Fouling and Chemical Cleaning of Microfiltration Membranes: A Mini-Review

Dispersion-free inertial focusing (DIF) for high-yield polydisperse micro-particle filtration and analysis

Inertial focusing excels at the precise spatial ordering and separation of microparticles by size within fluid flows. However, this advantage, resulting from its inherent size-dependent dispersion, could turn into a drawback that challenges applications requiring consistent and uniform positioning of polydisperse particles, such as microfiltration and flow cytometry. To overcome this fundamental challenge, we introduce Dispersion-Free Inertial Focusing (DIF). This new method minimizes particle size-dependent dispersion while maintaining the high throughput and precision of standard inertial focusing, even in a highly polydisperse scenario. We demonstrate a rule-of-thumb principle to reinvent an inertial focusing system and achieve an efficient focusing of particles ranging from 6 to 30 μm in diameter onto a single plane with less than 3 μm variance and over 95% focusing efficiency at highly scalable throughput (2.4-30 mL h-1) - a stark contrast to existing technologies that struggle with polydispersity. We demonstrated that DIF could be applied in a broad range of applications, particularly enabling high-yield continuous microparticle filtration and large-scale high-resolution single-cell morphological analysis of heterogeneous cell populations. This new technique is also readily compatible with the existing inertial microfluidic design and thus could unleash more diverse systems and applications.

Cleaning of Ultrafiltration Membranes: Long-Term Treatment of Car Wash Wastewater as a Case Study

Car wash wastewaters (CWWs) contain various pollutants with different contents. Hence, selecting an appropriate process for their treatment is a great challenge. Undoubtedly, the ultrafiltration (UF) process is one of the most interesting and reliable choices. Therefore, the main aim of the current study was to investigate the performance of the UF membranes used for the long-term treatment of real CWWs. For this purpose, two polyethersulfone (PES) membranes with molecular weight cut-off (MWCO) values equal to 10 and 100 kDa were applied. As expected, a significant decrease in the permeate flux during the UF run was observed. However, it was immediately demonstrated that the systematic cleaning of membranes (every day) with Insect agent (pH = 11.5) prevented a further decline in the process's performance. In addition, this study focused on the relative flux during the process run with breaks lasting a few days when the UF installation was filled with distilled water. The results of this research indicated that aqueous media favor microorganism adherence to the surface which leads to the formation of biofilms inside processing installations. As a consequence, many attempts have been made to restore the initial membrane performance. It has been found that the application of several chemical agents is required. More precisely, the use of an Insect solution, P3 Ultrasil 11 agent, and phosphoric acid increases the relative flux to a value of 0.8. Finally, it has been indicated that the membranes used in this work are resistant to the long-term exposure to bacteria and chemical agents. However, during the separation of CWWs for the membrane with an MWCO of 10 kDa, a lesser fouling influence and higher effectiveness of cleaning were obtained. Finally, the present study demonstrates a novel analysis and innovative implications towards applying the UF process for the CWW treatment.

Enhancing Rubber Industry Wastewater Treatment through an Integrated AnMBR and A/O MBR System: Performance, Membrane Fouling Analysis, and Microbial Community Evolution

This study explores the effectiveness of an integrated anaerobic membrane bioreactor (AnMBR) coupled with an anoxic/oxic membrane bioreactor (A/O MBR) for the treatment of natural rubber industry wastewater with high sulfate, ammonia, and complex organic contents. This study was conducted at the lab-scale over a duration of 225 days to thoroughly investigate the efficiency and sustainability of the proposed treatment method. With a hydraulic retention time of 6 days for the total system, COD reductions were over 98%, which reduced the influent from 22,158 ± 2859 mg/L to 118 ± 74 mg/L of the effluent. The system demonstrates average NH3-N, TN, and total phosphorus (TP) removal efficiencies of 72.9 ± 5.7, 72.8 ± 5.6, and 71.3 ± 9.9, respectively. Despite an average whole biological system removal of 50.6%, the anaerobic reactor eliminated 44.9% of the raw WW sulfate. Analyses of membrane fouling revealed that organic fouling was more pronounced in the anaerobic membrane, whereas aerobic membrane fouling displayed varied profiles due to differential microbial and oxidative activities. Key bacterial genera, such as Desulfobacterota in the anaerobic stage and nitrifiers in the aerobic stage, are identified as instrumental in the biological processes. The microbial profile reveals a shift from methanogenesis to sulfide-driven autotrophic denitrification and sulfammox, with evidence of an active denitrification pathway in anaerobic/anoxic conditions. The system showcases its potential for industrial application, underpinning environmental sustainability through improved wastewater management.

Advancement of membrane separation technology for organic pollutant removal

In the face of growing global freshwater scarcity, the imperative to recycle and reuse water becomes increasingly apparent across industrial, agricultural, and domestic sectors. Eliminating a range of organic pollutants in wastewater, from pesticides to industrial byproducts, presents a formidable challenge. Among the potential solutions, membrane technologies emerge as promising contenders for treating diverse organic contaminants from industrial, agricultural, and household origins. This paper explores cutting-edge membrane-based approaches, including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, gas separation membranes, and pervaporation. Each technology's efficacy in removing distinct organic pollutants while producing purified water is scrutinized. This review delves into membrane fouling, discussing its influencing factors and preventative strategies. It sheds light on the merits, limitations, and prospects of these various membrane techniques, contributing to the advancement of wastewater treatment. It advocates for future research in membrane technology with a focus on fouling control and the development of energy-efficient devices. Interdisciplinary collaboration among researchers, engineers, policymakers, and industry players is vital for shaping water purification innovation. Ongoing research and collaboration position us to fulfill the promise of accessible, clean water for all.

Non-destructive monitoring and prediction of fouling by organic matters and residual anionic coagulant during membrane process

Physical fouling characteristics on silicon carbide (SiC) membranes induced by various organic matter compounds vary depending on the presence of calcium ions (Ca2+). Both destructive techniques (morphological surface analysis) and non-destructive techniques (fouling properties monitoring) were used to determine the fouling mechanisms and behavior during the membrane filtration systems. Destructive analysis and a modified Hermia model were employed to assess the fouling mechanisms. Fouling behavior was also analyzed through non-destructive monitoring techniques including optical coherence tomography (OCT) and three-dimensional laser scanning confocal microscopy (3D-LSM). At concentrations of 10, 30, and 100 mg/L without Ca2+, the flux decreased by 57-95% for humic acid (HA) and anionic polyacrylamide (APAM). APAM exhibited a notable removal rate of up to 56% without Ca2+. At concentration of 10, 30, and 100 mg/L in the absence of Ca2+, the flux decreased by 6-8% for sodium alginate (SA). However, the addition of Ca2+ led to a reduction in the flux for SA by up to 91% and resulted in a removal rate of 40%. Furthermore, addition of Ca2+ led to an alteration of the fouling characteristics of HA and SA. In the case of HA, higher concentrations resulted in elevated thickness and roughness with correlation coefficients of 0.991 and 0.992, respectively. For SA, increased SA concentration led to a thicker (correlation coefficient of 0.999) but smoother surfaces (correlation coefficients of 0.502). Monitoring of these physical characteristics of the fouling layer through non-destructive analysis is crucial for effective fouling management, optimization of the system performance and extending the lifespan of the membrane. By continuously assessing the fouling layer thickness and surface roughness, we expect to be able to provide insights on the fouling behavior, identify trends, that can help scientists and engineers to make informed decisions regarding fouling control strategies in future.

