Synthesis of tio2-pvdf membrane with enhanced wetting resistance for membrane distillation application

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Date
2018-08-01
Authors
Nur Suhaili Mohd Yatim
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Membrane distillation (MD) has emerged as an important technology for applications in industries such as seawater desalination and wastewater treatment due to lower energy requirement and theoretically low fouling propensity. However, the main obstacle to obtain high separating efficiency in MD lies on the availability of porous hydrophobic membrane that can withstand pore wetting and membrane fouling. A dual coagulation bath method was introduced to fine tune the membrane morphology to increase its porosity, surface roughness as well as polymer crystallinity. To increase the membrane hydrophobicity, membrane roughness was induced by adding TiO2 nanoparticles. However, this brought concomitant impacts on lower porosity due to the pore blocking and it also reduces hydrophobicity due to availability of hydroxyl group. The pore blocking problem can be solved by minimizing the particle size via surface acid modification. Nonetheless, the intrinsically hydrophilic nature of TiO2 still persist which brings unwanted wetting problem. By decreasing the particle size, it was interesting to note that the antibacterial properties on membrane towards E.Coli also improved, which means that the membrane bio-fouling problem can be mitigated by incorporating acid modified TiO2/PVDF membrane. To further enhance the hydrophobicity of the membrane, TiO2 was treated with flurosilane which was modified under acid, neutral and alkaline conditions. Silanized TiO2 with pH 7 gave higher contact angle (131.7±4), higher permeation flux (12kg/m2.h), excellent nutrient removal of 99.65%, high LEPw value and smaller pore size which can reduce the possibility of pore wetting. This optimum membrane was tested for treatment of high solid content wastewater namely paper mill SBR effluent (PSME) and palm oil mill effluent (POME) for a span of 7 hours. Consistent flux around 6 kg/m2.h for paper mill SBR effluent (PMSE) could be achieved showing that the membrane wetting and fouling resistance are good. The system efficiency is around 55% which is comparable to the pure water treatment process (50%). However, the membrane is not suitable to be used for treatment of the oil-rich palm oil mill (POME) effluent as the flux dropped from 6 to 2 kg/m2.h after 7 hours of operation. It was also found that palm oil mill effluent gave the lowest thermal efficiency of 26% compared to other processes due to fouling phenomena.
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