Multi-stage Membrane Concentration Of Desizing Wastewater And Its Co-treatment With Dyeing Wastewater

The desizing wastewater has high organic content,strong alkalinity,and low biodegradability.It is a typical and refractory organic wastewater.How to effectively treat the desizing wastewater and ultimately utilize is a hotspot and difficult issue currently.In this paper,desizing wastewater including polyvinyl alcohol(PVA)was studied as the research object.Membrane distillation-ultrafiltration combined process was used for multi-stage membrane concentration of desizing wastewater.Because PVA could easily combine with reactive dyes by covalent bond,the co-treatment of desizing wastewater and dyeing wastewate was done.In the base of co-settlement of PVA and reactive dyes,with the flocculation of PSAZ under alkaline conditions,the desizing wastewater including PVA and the dyeing wastewater could be removed efficiently.The specific contents are as follows:Firstly,in this study,the desizing wastewater was set as the research object,using the combination of membrane distillation and ultrafiltration by multi-stage membrane treatment,the purification effectiveness of desizing wastewater and the concentration effectiveness of the polyvinyl alcohol were researched.With optimized working conditions,the combined process of membrane distillation and ultrafiltration can achieve a COD removal rate of the desizing wastewater more than 95%,and the original concentration of 1% PVA was concentrated to about 7%,for further treatment and utilization.In the meantime,based on the change of membrane flux decay after ultrafiltration and membrane distillation,the type of membrane fouling was obtained by fitting,and the SEM,contact angle were used to characterize the membrane fouling.Secondly,in this study,PVA was used to combine with reactive dyes by covalent bond,and desizing wastewater including PVA and dyeing wastewater were jointly treated to achieve the purpose of “wastes to treat wastes”.FT-IR,XPS,XRD and other characterization results show that the hydroxyl groups in the PVA structure can combine with the s-triazine or vinylsulfone groups in the reactive dyes structure by covalent bond under basic conditions to achieve copolymerization of PVA and reactive dyes.Studies have shown that the molar ratio of PVA and RB5,pH,ionic strength and reaction temperature are the main factors affecting copolymerization.The results showed that when the molar ratio of PVA and RB5 was 400:1,the heating temperature was 60°C,the heating time was 15 min,pH was 10,and the amount of sodium sulfate added was 40 g/L,the copolymerization effection was the best.The removal rates of chroma,COD and PVA concentrations were 62.7%,71.1% and 82.6% respectively.In addition,in order to further remove the residual chroma,PVA and COD after copolymerization of PVA and reactive dyes,PSAZ was used as a coagulant in this study to further treat the wastewater after copolymerization.The results show that the PSAZ has higher solubility in alkaline conditions than conventional coagulants such as iron salts and aluminum salts,which can neutralize reactive dyes to destabilize them to form flocculent precipitates.At the same time,the residual PVA in wastewater has a good coagulation effection as a macromolecule,which can effectively promote the coagulation and effective sedimentation of reactive dyes by PSAZ.At room temperature,when the pH value is 11 and the PSAZ dosing amount is 3 g/L,the color removal rate of the PVA and RB5 exceeds 99%,and the COD and PVA concentration can further reach over 80%.In summary,the membrane distillation-ultrafiltration combined process can effectively concentrate the lower concentration of desizing wastewater to a higher concentration,which facilitates further resource utilization.And the use of covalent bond between PVA and reactive dyes can make PVA and chroma removed effectively to achieve the purpose of “wastes to treat wastes”.At the same time,PSAZ is suitable for dye coagulation to remove color under alkaline conditions.Residual polymer PVA can play a role in coagulation,so that the residual chroma and PVA are further removed after co-polymerization of the waste liquid.The proposed method and mechanism study of these methods are expected to provide new ideas for the efficient treatment of desizing wastewater including PVA and dyeing wastewater.