Separation performance of horizontal and vertical polyethersulfone hollow fiber UF modules

The effect of hollow fiber module positions （ horizontal and vertical） on separation performance for PVA solution by using polyethersulfone （PES） hollow fiber ultrafiltration （UF） membrane with the molecular weight cut-off （MWCO） 30 000 has been discussed. Experimental results illustrated that the suitable operation conditions for PVA solution were as follows： trans-membrane pressure 2.1 bar, solution temperature 75℃ and feed velocity 0.32 m/s. Under these suitable operation conditions, the permeate flux is from 36.8 L/（m^2 ·h·bar） to 42.9 L/（m^2 ·h·bar） for the horizontal module and from 39.8 L/（m^2 ·h·bar） to 66.6 L/（m^2 ·h·bar） for the vertical module. Besides, the Separation performance of PES hollow fiber UF membrane was better by using vertical hollow fiber module than by using horizontal hollow fiber module. When the trans-membrane pressure increased from 1 bar to 2.1 bar, solution temperature from 50 ℃ to 75 ℃, feed solution velocity from 0.16 m/s to 0.32 m/s, the PVA rejection would increase from 95.8% to 99.7%, 95.4 96 to 98.6 %, 95.8 96 to 99.2 96 for horizontal module respectively, and from 98.8 96 to 99.8 %, 98.6 96 to 99.4 96, 98.5 96 to 99.4 96 for vertical module respectively. Therefore, PVA rejection in PES hollow fiber UF process was more than 98.5 96 for vertical module, and it is suitable for PVA recovery from wastewater.

Fabrication of Cu(OH)_2 Nanowires Blended Poly(vinylidene fluoride) Ultrafiltration Membranes for Oil-Water Separation

Cu（OH）2 nanowires were prepared and incorporated into poly（vinylidene fluoride）（PVDF） to fabricate Cu（OH）2-PVDF ultrafiltration（UF） membrane via immersion precipitation phase inversion process. The effect of Cu（OH）2 nanowires on the morphology of membranes was investigated by X-ray photoelectron spectroscopy（XPS）, Fourier transform infrared（FTIR） spectroscopy, atomic force microscopy（AFM）, scanning electron microscopy（SEM） and X-ray diffraction（XRD） measurements. The results showed that all the Cu（OH）2-PVDF membranes had wider fingerlike pore structure and better hydrophilicity, smoother surface than pristine PVDF membrane due to the incorporation of Cu（OH）2 nanowires. In addition, water flux and bovine serum albumin（BSA） rejection were also measured to investigate the filtration performance of membranes. The results indicated that all the Cu（OH）2-PVDF membranes had high water flux, outstanding BSA rejection and excellent antifouling properties. It is worth mentioning that the optimized performance could be obtained when the Cu（OH）2 nanowires content reached 1.2 wt%. Furthermore, the membrane with 1.2 wt% Cu（OH）2 nanowires showed outstanding oil-water emulsion separation capability.

Aging of PVDF and PES ultrafiltration membranes by sodium hypochlorite:Effect of solution pH

Sodium hypochlorite(NaClO)is a commonly applied cleaning agent for ultrafiltration membranes in water and wastewater treatment.Long-term exposure to NaClO might change the properties and performance of polymeric membranes,and ultimately shorten membrane lifespan.Active species in NaClO solution vary with solution pH,and the aging effects can change depending on the membrane material.In this study,the aging of polyvinylidene fluoride(PVDF)and polyethersulfone(PES)membranes by NaClO at pH 3–11 was investigated by examining variations in chemical composition,surface charge,surface morphology,mechanical strength,permeability,and retention ability.Polyvinyl pyrrolidone(PVP),which was blended in both membranes,was oxidized and dislodged due to NaClO aging at all investigated pH values,but the oxidation products and dislodgement ratio of PVP varied with solution pH.For the PVDF membrane,NaClO aging at pH 3–11 caused a moderate increase in permeability and decreased retention due to the oxidation and release of PVP.The tensile strength decreased only at pH 11 because of the defluorination of PVDF molecules.For the PES membrane,NaClO aging at all investigated pH resulted in chain scission of PES molecules,which was favored at pH 7 and 9,potentially due to the formation of free radicals.Therefore,a decrease in tensile strength and retention ability,as well as an increase in permeability,occurred in the PES membrane for NaClO aging at pH 3–11.Overall,the results can provide a basis for selecting chemical cleaning conditions for PVDF and PES membranes.