The Preparation Of High Strength And Hydrophilic Hollow Fiber Composite Membrane And The Application Of Composite Membrane In SMBR System

This paper mainly investigated the preparation of high strength and hydrophilichollow fiber composite membrane and the application of composite membrane inSMBR. Developed the technology of coating-immersion precipitation phase inversionfor preparing high strength hollow fiber composite membrane, and used hydrophilicmodifier modified the composite membrane, study the membrane formation conditionsof modified composite membrane and effects of casting solution component ratio onthe performance of composite membrane. Analyzed the pure water flux, average porediameter, porosity, bursting pressure of the membrane. By using scanning electronmicroscopy （SEM） analysis the membrane structure, and examines the removal effectof particles and organics in secondary effluent by hydrophilic composite membrane.The composite membrane which has best performance is made of membranemodule and used in SBR reactor in order to construct SMBR system for treatingsimulation municipal wastewater. Investigated the removal efficiency of nitrogen andphosphorus and the changes of membrane performance under various conditions of thesystem were studied, optimized the operating parameters of membrane bioreactor inorder to achieve highly effectives and stability, low power consumption. The mainconclusions of this study are as follows:The preparation of high strength hollow fiber composite membrane. With400D/96F low elastic polyester fiber as raw material, using high speed braidingmechanism prepared fiber braided tube which has internal diameter2.0mm, the number of spindles for24pounds,40objective polyester, and the braided tube was pretreatedwith NaOH aqueous solution. The casting solution system is PVDF/LiCl/DMAC, thecasting solution temperature is40℃and the bath gel is35℃water Throughcoating-immersion precipitation phase inversion method, the homogeneous cast solutionis coated on the surface of the braided tube after the pretreatment by self-made coatingdevice. The hollow fiber composite membrane with high strength is prepared afterphase separation, the coating layer and the woven tube of composite membranecombinated closely. The structure of coating layer is thin and dense, the tensile strengthof the composite membrane has exceeded the test range of laboratory instrumentbecause the exist of the braided tube support layer.The composite membrane is modified by hydrophilic through adding the PVPhydrophilic modification additive in the PVDF/LiCl/DMAC casting solution system,using the hydrophilic composite membrane treat the high turbidity raw water andsecondary effluent.1)With the increase of PVDF concentration in casting solution,composite membrane pure water flux and the average pore diameter decreased, whilebursting pressure increased, and porosity first increased and then decreased.2) Whilewith the increase of PVP concentration in costing solution, composite membrane purewater flux and the average pore diameter decreased, while the porosity and intensityincreased. When the PVP concentration in casting solution exceed8%, the average porediameter increased, and porosity and intensity decreased.3) The hydrophilic compositemembrane has very good removal efficiency on particulate, the turbidity of membraneeffluent is below0.1NTU; and the membrane also has a certain effect on the removal oforganic compounds in the sencondary effluent.4) In the research, composite membranepure water flux up to4300L m^-2 h^-1, burst pressure up to0.32MPa, the porosity ofcomposite membrane matain45-60%, burst pressure is higher than0.30MPa. When thecasting solution system of PVDF/PVP/LiCl/DMAC ratio is12:6:3:79, the castingsolution temperature is40℃, the bath gel is35℃water, the separation performanceand structure of the composite membrane is the best.Study the effect of three kinds of hydrophilic polymer additive PVP, PEG, PVA onmembrane hydrophilic modified process, the contribution to the membrane performancethat adding PVP and PVA is more outstanding than PEG. The composite membrane module is used in SBR reactor in order to constructSMBR system for treating simulation municipal wastewater.1) The compositemembrane has good tensile and compressive strength and anti-pollution performance.During the experiment, the membrane operates in high water flux (water flux was20L m^-2 h^-1) and without any cleaning of membrane for2months, but the TMP alwaysbelow6.0kPa. The process of membrane fouling is slow, the composite membrane canmaintain stable operation in high water flux and low pressure in SMBR. The averageturbidity of membrane effluent is0.02NTU;2) The system has very good removalefficency of organics and ammonia nitrogen. The COD removal rate was above90%,the average COD concentration of effluent is32mg L^-1, ammonia nitrogen removal rateis greater than95%, the average concentration of ammonia is0.2mg L^-1;3), Theaverage total nitrogen removal rate of SMBR system is greater than70%. The effect ofremoval efficiency of phosphorus in different conditions is much larger, appropriatelyincreasing the reactor water filling ratio and prolonging stirring time can effectivelyimprove the removal efficiency of phosphorus;4) When the filling ratio is43%and thestirring time is2hours, the system has best treatment efficiency. The CODconcentration of effluent is less than35mg L^-1, the ammonia concentration lower than0.35mg L^-1, the total nitrogen concentration is below12.5mg L^-1, the total phosphorusconcentration is below0.25mg L^-1.