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The main challenge with membrane bioreactors is fouling, which leads to decreased flux performance and a shortened membrane lifespan. This study aims to provide a solution for the flux recovery and removal of irreversible fouling on Polyvinylidene Fluoride (PVDF) membranes without damaging their structure using sulfate radicals. Sulfate radicals are formed via peroxodisulfate precursors that are activated by Fe2+. The membrane flux recovery and irreversible fouling ratio were 88.45-99.04% and 11.60-0.96%, respectively, at operating temperatures of 298-308 K. The PVDF membrane has been tested for microfiltration and washed up to 6 times per cycle. The mechanical properties, XRD, SEM-EDX, and ATR-FTIR characterization of the PVDF membrane after washing with PDS/Fe2+ did not show a negative effect on the PVDF structure. Additionally, the results of the kinetic and thermodynamic studies showed that washing with PDS/Fe2+ inhibited the formation of fouling particles on the membrane surface. Based on this study, sulfate radical oxidants with PDS precursors activated by Fe2+ can be applied as cleaning chemicals for PVDF membranes without damaging their structures.

The effects of pore size and surface modification on the fouling and cleaning properties in membrane bioreactor (MBR) with backwashing were studied using porous alumina microfiltration membranes with pore sizes of 0.2, 0.5, 0.7, and 1.5 μm. The surface modifications were conducted using silane coupling agents, 3-Aminopropyltrimethoxysilane (APTMS) for a positively charged surface, Chlorotrimethylsilane (TMS) for a weak hydrophobic surface, and Trichlorooctadecylsilane (ODS) for the strong hydrophobic surface. The two-stage fouling behaviors were typically observed and elucidated by shifting the fouling mechanism from adsorption to cake formation during operation. The fouling properties were characterized by the filtration resistance of cake layer Rc, the filtration resistance caused by adsorption Ra, which were determined from the difference in the filtration resistance for the filtration direction and the backwash direction, and Transition Point (TP) which divides the fouling stages. From the effect of pore size, the membrane having 0.2 μm, which was the smallest pore size in this study, showed the highest anti-fouling performance. This result was elucidated by pore blocking caused by particulate foulants having particle sizes close to the membrane pore size. The effect of the surface modification was mainly found in the adsorption properties of foulants. The TMS-modified membrane, which had a weak hydrophobic pore surface, showed the highest anti-fouling performance, which would be provided by blocking the further accumulation of foulants by the adsorption layer formed in the initial stage of the operation. From the cleaning properties of the fouled membranes by physical and chemical cleanings, the unmodified membrane, which has a hydrophilic surface, showed the best cleaning properties. The decrease in the absolute value of the zeta potential due to fouling was observed as a general trend and the adsorption of foulants in MBR was one of the causes of the decrease.

The presence of humic acid in surface water poses a challenge to water treatment processes. Furthermore, membrane fouling induced by humic acid is facilitated by the hydrophobic nature of the membrane material. In response, this study explores the use of hydrophilic additives, specifically vanillin, to modify the properties and performances of polyvinylidene fluoride (PVDF) membranes. Four different types of membrane flat sheets were prepared by non-solvent induced phase method. The modification of the membrane was carried out by blending vanillin (at a concentration of 0–5% w/w) with PVDF polymer. The results show that the incorporation of 3% w/w vanillin has a positive influence, increasing membrane hydrophilicity, porosity, and pore number and size. As a result, the permeate performance of the PVDF-vanillin membrane showed a significant improvement, with an increase in water flux to 30.9 Lm−2h−1, a humic acid rejection of 81.78%, and a high flux recovery ratio (FRR) of 108.68%. Adverse side effects were observed beyond the optimal concentration of 3% w/w vanillin. In conclusion, this study provides valuable insights for the development of PVDF membranes tailored for humic acid removal and organic fouling reduction.

