Publication: Fabrication of superhydrophobic microsphere electrospun membrane through template printing technique to enhance membrane distillation for aquaculture wastewater treatment
Date
2023-05-01
Authors
Zhou Lei
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Abstract
Membrane distillation (MD) is one of the promising technologies for
desalination and wastewater treatment. Electrospinning membranes (EMs) is
frequently used in MD applications because it has an interconnected pores structure
to facilitate the transport of water vapor, which can increase the permeation flux of
MD. Aquaculture wastewater contains a large amount of inorganic and organic
compounds, which can cause wetting and fouling of MD membrane. The
superhydrophobic membrane can reduce the wettability of the membrane and
maintain a long-term stable desalination process during MD. In this work,
superhydrophobic poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)
electrospun membranes were fabricated by template printing technique to construct
hierarchical microtextures on membrane surfaces. When the injection rate was 1.0
mL/h and the solvent weight ratio of N-methyl-2-pyrrolidone (NMP) and
tetrahydrofuran (THF) was 1:1, the membrane exhibited optimal printed
microtextures when electrospun at the temperature of 30±2 ℃ and the relative humidity of 70±5 %. The microtexture template structure provides hierarchical
micro-and nano-roughness on the membrane surface. The optimal membrane exhibits
superhydrophobicity, with a static contact angle of 158° and a sliding angle of 8.5°.
In the direct contact membrane distillation (DCMD) for treating high saline water
and aquaculture wastewater, the initial permeation fluxes of the optimal membrane
were as high as 40.76 kg·m-2·h-1 and 33.45 kg·m-2·h-1, which were 161% and 174%
higher than the non-printed membrane. To further enhance the superhydrophobicity
of the templated PVDF-HFP membrane, microsphere beads were integrated in the
membrane matrix. The fabricated membrane exhibited interconnected microspherenanofiber
structure with hierarchical micro-nano roughness. Due to the intrinsic
microspheres on the nanofibers, the water contact angle of all microsphere/nanofiber
membranes were higher than 150°. The optimal membrane exhibited
superhydrophobicity, with a static contact angle of 157° and a low sliding angle of
6.4°. In DCMD, the optimal membrane shows a high permeation flux of 38.8 kg·m-
2·h-1 and a salt rejection of 99.99% in separating high saline water as well as a
permeate flux of 32.68 kg·m-2·h-1 and a salt rejection of 99.98% in treating
aquaculture wastewater. In addition, the microsphere-nanofiber membrane also
exhibited a stable separation process and excellent anti-fouling for 72-hours longterm
DCMD. Overall, the surface microtexture printed superhydrophobic membrane
show great potential in practical desalination applications.