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Hollow fiber microfiltration (MF) and ultrafiltration (UF) membrane processes have been extensively used in water purification and biotechnology. However, complicated filtration hydrodynamics wield a negative influence on fouling mitigation and stability of hollow fiber MF/UF membrane processes. Thus, establishing a mathematical model to understand the membrane processes is essential to guide the optimization of module configurations and to alleviate membrane fouling. Here, we present a comprehensive overview of the hollow fiber MF/UF membrane filtration models developed from different theories. The existing models primarily focus on membrane fouling but rarely on the interactions between the membrane fouling and local filtration hydrodynamics. Therefore, more simplified conceptual models and integrated reduced models need to be built to represent the real filtration behaviors of hollow fiber membranes. Future analyses considering practical requirements including complicated local hydrodynamics and nonuniform membrane properties are suggested to meet the accurate prediction of membrane filtration performance in practical application. This review will inspire the development of high-efficiency hollow fiber membrane modules.

In this work, a conductive thin film composite forward osmosis (TFC-FO) membrane was firstly prepared via vacuum filtering MXenes nanolayer on the outer surface of polyethersulfone membrane followed by interfacial polymerization in the other side. Moreover, its feasibility of mitigating organic fouling under electric field was evaluated. Results indicated that the addition of MXenes greatly reduced the electric resistance of membrane from 2.1 × 1012 to 46.8 Ω, enhanced the membrane porosity and promoted the membrane performance in terms of the ratio of water flux to reverse salt flux. The modified TFC-FO membrane presented the optimal performance with 0.47 g/m2 loading amount of MXenes. Organic fouling experiments using sodium alginate (SA) and bovine serum albumin (BSA) as representative demonstrated that the introduction of MXenes could effectively enhance the anti-fouling ability of TFC-FO membrane under the electric field of 2 V. The interelectron repulsion hindered organic foulants attaching into membrane surface and thus effectively alleviated the membrane fouling. More importantly, the modified TFC-FO membrane showed good stability during the fouling experiment of 10 h. In all, our work proved that introducing MXenes into the porous layer of support is feasible to alleviate organic fouling of FO membrane.

The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na2SO4 circulating fluidized bed evaporator. The particle collision signals are analyzed with standard deviation by varying the amount of added particles e (1%–3%), circulation flow velocity u (0.37–1.78 m·s–1), and heat flux q (7.29–12.14 kW·m–2). The results show that the enhancement factor reach up to 14.6% by adding polytetrafluoroethylene particles at e = 3%, u= 1.78 m·s–1, and q= 7.29 kW·m–2. Both the standard deviation of the particle collision signal and enhancement factor increase with the increase inthe amount of added particles. The standard deviation increases with the increase in circulation flow velocity; however, the enhancement factor initially decreases and then increases. The standard deviationslightly decreases with the increase in heat flux at low circulation flow velocity, but initially increases and then decreases at high circulation flow velocity. The enhancement factor decreases with the increase in heat flux. The enhancement factor in Na2SO4 solution is superior to that in water at high amount of added particles. The empirical correlation for heat transfer is established, and the model results agree well with the experimental data.

A new variant of the fluid dynamic gauging technique for determining the thickness of soft fouling layers in situ and in real time is reported. The sideways fluid dynamic gauging (SiDG) device allows measurements to be made shortly after a deposit layer contacts a solution, allowing processes such as swelling to be characterized accurately. Two applications of the device are reported: (i) in cleaning, monitoring the change of thickness of a complex food soil when it is contacted with aqueous solutions at different temperatures, pH and surfactant content, and (ii) in fouling, in determining the thickness, thermal conductivity and strength of deposits generated from whey protein solutions on heated stainless steel substrates. The evolution of fouling resistance for the whey protein deposits indicates that significant aging takes place during the fouling test, which is confirmed by changes in the thermal properties and strength of the deposit layer as measured by the SiDG device.

Contaminants on architectural ceramics have become a major problem in people's lives. Interestingly, superhydrophobic surfaces offer a new avenue for anti-fouling applications. In this work, a UV-laser process for constructing groove-like microstructures on architectural ceramics and subsequent fluoridation treatment were used to create superhydrophobic surfaces. After laser processing, nanoporous structures were generated inside the grooves, while the cracked layer was deposited on the non-irradiated area, building up a micro/nanoscale morphology on the ceramic surface. Moreover, the effects of groove pitch and laser scanning cycle on surface morphology and wettability were investigated. Results indicate that the fluoridated groove-like microstructured surface showed good superhydrophobicity based on the Cassie-Baxter model. Dynamic behavior of water droplets impacting on the as-prepared superhydrophobic surface was studied to verify its low adhesion. Additionally, the superhydrophobic surface exhibited remarkable repellency to various stain liquids and outstanding self-cleaning properties. These findings may contribute to developing anti-fouling applications for the architectural ceramics industry.

Addressing thrombosis and biofouling of indwelling medical devices within healthcare institutions is an ongoing problem. In this work, two types of ultra-low fouling surfaces (i.e., superhydrophobic and lubricant-infused slippery surfaces) were fabricated to enhance the biocompatibility of commercial medical grade silicone rubber (SR) tubes that are widely used in clinical care. The superhydrophobic (SH) coatings on the tubing substrates were successfully created by dip-coating in superhydrophobic paints consisting of polydimethylsiloxane (PDMS), perfluorosilane-coated hydrophobic zinc oxide (ZnO) and copper (Cu) nanoparticles (NPs) in tetrahydrofuran (THF). The SH surfaces were converted to lubricant-infused slippery (LIS) surfaces through the infusion of silicone oil. The anti-biofouling properties of the coatings were investigated by adsorption of platelets, whole blood coagulation, and biofilm formation in vitro. The results revealed that the LIS tubes possess superior resistance to clot formation and platelet adhesion than uncoated and SH tubes. In addition, bacterial adhesion was investigated over 7 days in a drip-flow bioreactor, where the SH-ZnO-Cu tube and its slippery counterpart significantly reduced bacterial adhesion and biofilm formation of Escherichia coli relative to control tubes (>5 log10 and >3 log10 reduction, respectively). The coatings also demonstrated good compatibility with fibroblast cells. Therefore, the proposed coatings may find potential applications in high-efficiency on-demand prevention of biofilm and thrombosis formation on medical devices to improve their biocompatibility and reduce the risk of complications from medical devices.

