Assessing the fouling behavior of PTFE membrane in air-gap membrane distillation against oil-in-brine stabilized emulsions

Understanding the fouling behavior in membrane operations is crucial for designing an effective treatment sequence. The membrane materials, feed characteristics, and operating conditions affect the fouling behavior. In this study, the fouling behavior of polytetrafluoroethylene (PTFE) membrane in membrane distillation was assessed after the treatment of oil-in-brine stabilized emulsions. Membrane backwash by water in membrane distillation partially restored the membrane’s initial condition and eliminated salt fouling. Moreover, the effect of feed pretreatment by ultrafiltration on the fouling of the subsequent PTFE membrane was investigated. Remarkable improvements in salt rejection (> 98.5%) and oil rejection (> 96%) were observed for the hybrid system. Extensive characterizations were carried out to evaluate the fouling behavior. Surface morphology and elemental analysis revealed the nature of foulants. Fourier transform infrared spectroscopy was utilized to study the change in the surface chemistry of the membranes after being subjected to the oily brine feed. No peak shifting was observed indicating no chemical bonding between the organic contaminants and the membrane surface. Further elaboration of the results was achieved by measuring the mechanical stability and contact angle of the membranes. Reduction in the mechanical properties and water contact angle of the membranes was observed after fouling and wetting. Results indicated that ultrafiltration was an effective pretreatment process for membrane distillation using PTFE membrane. However, more unit operations should be incorporated to enhance the membranes’ integrity.