Preparation Of PVDF Hollow Fiber Membrane And Its Application In The Repair Of Polluted River

Hollow fiber membrane aeration is a technology that can effectively solve river pollution and restore river ecology.The preparation of high quality hollow fiber membrane is the key to the successful application of this technology.Aiming at the problems of low strength and hydrophilicity of ordinary hollow fiber membranes,the paper studies the preparation of polyester woven tube reinforced PVDF hollow fiber membranes and the effects of the use of porogens and surfactants on the hydrophilicity of hollow fiber membranes.And the hollow fiber membrane was used to design and manufacture the aeration system and its practical application.In this paper,polyester braided tube is introduced as the reinforcement of hollow fiber membrane,and the self-made coating device and spinning equipment are used to prepare reinforced hollow fiber membrane.The method has the advantages of simple operation,high production efficiency,and is beneficial to industrialized production.On this basis,the effects of two porogens PVP-K30 and PEG-400 on the properties of reinforced hollow fiber membranes were studied.Studies have shown that the introduction of reinforcements can greatly increase the strength of the membrane,and its breaking strength is as high as 190 MPa,which is nearly 20 times higher than that,which greatly expands the application field of hollow fiber membranes.At the same time,both PVP-K30 and PEG-400 can improve the porosity and permeability of the membrane.However,the opening effect of PVP-K30 on the surface of the membrane and the convenience of improving the pull-out and burst strength of the membrane are better than that of PEG-400,and PEG-400 has obvious advantages in inhibiting the generation of macropores and reducing the contact angle of the membrane surface.When two porogens are added at the same time,the effects produced by the two are superimposed.When 6wt%PVP-K30 and 4wt%PEG-400 are added,the removal and blasting strengths are slightly reduced,and other properties are very low.Excellent,pure water flux reaches 713.70 L·m-2·h-1.In the dissertation,a hydrophilic,high-throughput reinforced hollow fiber membrane suitable for hollow fiber membrane aeration was prepared by adding the surfactant Tween-80 to the casting membrane solution.Studies show that Tween-80 can significantly improve the permeability of the membrane and reduce the contact angle of the membrane.The highest pure water flux can reach 1142.77 L·m-2·h-1.When the amount of Tween-80 is 2wt%-At 5wt%,the contact angle is around 65".In addition,when the amount of Tween-80 is 2wt%-3wt%,it has the effect of reducing the surface pore diameter of the membrane,thereby increasing the bubble point pressure of the membrane.The thesis designed an aeration system using reinforced and hydrophilic PVDF hollow fiber membranes as aeration materials,carried out on-site repair of polluted river channels,and conducted long-term operation monitoring of the system for 3 months.Practical application shows that in the natural environment,it takes about 3 weeks to 1 month to hang the membrane.The hollow fiber membrane non-foam aeration system can effectively increase the DO content in the water body,inhibit the anaerobic fermentation of the sludge,and solve the problem of black odor in the river.Due to the role of biofilm,this system can effectively reduce the content of COD,NH3-N and TP in water,and the removal rates reach 64.42%,90%and 74.19%,respectively.After the restoration,all water quality standards of the river channel reached Class Ⅳ water standard.