Hypothesis Transparent superhydrophilic coatings are very promising in various scenarios. Appropriate fabrication of colloid coatings with superhydrophilicity both in air and under oil would enlarge their application potential in anti-oil fouling and facilitate anti-fogging of transparent surfaces. Experiments The Barite colloid was obtained from a one-step precipitation method and was transferred onto glasses to prepare transparent coatings with different thicknesses simply by dip-coating. Then, the impact of thickness on wettability and property was studied through the investigation of wettability in various phase, anti-crude oil fouling performance and anti-fogging ability. Findings Similar surface morphology and roughness of these coatings were achieved and all the coated surfaces showed ultra-hydrophilicity both in air and under oil. Moreover, the hydrophilicity in air and under oil was found to deteriorate with the decrease of coatings’ thickness and dual superhydrophilicity could be achieved on thick coatings. More importantly, excellent anti-crude oil fouling property and durable anti-fogging ability were realized on these transparent coatings with dual superhydrophilicity.

Superhydrophobic coatings have potential applications in fouling resistance, self-cleaning, waterproofing, and drag reduction. In this work, using a facile brush-painting method for outdoor application, superhydrophobic silica coating layers were developed with high contact angle above 150°, high light-transmittance above 90 %, and strong weather resistance via three strategies: (i) hexadecyltrimethoxysilane-modified SiO2 (H-SiO2) particle agglomeration in colloidal coating solutions, and the formation of (ii) two-dimensional (2D) mud-crack patterns and (iii) three-dimensional (3D) micro-bumps. First, particle agglomeration was optimized in a mixed solution of water and ethanol with a relative permittivity of e = 48.0. Second, high transmittance and full-covered hydrophobic properties were achieved from the silica coating layers with 2D mud-crack patterns. Third, maximal contact angle of 152.6° was obtained from the superhydrophobic silica coating layers consisting of heterogeneous 3D micro-bumps on the 2D mud-crack patterns. The superhydrophobic coating layers exhibited high light-transmittance of 90.2 % and near-zero sliding angle, making them suitable for use as self-cleaning solar panels. These brush-painted superhydrophobic silica layers have potential uses in industrial coating applications by providing self-cleaning capability, weather resistance, flexibility, and transparency.

Due to the great fouling resistance property, (super)hydrophilic/underwater superoleophobic membranes are prevalent candidates for oil-polluted wastewater treatment. Even so, membrane fouling inevitably occurs during long-term operation. Therefore, it is of great significance to construct anti-fouling membranes with robust flux recovery. Herein, a polyvinyl pyrrolidone (PVP) coated porous potassium-doped g-C3N4 (PKCN) membrane was fabricated for the first time by vacuum filtration. The as-prepared membrane displays enhanced hydrophilicity and underwater superoleophobicity. The permeability of the membrane increased significantly after sonication treatment, which is attributed to the increased pore volume and small nanosheets size that shorten the transport pathway of water molecules. Importantly, owing to the high photo-Fenton activity, the PKCN membrane exhibits fast (within 15 min) and excellent flux recovery (96.5%) after the photo-Fenton cleaning process. Furthermore, after 10 repeated usages, the PKCN membrane still keeps stable permeability and excellent purification efficiency. This work opens a door for developing self-cleaning membranes with the superior anti-fouling ability for effective oil/water separation.

Enormous demands on the separation of oil/water (O/W) emulsions in various industries, such as petrochemical, food and pharmaceutical industries, are looking for high performance and energy-efficient separation methods. Ceramic membranes have been used to deal with O/W emulsions, for its outstanding characteristics of easy-operation, high-flux, and long-term stability. However, membrane fouling is still a challenge in the industrial application of ceramic membranes. Herein, antifouling ceramic membranes were fabricated by grafting zwitterions on the membrane surface via an environment-friendly two-step grafting method, which improves the antifouling property and permeability. Successful grafting of such zwitterion on the ceramic surface was assessed by the combination of FTIR and XPS characterization. More importantly, the hydration can be formed by electrostatic interactions layer on the modified membrane, which was confirmed by TGA characterization. The antifouling performance of prepared zwitterionic ceramic membranes in the separation of O/W emulsions was systematically tested. The results suggested that zwitterion can significantly improve the flux of ceramic ultrafiltration membrane, and can also improve antifouling property dramatically by reducing the irreversible fouling in the separation of O/W emulsions. Therefore, zwitterionic ceramic membranes hold promising potentials as an antifouling, highly efficient and green method in the practical purification of the O/W emulsions.

Sterilizing filtration is a common unit operation for the manufacture of parenteral drug products. However, filter performance can be impacted by properties of both the membrane material and the solution being filtered, requiring extensive multi-factor studies to optimize the filtration process for a given drug product. Here, we report the use of a modified bundle of capillaries approximation to predict filter performance. The model is directly applicable for both Newtonian and non-Newtonian solutions and does not require assumptions of steady state. Using a hydrophilic polyvinylidene difluoride (PVDF) filter as a test case, we show that the model fitting parameters align with expected values and both flux and shear are well predicted. Moreover, two case studies are presented to demonstrate the model's utility for filtration process optimization: 1) protein adsorption of an antibody formulation and 2) filter fouling of a 1% (w/v) carboxymethylcellulose (CMC) solution. In both cases, the model was able to accurately identify optimal filtration parameters to reduce the amount of adsorption or improve the filter capacity, respectively. This methodology can be easily extended to alternate filter types and provides an additional predictive tool to speed process development and minimize trial and error during filtration process design.