Reverse osmosis (RO) and nanofiltration (NF) are ubiquitous technologies in modern water treatment, finding applications across various sectors. However, the availability of high-quality water suitable for RO/NF feed is diminishing due to droughts caused by global warming, increasing demand, and water pollution. As concerns grow over the depletion of precious freshwater resources, a global movement is gaining momentum to utilize previously overlooked or challenging water sources, collectively known as “marginal water”. Fouling is a serious concern when treating marginal water. In RO/NF, biofouling, organic and colloidal fouling, and scaling are particularly problematic. Of these, organic fouling, along with biofouling, has been considered difficult to manage. The major organic foulants studied are natural organic matter (NOM) for surface water and groundwater and effluent organic matter (EfOM) for municipal wastewater reuse. Polymeric substances such as sodium alginate, humic acid, and proteins have been used as model substances of EfOM. Fouling by low molecular weight organic compounds (LMWOCs) such as surfactants, phenolics, and plasticizers is known, but there have been few comprehensive reports. This review aims to shed light on fouling behavior by LMWOCs and its mechanism. LMWOC foulants reported so far are summarized, and the role of LMWOCs is also outlined for other polymeric membranes, e.g., UF, gas separation membranes, etc. Regarding the mechanism of fouling, it is explained that the fouling is caused by the strong interaction between LMWOC and the membrane, which causes the water permeation to be hindered by LMWOCs adsorbed on the membrane surface (surface fouling) and sorbed inside the membrane pores (internal fouling). Adsorption amounts and flow loss caused by the LMWOC fouling were well correlated with the octanol-water partition coefficient (log P). In part 2, countermeasures to solve this problem and applications using the LMWOCs will be outlined.

Membrane technologies play a pivotal role in various industrial sectors, including food processing. Membranes act as barriers, selectively allowing the passage of one or other types of species. The separation processes that involve them offer advantages such as continuity, energy efficiency, compactness of devices, operational simplicity, and minimal consumption of chemical reagents. The efficiency of membrane separation depends on various factors, such as morphology, composition, and process parameters. Fouling, a significant limitation in membrane processes, leads to a decline in performance over time. Anti-fouling strategies involve adjustments to process parameters or direct modifications to the membrane, aiming to enhance efficiency. Recent research has focused on mitigating fouling, particularly in the food industry, where complex organic streams pose challenges. Membrane processes address consumer demands for natural and healthy products, contributing to new formulations with antioxidant properties. These trends align with environmental concerns, emphasizing sustainable practices. Despite numerous works on membrane modification, a research gap exists, especially with regard to the application of modified membranes in the food industry. This review aims to systematize information on modified membranes, providing insights into their practical application. This comprehensive overview covers membrane modification methods, fouling mechanisms, and distinct applications in the food sector. This study highlights the potential of modified membranes for specific tasks in the food industry and encourages further research in this promising field.

The commercial ultrafiltration tubular polyvinylidene fluoride (PVDF) (100 and 200 kDa) and polyethersulfone (PES) (4 kDa) membranes were applied for filtration of car wash wastewater. Intensive fouling was noticed, which caused an over 50% flux reduction during 3–5 h of the filtration process. This phenomenon was reduced by washing the membranes with an alkaline cleaning agent (pH = 11.5), which is used in car washes to remove insects. The filtration/membrane washing cycle was repeated many times to achieve stable operation of the membrane modules. It has been found that cyclic repeated washing did not deteriorate the performance of the membranes. Despite frequent cleaning of the membranes (every 5–7 h), irreversible fouling occurred, resulting in a 20% reduction in the initial permeate flux. However, the formation of a filter cake definitely improved the separation degree and, for the 200 kDa membranes, separation of the wastewater components was obtained as it was for the 4 kDa membranes, while, at the same time, the permeate flux was 5 times higher.