Characterization of novel solar based nitrogen doped titanium dioxide photocatalytic membrane for wastewater treatment

The increasing presence of microbial and emerging organic contaminants pose detrimental effects on the environment and ecosystem such as diseases, pandemics and toxicity. Most of these synthetic pollutants are biorecalcitrant and therefore persist in the environment. Conventional water treatment methods are not effective thereby necessitating the development of advanced techniques such as photocatalysis and membrane processes. In this study, visible light-driven photocatalytic membrane was synthesized through the immobilization of nitrogen-doped nanoparticles onto the polyvinylidene fluoride (PVDF) membrane and performance evaluated with E.coli microbial contaminant removal. Characterization was done using Fourier transform infrared spectra, X-ray diffraction (XRD), water contact angle, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX). The Nitrogen-doping of titanium dioxide red-shifted the light absorption to a visible range of 440 nm from 400 nm. Nitrogen dopant was detected at 1420 cm-1and 1170 cm-1 for nitrogen doped nanoparticles and 1346-1417 cm-1 for nitrogen doped titanium dioxide PVDF membrane. SEM-EDX confirmed presences of nitrogen in nitrogen doped titanium dioxide nanoparticles on membrane surface with nitrogen elemental composition of 0.01 % wt. The water contact angle reduced by 81.39o from 120.14o to 38.75o because of PVA immobilization of nitrogen-doped titanium dioxide and glutaraldehyde crosslinking. Nitrogen doping resulted in visible light active photocatalytic membranes with better hydrophilicity and fouling resistance. 8.42 E.coli log removal and a relative flux of 0.35 was obtained within 75 min. The developed photocatalytic membrane enables the use of sunlight hence a less costly method for decontamination of wastewater.

Recent advances in membrane technologies applied in oil-water separation

Effective treatment of oily wastewater, which is toxic and harmful and causes serious environmental pollution and health risks, has become an important research field. Membrane separation technology has emerged as a key area of investigation in oil-water separation research due to its high separation efficiency, low costs, and user-friendly operation. This review aims to report on the advances in the research of various types of separation membranes around emulsion permeance, separation efficiency, antifouling efficiency, and stimulus responsiveness. Meanwhile, the challenges encountered in oil-water separation membranes are examined, and potential research avenues are identified.

High Recovery of Ceramic Membrane Cleaning Remediation by Ozone Nanobubble Technology

The persistent issue of ceramic membrane fouling poses significant challenges to its widespread implementation. To address this concern, ozone nanobubbles (ozone-NBs) have garnered attention due to their remarkable mass transfer efficiency. In this investigation, we present a novel ozone-NB generator system to effectively clean a fouled ceramic membrane that is typically employed in the dye industry. The surface characteristics of the ceramic membrane underwent significant alterations, manifesting incremental changes in surface roughness and foulant accumulation reduction, as evidenced in atomic force microscopy, scanning electron microscopy, X-ray fluorescence, and energy-dispersive spectroscopy. Remarkably, the sequential 4 h cleaning process demonstrates an effective outcome leading to an almost 2-fold enhancement in the membrane flux. The initial fouled state of 608 L/h/m2 increased to 1050 L/h/m2 in the 4 h state with a recovery of 50%. We propose such membrane performance improvement governed by the ozone-NBs with a size distribution of 213.2 nm and a zeta potential value of -20.26 ± 0.13 mV, respectively. This effort showcases a substantial innovative and sustainable technology approach toward proficient foulant removal in water treatment applications.

Hydrodynamic studies of innovative membrane reactor for enzymatic hydrolysis of lignocellulosic waste

This paper presents the study concerning the impact of the basic operational parameters on the performance of an innovative microfiltration membrane reactor applied for enzymatic hydrolysis of lignocellulosic biomass. The concept and basic hydrodynamics of the reactor with tubular ceramic membranes and a propeller agitator were shown. Besides, the efficiency of enzymatic hydrolysis of corn straw was studied to check reactor functionality. It has been proven that the proposed reactor construction can improve the microfiltration of lignocellulosic suspension by reducing the cake layer on the membrane surface. Increasing the rotational speed of the propeller agitator also improved the filtration efficiency. The permeate flux during the microfiltration experiments was lower for smaller lignocellulose biomass fraction (D < 425 μm) when compared to the less fragmented corn straw (425 < D < 900 μm). For larger solid fractions, a stirring speed increase enhanced the separation efficiency regardless of the differences in biomass concentration. In contrast, this trend for the finer biomass fraction was only noticeable for the highest used biomass concentration (C = 2.0%). Considering the enzymatic hydrolysis of corn straw, membrane separation of reaction products positively influenced the process yield, and the results depended on the applied operational parameters.

High efficiency sperm enrichment from forensic mock samples in bubble-based acoustic filtration devices for short tandem repeat (STR) analysis

A bubble-based acoustofluidic filtration (BAF) microfluidic device, which employs cross-flow filtration (CFF) and acoustic streaming, separates cells with high efficiency for forensic analysis. Forensic samples are typically complex and contain a substantial number of squamous epithelial cells from the female vagina, which tend to have fouling problems during filtration due to their morphological and cell adhesion differences. To overcome this issue, the BAF device utilizes bubble oscillation by bulk acoustic wave (BAW) to generate acoustic streaming, which offers additional hydrodynamic forces for side flushing cleaning and achieves effective removal within a mere 0.5 seconds. Our device is tested with imbalanced cell mixtures of sperm and epithelial cells with large disparity ratios. By concurrently employing CFF and acoustic streaming, the samples with our sperm-enrichment can achieve 91.72-97.78% for the recovery rate and 74.58-89.26% for the purity in the sperm enrichment. They are further subjected to short tandem repeat (STR) profiling, enabling the identification of perpetrators. Notably, even samples with minimal sperm cells demonstrated a significant increase in the male donor DNA ratio, while the peak heights of female alleles became virtually undetectable. The exceptional cell separation capability demonstrated by our BAF device highlights its potential applications in forensic sciences and other areas of cell biology.

