Membrane oscillation and slot (pore) blocking in oil–water separation

Recent Advances in the Support Layer, Interlayer and Active Layer of TFC and TFN Organic Solvent Nanofiltration (OSN) Membranes: A Review

Although separation of solutes from organic solutions is considered a challenging process, it is inevitable in various chemical, petrochemical and pharmaceutical industries. OSN membranes are the heart of OSN technology that are widely utilized to separate various solutes and contaminants from organic solvents, which is now considered an emerging field. Hence, numerous studies have been attracted to this field to manufacture novel membranes with outstanding properties. Thin-film composite (TFC) and nanocomposite (TFN) membranes are two different classes of membranes that have been recently utilized for this purpose. TFC and TFN membranes are made up of similar layers, and the difference is the use of various nanoparticles in TFN membranes, which are classified into two types of porous and nonporous ones, for enhancing the permeate flux. This study aims to review recent advances in TFC and TFN membranes fabricated for organic solvent nanofiltration (OSN) applications. Here, we will first study the materials used to fabricate the support layer, not only the membranes which are not stable in organic solvents and require to be cross-linked, but also those which are inherently stable in harsh media and do not need any cross-linking step, and all of their advantages and disadvantages. Then, we will study the effects of fabricating different interlayers on the performance of the membranes, and the mechanisms of introducing an interlayer in the regulation of the PA structure. At the final step, we will study the type of monomers utilized for the fabrication of the active layer, the effect of surfactants in reducing the tension between the monomers and the membrane surface, and the type of nanoparticles used in the active layer of TFN membranes and their effects in enhancing the membrane separation performance.

Smart Superhydrophobic Filter Paper for Water/Oil Separation and Unidirectional Transportation of Liquid Droplet

Water/oil separation from their mixture and emulsion has been a prominent topic in fundamental research and in practical applications. In this work, a smart superhydrophobic membrane (SHP) was obtained by dipping an off-the-shelf laboratory filter paper in an ethanol suspension of trichloro (1H,1H,2H,2H-tridecafluoro-n-octyl) silane, tetraethyl orthosilicate, and titanium dioxide nanoparticles with different dimensions of 20 and 100 nm. The selection of membrane substrates was optimized including different quantitative and quantitative filter papers with different filtration velocity (slow, intermediate, and fast). The as-prepared SHP was demonstrated to be superhydrophobic and photosensitive, which was used in the separation of carbon tetrachloride and water from their mixture and emulsion. Moreover, orderly aligned micropores were formed for the modified superhydrophobic filter papers by using nanosecond laser. Unidirectional penetration was obtained for the UV-irradiated paper with a bored pore in the range of 50-500 μm in the systems of air/water and water/oil. This study may promote the understanding of unidirectional transportation of liquid droplet and facilitate the design of interfacial materials with Janus-type wettability.

Evaluating Fouling Control and Energy Consumption in a Pilot-Scale, Low-Energy POREFLON Non-Aerated Membrane Bioreactor (LEP-N-MBR) System at Different Frequencies and Amplitudes

Continual aeration, a fouling control strategy that causes high energy consumption, is the major obstacle in the deployment of membrane bioreactors (MBRs) for wastewater treatment. In recent years, a technology has been developed which adopts mechanical reciprocity for membrane vibration, and it has been proven efficient for membrane scouring, as well as for saving energy: the low-energy POREFLON non-aerated membrane bioreactor (LEP-N-MBR). In this study, a pilot-scale LEP-N-MBR system was designed, established, and operated at various frequencies and amplitudes, and with various membrane models, so as to evaluate energy usage and membrane fouling. The results showed that a slower TMP rise occurred when the frequency and amplitude were set to 0.5 Hz and 10 cm, respectively. Under a suitable frequency and amplitude, the TMP increasing rate of model B (sealed only with epoxy resin) was slower than that of model A (sealed with a combination of polyurethane and epoxy resin). The average specific energy demand (SED) of the LEP-N-MBR was 0.18 kWh·m^-3, much lower than the aerated MBR with 0.43 kWh·m^-3 (obtained from a previous study), indicating a significant decrease of 59.54% in the SED. However, the uneven distribution of sludge within the membrane tank indicated that the poor hydraulic mixing in the reactor may result in sludge accumulation, which requires further operational optimization. The findings of this pilot-scale study suggest that the LEP-N-MBR system is promising and effective for municipal wastewater treatment with a much lower level of energy usage. More research is needed to further optimize the operation of the LEP-N-MBR for wide application.