Alternating crossflow filtration is an emerging technology to mitigate fouling in crossflow microfiltration of cell-protein mixtures by periodically reversing the direction of flow. So far, it is understood that the anti-fouling effects are mostly related to the pressure fluctuations upon changing from forward to reversed flow direction and to a smaller extent to the flow reversal along the membrane as such. However, it is not yet clear how pressure fluctuations and flow reversal influence the axial distribution of fouling and the prevailing types of fouling. We conducted alternating crossflow filtrations of a model suspension containing yeast cells (4.2% dry matter) and bovine serum albumin (0.8 g l−1), where the duration and crossflow velocity of the forward and the backwards phase were varied independently. We found that the material, which deposits in the forward phase, can be better removed or loosened during the backwards phase, and vice versa, if forward and backwards flow conditions are equal in terms of time, crossflow velocity and overall transmembrane pressure. This leads to a detectable overall lower resistance due to deposit layer formation. Despite the positive effects of alternating crossflow filtration on filtration resistance, flux, and solute transmission, the less compact deposit layer also allows for an easier penetration of solutes and small particles into the membrane pores, which was detectable in terms of an increased ratio of irreversible fouling resistance.

During the past decade, the growth in membrane research and technology advanced and multiplied in usage for many industries including water and wastewater. A major limitation of the application is due to membrane fouling. In this work, the construction, start-up calibration and testing of a membrane unit as well as an examination into the fouling and cleaning aspect of the ceramic membranes are investigated. An aqueous solution containing precipitate is fed to the unit in order to observe fouling behaviour. Effluent wastewater from a bioreactor, CUBEN, is also tested with the unit and membrane cleaning is performed using various chemical agents. For both chemically enhanced backwash (CEB) and membrane soaking, hydrochloric acid cleaning agent (

A submerged membrane system was used in this work to investigate the effect of the polyaluminum chloride (PAC) coagulant on the antifouling performance of the polyvinyl chloride/alumina (PVC/Al2O3) nanocomposite membrane. The prepared nanocomposite membranes were characterized with field emission scanning electron microscopy (FE-SEM), atomic force microscopy, contact angle, porosity measurement, and pure water flux. The results revealed that the membrane containing Al2O3 nanoparticles (the mass ratio of PVC to Al2O3 was 98.5/1.5) had a higher hydrophilicity, porosity, and pure water flux than other membranes. The FE-SEM images showed that when Al2O3 nanoparticles were present in the PVC membrane, large pores and macrovoids formed on the surface and cross-section of the membrane. The fouling behavior of membranes was investigated through the filtration of humic acid (HA) solution with and without the PAC coagulant. Without PAC addition, the PVC/Al2O3 membrane significantly decreased the irreversible fouling ratio from 60.7% to 19.4% and showed a high HA removal efficiency of approximately 90.5%. The Hermia model confirmed that the cake formation mechanism best described the experimental data for the neat PVC and nanocomposite membranes with the presence and absence of the PAC coagulant. This confirms that the PAC coagulant can significantly mitigate fouling and improve HA removal in the submerged membrane system.

Solar-driven interfacial evaporation (SIE) is very promising to alleviate the freshwater scarcity issue. However, salt deposition on the sample surface will reduce evaporation performance, and compromised light absorption will result in a low water collection rate in conventional SIE apparatuses. Here, we report the design of a separated SIE system composed of a polypyrrole@Co3O4@aluminum sheet and a T-shaped superhydrophilic polyethylene/polypropylene nonwoven fabric right under the sheet. The photothermal surface exposed outside the closed SIE system is separated from the evaporation surface. Thus, salt fouling of solar evaporators is thoroughly avoided and the freshwater collection rate is greatly enhanced. Compared with conventional SIE systems, the separated SIE system has many advantages: simultaneous water and salt collection, a long-term stable evaporation rate even for concentrated brine (1.25 kg m-2 h-1 under 1 kW m-2 (1 sun) illumination, 15 wt % NaCl(aq), ≥120 h), high salt collection efficiency (≥97%), and a high water collection rate under natural sunlight, e.g., 0.72 kg m-2 h-1 in early spring (0.5-0.6 sun, 19-24 °C) and 0.33 kg m-2 h-1 in cold winter (0.3-0.4 sun, -6 to 4 °C). We foresee that the separated SIE system holds great potential for practical freshwater and salt collection from seawater.

Engineering systems continuously interact with nano-sized particles coming from natural or artificial sources. Considering nano-sized contaminants the detrimental effects are known as soiling and fouling phenomena. The objective of the present work is to gather morphological and three-dimensional quantitative information of discontinuities such as voids and pores within the nano-sized particle layer and in correspondence to the substrate/layer interface using microtomography. Deposits are obtained through impact tests using fine powder (soil and soot), and there are realized on a low-density material substrate characterized by different surface roughness values. The packing process and the discontinuities at the substrate-to-layer interfaces explain macroscopic effects as detachment and spallation but at the same time, give the possibility to understand more in detail the process related to the deposition mechanisms involved in this type of test defining general guidelines to predict the fouling phenomenon and to improve the capability of the removal process.

Nanoparticle surface interaction is a common phenomenon, even if a general explanation of nanoparticle deposit growth is still unknown. For several applications, the adhesion of such nanoparticles is detrimental, generating safety and performance issues. The present work shows an interpretation of deposit growth due to nanoparticle deposition, capable of predicting particle adhesion and layer accretion. The nanoparticle deposits grow analogously to a typical autonomous population settlement in a virgin area following statistical rule, which includes the initial growth, the successive stable condition (development), and catastrophic events able to destroy the deposited layer. This statistical population model allows the generalization of the nanoparticle adhesion/deposition behavior, and it could be used for improving the prediction capability of nanoparticle deposition to common engineering applications.