Impact of Cleaning on Membrane Performance during Surface Water Treatment: A Hybrid Process with Biological Ion Exchange and Gravity-Driven Membranes

In this study, the hybrid biological ion exchange (BIEX) resin and gravity-driven membrane (GDM) process was employed for the treatment of coloured and turbid river water. The primary objective was to investigate the impact of both physical and chemical cleaning methods on ceramic and polymeric membranes in terms of their stabilised flux, flux recovery after physical/chemical cleaning, and permeate quality. To address these objectives, two types of MF and UF membranes were utilised (M1 = polymeric MF, M2 = polymeric UF, M3 = ceramic UF, and M4 = lab-made ceramic MF). Throughout the extended operation, the resin functioned initially in the primary ion exchange (IEX) region (NOM displacement with pre-charged chloride) and progressed to a secondary IEX stage (NOM displacement with bicarbonate and sulphate), while membrane flux remained stable. Subsequently, physical cleaning involved air/water backwash with two different flows and pressures, and chemical cleaning utilised NaOH at concentrations of 20 and 40 mM, as well as NaOCl at concentrations of 250 and 500 mg Cl2/L. These processes were carried out to assess flux recovery and identify fouling reversibility. The results indicate an endpoint of 1728 bed volumes (BVs) for the primary IEX region, while the secondary IEX continued up to 6528 BV. At the end of the operation, DOC and UVA254 removal in the effluent of the BIEX columns were 68% and 81%, respectively, compared to influent water. This was followed by 30% and 57% DOC and UVA254 removal using M4 (ceramic MF). The stabilised flux remained approximately 3.8-5.2 LMH both before and after the cleaning process, suggesting that membrane materials do not play a pivotal role. The mean stabilised flux of polymeric membranes increased after cleaning, whereas that of the ceramics decreased. Enhanced air-water backwash flow and pressure resulted in an increased removal of hydraulic reversible fouling, which was identified as the dominant fouling type. Ceramic membranes exhibited a higher removal of reversible hydraulic fouling than polymeric membranes. Chemical cleaning had a low impact on flux recovery; therefore, we recommend solely employing physical cleaning.

Inducing Deep Sweeps and Vortex Ejections on Patterned Membrane Surfaces to Mitigate Surface Fouling

Patterned membrane surfaces offer a hydrodynamic approach to mitigating concentration polarization and subsequent surface fouling. However, when subjected to steady crossflow conditions, surface patterns promote particle accumulation in the recirculation zones of cavity-like spaces. In order to resolve this issue, we numerically subject a two-dimensional, patterned membrane surface to a rapidly pulsed crossflow. When combined with cavity-like spaces, such as the valleys of membrane surface patterns, a rapidly pulsed flow generates mixing mechanisms (i.e., the deep sweep and the vortex ejection) and disrupts recirculation zones. In only four pulses, we demonstrate the ability of these mechanisms to remove over half of the particles trapped in recirculation zones via massless particle tracking studies (i.e., numerical integration of the simulated velocity field). The results of this work suggest that when combined with a rapidly pulsed inlet flow, patterned membrane surfaces can not only alleviate concentration polarization and the surface fouling that follows but also reduce the need for traditional cleaning methods that require operational downtime and often involve the use of abrasive chemical agents.

Fur flutter in fluid flow fends off foulers

The fouling of submerged surfaces detrimentally alters stratum properties. Inorganic and organic foulers alike attach to and accumulate on surfaces when the complex interaction between numerous variables governing attachment and colonization is favourable. Unlike naturally evolved solutions, industrial methods of repellence carry adverse environmental impacts. Mammal fur demonstrates high resistance to fouling; however, our understanding of the intricacies of such performance remains limited. Here, we show that the passive trait of fur to dynamically respond to an external flow field dramatically improves its anti-fouling performance over that of fibres rigidly fixed at both ends. We have previously discovered a statistically significant correlation between a group of flow- and stratum-related properties, and the quantified anti-fouling performance of immobile filaments. In this work, we improve the correlation by considering an additional physical factor, the ability of hair to flex. Our work establishes a parametric framework for the design of passive anti-fouling filamentous structures and invites other disciplines to contribute to the investigation of the anti-fouling prowess of mammalian interfaces.

Nano-clay modified membranes: A promising green strategy for microalgal antifouling filtration

Membrane fouling is a major challenge which limits the sustainable application of membrane filtration-based microalgal harvesting at industrial level. Membrane fouling leads to increased operational and maintenance costs and represents a major obstacle to microalgal downstream processing. Nano-clays are promising naturally occurring nanoparticles in membrane fabrication due to their low-cost, facile preparation, and their superior properties in terms of surface hydrophilicity, mechanical stability, and resistance against chemicals. The membrane surface modification using nano-clays is a sustainable promising approach to improve membranes mechanical properties and their fouling resistance. However, the positive effects of nano-clay particles on membrane fouling are often limited by aggregation and poor adhesion to the base polymeric matrix. This review surveys the recent efforts to achieve anti-fouling behavior using membrane surface modification with nano-clay fillers. Further, strategies to achieve a better incorporation of nano-clay in the polymer matrix of the membrane are summarised, and the factors that govern the membrane fouling, stability, adhesion, agglomeration and leaching are discussed in depth.

Optimization of membrane filtration and cleaning strategy in a high solid thermophilic AnMBR treating food waste

Anaerobic membrane bioreactor is advantageous over traditional processes for food waste treatment, i.e. short retention time, high loading rate, and particulate clean permeate. However, establishing a sustainable membrane filtration is a long-standing challenge because of its high viscosity and solids concentration characteristics. Therefore, this study investigated the changes in the membrane permeability before and after the cleaning during a 130-day thermophilic anaerobic experiment. Results show that the AnMBR system could maintain high stability even under a short HRT of 10 days and OLR of 9.0 kg-COD/(m3·d) with low volatile fatty acid of 50 mg/L. The membrane filtration deteriorates with the concurrence of a sharp increase of viscosity when the volatile solids reached 23 g/L. A critical flux was achieved at 5.5 L/(m2·h) under optimized operation conditions, membrane filtration/relaxing ratio with less than 4:1 at a hydraulic retention time of 15 d. Membrane fouling can be removed by soaking the membrane in NaClO (1 g/L, 15 h) and citric acid (2 g/L, 2 h). Conclusively, this work provides insight to establish the operation strategy for a thermophilic AnMBR treating food waste.

