Robust zirconia ceramic membrane with exceptional performance for purifying nano-emulsion oily wastewater

While membrane-based oil-water separation has been widely explored, using conventional membranes to treat oily wastewaters remains practically challenging especially when such wastewaters contain more stable nano sized oil droplets and are of high oil content, and harsh chemical conditions. Herein, we report a novel protocol of efficiently separating both synthetic and real oil nano-emulsions via specially designed robust zirconia membranes. The best-performing zirconia membrane, fabricated at low sintering temperature, has relatively uniform sub-100 nm pores and is underwater superoleophobic. Such zirconia membranes possess not only outstanding separation performance under long-term operation but robust structural stability at harsh conditions. At different cross-flow velocities, a combined model of intermediate pore blocking and cake filtration dominated membrane fouling behavior. Specifically, at high pH value (especially > pH((IEP))), membrane fouling was effectively mitigated due to a dominant role of electrostatic repulsion interaction at membrane-oil interface. Compared with conventional and commercial ceramic membranes, our zirconia membrane is the first reported in literature that can effectively reject nano-sized oil droplets (-18 nm) with over 99% rejection. Moreover, the zirconia membrane has also been challenged with real degreasing wastewater with very high oil content (-4284 mg L-1) and pH (-12.4) and delivered consistently high separation performance over many operation cycles.

Automated summary

The study reports a novel method of efficiently separating oil nano-emulsions using zirconia membranes with sub-100 nm pores and superoleophobic properties. The membrane fouling behavior is dominated by a combined model of intermediate pore blocking and cake filtration, with effective mitigation under high pH conditions. Overall, the zirconia membrane demonstrates high rejection efficiency for nano-sized oil droplets and consistent separation performance for real oily wastewaters.