Renewable bamboo materials have broad application prospects in the fields of structural construction, insulation and acoustic management due to their multi-layer porous structure, attractive directional layout texture, ultra-fast growth rate, and excellent mechanical strength. However, the annual loss of bamboo material due to the microbial corrosion accounts for one-tenth of the total output. In this work, the hydrophobic associating hydrogel (HAH) with chitosan (CS) and zinc oxide (ZnO) has been in situ filled in the micro-nano-scale pores of natural bamboo materials to significantly enhance their anti-microbial fouling performance. It is difficult for the mildew and oxygen in the air to come into the bamboo materials due to the artificial hydrogel barrier layer. CS and ZnO nanomaterials further increase the anti-bacterial rate of bamboo composites to 100%. Based on the physical crosslinking between the polyacrylamide (PMA) of HAH hydrogel and natural bamboo fibers, CS and ZnO bacteriostatic media are not easy to be lost from the bamboo materials. The 100% anti-bacterial rate of the bamboo composite materials can be maintained for at least 56 days. Therefore, the bamboo composites have great application potential as building materials in the future. In-situ polymerization method was used to fill the micropores of bamboo with super-elastic hydrogel to enhance its anti-microbial fouling performance.

Protein fouling on critical biointerfaces causes significant public health and clinical ramifications. Multiple strategies, including superhydrophobic (SHP) surfaces and coatings, have been explored to mitigate protein adsorption on solid surfaces. SHP materials with underwater air plastron (AP) layers hold great promise by physically reducing the contact area between a substrate and protein molecules. However, sustaining AP stability or lifetime is crucial in determining the durability and long-term applications of SHP materials. This work investigated the effect of protein on the AP stability using model SHP substrates, which were prepared from a mixture of silica nanoparticles and epoxy. The AP stability was determined using a submersion test with real-time visualization. The results showed that AP stability was significantly weakened by protein solutions compared to water, which could be attributed to the surface tension of protein solutions and protein adsorption on SHP substrates. The results were further examined to reveal the correlation between protein fouling and accelerated AP dissipation on SHP materials by confocal fluorescent imaging, surface energy measurement, and surface robustness modeling of the Cassie-Baxter to Wenzel transition. The study reveals fundamental protein adsorption mechanisms on SHP materials, which could guide future SHP material design to better mitigate protein fouling on critical biointerfaces.

Fouling reduces the heat transfer and increases the heat loss of the process units such as heat exchangers. Due to fouling, the costs of operation and maintenance are increasing significantly. In addition, heat transfer equipment is often overworked because of the expected fouling. Therefore, fouling is a major element in design and operation of heat exchangers. Through the grey correlation analysis, the relationship among microbial fouling thermal resistance, flow rate and water quality parameters are investigated. The fouling experiments are finished in a laboratory scale set-up of a tubular type heat exchangers. The fouling thermal resistance under different flow rates and different water quality parameters are obtained. And the changes of water quality parameters under different flow rates are also obtained. The results are analyzed. The analysis shows that the fouling resistance decreases with the increase of flow velocity under the same conditions of temperature and concentration, and it has different influences on thermal resistance when water quality parameters change in different periods. With the change of water quality parameters, the fouling resistance of slime forming bacteria gradually stabilized after 62 h. The correlation analysis of the three shows that the change of flow rate will affect the water quality parameters, and then affect the fouling resistance. The OD, pH and the conductivity are found to be related to changes of velocity. The strongest correlation is 0.6273 between conductivity and flow rate. The strongest correlation is 0.8755 between OD and fouling resistance. When the velocity increases, pH change rate increase 20%, but the changes rate in fouling resistance is slower than other two factors. It is necessary to analyze and study fouling from the perspective of heat and mass transfer.

There is a need for solutions to provide sufficient cooling from power devices, which produce large amounts of heat. This paper focuses on the influence of design of bifurcated fluid streams to dissipate heat. In this study, a single Y-tubes, a double Y-tubes, and an X-tubes designs are studied numerically under space constraints. For a comprehensive and in-depth performance analysis, both heat dissipation and hydraulic performances are analyzed. The distributions of velocity and temperature in the fluid streams is simulated, also the flow resistances and dissipated heat are calculated. Based on the results obtained, a thermo-hydraulic performance factor is introduced for the designs under study. In addition, the accumulation of undesired substances on the wall surface (fouling) that may influence the heat exchanging capability is studied.

Membrane distillation (MD) has gained the interest of many researchers since it is a promising method for the separation and purification process. Membrane distillation (MD) is a non-isothermal separation process in which differential vapor pressure between porous hydrophobic membrane surfaces acts as a driving factor. A hydrophobic membrane is used in the application of MD, which permits only the passage of vapor produced on the feed side through its pores to the permeate side. One of the most significant obstacles to the commercialisation of the MD method is a lack of appropriate membranes for the process. On the other hand, conventional hydrophobic membranes are subjected to rapid wetting and severe fouling, mainly when low surface tension compounds are present in saline water, resulting in decreased MD performance. In recent decades, MD membranes have received exceptional scientific interest, with substantial progress being made in the design and production of MD membranes appropriate for use in many applications. This review gives a comprehensive overview of recent research developments in the tailoring morphological structure of hydrophobic membranes, emphasising advancements in the fabrication and modification of membranes towards exhibiting high efficiency in the MD process. In addition, the critical morphology characteristics, mainly surface roughness, wettability, and water contact angle, are analysed. Finally, the challenges faced and future research direction is highlighted.

