Understanding Submicron Foulants in Produced Water and their Interactions with Ceramic Materials

Abstract

Produced water (PW), or water associated with crude oil extraction, is the largest oily wastewater stream generated worldwide. The reuse and reclamation of these important water volumes are critical for more sustainable operation in the oilfield. Ceramic membrane filtration is a promising technology for PW treatment; however, fouling is the major drawback for a broader application. Fouling leads to higher resistance to flow, reducing membrane lifetime, and ultimately leading to higher capital expenditures and operating expenses. Further understanding of the interactions between PW foulants and the ceramic materials is needed for designing fouling control strategies and cleaning protocols for ceramic membranes. This work explored different techniques to characterize, visualize, and quantify the submicron PW contaminants content and its adsorption interactions with metal oxides. We visualized and characterized submicron oil droplets in oilfield PW samples by applying suitable advanced microscopy techniques. For the first time, crude oil droplets as small as 20 nm were found in oilfield PW together with other submicron contaminants. The adsorption studies performed by quartz crystal microbalance with dissipation (QCM-D) showed that the interactions of organic surface-active compounds with the metal oxides are driven by the nature of the surfactant and not by the surface properties. This has implications in the selection of the ceramic membrane material, wherein electrostatic interactions should not be taken as the only predicting factor of adsorption and fouling during PW treatment. Furthermore, our results suggested that the more fluid or viscoelastic-like the contaminant layer, the more difficult the cleaning process from the metal oxide. It demonstrates that the mechanical property of the attached films is a crucial factor in designing appropriate cleaning protocols for ceramic membranes. Finally, QCM-D and advanced microscopy techniques were applied to analyze adsorption and cleaning of contaminants in a complex Bahraini PW into alumina as a case study. Bacteria were found to attach irreversibly on the alumina surface, promoting nucleation points for calcium precipitates. The protocols developed in this work are suitable for understanding membrane fouling phenomena in the micron scale and could be implemented before filtration pilot testing to save time and expenses at larger scales.