Engineering Omniphobic Slippery Membrane Surface for Wetting and Fouling Prevention: The Expanded Application of Membrane Distillation for Resource Recovery from Wastewater

The unprecedented demand for water, energy, and food, coupled with the impact of climatechange, has presented serious global challenges. The inextricable linkage among the water-energy-food nexus makes a vibrant research question for many scientists to explore innovativetechnologies for achieving global sustainable development. Hong Kong is no exception to thischallenge and to strengthen the growing city’s water security, a new desalination plant has beencommissioned. At the same time, considering the excessive concentration of nutrients in HongKong’s wastewater, many studies now focus on the development of new technologies with thepotential to recover resource from wastewater.Nitrogen removal by conventional treatment methods requires substantial energy to release itonly back to the atmosphere as gaseous nitrogen. In contrast, an emerging membranedistillation (MD) possesses several advantageous characteristics such as high rejection ofinorganic ions and non-volatile compounds thus guaranteeing a high quality of permeate water;insensitivity to feed concentration and not rigid requirements on membrane mechanicalproperties. Moreover, MD poses as a viable option for Hong Kong, mainly because the existingfacilities under operation by the city’s Drainage Service Department (DSD) can recover lowgrade heat to reduce energy consumption and MD can facilitate ammonia recovery bycontrolling the volatility and pressure of vapor transport across the membrane to concentrateammonia in the permeate stream.Like many other membrane applications, MD also cannot be free from membrane fouling andwetting, which is one of the major issues that huddle MD’s long-term performance. Based onour preliminary study, membrane wetting and fouling are not only attributed to membranehydrophobicity, but also the interaction between membrane surface charge and the foulants.To mitigate deleterious membrane fouling and wetting and to achieve maximum nutrientrecovery, it is integral to develop robust omniphobic MD membranes with superior anti-wettingand anti-fouling properties. Therefore, we propose to fabricate an engineered membrane bycontrolling the polymeric microspheres and fluorous coating which is highly resistant to foulingand wetting, then, to conduct a systematic study on the relationship between thephysicochemical properties of the membrane and foulants with different charges and surfacetension in real time using optical coherence tomography. This much-needed study on the role ofmembrane surface in attaining omniphobic feature with anti-fouling and anti-wetting properties inMD membranes will invigorate further research in this direction, bringing MD commercializationcloser within our reach.?