In-depth insight on microbial electrochemical systems coupled with membrane bioreactors for performance enhancement: a review

A conventional activated sludge (CAS) system has traditionally been used for secondary treatment in wastewater treatment plants. Due to the high cost of aeration and the problem of sludge treatment, researchers are developing alternatives to the CAS system. A membrane bioreactor (MBR) is a technology with higher solid-liquid separation efficiency. However, the use of MBR is limited due to inevitable membrane fouling and high energy consumption. Membrane fouling requires frequent cleaning, and MBR components must be replaced, which reduces membrane lifetime and operating costs. To overcome the limitations of the MBR system, a microbial fuel cell-membrane bioreactor (MFC-MBR) coupling system has attracted the interest of researchers. The design of the novel bioelectrochemical membrane reactor (BEMR) can effectively couple microbial degradation in the microbial electrochemical system (MES) and generate a microelectric field to reduce and alleviate membrane fouling in the MBR system. In addition, the coupling system combining an MES and an MBR can improve the efficiency of COD and ammonium removal while generating electricity to balance the energy consumption of the system. However, several obstacles must be overcome before the MFC-MBR coupling system can be commercialised. The aim of this study is to provide critical studies of the MBR, MES and MFC-MBR coupling system for wastewater treatment. This paper begins with a critical discussion of the unresolved MBR fouling problem. There are detailed past and current studies of the MES-MBR coupling system with comparison of performances of the system. Finally, the challenges faced in developing the coupling system on a large scale were discussed.

Multifunctional Bacterial Cellulose/Covalent Organic Framework Composite Membranes with Antifouling and Antibacterial Properties for Dye Separation

Covalent organic frameworks (COFs) have a wide application prospect in wastewater treatment because of their unique structure and properties; however, the preparation of pure COF membranes remains a great challenge by reason of the insolubility and unprocessability of COF powders formed at high temperature and high pressure. In this study, a continuous and defect-free bacterial cellulose/covalent organic framework composite membrane was prepared by using bacterial cellulose (BC) and a porphyrin-based COF with their unique structures and hydrogen bonding forces. The dye rejection rate of this composite membrane toward methyl green and congo red was up to 99%, and the permeance was about 195 L m^-2 h^-1 bar^-1. It showed excellent stability under different pH conditions, long-time filtration, and cyclic experimental conditions. In addition, the hydrophilicity and surface negativity of the BC/COF composite membrane made it have certain antifouling performance, and the flux recovery rate can reach 93.72%. More importantly, the composite membrane exhibited excellent antibacterial properties due to the doping of the porphyrin-based COF, and the survival rates of both Escherichia coli and Staphylococcus aureus were less than 1% after exposure to visible light. The self-supporting BC/COF composite membrane synthesized by this strategy also has outstanding antifouling and antibacterial properties, in addition to excellent dye separation effects, which greatly broaden the application of COF materials in water treatment.

Emerging integrated SERS-microfluidic devices for analysis of cancer-derived small extracellular vesicles

Cancer-derived small extracellular vesicles (sEVs) are specific subgroups of lipid bilayer vesicles secreted from cancer cells to the extracellular environment. They carry distinct biomolecules (e.g., proteins, lipids and nucleic acids) from their parent cancer cells. Therefore, the analysis of cancer-derived sEVs can provide valuable information for cancer diagnosis. However, the use of cancer-derived sEVs in clinics is still limited due to their small size, low amounts in circulating fluids, and heterogeneous molecular features, making their isolation and analysis challenging. Recently, microfluidic technology has gained great attention for its ability to isolate sEVs in minimal volume. In addition, microfluidics allows the isolation and detection of sEVs to be integrated into a single device, offering new opportunities for clinical application. Among various detection techniques, surface-enhanced Raman scattering (SERS) has emerged as a promising candidate for integrating with microfluidic devices due to its ultra-sensitivity, stability, rapid readout, and multiplexing capability. In this tutorial review, we start with the design of microfluidics devices for isolation of sEVs and introduce the key factors to be considered for the design, and then discuss the integration of SERS and microfluidic devices by providing descriptive examples of the currently developed platforms. Lastly, we discuss the current limitations and provide our insights for utilising integrated SERS-microfluidics to isolate and analyse cancer-derived sEVs in clinical settings.

Determination of Sustainable Critical Flux through a Long-Term Membrane Resistance Model

A long-term membrane resistance model (LMR) was established to determine the sustainable critical flux, which developed and simulated polymer film fouling successfully in a lab-scale membrane bioreactor (MBR) in this study. The total polymer film fouling resistance in the model was decomposed into the individual components of pore fouling resistance, sludge cake accumulation and cake layer compression resistance. The model effectively simulated the fouling phenomenon in the MBR at different fluxes. Considering the influence of temperature, the model was calibrated by temperature coefficient τ, and a good result was achieved to simulate the polymer film fouling at 25 and 15 °C. The relationship between flux and operation time was simulated and discussed through the model. The results indicated that there was an exponential correlation between flux and operation time, and the exponential curve could be divided into two parts. By fitting the two parts to two straight lines, respectively, the intersection of the two straight lines was regarded as the sustainable critical flux value. The sustainable critical flux obtained in this study was just 67% of the critical flux. The model in this study was proven to be in good agreement with the measurements under different fluxes and different temperatures. In addition, the sustainable critical flux was first proposed and calculated in this study, and it was shown that the model could be used to predict the sustainable operation time and sustainable critical flux, which provide more practical information for designing MBRs. This study is applicable to polymer films used in a wide variety of applications, and it is helpful for maintaining the long-term stable operation of polymer film modules and improving the efficiency of polymer film modules.

Enantioseparation Membranes: Research Status, Challenges, and Trends

The purity of enantiomers plays a critical role in human health and safety. Enantioseparation is an effective way and necessary process to obtain pure chiral compounds. Enantiomer membrane separation is a new chiral resolution technique, which has the potential for industrialization. This paper mainly summarizes the research status of enantioseparation membranes including membrane materials, preparation methods, factors affecting membrane properties, and separation mechanisms. In addition, the key problems and challenges to be solved in the research of enantioseparation membranes are analyzed. Last but not least, the future development trend of the chiral membrane is expected.

Removal of natural organic matter from surface water sources by nanofiltration and surface engineering membranes for fouling mitigation - A review

Given that surface water is the primary supply of drinking water worldwide, the presence of natural organic matter (NOM) in surface water presents difficulties for water treatment facilities. During the disinfection phase of the drinking water treatment process, NOM aids in the creation of toxic disinfection by-products (DBPs). This problem can be effectively solved using the nanofiltration (NF) membrane method, however NOM can significantly foul NF membranes, degrading separation performance and membrane integrity, necessitating the development of fouling-resistant membranes. This review offers a thorough analysis of the removal of NOM by NF along with insights into the operation, mechanisms, fouling, and its controlling variables. In light of engineering materials with distinctive features, the potential of surface-engineered NF membranes is here critically assessed for the impact on the membrane surface, separation, and antifouling qualities. Case studies on surface-engineered NF membranes are critically evaluated, and properties-to-performance connections are established, as well as challenges, trends, and predictions for the field's future. The effect of alteration on surface properties, interactions with solutes and foulants, and applications in water treatment are all examined in detail. Engineered NF membranes containing zwitterionic polymers have the greatest potential to improve membrane permeance, selectivity, stability, and antifouling performance. To support commercial applications, however, difficulties related to material production, modification techniques, and long-term stability must be solved promptly. Fouling resistant NF membrane development would be critical not only for the water treatment industry, but also for a wide range of developing applications in gas and liquid separations.