To reduce membrane fouling during the processing of highly pulpy fruit juices into clarified beverages, a crossflow Sono-Microfiltration (SMF) system was employed, strategically equipped with an ultrasonic probe for the direct application of low-frequency ultrasound (LFUS) to the juice just before the entrance to the ceramic membrane. Operating conditions were standardized, and the application of LFUS pulses in both corrective and preventive modes was investigated. The effect of SMF on the physicochemical properties and the total soluble phenol (TSP) content of the clarified juice was also evaluated. The distance of ultrasonic energy irradiation guided the selection of the LFUS probe. Amplitude conditions and ultrasonic pulses were more effective in the preventive mode and did not cause membrane damage, reducing the operation time of jackfruit juice by up to 50% and increasing permeability by up to 81%. The SMF did not alter the physicochemical parameters of the clarified juice, and the measured LFUS energy ranges did not affect the TSP concentration during the process. This study is the first to apply LFUS directly to the feed stream in a pilot-scale crossflow microfiltration system to reduce the fouling of ceramic membranes and maintain bioactive compounds in jackfruit juice.

Kondensor merupakan komponen pendingin yang sangat penting yang berfungsi untuk memaksimalkan efisiensi pada mesin pendingin. Penelitian bertujuan untuk menganalisis pengaruh perubahan temperatur, heat duty, dan pressure drop terhadap nilai Rd pada alat penukar panas kondensor dengan menggunakan EDR serta membandingkan hasil data design dan aktual yang didapatkan. Aspen Exchanger Design and Rating (EDR) dapat digunakan untuk membuat, mengevaluasi dan menyimpan design serta memungkinkan untuk memaksimalkan desain untuk alat penukar panas yang dibutuhkan berdasarkan biaya. Metodologi yang dilakukan berupa pemodelan ulang proses pabrik ammonia II kemudian mengekspor nilai yang telah didapatkan pada kondensor ke aplikasi EDR lalu lakukan rating/checking pada run mode, masukkan data laju alir, temperatur serta data geometri yang dibutuhkan. Kemudian dilakukan pengecekan (runing) dengan aplikasi tersebut, setelah hasil yang dibutuhkan didapatkan maka dilakukan pendataan. Hasil penelitian didapatkan bahwa selisih nilai Q design lebih besar daripada nilai Q pada data aktual (data I) yaitu sebesar 4.359.780 Kcal/h, sedangkan nilai Rd shell side design dan aktual sama yaitu 0,00009 m2 K/W begitu pula dengan nilai Rd tube side design dan aktual didapatkan 0,00024 m2 K/W. Didapatkan juga perbandingan nilai pressure drop pada kondisi design dan aktual pada sisi shell sebesar 0,585 Psi, sedangkan pada sisi tube pressure drop mengalami kenaikan dengan selisih antara data design dan aktual sebesar 3,145 Psi. Berdasarkan penelitian yang dilakukan, didapatkan beberapa kesimpulan bahwa semakin tinggi nilai temperatur, maka nilai Q juga akan semakin tinggi dan begitu pula sebaliknya. Nilai Rd dipengaruhi oleh nilai Uc dan Ud, sehingga jika nilai Uc dan Ud rendah maka nilai Rd mengalami kenaikan yang disebabkan oleh suhu yang tertransfer kecil. Fouling factor yang tinggi dapat menyebabkan nilai pressure drop tinggi sehingga menyebabkan terjadinya penurunan kinerja heat exchanger. Pressure drop di pengaruhi beberapa faktor lainnya yaitu kecepatan aliran massa fluida melalui tube, panjang tube, jumlah pass dan kebersihan air pendingin yang masuk kedalam kondensor.

