Chi Siang Ong

Treatment of dyeing solution by NF membrane for decolorization and salt reduction

Abstract A synthesized dyeing solution consisted of reactive dye, salts, and polyvinyl alcohol was prepared and treated by two different types of commercial nanofiltration (NF) membranes, i.e. NF90 and NF270 under various process conditions. These NF membranes were evaluated for permeate flux, salt, and color rejection as well as fouling propensity for a certain period of operation. Results revealed that NF90 suffered significant flux decline compared to NF270 after four operation cycles of treatment process, indicating its high sensitivity to foulant attachment. With respect to color removal, it is found that NF270 demonstrated greater stability in maintaining its separation efficiency (between 94 and 98% rejection) regardless of the feed properties and number of operation cycles. Though the salt rejection of NF270 was not as high as NF90, its consistent separation performance throughout the study period proved its reliability in long run. Recommended chemical cleaning process was also conducted in an ef...

Effect of PVP Molecular Weights on the Properties of PVDF-TiO2 Composite Membrane for Oily Wastewater Treatment Process

Polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes consisted of TiO2 and different molecular weight (Mw) of polyvinylpyrrolidone (PVP) (i.e., 10, 24, 40, and 360 kDa) were prepared to treat synthesized oily wastewater. The membrane performances were characterized in terms of pure water flux, permeate flux, and oil rejection while their morphological properties were studied using SEM, AFM, and tensile tester. Results show that the PVDF-TiO2 composite membrane prepared from PVP40k was the best performing membrane owing to its promising water flux (72.2 L/m2.h) coupled with good rejection of oil (94%) when tested with 250 ppm oily solution under submerged condition. It is also found that with increasing PVP Mw, the membrane tended to exhibit higher PVP and protein rejection, greater mechanical strength, smaller porosity, and a smoother surface layer. Regarding the effect of pH, the permeate flux of the PVDF-PVP40k membrane was reported to increase with increasing pH from 4 to 7, followed by decrease when the pH was further increased to 10. Increasing oil concentration in the feed solution was reported to negatively affect the water flux of PVDF-PVP40k membrane, owing to the formation of thicker oil layer on the membrane surface which increased water transport resistance. A simple backflushing process on the other hand could retrieve approximately 60% of the membrane original flux without affecting the oil separation efficiency. Based on the findings, the PVDF-TiO2 membrane prepared from PVP40k can be potentially considered for oily wastewater treatment process due to its good combination of permeability and selectivity and reasonably high water recovery rate.

Study on the thin film composite poly(piperazine-amide) nanofiltration membranes made of different polymeric substrates: Effect of operating conditions

Three composite nanofiltration (NF) membranes made of different substrate materials—polysulfone (PSf), polyethersulfone (PES) and polyetherimide (PEI)—were successfully prepared by interfacial polymerization technique. Prior to filtration tests, the composite NF membranes were characterized using field emission scanning electron microscope (FESEM), atomic force microscope (AFM) and X-ray photoelectron spectroscope (XPS). It was observed that the surface properties of composite NF membranes were obviously altered with the use of different substrate materials. The separation performance of the prepared composite NF membranes was further evaluated by varying operating conditions, which included feed salt concentration and operating temperature. Experimental results showed that the water flux of all TFC membranes tended to decrease with increasing Na2SO4 concentration in feed solution, due to the increase in feed osmotic pressure. Of the three TFC membranes studied, PSf-based membrane demonstrated the highest salt rejection but lowest water flux owing to its highest degree of polyamide cross-linking as shown in XPS data. With respect to thermal stability, PEI-based TFC membrane outperformed the rest, overcoming the trade-off effect between permeability and rejection when the feed solution temperature was gradually increased from 30 °C to 80 °C. In addition, the relatively smoother surface of hydrophilic PEI-based membrane when compared with PSf-based membrane was found to be less susceptible to BSA foulants, leading to lower flux decline. This is because smoother surface of polyamide layer would have minimum “valley clogging,” which improves membrane anti-fouling resistance.

Degradation of PVDF-based composite membrane and its impacts on membrane intrinsic and separation properties

Abstract In this work, an attempt was made to evaluate the effects of ultraviolet (UV) irradiation period on the intrinsic and separation properties of composite membrane composed of organic polyvinylidene fluoride and inorganic titanium dioxide (TiO2) nanoparticles by exposing the membrane to UV-A light for up to 250 h. The changes on membrane structural morphologies and chemical characteristics upon UV exposure were studied by field-emission scanning electron microscope and Fourier transform infrared, respectively. It was observed that some cracks and fractures were formed on the membrane outer surface when it was exposed to 120-h UV light. Further increase in UV irradiation time to 250 h had caused membrane structure to collapse, turning it into powder form. Filtration experiments showed that the permeate flux of irradiated membrane was significantly increased from 10.89 L/m2 h to 21.84 L/m2 h (>100% flux increment) while oil rejection decreased with increasing UV exposure time from 0 h to 120 h. Furthermore, the mechanical strength and thermal stability of irradiated membrane were also reported to decrease with increasing UV exposure time, suggesting the negative impacts of UV light on the membrane overall stability. This research is of particular importance to evaluate the suitability and sustainability of polymeric membrane, which is widely considered as the host for photocatalyts and used for wastewater treatment process under UV irradiation.