Abstract
Managing the wastewater discharged from oil and shale gas fields is a big challenge, because this kind of wastewater is normally polluted by high contents of both oils and salts. Conventional pressure-driven membranes experience little success for treating this wastewater because of either severe membrane fouling or incapability of desalination. In this study, we designed a new nanocomposite forward osmosis (FO) membrane for accomplishing simultaneous oil/water separation and desalination. This nanocomposite FO membrane is composed of an oil-repelling and salt-rejecting hydrogel selective layer on top of a graphene oxide (GO) nanosheets infused polymeric support layer. The hydrogel selective layer demonstrates strong underwater oleophobicity that leads to superior anti-fouling capability under various oil/water emulsions, and the infused GO in support layer can significantly mitigate internal concentration polarization (ICP) through reducing FO membrane structural parameter by as much as 20%. Compared with commercial FO membrane, this new FO membrane demonstrates more than three times higher water flux, higher removals for oil and salts (>99.9% for oil and >99.7% for multivalent ions) and significantly lower fouling tendency when investigated with simulated shale gas wastewater. These combined merits will endorse this new FO membrane with wide applications in treating highly saline and oily wastewaters.
Highlights
Successful story with RO membranes for treating shale gas produced wastewater
Our previous studies showed an interesting phenomenon that using nanomaterial as support layer of forward osmosis (FO) membrane can effectively improve the membrane structure, which results in reduced internal concentration polarization (ICP, see the concept of ICP in Supplementary Information (SI)) and significantly enhanced water flux[38,39]
In contrast to previously reported electrospun nanofibers, this GO infused polymeric support layer was synthesized by established phase inversion technique[40] that is ready for commercial scale up
Summary
Successful story with RO membranes for treating shale gas produced wastewater. In contrast to reverse osmosis, forward osmosis (FO) membrane process is driven by an osmotic gradient between the feed solution and the draw solution on the permeate side that has a higher osmotic pressure than the feed solution[13,14,15]. The only commercially available FO membrane (HTI, USA) has intrinsic drawbacks with: (1) high membrane fouling propensity because of the relatively hydrophobic property of its membrane material (cellulose triacetate, whose water contact angle is ~87°, as shown in this study); and (2) low water flux because of its unfavorable membrane structure (low porosity and high tortuosity, which cause severe internal concentration polarization)[23,24,25] It is in high demand for FO membranes that are custom-designed for treating shale gas produced wastewater with the merits of ultralow membrane fouling and high water flux. We report a new nanocomposite FO membrane that is custom-designed for treating shale gas produced wastewaters with combined merits of ultralow membrane fouling, high water flux and high salt rejection This nanocomposite FO membrane consists of a highly underwater oleophobic hydrogel selective layer on top of a nanomaterial infused polymeric support layer. This is the first report on a FO membrane with integrated properties of oil repellency, salt rejection and high water flux that targets at shale gas produced wastewaters
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