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
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.