Efficient separation of oil from oily wastewater is a great environmental challenge. Nano- and microfiber electrospun membranes can be used to remove oils and organics in wastewater through the nano- or microfiltration process. Due to the low degree of fouling and relatively high-water flux, electrospun membranes exhibit promising applications for wastewater treatment. This paper reports the fabrication and evaluation of electrospun membranes based on cellulose acetate (CA) and nano-zeolites. By carefully controlling different parameters, CA and CA/zeolite electrospun membranes were fabricated. Various characterization techniques were used to evaluate the electrospun membranes. The optimum CA concentration to fabricate the membrane was 16% (w/v), and 10% (w/w) nano-zeolites were successfully incorporated into the membrane. The scanning electron micrographs revealed that the fabricated membranes had a fiber diameter range of 100–3000 nm. The apparent pore sizes of the as-fabricated membranes were in micro-/submicrometer. The zeolite nanoparticles were observed to be incorporated successfully throughout the membranes and the presence of the zeolites was confirmed using the EDX spectrum and EDX elemental mapping. The resulting membranes exhibited super hydrophilicity. The final quality of filtered water was investigated by measuring the oil droplets using optical microscopy, and the absorbance of unfiltered and filtered water was measured using UV–Vis spectrophotometer. The microfiltration process allowed the water phase to pass through the CA and CA/zeolite electrospun membranes which repelled the dispersed oil droplets restricting them to stay on the surface. The oil separation efficiency was up to 97%. Owing to biodegradability, non-toxic properties, and cost-effectiveness of the fabrication process, the membranes can be potentially used in microfiltration to remove oil in oily wastewater.

Modified graphene oxide with 5,10,15,20-tetrakis-(4-hexyloxyphenyl)-porphyrin and palladium (II) (signified by GO-CPTMS@Pd-TKHPP) prepared as a novel antifouling polyether sulfone (PES) blended nanofiller membrane. The membrane efficiency has been analyzed such as pure water flux (PWF), hydrophilicity, and antifouling features. By increasing of modified graphene oxide percentage from 0 to 0.1 wt.% in the polymer matrix, the PWF was incremented from 14.35 to 37.33 kg/m2·h at 4 bar. The membrane flux recovery ratio (FRR) has been investigated by applying powdered milk solution; the FRR results indicated that the 0.1 wt.%-modified graphene oxide membrane showed a positive effect on fouling behavior with Rir and FRR value 8.24% and 91.76%, respectively. The nanofiltration membrane performance was assessed applying the Direct Red 16 dye rejection. It was demonstrated that the optimal membranes (0.1 wt.%-modified graphene oxide) had notable dye removal (99.58% rejection). The results are also verified by measuring the scanning electron microscopy (SEM), water contact angle (WCA), and atomic microscopy analysis (AFM).

Heating tower heat pumps are increasingly used in subtropical areas due to their frost-free characteristics. The spray heating tower (SHT) solves the fouling problem suffered by the packing heating tower and ensures thermal performance. However, the heat and mass transfer characteristics of SHT have not been fully revealed and the power consumption of SHT is higher than that of packing heating towers. In the present study, the effects of tower height, air temperature, solution concentration/type, and liquid to gas ratio on the thermal performance of SHT were analyzed using a mathematical model. The heat and mass transfer characteristics of SHT with 100% thermal efficiency and/or 100% tower effectiveness were investigated. The results showed that when thermal efficiency approached 100% and liquid to gas mass ratio was 0.28, evaporation and condensation occurred at the bottom and top of the tower, respectively. Based on the parametric analysis results, a parameter design strategy to reduce pump power consumption while ensuring thermal performance was determined, which reconciled the contradiction between power consumption and thermal performance of SHT. The results of this investigation may provide a reference for the design and operation of SHT.

As an emerging thermal-driven membrane technology, membrane distillation (MD) has attracted immense attention for desalination and water purification. The membranes for MD generally have hydrophobic or superhydrophobic properties to enable vapor permeation without liquid passage (e.g., wetting). However, conventional MD membranes cannot undergo long term stable operations due to gradual wetting in practical applications where the feed solution often contains multiple low-surface tension contaminants (e.g., oil). Recently, omniphobic membranes repelling all sorts of liquids and typically having ultralow surface energy and re-entrant structures have been developed for robust MD to mitigate wetting and fouling. In this paper, we aim to provide a comprehensive review of recent progress on omniphobic membranes. Fundamentals, desirable properties, advantages and applications of omniphobic membranes are discussed. We also summarize the research efforts and methods to engineer omniphobic membranes. Finally, the challenges and future research directions on omniphobic membranes are discussed.

Reverse osmosis concentrate (ROC) is one of the major drawbacks in membrane treatment technologies specifically due to the scale-forming ions. It is important to remove these ions from ROC to enhance total water recovery and reuse in the textile industry that is the largest water-consumer and polluter industry. In this work, coagulation/high pH precipitation (CP) integrated with ceramic microfiltration (CMF) was studied as a pre-treatment method followed by nanofiltration (NF) to increase the efficiency of water recovery. To prevent organic fouling, ferric chloride (FeCl3) was applied at a concentration of 3 mM, and ceramic membranes were used for the removal of non-precipitating crystals and/or suspended solids (at high pH) before the NF processes. The CP-CMF method successfully removed calcium (Ca2+), magnesium (Mg2+), silica (SiO2), and TOC up to 97, 83, 92, and 87% respectively, which resulted in higher performance of the NF process. Moreover, this method provided higher flux at lower pressure that ultimately increased overall water recovery of the NF process to achieve near-zero liquid discharge (n-ZLD). A cost–benefit estimation showed that a high-quality effluent (COD

To take full advantage of the reagent- and label-free sensing capabilities of electrochemical sensors, a frequent and remaining challenge is interference and degradation of the sensors due to uncontrolled pH or salinity in the sample solution or foulants from the sample solution. Here, we present an oil-membrane sensor protection technique that allows for the permeation of hydrophobic (lipophilic) analytes into a sealed sensor compartment containing ideal salinity and pH conditions while simultaneously blocking common hydrophilic interferents (proteins, acids, bases, etc.) In this paper, we validate the oil-membrane sensor protection technique by demonstrating continuous cortisol detection via electrochemical aptamer-based (EAB) sensors. The encapsulated EAB cortisol sensor exhibits a 5 min concentration-on rise time and maintains a measurement signal of at least 7 h even in the extreme condition of an acidic solution of pH 3.