Experimental Investigation of the Novel Periodic Feed Pressure Technique in Minimizing Fouling during the Filtration of Oily Water Systems Using Ceramic Membranes

Fouling represents a bottleneck problem for promoting the use of membranes in filtration and separation applications. It becomes even more persistent when it comes to the filtration of fluid emulsions. In this case, a gel-like layer that combines droplets, impurities, salts, and other materials form at the membrane's surface, blocking its pores. It is, therefore, a privilege to combat fouling by minimizing the accumulation of these droplets that work as seeds for other incoming droplets to cluster and coalesce with. In this work, we explore the use of the newly developed and novel periodic feed pressure technique (PFPT) in combating the fouling of ceramic membranes upon the filtration of oily water systems. The PFPT is based on alternating the applied transmembrane pressure (TMP) between the operating one and zero. A PFPT cycle is composed of a filtration half-cycle and a cleaning half-cycle. Permeation occurs when the TMP is set at its working value, while the cleaning occurs when it is zero. Three PFPT patterns were examined over two feeds of oily water systems with oil contents of 100 and 200 ppm, respectively. The results show that the PFPT is very effective in minimizing the problem of fouling compared to a non-PFPT normal filtration. Furthermore, the overall drops in permeate flux during the cleaning half-cycles are compensated by appreciable enhancement due to the significant elimination of fouling development such that the overall production of filtered water is even increased. Inspection of the internal surface of the membrane post rinsing at the end of the experiment proves that all PFPT cycles maintained the ceramic membranes as clean after a 2-h operation. This can ensure a prolonged lifespan of the ceramic membrane use and a continuous greater permeate volume production. The advantage of the PFPT is that it can be implemented on existing units with minimal modification, ease of operation, and saving energy.

Modelling of transmembrane pressure using slot/pore blocking model, response surface and artificial intelligence approach

This work investigates the application of empirical, statistical and machine learning methods to appraise the prediction of transmembrane pressure (TMP) by oscillating slotted pore membrane for the treatment of two kinds of deformable oil drops. Here, we utilized the previous experimental runs with permeate flux, shear rate and filtration time as features, while TMP of crude oil and Tween-20 were two distinct targets. For 87 experimental runs, Response surface methodology (RSM) and Artificial Neural network (ANN) modelling were opted as statistical and machine learning tools, respectively, which were comprehensively compared with empirical slot-pore blocking model (SBM) considering accuracy and generalization. ANN with 10 neurons in the hidden layer could approximate the TMP of both oils better than RSM and SBM, which is reflected by computed performance metrics. Under the given conditions, almost similar analysis were predicted for TMP of both oils except changes in magnitude which were interpreted by (1) line plots, which showed that TMP of crude oil and Tween-20 were linearly related to flux rate and filtration time, and there was an inverse relationship between TMP and shear rate, (2) contour plots, which illustrated the strong interaction effect of flux rate and time on TMP, and (3)- sensitivity analysis, which revealed the influential sequence of variables on TMP as; flux rate > filtration time > shear rate, for both cases. The optimisation of the process showed that minimum TMP can be attained by maintaining higher shear rate and lower flux rate and time. Conclusively, the current findings indicate the utilization of ANN for the accurate assessment of TMP and can be helpful for the process designing and scale up.

Crude Oil Drop Penetration into Permeates Using a Slotted Pore Membrane

The primary focus of the presented research is to come up with a model that could be utilized to evaluate the permeate content (concentration) of oil drops using a straight (nonconverging) slotted microstructured membrane. The content (concentration) of crude drops in the permeate with a nonconverging slit structure membrane has not been studied before, and the study presented would be a good contribution to the literature. A comparison between the use of a converging (narrowing toward the inside) and a nonconverging slotted pore microstructured membrane is made for the purpose of removing oil content from the produced water. Due to the drag force, the droplets pass through the membrane slots; however, the static force acts in the opposite direction and tries to reject droplets by the membrane. At a certain point, these two forces balance the effect of each other, which is known as "100% cutoff through the membrane". A linear line is obtained by joining the 100% cutoff or rejection point to the 0% rejection point, which is referred to as the "linear fit" in this paper. The linear fit approach could be utilized for estimating rejection below the 100% cutoff point. Various types of crude oil drops obtained from different locations were analyzed experimentally, and the results were compared with the presented model. The proposed model was found to be in agreement with the different types of oil drops. Experimental and predicted results showed that the nonconverging slotted microstructured membrane provided low friction to oil drops through the membrane as compared to the converging slots. Furthermore, the developed model can be utilized to predict the overall oil content in the permeate. This research has great importance and will allow researchers around the globe to estimate crude oil concentration within the allowable limits.

Influence of Membrane Vibration on Particles Rejection Using a Slotted Pore Membrane Microfiltration

A new method is proposed to increase the rejection in microfiltration by applying membrane oscillation, using a new type of microfiltration membrane with slotted pores. The oscillations applied to the membrane surface result in reduced membrane fouling and increased separation efficiency. An exact mathematical solution of the flow in the surrounding solution outside the oscillating membrane is developed. The oscillation results in the appearance of a lift velocity, which moves oil particles away from the membrane. The latter results in both reduced membrane fouling and increased oil droplet rejection. This developed model was supported by the experimental results for oil water separation in the produced water treatment. It was proven that the oil droplet concentration was reduced notably in the permeate, due to the membrane oscillation, and that the applied shear rate caused by the membrane oscillation also reduced pore blockage. A four-times lower oil concentration was recorded in the permeate when the membrane vibration frequency was 25 Hz, compared to without membrane vibration. Newly generated microfiltration membranes with slotted pores were used in the experiments.