Exploration of advanced cellulosic material for membrane filtration with outstanding antifouling property

Membranes, at times, have issues due to membrane fouling. The membrane fouling leads to performance deterioration and poses a potential to clog the membrane. Here we present experimental works carried out with emphasis on the antifouling properties, chlorine resistance, and mechanical properties of cellulose triacetate (CTA) and cellulose esters. We present that antifouling performance of cellulose esters evaluated by means of the VCG theory decreases with increasing carbon number in the substituent because of the high electron-donating nature of short aliphatic ester groups. When a long aliphatic ester group is required in terms of other properties such as resistance to chlorine, introducing it together with another substituent with an electron-donating nature such as an ethylene glycol moiety may strike a balance between antifouling and other performances.

Effects of Critical Operation and Cleaning Parameters on Performances and Economic Benefits of Biogas Slurry Concentration by Forward Osmosis Membrane

Forward osmosis membrane technology (FO) shows potential application prospects in biogas slurry concentration, which is conducive to promoting the sustainable development of biogas projects. However, at present, the key influencing factors of membrane concentration using FO are not well understood. Therefore, this study analyzed the influence of draw solution concentration, pH, temperature and cross-flow velocity on the concentration efficiency of FO membrane, and optimized the operation parameters of FO membrane. The results showed that the concentration effect of the NaCl draw solution at pH 5 or 9 was better than that at pH 7. The order of factor influencing the water flux was as follows: draw liquid concentration > cross-flow velocity > operating temperature. The optimal combination obtained by orthogonal analysis was under 45 °C, with a cross-flow velocity of 1 L/min and the use of 1.5 mol/L NaCl as draw solution. The results of the membrane cleaning implied that the recovery rate of the fouled membrane after acid-base cleaning is significantly higher (88%) than other cleaning solutions. This research offers a scientific reference for applying positive osmosis technology to re-utilize biogas slurry resources.

The Performance of Microfiltration Process for Purifying Lactic Acid in the Fermented Broth of Kitchen Waste

Fermentation broth is plentiful with lactic acid, an important chemical applied in many fields, such as food processing, the chemical industry, and cosmetics. However, the purification of the lactic acid from the broth is still troublesome, when considering the economy. This study first investigated the purification performance of microfiltration (MF) membrane technology for a fermentation broth from kitchen waste. The effect of operation pressure, broth pH, and membrane flushing mode on the membrane filtration performance were investigated. In addition, the change in filtration performance over the increase in cycle time was also investigated. The results showed that under the optimum pressure of 100 KPa, pH of 6.0, and a backflushing mode with deionized water for 3 min, the best performance was achieved, with chroma removal, turbidity removal, protein removal and total sugar removal efficiencies of 60, 92.8, 57.64 and 32.93%, respectively. The results indicated that the MF process could be a desirable broth purification process to some extent, and it is promising in actual application. The MF process combined with other post-purification processes will form the ideal process system, which should be explored in future research.

Nanofibrous/biopolymeric membrane a sustainable approach to remove organic micropollutants: A review

Aquifers are severely polluted with organic and inorganic pollutants, posing a serious threat to the global ecological system's balance. While various traditional methods are available, the development of innovative methods for effluent treatment and reuse is critical. Polymers have recently been widely used in a variety of industry sectors due to their unique properties. Biopolymers are a biodegradable material that is also a viable alternative to synthetic polymers. Biopolymers are preferably obtained from cellulose and carrageenan molecules from various biological sources. While compared with conventional non-biodegradable polymeric materials, the biopolymer possesses unique characteristics such as renewability, cost-effectiveness, biodegradability, and biocompatibility. The improvements towards the biopolymeric (natural) membranes have also been thoroughly discussed. The use of nanofillers to stabilise and improve the effectiveness of biopolymeric membranes in the elimination of organic pollutants is one of the most recent developments. This was discovered that the majority of biopolymeric membranes technology consolidated on organic pollutants. More research should be directed toward against emerging organic/persistent organic pollutants (POP) and micropollutants. Furthermore, processes for regenerating and reusing utilized biopolymer-based carbon - based materials are emphasized.

A Review on Membrane Biofouling: Prediction, Characterization, and Mitigation

Water scarcity is an increasing problem on every continent, which instigated the search for novel ways to provide clean water suitable for human use; one such way is desalination. Desalination refers to the process of purifying salts and contaminants to produce water suitable for domestic and industrial applications. Due to the high costs and energy consumption associated with some desalination techniques, membrane-based technologies have emerged as a promising alternative water treatment, due to their high energy efficiency, operational simplicity, and lower cost. However, membrane fouling is a major challenge to membrane-based separation as it has detrimental effects on the membrane's performance and integrity. Based on the type of accumulated foulants, fouling can be classified into particulate, organic, inorganic, and biofouling. Biofouling is considered the most problematic among the four fouling categories. Therefore, proper characterization and prediction of biofouling are essential for creating efficient control and mitigation strategies to minimize the damage associated with biofouling. Moreover, the use of artificial intelligence (AI) in predicting membrane fouling has garnered a great deal of attention due to its adaptive capability and prediction accuracy. This paper presents an overview of the membrane biofouling mechanisms, characterization techniques, and predictive methods with a focus on AI-based techniques, and mitigation strategies.

Air-liquid interface cultivation of Navicula incerta using hollow fiber membranes

Microalgae cultivation in open ponds requires a large footprint, while most photobioreactors need improvement in the ratio of surface to volume and energy consumption. In this study, polyethersulfone (PES) and poly(vinylidene fluoride) (PVDF) hollow fiber membranes with a large surface area were rearranged into open-ended and dead-ended configurations to improve the air-liquid interface cultivation of Navicula incerta. N. incerta were successfully grown on the porous membrane surface with the nutrients circulating inside the lumen. Fourier-transform infrared spectra showed the accumulation of polysaccharides, proteins and humic acids. Hydrophilic polysaccharides reduced water contact angles on PES and PVDF membranes to 37.2 ± 2.6° and 55.7 ± 3.3°, respectively. However, the porosity of PES (80.1 ± 1.1%) and PVDF (61.3 ± 4.5%) membranes were not significantly affected even after cultivation and harvesting of N. incerta. Scanning electron images further confirmed that N. incerta, cell debris and extracellular organic matter accumulated on the membrane. With large pores and a hydrophobic surface, PVDF hollow fiber membranes offered a greater improvement in N. incerta cell growth rate compared to PES hollow fiber membranes despite using different configurations. In the dead-ended configuration, they even attained the greatest improvement in N. incerta growth rate, up to 54.0%. However, PES hollow fiber membranes only achieved improvement in harvesting efficiency within the range of 18.7-38.0% due to weak cell adhesion. PVDF hollow fiber membranes significantly promoted the growth of microalgae N. incerta through the air-liquid interface system, leading to potential applications in wastewater treatment.

