Dejun Feng,Shaodan Xie,Wenting Zhou,Yuanmiaoliang Chen,Zhangxin Wang
Membrane wetting is a prominent challenge in the practical applications of membrane distillation (MD). In this study, we hypothesize that increasing the hydraulic pressure on the distillate side (Pd) can mitigate membrane wetting, an operation mode we refer to as pressurizing distillate membrane distillation (PDMD). To implement PDMD, an accurate measurement of the liquid entry pressure (LEP) of the membrane with the feed solution is essential. However, the conventional LEP measurement method struggles with solutions containing amphiphilic agents. Herein, we develop an impedance-based LEP measurement method and validate it by measuring the LEPs of a commercial poly(tetrafluoroethylene) (PTFE) membrane with ethanol–water mixtures. Further, we demonstrate that this method can accurately measure the LEPs of the PTFE membrane with solutions containing sodium dodecyl sulfate (i.e., a representative amphiphilic agent) by capturing the subtle changes of the feed solutions within the membrane. Additionally, we show that PDMD can effectively mitigate membrane wetting induced by various wetting agents, as the elevated Pd results in a transmembrane hydraulic pressure lower than the LEP of the membrane. Overall, our study provides an effective wetting mitigation approach that can be easily applied in practical MD and membrane contactor applications.
Recovering oil from oily wastewater is not only for economic gains but also for mitigating environmental pollution. However, demulsification of oil droplets stabilized with surfactants is challenging because of their low surface energy. Although the widely used oil/water separation membrane technologies based on size screening have attracted considerable attention in the past few decades, they are incapable of demulsification of stabilized oil emulsions and the membrane concentrates often require post-processing. Herein, the piezoelectric ceramic membrane (PCM), which can respond to the inherent transmembrane pressure in the pressure-driven membrane processes, was employed to transform hydraulic pressure pulses into electroactive responses to in situ demulsification. The pulsed transmembrane pressure on the PCM results in the generation of considerable rapid voltage oscillations over 3.2 V and a locally high electric field intensity of 7.2 × 10 7 V/m, which is capable of electrocoalescence with no additional stimuli or high voltage devices. Negative dielectrophoresis (DEP) force occurred in this membrane process and repelled the large size of oil after demulsification away from the PCM surface, ensuring continuous membrane demulsification and oil/water separation. Overall, PCM provides a further opportunity to develop an environmentally friendly and energy-saving electroresponsive membrane technology for practical applications in wastewater treatment.
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