Preparation Of Enhanced Hollow Fiber Membrane And Its Application In The Treatment Of Tetracycline Wastewater

This paper systematically studied enhanced polyvinylidene fluoride?PVDF?hollow fiber membrane,which is the core technology of membrane based water treatment process.Applying the self-prepared enhanced PVDF hollow fiber membrane coupled with attapulgite?APT?sorption was proposed for tetracycline?TC?removal from water.The effects of different pretreatment methods on the bonding properties between the separation layer and the support layer are systematically studied in order to solve the problem that hollow fiber membranes are easy to break.APT which is a highly hydrophilic fibrillar mineral in nature was added into the casting solution as an addictive to improve the comprehensive performance of PVDF membrane.A hybrid ultrafiltration membrane is prepared via a phase inversion method.The morphology,hydrophilicity,filtration ability,thermal stability and anti-fouling ability of the modified membrane were investigated.The effects of these factors on membrane structure and performance were investigated:PVDF content,additive composition,coagulation bath,coagulation bath temperature,and air gap.Here a process coupling palygorskite sorption and ultrafiltration was proposed for tetracycline removal from water.The efficiency of this process under different conditions was studied.The results show that:1.The separation layer and the support layer are easy to be peeled when the braided tube is used as the support body.The delamination problem can be solved by impregnating the braided tube with 2wt%PVA for 2 h.However,bleeding is a serious problem.The pretreatment method of impregnation crochet tube with 11wt%PEG10000 for 2h can solve the bleeding problem to some extent,and finally got enhanced membrane with high peel strength.2.Compared with the pure PVDF sample,the APT particle blended membrane had smaller pore size,better hydrophilicity,improved pure water flux,BSA rejection rate and anti-fouling ability.The statistic showed that the contact angle was decreased from87.4°to 78.8°.When the additive amount was below 6wt%,the pure water flux was increased from 104.1 to 232.4 L?m^-2?h^-1 and the recovery rate after fouled by BSA was increased from 37.9%to 59.4%.Thus,APT is a favorable addictive for fabrication of ultrafiltration membranes and the hybrid membrane shows better performance when the amount of additive is 6wt%.3.The pores become smaller and more uniform as the amount of PVDF increases within a certain range of PVDF content.The increase of the molecular weight of PVP leads to an increase in the viscosity of the casting solution,which restricts the formation of macropores and limits the number of cavities.The solvent influences the structure and the properties of the membrane by affecting the exchange rate between solvent and non-solvent and the precipitation rate of PVDF.When using ethanol as non-solvent,the pore size becomes smaller,more finger-like pores are formed,and the hydrophilicity of the solution increases,the contact angle decreases.The high coagulation bath temperature leads to the increase of membrane pore size and number of cavities.Low temperature is beneficial for the formation of small pores and finger-like pores.With the increase of air gap,the separation layer has the tendency of becoming thinner due to the gravity of the casting solution.The water flux decreases with the increase of air gap.4.Coupled system effectively removed tetracycline from water up to 90-98%.When using real wastewater as feed,reduction of COD_Cr,tetracycline removal rate and turbidity decrease were respectively 56±1%,95.3±0.4%,and 99.7±0.2%.The optimum conditions for the maximum removal rate were:p H 7.6,palygorskite 10 g?L^-1,dissolved oxygen 9.56 mg?L^-1,and hydraulic retention time 4.0 h.For the sorption of tetracycline on palygorskites,FTIR spectra and X-ray diffraction patterns before and after tetracycline sorption indicated that the structure of palygorskites was not altered and the sorbed tetracycline molecules did not affect the interlayer distance nor cause any exfoliation or reaction.5.Palygorskite could be successfully regenerated by exposure to 0.004 mol?L^-1sodium hydroxide with a recovery rate of 87%.6.In the combined system,membrane fouling was demonstrated to be reversible with regular backwash for flux recovery.Overall,the palygorskite sorption and ultrafiltration coupled system was a cost-effective technology to remove tetracycline from wastewater.