It has been widely known that polymeric membrane such as polyvinylidene fluoride (PVDF) is very prone to fouling that occurs during the filtration process. In the same light, membrane cleaning has also been popularly used as a mean to remove foulants which accumulated on or inside the membrane. In this paper, the utilization of domestic bleach, which is affordable and easily found in the nearest markets, as the membrane cleaning agent is discussed. The performance evaluation is conducted on three kinds of commercial domestic bleaches, namely Bayclin, Proclin, and Soclin. In order to study deeper about those product potentials, the performance is compared with the pure sodium hypochloride (NaOCl) which has been known as a common chemical cleaning agent, and distillate water. The results show that the bleach products work excellence in cleaning the fouled membrane which confirmed by the scanning electron microscopy (SEM) analysis results, in which membranes cleaned with the bleaches have cleaner surface compared to that cleaned with distillate water. Interestingly, the positive outcome can also be seen in the flux recovery ratio (FRR) of the membranes after cleaning which managed to recover up to 95% of the lost flux. Overall, all three bleach products showed closely similar performance as the original NaOCl, and showed far better performance than distillate water. This result emphasizes that the domestic bleaches are highly promising to be membrane chemical cleaning agents, replacing the common chemicals. This work makes a significant contribution toward giving reasonably priced options for alternative methods of cleaning membranes.

The reverse osmosis water treatment process is prone to fouling issues, prompting the exploration of various membrane modification techniques to address this challenge. The primary objective of this study was to develop a precise method for modifying the surface of reverse osmosis membranes to enhance their antifouling properties. The Langmuir–Blodgett technique was employed to transfer aminated graphene oxide films assembled at the air–liquid interface, under specific surface pressure conditions, to the polyamide surface with pre-activated carboxylic groups. The microstructure and distribution of graphene oxide along the modified membrane were characterized using SEM, AFM, and Raman mapping techniques. Modification carried out at the optimal surface pressure value improved the membrane hydrophilicity and reduced the surface roughness, thereby enhancing the antifouling properties against colloidal fouling. The flux recovery ratio after modification increased from 65% to 87%, maintaining high permeability. The modified membranes exhibited superior performance compared to the unmodified membranes during long-term fouling tests. This membrane modification technique can be easily scaled using the roll-to-roll approach and requires minimal consumption of the modifier used.

In this study, we report the robust hydrophobicity, lower fouling propensity, and high thermal efficiency of the 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS)-coated, carbon nanotube-immobilized membrane (CNIM) when applied to desalination via membrane distillation. Referred to as FAS-CNIM, the membrane was developed through a process that combined the drop-casting of nanotubes flowed by a dip coating of the FAS layer. The membranes were tested for porosity, surface morphology, thermal stability, contact angle, and flux. The static contact angle of the FAS-CNIM was 153 ± 1°, and the modified membrane showed enhancement in water flux by 18% compared to the base PTFE membrane. The flux was tested at different operating conditions and the fouling behavior was investigated under extreme conditions using a CaCO3 as well as a mixture of CaCO3 and CaSO4 solution. The FAS-CNIM showed significantly lower fouling than plain PTFE or the CNIM; the relative flux reduction was 34.4% and 37.6% lower than the control for the CaCO3 and CaCO3/CaSO4 mixed salt solution. The FAS-CNIM exhibited a notable decrease in specific energy consumption (SEC). Specifically, the SEC for the FAS-CNIM measured 311 kwh/m3 compared to 330.5 kwh/m3 for the CNIM and 354 kwh/m3 for PTFE using a mixture of CaCO3/CaSO4. This investigation underscores the significant contribution of the carbon nanotubes’ (CNTs) intermediate layer in creating a durable superhydrophobic membrane, highlighting the potential of utilizing carbon nanotubes for tailored interface engineering to tackle fouling for salt mixtures. The innovative design of a superhydrophobic membrane has the potential to alleviate wetting issues resulting from low surface energy contaminants present in the feed of membrane distillation processes.

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.

