Study On The Preparation Of Poly(Vinylidene Fluoride) Flat Composite Membranes And Their Performances In The Membrane Bioreactor

In this thesis, flat composite polyvinylidene fluoride (PVDF) porous membranes were prepared by phase inversion method. The effects of preparation conditions on the structures and properties of PVDF membranes were studied. The obtained composite membrane was applied to the submerged membrane bioreactors (SMBRs) for wastewater treatments. The effects of processing parameters on the water quality, the energy consumption, the membrane fouling and membrane recovery were investigated.It was found that with the increasing of PVDF concentration in casting solution, the pore density and size on the surface of the membrane decreased, and the water flux of membrane also decreased gradually. When hydrophilic substance including polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG) and inorganic salt of LiCl were used as additives in casting solution, the water flux and average pore diameter of the obtained membranes is higher than that of membranes prepared from additive-free casting solution. Also, both of PVP and PEG resulted in a better hydrophilic surface of membrane. While the temperature of coagulation bath was increased, the water flux and average pore diameter of obtained membranes became larger. In addition, when the non-woven fabric was chosen as the support, the membrane revealed better performance because of the pores.Membrane bioreactors (MBRs) of PVDF flat composite membrane were used to wastewater treatment in a continuously running with better stability. The treated water, CODcr could be smaller than 20 mg/L, and more than 95% CODcr was removed. In comparison, the final stable membrane flux of above PVDF flat composite membranes was double times and two point five times for PE and PP hollow fiber membrane respectively. When trans-membrane pressure varied from 10 to 30 KPa, the flux had linear increasing trend with increased pressure. Added 0.5g/(L sludge mixture) powdered activated carbon (PAC) and intermission operation can reduce membrane fouling and enhance water flux. The fouling membrane was washed with water, alkali dipping/water, and alkali dipping/acid dipping/water respectively. Forthe systems without PAC, the recovered degree of flux could reach 58%, 90% and 94 %; For the PAC used systems, the recovered degree of flux was 80%, 92% and 95 % respectively.