Removal of glycerol from biodiesel using multi-stage microfiltration membrane system: industrial scale process simulation

Biodiesel purification is one of the most important downstream processes in biodiesel industries. The removal of glycerol from crude biodiesel is commonly conducted by an extraction method using water, however this method results in a vast amount of wastewater and needs a lot of energy. In this study, microfiltration membrane was used to remove glycerol from biodiesel, and a process simulation was carried out for an industrial scale biodiesel purification plant using a microfiltration membrane system. The microfiltration experiment using a simulated feed solution of biodiesel containing glycerol and water showed that the membrane process produced purified biodiesel that met the international standards. The result of the process simulation of a multi-stage membrane system showed that the membrane area could be minimized by optimizing the concentration factor of every stage with the aid of a computer program that was written in Phyton programming language with Visual Studio Code. The overall productivity of a single stage membrane system was the same with that of the multi-stage system, however the single stage system required a larger membrane area. To produce 750 m3 day−1 of purified biodiesel, a multi-stage membrane system consisting of 10 membrane modules required a total membrane area of 1515 m2 that was 57% smaller compared to the single stage system consisting of one membrane module. This membrane area reduction was equivalent to a reduction of the total capital cost of 30%. Based on the analysis of the total capital cost, it was found that the optimum number of stages was 4 since it showed a minimum value of the total capital cost with a membrane area of 1620 m2 that was equivalent to the reduction of the total capital cost of 34%. The result of this simulation showed that the multi-stage microfiltration membrane has great potential to replace the conventional method in biodiesel industries.

Unveiling the Impacts of Sodium Hypochlorite on the Characteristics and Fouling Behaviors of Different Commercial Polyvinylidene Fluoride Hollow Fiber Membranes

Sodium hypochlorite (NaOCl) is a commonly used cleaning agent for recovering membrane performance in membrane technologies. A thorough understanding of the impacts of NaOCl exposure on membrane properties and fouling behavior is important for optimizing chemical cleaning process and extending membrane lifespan. In this study, three commercial polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes (SMM-1010, MEMCOR^® CS II and ZeeWeed 500) were used to systematically explore the effects of NaOCl dose and solution pH (8 and 10) on membrane properties. The results showed that membrane pores increased with exposure time prolonging, and more pores were observed at pH 8 aging condition. The amide group in the Fourier transformation infrared spectra was disappeared, while the carboxylic acid and succinimide groups were formed at pH 10 and pH 8 conditions, respectively. The hydrophilicity and pure water permeability (PWP) of SMM-1010 and MEMCOR^® CS II membranes had insignificant changes during NaOCl aging process, whereas the hydrophilicity of ZeeWeed 500 membrane slightly decreased and its PWP increased by 1.4-fold. The antifouling properties of NaOCl-aged SMM-1010 and MEMCOR^® CS II membranes were slightly improved, whereas the NaOCl-aged ZeeWeed 500 membrane showed severer flux decline with humic acid filtration. Our findings could provide guidance for practical chemical cleaning process optimization.

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.

Constitutive and extracellular expression of pectin methylesterase from Pectobacterium chrysanthemi in Pichia pastoris

Pectin methylesterase (PME) which is widely used in the cosmetic, food and pharmaceutical industries catalyses the hydrolysis of the methyl ester of pectin to yield methanol and free carboxyl groups. This study was performed to produce active pectin methylesterase (PME) extracellularly from Pectobacterium chrysanthemi in Pichia pastoris. Firstly, pGKBα was constructed for the secretion of heterologous protein. After it was cloned in Escherichia coli cells and the sequence was affirmed, PME gene was inserted into pGKBα. So, pGKBα-PME carried the PME gene in correct position was cloned in E. coli cells. Then, P. pastoris X-33 cells were transformed with linearized pGKBα-PME and six transformants were cultivated for recombinant PME production. It was observed that one of them had a high-capacity secretion of active PME. The molecular mass of extracellular PME enzyme was found to be about 59 kDa. The PME enzyme from P. chrysanthemi was produced by P. pastoris for the first time in this study. This recombinant enzyme might be produced in a large scale and also purified from the culture medium. Then, the purified enzyme might be used for clarification and increasing yield of juice in food industrial applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03291-3.

The comparison between two methods of membrane cleaning to control membrane fouling in a hybrid membrane photobioreactor (HMPBR)

In this study, the effect of two membrane cleaning methods, such as aeration and addition of granular particles in a hybrid membrane photobioreactor (HMPBR) including Spirulina sp. with the concentration of 1.5 g·L^-1 was investigated. Three different spargers [i.e., different diameters of orifice (d_o): 0.5, 1, and 1.5 mm] and granular particles (i.e., three packing ratios of 0.5, 1, and 1.5%) were used. The results showed that with the increase in granular packing ratio, R_c/R_t decreased significantly. The best result was achieved by combining aeration with an orifice diameter of 1.5 mm and a granular packing ratio of 1.5%, which led to the lowest R_c/R_t value (0.38), while R_c/R_t value with a d_o of 1.5 mm was 0.68 without particles. In contrast, the ratio of pore blocking resistance to total resistance (R_p/R_t) increased by 4.2% under the combined application of 1.5 mm of orifice diameter and 1.5% of granular packing ratio. The results from protein concentrations in the cake layer showed that as the d_o became larger, cake protein concentration decreased by 40%, whereas increasing the granular packing ratio from 0.5 to 1.5% increased protein concentration by 60% in the cake layer.