The low mechanical properties of polybutylene succinate (PBS) limit its applications in the preparation of biodegradable filtration membranes. In this work, acrylonitrile butadiene styrene (ABS) was used to improve the mechanical properties of filtration membranes for the first time. Polybutylene succinate (PBS)/acrylonitrile butadiene styrene (ABS) blends containing 10, 20, and 30 wt% ABS were prepared by dissolving in N-methyl-2-pyrrolidone (NMP), and then membranes were prepared through immersion precipitation. Surface and cross-sectional scanning electron microscopy (SEM), porosity measurement, Fourier transform infrared spectroscopy (FTIR), water contact angle and water content measurements, tensile test, and thermogravimetric analysis (TGA) were conducted to characterize the membranes. Filtration experiments were performed to treat fruit juice production wastewater to determine the rejection of turbidity and chemical oxygen demand (COD). Also, the membrane tendency to fouling was assessed. The results of mechanical properties showed that with increasing the amount of ABS, the mechanical properties of the samples improved so that by increasing the ABS loading to 10, 20, and 30 wt%, the tensile strength increased by 44%, 131%, and 188%, and the elastic modulus increased by 17%, 78%, and 99%, respectively, compared to the mechanical properties of pure PBS. The blend membranes had less tendency to irreversible fouling than the neat PBS membrane regarding the filtration results. The results of wastewater filtration indicate that the COD rejection dropped and steady permeate flux raised with increasing ABS amount. All the membranes rejected 100% of turbidity and thus can be utilized in wastewater pretreatment.

Hydrophilic modification is a promising method to inhibit fouling formation on ultrafiltration membrane. In this work, different mass concentrations (1%–16%) of hydrophilic polyvinylpyrrolidone were incorporated into polyethersulfone (PES) membranes fabricated by none-solvent induced phase separation. Then, polydopamine (PDA) coating on the surface of prepared membrane was carried out at pH 8.5. The morphology and structure, surface hydrophilicity, permeation flux, BSA rejection, antifouling and stability performances of PES and PDA/PES modified membranes were investigated in detail. The results indicated that PDA was successfully attached onto the membranes. Membrane hydrophilicity was evaluated by water contact angle measurement. The contact angles of modified membranes reduced remarkably, suggesting that the membrane hydrophilicities were significantly increased. The results of filtration tests, which were done by dead-end filtration of bovine serum albumin solution, showed that the properties of permeability and fouling resistance were obviously improved by PDA modification. When polyvinylpyrrolidone mass content reached 10%, flux recovery ratio of modified membrane was up to 91.23%, and its BSA rejection were over 70%. The results of stability tests showed that the modified membranes had good mechanical stability and chemical stability. This facile fabrication procedure and outstanding performances suggested that the modified membranes had a potential in treating fouling.

Separation process based on polyamide (PA) thin film composite (TFC) membrane is the dominant desalination technology in the 21st century to produce potable water to meet the growing global freshwater demand. Despite offering good filtration performance and exhibiting stable chemical and mechanical properties, TFC membrane still encounters other technical challenges such as surface fouling and trade-off feature between water permeability and solute selectivity which prompt continuous research efforts. There has been growing interest in recent years among researchers to alter the surface properties of PA layer via various modification methods to overcome the drawbacks of typical selective layer. But the question that remains to be answered – Does the modified PA layer effective for performance improvement? It is the aim of this article to provide a comprehensive review on the modification techniques (i.e., surface coating, surface grafting, plasma treatment and layer-by-layer assembly) and the modifying materials (both organic and inorganic materials) that have been commonly employed to establish a functionalized layer atop PA layer to improve its characteristics for desalination process. We hope this review that covers the relevant articles published over the past 10 years could provide insights to scientists in modifying selective layer of TFC membranes for better performance in water treatment processes.

Photocatalytic materials can be used as self-cleaning functional materials to alleviate the irreversible fouling of ultrafiltration membranes. In this work, the small size g-C3N4/Bi2MoO6 (SCB) blended polysulfone (PSF) ultrafiltration membranes was fabricated by hydrothermal and phase inversion methods. As a functional filler of ultrafiltration membranes, the small size g-C3N4 nanosheet decorated on the surface of Bi2MoO6 can enhance the photocatalytic performance for bovine serum albumin (BSA) degradation, and remove irreversible fouling under visible light irradiation. In addition, the introduction of SCB microspheres into PSF matrix obviously increased the porosity of ultrafiltration membranes. Therefore, the SCB-PSF ultrafiltration membranes displayed excellent antifouling performance (flux recovery ratio is 82.53%) and BSA rejection rates (94.77%). SCB-PSF also had high photocatalytic self-cleaning activity, indicating excellent application prospects in organic wastewater treatment.

At the IMKF, eight different elastomer compounds with different polymer compositions were examined for their demolding characteristics and mold fouling. Ten demolding cycles were carried out for each compound and the fouling of the mold was photo-technical recorded after ten demolding cycles. The used polymer composition does not seem to have any significant influence. However, the components of the compound have a significant influence on the friction characteristics while removing of the vulcanizate from the mold. Crosslinking that begins very early has an initiating influence on mold fouling. The measurable fluctuations in the maximum demolding force that occur could correlate with the internal friction of the polymer with the filler.

