Produced water is the largest single wastewater stream in oil and gas production1. In 2002, more than 14 billion barrels were handled in the U.S. alone2,3. This water often contains salts, heavy metals, emulsified oil and other organics1,2, rendering it unsuitable for human or animal consumption, or even agricultural use. Often, the most viable disposal option is subsurface injection. Subsurface injection costs vary from $0.50 to $1.75 per barrel3, representing annual operating costs of over 7 billion dollars per year for U.S. oil and gas operators. Water is an increasingly valuable commodity. In the arid western and mid-western states [e.g., Colorado, Montana, New Mexico, Utah, Texas and Wyoming], produced water could provide a valuable source of irrigation, industrial and even potable water if the organic content and salinity could be reduced to acceptable limits3. Produced water, therefore, represents an interesting opportunity as a new water source for a wide variety of uses.

The use of produced water requires removing suspended materials such as solids and emulsified oil. A palette of treatment technologies is available for removing organics and/or desalinating produced water. These technologies include reverse osmosis (RO) and nanofiltration (NF) membranes, freeze/thaw evaporation, ultraviolet radiation, chemical treatment with chlorine and other biocides, ion exchange membranes, electrodialysis, distillation and capacitive desalination2. Among these technologies, polymeric RO or NF membranes could represent the most flexible and viable long-term strategy. Moreover, polymer membranes are rapidly becoming the technology of choice for water desalination because they are cost-effective, small, and simple to operate and maintain4. RO membranes have been optimized over the past three decades for high water flux and high salt rejection. If less rigorous salt removal is required for other potential uses of produced water (e.g., agricultural or landscape watering, etc.), then less selective, higher flux NF membranes provide even higher production rates of purified water and higher recovery. Moreover, if only emulsified oil and suspended solids removal is required, higher flow, porous ultrafiltration (UF) membranes could be used5. When commercially available UF, RO, and NF membranes are exposed to a mixture of salt, emulsified oil droplets, and other particulate matter, their lifetime decreases catastrophically due to dramatic and largely irreversible permeate flux reduction which causes fouling of the membranes by organic components5. Fouling is the most significant roadblock to wider adoption of membrane technology for desalination specifically and water purification in general6.

We explored a new approach to improve the fouling resistance of commercial UF membranes by applying a thin coating of fouling-resistant polymer to the surface of such membranes. The water permeability and solute rejection of the coating materials will be reported. The oil droplet size and size distribution of oil/water emulsions were studied. The results of oil/water emulsion crossflow filtration experiments on uncoated and coated membranes will be presented. The effects of crossflow operation conditions on membrane separation performance were also investigated.