Reagent-Free Immobilization of Industrial Lipases to Develop Lipolytic Membranes with Self-Cleaning Surfaces

Biocatalytic membrane reactors combine the highly efficient biotransformation capability of enzymes with the selective filtration performance of membrane filters. Common strategies to immobilize enzymes on polymeric membranes are based on chemical coupling reactions. Still, they are associated with drawbacks such as long reaction times, high costs, and the use of potentially toxic or hazardous reagents. In this study, a reagent-free immobilization method based on electron beam irradiation was investigated, which allows much faster, cleaner, and cheaper fabrication of enzyme membrane reactors. Two industrial lipase enzymes were coupled onto a polyvinylidene fluoride (PVDF) flat sheet membrane to create self-cleaning surfaces. The response surface methodology (RSM) in the design-of-experiments approach was applied to investigate the effects of three numerical factors on enzyme activity, yielding a maximum activity of 823 ± 118 U m⁻² (enzyme concentration: 8.4 g L⁻¹, impregnation time: 5 min, irradiation dose: 80 kGy). The lipolytic membranes were used in fouling tests with olive oil (1 g L⁻¹ in 2 mM sodium dodecyl sulfate), resulting in 100% regeneration of filtration performance after 3 h of self-cleaning in an aqueous buffer (pH 8, 37 °C). Reusability with three consecutive cycles demonstrates regeneration of 95%. Comprehensive membrane characterization was performed by determining enzyme kinetic parameters, permeance monitoring, X-ray photoelectron spectroscopy, FTIR spectroscopy, scanning electron microscopy, and zeta potential, as well as water contact angle measurements.

Influence of the Zeolite ZSM-22 Precursor on a UF-PES Selective Substrate Layer for Salts Rejection

Fabrication of the ZSM-22/Polyethersulfone (ZSM-22/PES) membranes as selective salt filters represent a growing membrane technological area in separation with the potential of high economic reward based on its low energy requirements. The incorporation of ZSM-22 zeolite material as additives into the PES polymer matrix has the prospective advantage of combining both the zeolite and polymer features while overcoming the limitations associated with both materials. This work investigated the influence of the nature of the silica precursor on ZSM-22 zeolite hydrothermally synthesised using colloidal (C60) and fumed (C60) silica to Si/Al of 60. The successful synthesis of the highly crystalline zeolitic materials was confirmed through XRD, FTIR, and SEM with EDX. The ZSM-22 additives were directly dispersed into a PES polymeric matrix to form a casting solution for the preparation of the ZSM-22/PES selective substrate layers via a phase inversion method for salts rejection. The polymeric PES was selected as an organic network in which the content of the ZSM-22 zeolite (ranging between 0 and 1.0 wt.%), was obtained and characterised by XRD, FTIR, and SEM analysis, as well as water contact angle (WCA) measurement and dead-end filtration cell. The phase inversion preparation method has induced the resulting ZSM-22/PES NF substrates anisotropy, as attributed to a high water flux to the above 700 L·m−2·h−1; high selectivity and rejection of salts to above 80% is revealed by the obtained results. The materials also exhibited improved antifouling behavior to above 70% flux recovery ratios. As such, the nature of the silica precursor influences ZSM-22 zeolite synthesis as a potential additive in the PES polymer matrix and led to the enhanced performance of the pure PES ultrafiltration membrane.

Chemical Cleaning Process of Polymeric Nanofibrous Membranes

Membrane fouling is one of the most significant issues to overcome in membrane-based technologies as it causes a decrease in the membrane flux and increases operational costs. This study investigates the effect of common chemical cleaning agents on polymeric nanofibrous membranes (PNM) prepared by polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyamide 6 (PA6) nanofibers. Common alkaline and acid membrane cleaners were selected as the chemical cleaning agents. Membrane surface morphology was investigated. The PAN PNM were selected and fouled by engine oil and then cleaned by the different chemical cleaning agents at various ratios. The SEM results indicated that the use of chemical agents had some effects on the surface of the nanofibrous membranes. Moreover, alkaline cleaning of the fouled membrane using the Triton X 100 surfactant showed a two to five times higher flux recovery than without using a surfactant. Among the tested chemical agents, the highest flux recovery rate was obtained by a binary solution of 5% sodium hydroxide + Triton for alkaline cleaning, and an individual solution of 1% citric acid for acidic cleaning. The results presented here provide one of the first investigations into the chemical cleaning of nanofiber membranes.

Fermentation strategies to improve propionic acid production with propionibacterium ssp.: a review

Propionic acid (PA) is a carboxylic acid applied in a variety of processes, such as food and feed preservative, and as a chemical intermediate in the production of polymers, pesticides and drugs. PA production is predominantly performed by petrochemical routes, but environmental issues are making it necessary to use sustainable processes based on renewable materials. PA production by fermentation with the Propionibacterium genus is a promising option in this scenario, due to the ability of this genus to consume a variety of renewable carbon sources with higher productivity than other native microorganisms. However, Propionibacterium fermentation processes present important challenges that must be faced to make this route competitive, such as: a high fermentation time, product inhibition and low PA final titer, which increase the cost of product recovery. This article summarizes the state of the art regarding strategies to improve PA production by fermentation with the Propionibacterium genus. Firstly, strategies associated with environmental fermentation conditions and nutrition requirements are discussed. Subsequently, advantages and disadvantages of various strategies proposed to improve process performance (high cell concentration by immobilization or recycle, co-culture fermentation, genome shuffling, evolutive and metabolic engineering, and in situ recovery) are evaluated.

Effects of electroflocculation/oxidation pretreatment on the fouling characteristics of ultrafiltration membranes

In order to reduce the membrane pollution of ultrafiltration caused by natural organic matter and improve the treatment efficiency, electroflocculation/oxidation is used as the premembrane treatment method. The membrane specific flux attenuation characteristics was compared and analyzed under the conditions of direct ultrafiltration and electroflocculation/oxidation-ultrafiltration. Combined with the analysis of the reversibility of membrane fouling, the mechanism of electroflocculation/oxidation pretreatment to alleviate ultrafiltration membrane fouling was evaluated, and the membrane pore clogging model was used to fit the fouling law. The results show that, in the continuously fed filtration experiment, the electroflocculation/oxidation process involved in the pretreatment and the direct ultrafiltration membrane filtration decreased the ultrafiltration membrane flux to 79.1% and 28.5%, respectively. The reversible resistance generated by ultrafiltration and electroflocculation/oxidation-ultrafiltration processes accounted for 37.70% and 62.26% of their total pollution resistance, whereas the irreversible resistance generated accounted for 47.30% and 12.40%, respectively. Meanwhile, the direct correlation between the the flux dropped and complete clogging became less than that of the ultrafiltration process. The pretreatment significantly strengthened irreversible fouling resistance of the membrane pores. The membrane permeation flux was significantly increased after the electroflocculation/oxidation pretreatment.

