Abstract
Membrane-based processes are attractive for treating oily wastewaters. However, membrane fouling due to the deposition of oil droplets on the membrane surface compromises performance. Here, real-time observation of the deposition of oil droplets by direct confocal microscopy was conducted. Experiments were conducted in dead-end and crossflow modes. Base NF 270 nanofiltration membranes as well as membranes modified by grafting poly(N-isopropylacrylamide) chains from the membrane surface using atom transfer radical polymerization were investigated. By using feed streams containing low and high NaCl concentrations, the grafted polymer chains could be induced to switch conformation from a hydrated to a dehydrated state, as the lower critical solution temperature for the grafted polymer chains moved above and below the room temperature, respectively. For the modified membrane, it was shown that switching conformation of the grafted polymer chains led to the partial release of adsorbed oil. The results also indicate that, unlike particles such as polystyrene beads, adsorption of oil droplets can lead to coalescence of the adsorbed oil droplets on the membrane surface. The results provide further evidence of the importance of membrane properties, feed solution characteristics, and operating mode and conditions on membrane fouling.
Highlights
Membrane fouling compromises the performance of all membrane-based separation processes.Rejected and unwanted species can adsorb on the membrane surface
The present work focused on the fouling of nanofiltration (NF) membranes by oil–water emulsions
Developed initially for softening of surface and ground water [3], today, these membranes are used for many other applications, one of which is treating oily wastewaters
Summary
Rejected and unwanted species can adsorb on the membrane surface. One strategy to minimize the effect of fouling is to modify the surface of the membrane in order to reduce adsorption of unwanted species on the membrane surface [1,2]. In this way, desirable bulk membrane properties, such as pore size, pore size distribution, and morphology, are preserved while tuning membrane surface properties. Depending on the source of the oily wastewater, many other contaminants can be present such as dissolved salts, surfactants, polar organic compounds, etc.
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