oxidized into alkane molecular fragments containing carboxylic acid or carbon-carbon double bond in Fenton system,which can form complexes with Fe³⁺and Fe²⁺to enhance the efficiency of Fenton treatment,so that high concentration of PVA can still maintain the ideal treatment efficiency.In the PMS/Co activation system,the free radical with higher activity will take hydrogen from PVA and generate PVA free radical R·,which will strengthen the generation of·OH with the participation of oxygen,thus strengthening the advanced oxidation system.（2）Aimed at p-nitrophenol as the typical dye degradation product,the effect of coexisting PVA on the advanced oxidation process of simulated wastewater was investigated.The degradation efficiency of p-nitrophenol was low in persulfate system（PMS/Co and PS/heat）.The coexistence of PVA not only reduced the degradation efficiency of p-nitrophenol,but also significantly increased the species of residual products,which may be related to the quenching effect of p-nitrophenol on sulfate radicals.The ozone system is still the best among the four advanced oxidation systems.The TOC removal rate of p-nitrophenol wastewater containing PVA（10～500 mg/L）can reach to more than 70%.The direct reaction of ozone is the main reason for the degradation of p-nitrophenol.In Fenton system,the co-existence of PVA has little effect on the degradation efficiency of p-nitrophenol,and can reduce a variety of intermediates containing aromatic rings.（3）PVA wastewater after Fenton pre-oxidation treatment contains a large number of Fe（III）-organic ligand complexes,which has a high Fe（III）/Fe（II）cycle efficiency.As an iron-containing reagent for the degradation of dye pollutants,it has stronger stability and higher degradation efficiency than conventional Fenton reagent.Using boric acid-calcium chloride-persulfate crosslinking technology,PVA and sodium alginate in simulated desizing wastewater can be prepared into gel particles,which have strong adsorption capacity for cationic dye pollutants and can also catalyze the degradation of reactive dyes by persulfate.These two methods are expected to PVA-containing wastewater for effective resource utilization,reduce secondary pollution and reduce processing costs.