In the last decade, oil-water separation has gained global interest due to the large volumes of oily wastewater produced by various industries (e.g. food and beverage, metal and machining, pharmaceuticals) and the frequent oil spill accidents. Oil pollution is not only a pressing environmental problem, but it can also adversely impact human health due to contaminated water resources and crop production. Compared to other de-oiling technologies, membrane filtration offers several advantages including high quality permeate and ease of operation. To improve the feasibility of membranes for oil-water separation, a thorough understanding of oil deposition at the membrane surface during separation is needed to both optimally design and operate such processes.In this dissertation, Direct Observation Through the Membrane (DOTM) technique was employed to visualize oil drops in real-time at the membrane surface under conditions of hydrodynamic shear. This work was complemented by modeling of oil-membrane interactions and bench-scale crossflow filtration tests to gain quantitative understanding of oil droplet deposition on porous ultrafiltration (UF) and salt rejecting nanofiltration (NF) membranes. Experimental variables included surfactant type, salt type and concentration, and membrane material as well as pore size. Membrane fouling by emulsified oil was found to be a strong function of surfactant type. Visualization tests revealed that the worst type of fouling was observed when droplet coalescence resulted in contiguous oil films sealing large areas of the membrane. The visualization work was supplemented by deposition kinetics model that describes the three distinct stages of UF membrane fouling: (1) droplet deposition when the membrane surface is oil-free; (2) droplet deposition when membrane is coated by droplets; and (3) surface coalescence of droplets resulting in film formation. Nanofiltration of highly saline oil-water emulsions revealed that NF membrane fouling by emulsified oil enhances concentration polarization of rejected salt. However, headloss analysis showed that over the longer term, the additional hydraulic resistance due to a layer of oil droplets on the membrane surface became the dominant fouling mechanism.For both NF and UF membranes, when droplet-membrane interactions were favorable, this scenario led to formation and growth of surface films. These findings call for membrane materials or coatings that stunt the movement of the three-phase contact line to prevent oil film formation and spreading over the membrane surface. From the process engineering perspective, membrane surface sealing by oil films can be effectively managed by a hydraulic flush at zero transmembrane pressure.Finally, to achieve pipe parity, oil-water separation technologies need to consider legislature and regulations as well as environmental and social impacts (i.e. public perception).
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