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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Abstract
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.