The commercial ultrafiltration polyethersulfone (PES) membranes (10 and 100 kDa) blended with polyvinylpyrrolidone (PVP) were applied for the filtration of car wash wastewater. Periodical membrane rinsing with water did not prevent fouling and a decrease in permeate flux was observed. Fouling was reduced by washing the membranes with cleaning agents, which are used in car washes to clean wheels and remove insects. In addition to surfactants, these agents contain NaOH, hence the pH value of cleaning solutions was over 11. Long-term contact with such solutions resulted in the removal of PVP from the membrane matrix and an increase in pore size. The PES membranes were soaked in an alkaline solution (pH = 11.5) for 20 months, after which the 200 kDa dextran rejection decreased from 95% to 80%. To compare with the static degradation conditions, 8 weeks of alkaline agent filtration was realized, after which the dextran (200 kDa) rejection decreased below 50%. This indicated that the cross-flow of alkaline agents can accelerate the removal of components building the membrane matrix. Despite membrane degradation, the separation efficiency (the rejection of chemical oxygen demand—COD, turbidity, and surfactants) during the treatment of synthetic car wash wastewater was similar to that obtained for pristine membranes.

While efficient removal of uremic toxins and accumulated water is pivotal for the well-being of dialysis patients, protein adsorption to the dialyzer membrane reduces the performance of a dialyzer. Hydrophilic membrane modification with polyvinylpyrrolidone (PVP) has been shown to reduce protein adsorption and to stabilize membrane permeability. In this study we compared middle molecule clearance and filtration performance of nine polysulfone-, polyethersulfone-, and cellulose-based dialyzers over time. Protein adsorption was simulated in recirculation experiments, while β2-microglobulin clearance as well as transmembrane pressure (TMP) and filtrate flow were determined over time. The results of this study showed that β2-microglobulin clearance (−7.2 mL/min/m2) and filtrate flow (−54.4 mL/min) decreased strongly during the first 30 min and slowly afterwards (−0.7 mL/min/m2 and −6.8 mL/min, respectively, for the next 30 min); the TMP increase (+37.2 mmHg and +8.6 mmHg, respectively) showed comparable kinetics. Across all tested dialyzers, the dialyzer with a hydrophilic modified membrane (FX CorAL) had the highest β2-microglobulin clearance after protein fouling and the most stable filtration characteristics. In conclusion, hydrophilic membrane modification with PVP stabilizes the removal capacity of middle molecules and filtration performance over time. Such dialyzers may have benefits during hemodiafiltration treatments which aim to achieve high exchange volumes.

Tofu whey, a by-product of tofu production, is rich in nutrients such as proteins, minerals, fats, sugars and polyphenols. In a previous work, protein recovery from tofu whey was studied by using a coupled environmental process of ED + EDBM to valorize this by-product. This process allowed protein recovery by reducing the ionic strength of tofu whey during the ED process and acidifying the proteins to their isoelectric point during EDBM. However, membrane fouling was not investigated. The current study focuses on the fouling of membranes at each step of this ED and EDBM process. Despite a reduction in the membrane conductivities and some changes in the mineral composition of the membranes, no scaling was evident after three runs of the process with the same membranes. However, it appeared that the main fouling was due to the presence of isoflavones, the main polyphenols in tofu whey. Indeed, a higher concentration was observed on the AEMs, giving them a yellow coloration, while small amounts were found in the CEMs, and there were no traces on the BPMs. The glycosylated forms of isoflavones were present in higher concentrations than the aglycone forms, probably due to their high amounts of hydroxyl groups, which can interact with the membrane matrices. In addition, the higher concentration of isoflavones on the AEMs seems to be due to a combination of electrostatic interactions, hydrogen bonding, and π–π stacking, whereas only π–π stacking and hydrogen bonds were possible with the CEMs. To the best of our knowledge, this is the first study to investigate the potential fouling of BPMs by polyphenols, report the fouling of IEMs by isoflavones and propose potential interactions.

The wine industry is a sector of great importance in the Spanish economy, contributing substantial annual revenues. However, one challenge facing the industry is the amount of waste generated, reaching millions of tons annually. These residues consist of organic matter of industrial interest, such as polyphenols. These substances are characterised by their excellent antioxidant properties, making them ideal for use in the food, cosmetic, and pharmaceutical industries. Modern techniques, such as membrane technology, are explored for their extraction based on separating compounds according to size. This work studies a sequential filtration process using ultrafiltration (UF) and nanofiltration (NF) membranes at different operating conditions (2 bar and 9.5 bar for UF and NF, respectively, at 20 °C) to extract polyphenols from wine lees. The results show a total polyphenols rejection rate for each process of 54% for UF and 90% for NF. Pore blocking models have been studied for the UF process and an intermediate pore blocking of the membrane upon wine lees filtration has been identified. A mathematical model that justifies the behavior of a polymeric NF membrane with the filtration of pre-treated vinasse residues has been validated. This study shows a viable process for extracting polyphenols from wine lees with sequential membrane technology.

