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Novel electrospun membranes for membrane distillation
 
 
 
 

Novel electrospun membranes for membrane distillation

 
Ranil Wickramasinghe
 
University of Arkansas, USA
 
 

Development of new cost effective unit operations for recovery, recycle and reuse of wastewater is critical as the demand for water for beneficial uses increases. Unit operations that maximize water recovery are particularly appealing. Membrane distillation is an emerging unit operation that has the potential to maximize water recovery. However, membrane fouling and pore wetting are major challenges that limit the viability of this process. Here we focus on treating oily wastewaters from hydraulic fracturing operations as they are particularly challenging to treat given the range of contaminants present. Optimizing the membrane surface properties will be essential in order to develop fouling resistant membranes.

We have developed a novel PVDF based electrospun membrane to simultaneously solve fouling and pore wetting. Initially a PVDF blended with etyltrimethylammonium bromide electrospun membrane was prepared. Next a second layer was electrospun consisting of PVDF. Negatively charged silica nanoparticles were attached to the PVDF blended with etyltrimethylammonium bromide electrospun membrane by electrostatic adsorption. This creates an amphiphobic surface. Finally, the unmodified PVDF fibers were modified by grafting poly(glycidyl methacrylate-sulfobetaine methacrylate) (zwitterions) to the surface of the PVDF layer. The novel bilayer electrospun membrane was tested using both synthetic and real produced water feed Streams.

Our novel bilayer electrospun membranes showed excellent fouling resistance and salt rejection when compared to base PVDF membrane and the amphiphobic membrane without zwitterion grafting. When challenged with real produced water, the bilayer membrane showed superior flux compared to the two other membranes due to the presence of an antifouling hydrated layer. In practice it will be necessary pretreat the feed prior to membrane distillation. Thus, we have explored the use of electrocoagulation prior to membrane distillation.

Here we have challenged our bilayer electrospun membranes with hydraulic fracturing produced water. These wastewaters are particularly fouling as they contain dissolved salts, polar and non-polar organic compounds as well as surfactants. We highlight the importance of tailoring the surface properties of the membrane. Similarly developing membranes for treating other wastewaters e.g. brackish water, agriculture and aquaculture wastewaters will also require tailoring the membrane surface properties based on the contaminants that lead to membrane fouling.