Novel specially wettable membranes have been attracting significant attention for durable membrane distillation (MD). However, constructing a superhydrophobic interface often has to undergo complex modification procedures including roughness construction and hydrophobic modification. Herein, all-polymer and self-roughened superhydrophobic poly(vinylidene fluoride) fibrous membranes (PVDF FMs) with robustly stable pores were successfully constructed via electrospinning of fluorinated polyhedral oligomeric silsesquioxanes/PVDF (F-POSS/PVDF) emulsion solution in combination with hot-pressing. The comparative experiment reveals that proper hot-pressing, including adequate temperature and pressure, can help improve membrane pore stability by welding the intersecting fibers and increase the membrane surface hydrophobicity by transferring the inner fluorine chains to the outer fiber surface, simultaneously advancing membrane scaling and fouling resistance. Nevertheless, excessive temperature or pressure will destroy the interconnected pores and surface wettability of the PVDF FM. Significantly, the hot-pressing-treated F-POSS/PVDF FM shows a high water recovery (∼90%) and robust stability after five rounds of the concentration process toward concentrating natural seawater as a target. Thus, the all-polymer and self-roughened superhydrophobic PVDF FMs constructed via electrospinning combined with the thermal treatment have potential applications in concentrating hypersaline brines, which make up for the other membrane technology, including reverse osmosis and nanofiltration technologies that failed to concentrate hypersaline solutions.

1-Hexene is one of the comonomers used to produce mainly low linear density polyethylene (LLDPE) and high-density polyethylene (HDPE). The production of 1-hexene by ethylene trimerization method gained much interest in petrochemical industry due to its high selectivity towards 1-hexene in comparison to traditional ethylene oligomerization method. In literature, many catalyst systems are reported for ethylene trimerization reaction, but only few of them qualify for the commercial applications. In the present review, activity and selectivity of commercially viable catalyst systems and amount of polyethylene formed as a by-product on using these catalyst systems were discussed. Special attention is given to Chevron Phillips ethylene trimerization technology which is one of the dominant technologies in the production of 1-hexene. The challenges such as fouling issues at commercial plant due to polyethylene by-product formation were discussed and the progress made to overcome the challenges were also discussed. New generation nontoxic titanium catalysts look promising and challenges involved in commercializing these catalysts were presented in the review. Graphic abstract

Developing a feasible and efficient separation membrane for the purification of emulsified oily wastewater is challenging due to the critical limitations of serious fouling during membrane preparation. Herein, underwater superoleophobic paper-based materials with high wet strength were prepared by low cost and green papermaking technology. The fibrillation of cellulose fibers was achieved by beating to optimize the pore structure of paper sheets. Simple modification of paper sheets with 1,2,3,4-butanetetracarboxylic acid significantly improves the surface hydrophilicity and the wet strength through the crosslinking reaction between fibers. The maximum underwater oil contact angle and wet strength of the modified paper sheets are high up to 167.8°and 36.5 N·m/g, respectively. The water flux can be adjusted in the range of 25.8 L m−2 h−1–4920 L m−2 h−1 by controlling the average pore size from 6.64 μm to 18.9 μm. Lower pore size and higher carboxyl content of the paper-based materials are beneficial to improve the oil rejection, which can reach more than 99.3% even for submicron emulsified oils. Most of the paper sheets achieve efficient oil–water separation although the average pore size is remarkably larger than the emulsified oil droplet. The reason can be attributed to the zigzag pore structure of paper sheets, which is favorable to form liquid bridge on the surface as well as collision demulsification in the Z-direction channel, thereby promoting the mechanical interception effects. The low-cost, eco-friendly, easily-manufactured and highly efficient paper-based separation materials possess wide applications in oily wastewater treatment.

Realizing simultaneous antiwater and anti-oil-fouling adhesion is extremely challenging owing to the solvated overlayer on the surface of substrates. Herein, we develop a supertough polyacrylate-based tape bearing SiO2 as a reinforcing filler and a solvent to liquefy the surface. The SiO2 reinforcement enhances the cohesion strength, while the liquefied surface not only expels the solvated overlayer but also improves the interfacial wettability and interaction. This material design imparts the double-sided tape with admirable antiwater and anti-oil-fouling adhesion performance, which far exceeds that of commercial tapes, as well as high transparency and long-term stability. In addition, we carry out an in-depth study on the adhesive mechanism for the tape and clarify the role of the solvent and the interaction between SiO2 and a polymer matrix. This work provides a novel strategy for designing antiwater and anti-oil-fouling adhesives with wide applications in various fields such as leakage repair, antiseep, underwater adhesion, building materials, and biological adhesives.

Membrane separation processes have been considered as general techniques for separation and purification of water, for they guarantee a number of worldwide advantages in terms of their economics and outstanding practical selectivity. However, fouling restricts the efficiency of membranes, necessitating modification of their bulk and surface characteristics. Incorporation of nanomaterials into the membrane matrix has been intended as a prominent strategy, where carbon-based nanostructures played a key role in diminishing fouling. Graphitic carbon nitride (g-C3N4) composed of carbon and nitrogen has attracted significant attentions in membrane fabrication owing to its hydrophilic nature, acceptable thermal stability and photocatalytic property. In this review, a brief explanation of the history of g-C3N4 was provided, followed by classification and explanation of different ways attempted in fabrication of g-C3N4 membranes. In addition, the influence of g-C3N4 on the efficiency of membrane processes was comprehensively discussed. Finally, the challenging aspects of the future usage of g-C3N4 in industrial scale processes were discussed.

Energy and exergy analyses were performed on a glass furnace regenerator and hydrogen production via thermal catalytic ammonia decomposition. A novel integration between energy and exergy analyses was suggested to predict the performance of thermodynamic and hydrogen production systems. It was found that the heat recovered by the combustion air of the south side regenerator was higher than that on the north side because of the fouling effect of the deposit materials and the heat lost through the regenerator walls. The maximum energy and exergy efficiencies of the south side regenerator were 98% and 93%, respectively, while those of the north regenerator side were 96.3% and 80%, respectively. The integration between energy and exergy analyses was also applied to investigate the performance of H2 production from the catalytic NH3 decomposition system. The conversion rate results proved that an increase in the ammonia feeding pressure was unfavorable. Moreover, the maximum energy and exergy efficiencies of the NH3 thermal decomposition system were 73.5% and 13.34% at a feeding pressure of 100 kPa, respectively. Furthermore, the non-equilibrium of the system is identified from the integrated effectiveness and entropy generation number.