Current status of hypochlorite technology on the wastewater treatment and sludge disposal: Performance, principals and prospects

As cost-effective and high-efficient oxidants, the hypochlorite chemicals have been widely utilized for bleaching and disinfection. However, its potential applications in wastewater treatment and sludge disposal were less concerned. This paper mainly summarized the state-of-the-art applications of hypochlorite technology in wastewater and sludge treatment based on the main influencing factors and potential mechanisms of hypochlorite treatment. The results indicated that the hypochlorite approaches were not only effective in pollutants removal and membrane fouling mitigation for wastewater treatment, but also contributed to sludge dewatering and resource recovery for sludge disposal. The ClO^- and large generated free active radicals (i.e., reactive chlorine species and reactive oxygen species), which possessed strong oxidative ability, were the primary contributors to the pollutants decomposition, and colloids/microbes flocs disintegration during the hypochlorite treatment process. The performance of hypochlorite treatment was highly associated with various factors (i.e., pH, temperature, hypochlorite types and dosage). In combination with the reasonable activators (i.e., Fe²⁺ and ultraviolet), auxiliary agents, and innovative processes (i.e., hydrothermal and electro-oxidation), the operational performance of hypochlorite technology could be further enhanced. Finally, the feasibility and benefits of hypochlorite application for wastewater and sludge treatment were analyzed, and the existing challenges and future research efforts that need to be made have also prospected. The review can hopefully provide a theoretical basis and technical guidance to extend the application of hypochlorite technology for wastewater treatment and sludge disposal on large scale.

Electrospinning of Chitosan for Antibacterial Applications—Current Trends

Chitosan is a natural biopolymer that can be suitable for a wide range of applications due to its biocompatibility, rigid structure, and biodegradability. Moreover, it has been proven to have an antibacterial effect against several bacteria strains by incorporating the advantages of the electrospinning technique, with which tailored nanofibrous scaffolds can be produced. A literature search is conducted in this review regarding the antibacterial effectiveness of chitosan-based nanofibers in the filtration, biomedicine, and food protection industries. The results are promising in terms of research into sustainable materials. This review focuses on the electrospinning of chitosan for antibacterial applications and shows current trends in this field. In addition, various aspects such as the parameters affecting the antibacterial properties of chitosan are presented, and the application areas of electrospun chitosan nanofibers in the fields of air and water filtration, food storage, wound treatment, and tissue engineering are discussed in more detail.

Analyzing the phenolic enriched fractions from Nixtamalization wastewater (Nejayote) fractionated in a three-step membrane process

Nejayote is recognized as the main by-product resulting from the nixtamalization process of maize kernels, which is categorized as an alkaline residue with a chemical composition based on carbohydrates (37.8-55.7%), fiber (22.8-25.5%), protein (4.9-7.4%), and lipids (0.4-1.5%). In addition, Nejayote has an extensive content of simple (e.g., phenolic acids) and complex phenolic compounds (e.g., anthocyanins), which are responsible for the pigmentation and antioxidant activity of maize; therefore, there is a need of their identification depending on the type of maize. The current research has focused on the efficient extraction and identification of the phenolic acids contained in Nejayote after the processing of different types of maize. The target of this work was to fractionate Nejayote from white (NWM), red (NRM), and purple maize (NPM), using three different membranes, such as microfiltration (MF with a pore size of 1 μm) and ultrafiltration (UF100 and UF1 with a molecular weight cut-off of 100 kDa and 1 kDa, respectively), which were strategically applied to extract phenolic acids while retaining other molecules. Such a membrane system exhibited a retention in the first stage of almost all carbohydrates (MF-Retentate: ca. 12-19 g GE/L), while second stage (UF100-Permeate) a concentration of phenolic components was recovered ranging from 768 to 800 mg GAE/L. Finally, in the third stage (UF1-Permeate), 14 phenolic acids were identified, including ferulic and p-coumaric acids, derived from caffeic and ferulic acids, along with other molecules (e.g., glucose and fructose).

The Use of NaOH Solutions for Fouling Control in a Membrane Bioreactor: A Feasibility Study

Nowadays, the microbial production of 1,3-propanediol (1,3-PD) is recognized as preferable to the chemical synthesis. However, finding a technological approach allowing the production of 1,3-PD in the membrane bioreactor (MBR) is a great challenge. In the present study, a ceramic ultrafiltration (UF) membrane (8 kDa) for treatment of 1,3-PD broths was used. It has been demonstrated that the membrane used provides the stable permeate flux that is necessary to ensure the stability of the fermentation process in MBR technology. It was noticed that the broth pH has a significant impact on both the final 1,3-PD concentration and permeate flux. Moreover, the feasibility of using NaOH for fouling control in the MBR was evaluated. It has been shown that 1% NaOH solution is effective in restoring the initial membrane performance. To the best of our knowledge, this study is the first to shed light onto the possibility of reducing the amount of the alkaline solutions generated during the MBR operation. Indeed, it has been found that 1% NaOH solution can be successfully used several times for both membrane cleaning and to stabilize the broth pH. Finally, based on the results obtained, the technological conceptions of the MBR technology were designed.

Development of Environment-Friendly Membrane for Oily Industrial Wastewater Filtration

Latex phase blending and crosslinking method was used in this research work to produce nitrile butadiene rubber-graphene oxide (NBR-GO) membranes. This fabrication technique is new and yields environmentally friendly membranes for oil-water separation. GO loading was varied from 0.5 to 2.0 part per hundred-part rubber (pphr) to study its effect on the performance of NBR-GO membrane. GO was found to alter the surface morphology of the NBR matrix by introducing creases and fold on its surface, which then increases the permeation flux and rejection rate efficiency of the membrane. X-Ray diffraction analysis proves that GO was well dispersed in the membrane due to the non-existence of GO fingerprint diffraction peak at 2θ value of 10-12° in the membrane samples. The membrane filled with 2.0 pphr GO has the capability to permeate 7688.54 Lm-2 h-1 water at operating pressure of 0.3 bar with the corresponding rejection rate of oil recorded at 94.89%. As the GO loading increases from 0.5 to 2.0 pphr, fouling on the membrane surface also increases from Rt value of 45.03% to 87.96%. However, 100% recovery on membrane performance could be achieved by chemical backwashing.

A Way to Membrane-Based Environmental Remediation for Heavy Metal Removal

During the last century, industrialization has grown very fast and as a result heavy metals have contaminated many water sources. Due to their high toxicity, these pollutants are hazardous for humans, fish, and aquatic flora. Traditional techniques for their removal are adsorption, electro-dialysis, precipitation, and ion exchange, but they all present various drawbacks. Membrane technology represents an exciting alternative to the traditional ones characterized by high efficiency, low energy consumption and waste production, mild operating conditions, and easy scale-up. In this review, the attention has been focused on applying driven-pressure membrane processes for heavy metal removal, highlighting each of the positive and negative aspects. Advantages and disadvantages, and recent progress on the production of nanocomposite membranes and electrospun nanofiber membranes for the adsorption of heavy metal ions have also been reported and critically discussed. Finally, future prospective research activities and the key steps required to make their use effective on an industrial scale have been presented