Synergistic Application of Superhydrophilic Silanes Coating and Nanobubbles Turbulence to Mitigate Ceramic Nanofiltration Membrane Fouling

Abstract

Abstract Produced water and wastewater in the petroleum industry often have very high salinity. This incapacitates polymeric flocculants and flotation oil separation. Ceramic nanofiltration (NF) membranes seem like a natural solution for dispersed oils and macromolecules separations at high salinity and temperature. However, membrane fouling limits their application. We showed that by modifying wettability and surface charge and hydration of such membranes and promoting local turbulence one can mitigate membrane fouling. Based on our past work, we coated ceramic particles with nonionic silane coupling agents with ethylene oxide (CH2-CH2-O)6-9 or EO 9-12 groups. Titania has high surface charge and below isoelectric point attracts negative molecules and droplets. The opposite happens above the isoelectric point. Coating with ethylene oxide silane produced superhydrophilic surface with contact angle below 12 degrees and very low surface energy and zeta potential below +-5 mV. Such surfaces and oil droplets now did during pressure filtration attach in non-touching networks due to steric repulsions and hydration layers, where particles reside in the so called secondary interparticle force minimum that is much shallower. It was easy to clean so coated membranes from adsorbed oils and particles. Application of small nanobubbles with diameter between 50 and 225 nm further promoted turbulence and reduced fouling rate. During nanobubbles collapse, hydroxyl radicals are produced. Such turbulence and oxidative species significantly incapacitated bacteria and no biofouling were observed. Up to 85% reduction of fouling rate was achieved. Pulsed EC fields or radiofrequency RF electromagnetic fields can be used to further reduce nanobubbles’ size.