Alternating tangential flow (ATF) filtration is a cell retention technique of increasing importance in continuous biomanufacturing. Despite its frequent application, the role of flow reversal in fouling mitigation remains unclear this far. We implemented a customized pilot plant comprising a low-shear centrifugal pump and fast switching valves, which enables us to create alternating crossflow, where crossflow velocities and cycle times can be varied independently, as well as conventional steady forward and pulsatile forward crossflow. We then used a model feed containing yeast cells and bovine serum albumin (BSA) in order to simulate a fermentation broth and investigated the impact of alternating crossflow on microfiltration performance at this customized filtration plant. By comparing the results with filtration trials conducted at forward only pulsatile crossflow as well as steady crossflow using the same plant, we observed the true effect of flow reversal, corrected for effects induced by crossflow velocity, transmembrane pressure as well as transmembrane pressure fluctuations. We found that alternating crossflow, i.e. crossflow with flow reversal, leads to a reduced fouling resistance and a higher solute transmission in comparison to steady crossflow filtration. However, the flux increase is lower than for pulsatile crossflow filtration, which might be attributed to length dependency effects. The transmission of BSA, on the other side, is even higher at alternating crossflow filtration than for pulsatile crossflow. Thus, we conclude that flow reversal plays a part in fouling mitigation, but a greater part of the anti-fouling effect of alternating crossflow, however, is caused by the transmembrane pressure fluctuations.

The conventional Polyvinylidene Fluoride (PVDF) membrane was modified by polymerization Reversible addition−fragmentation chain-transfer (RAFT) with copolymer (PEGMA-co-BVIm-Br) on the upper bulk. This copolymer was obtained from the synthesis of (BVIm-Br) 3-butyl-1-vinyl-1-H-imidazole-3-ium bromide and the vinyl imidazole (VI) monomer N-vinyl imidazole (a hydrophilic monomer) and 1-bromobutane (C4H9Br). The analysis of such as ATR-FTIR, the magnetic resonance of H-NMR nuclei, zeta potential, Water Contact Angle (WCA), and Scanning Electron Microscopy (SEM) confirmed the presence of copolymer on the surface of the modified membrane. The bonding of this copolymer on the membrane surface reduced the WCA of the membrane water (from 89.5 ±1.96 to 33.8 ±1.55). The raw PVDF membrane (M1) and modified membrane (with total ratio-P(PEGMA-co-BVIm-Br) copolymer 2.5 % (M2), 5 % (M3), 10 % (M4), 20 % (M5), and 40% (M6) to (raw PVDF membrane) membrane showed appropriate hydrophilic nature and excellent separation of oil droplets from water/oil emulsions in the simulated effluent on the surface. This operation was performed for a comprehensive study on the determined parameters and by filtration with simulated petrochemical industry effluent (containing water/oil emulsion). Therefore, the recovery efficiencies of water flux, flow flux, oil recovery amount, as well as total fouling of M6 membrane were reported 96.14±0.99 and 428±2.6 L/ (m2 h), 96.1±1.3%, and 17.18±0.37%, respectively. This study aimed to prepare a copolymer-modified membrane that can show high performance in cleaning and resistance to various fouling, such as Rt, Rr, and Rir at the specified temperature, after long-term emulsion separation.

International audience; Drip irrigation is one of the most efficient irrigation techniques, but it is susceptible to dripper clogging. This study proposes a novel and non-destructive method based on visible and near infrared (Vis/NIR) spectroscopy coupled with chemometric methods for the discrimination and thickness estimation of physical and chemical fouling in drip-irrigation systems. Four representative materials linked to physical and chemical clogging (kaolin, bentonite, sand and calcium carbonate) at different thicknesses were selected to illustrate the potential of the approach. Partial least squares regression (PLSR) and its modification partial least squares with discriminant analysis (PLS-DA) were selected for the modelling of clogging materials. The PLS-DA model was able to predict with 96.97% accuracy all classes of materials. The PLSR models were able to estimate fouling thickness with relative prediction errors comprised between 134 μm and 164 μm. This difference appears mainly to be due to the physical properties of the selected materials. This prediction accuracy enabled the estimation of the clogging thickness between 10 and 21% of dripper channel coverage depending on the dripper channel section and the material under study. The proposed method offers an appropriate approach for clogging studies in drip irrigation systems that could be transferred to field applications.

In order to study the interaction between various fouling particles and ballast, a multi-layer and multi-scale discrete element model (DEM) including the sleeper, ballast bed and the surface layer of subgrade was developed. Two typical fouling particles, the hard particles (sand) and soft ones (coal fines), are considered. A support stiffness test of the ballast bed under various fouling conditions was conducted to calibrate the microscopic parameters of the contact model. With the model, the influence of fouling particles on the mechanical behavior and deformation of the ballast bed was analyzed from macro and micro perspectives. The results show that the increase in the strength of the fouling particles enlarges the stiffness of the ballast bed. Hard particles increase the uniformity coefficient of the contact force bond γ of ballast by 50.4%. Fouling particles increase the average stress in the subgrade, soft particles by 2 kPa and hard particles by 1 kPa. Hard particles can reduce the elasticity, plastic deformation and energy dissipation in the track structure. As the fouling particle changes from hard to soft, the proportion of the settlement in ballast bed increases to 40.5% and surface layer of swbgrade settlement decreases to 59.5%. Thus, the influence of fouling particles should be considered carefully in railway design and maintenance.