Fouling is a ubiquitous phenomenon occurring in heat transfer devices that inhibits the effective passage of thermal energy, leading to energy and economic losses. In recent years, micro/nanoscale surface modifications have emerged as promising pathways to mitigate the adverse effects of fouling. This review examines micro/nanoscale surface modification methods to mitigate heat exchanger fouling. Various coatings based on titanium, silicon, polymers, amorphous carbon (a-C), electroless nickel-phosphorus (Ni-P), and polyethylene glycol (PEG) are detailed. The coating characteristics in terms of surface chemical and mechanical stability are discussed, and limitations in their commercial utilization are identified. Further, the review outlines the effect of micro/nanoscale surface topographies and novel surface designs on the adhesion and removal of foulants. For instance, laser surface texturing, EDM, anodization, and sandblasting are discussed for generating micro/nanoscale surface topographies. These micro/nanoscale surface topographies play a crucial role in determining surface-foulant interactions and coating durability. It is concluded that the surface energy component is a critical parameter in reducing fouling effects, with low surface energy being favorable for early foulant removal under shear force. Several studies attempting to minimize changes in surface energy components under harsh fouling conditions are discussed in detail.

Membrane fouling caused by complex greywater synthesized by personal care products and detergents commercially available for household applications was investigated using dead-end microfiltration (MF) and analyzed systematically by a multistage Hermia blocking model as a first attempt. The highest flux decline was associated with the smallest pore size of the membrane (0.03 μm). This effectiveness was more pronounced at higher applied pressures to the membrane. A cake layer was formed on the membrane consisting mainly of silica particles present as ingredients in greywater. Although organic rejection was low by the porous MF membrane, the organic compound contributed to membrane fouling in the filtration stage. With a 0.03 μm pore size of the membrane, dominant fouling mechanisms were classified into three stages as applied pressure increased, such as complete pore blocking, intermediate pore blocking, and cake layer formation. Specifically, during the early stage of membrane filtration at 1.5 bar, membrane fouling was determined by complete pore blocking in the 0.10 μm pore size of the membrane. However, the later stage of membrane fouling was controlled mainly by intermediate pore blocking. Regardless of the applied pressure, pore constriction or standard blocking played an important role in the fouling rate with a 0.45 μm pore size of the membrane. Our results also support that complex formation can occur due to the concentration of organic and inorganic species present in simulated greywater. Thus, strategic approaches such as periodic, chemically enhanced backwashing need to be developed and tailored to remove both organic and inorganic fouling from MF membranes treating greywater.

Current development of membrane technology for purifying polluted water and wastewater is discussed in this review in accordance with its hybrid application with other types of water treatment methods such as adsorption, advanced oxidation processes (AOPs), and biological activated sludge. This hybrid implementation aims are to lengthen membrane lifespan and elude severe fouling on the surface and pore of the membrane. Membrane material and fabrication technology were concisely included. Two prominent materials to fabricate membrane namely polymeric and ceramic are reviewed well along with the exploration of biopolymers based-materials such as starch and alginate. Several fabrication methods available to be implemented in research or industrial large scale including interfacial polymerization technique, non-solvent induced phase separation, temperature induced phase separation, electrospinning, and sintering are deliberately discussed. The next section includes fouling analysis involving reliable fouling mechanism namely Hermia’s models to help with the explanation of fouling occurrence during filtration. These models covers four different mechanisms namely complete blocking, standard blocking, intermediate blocking, and cake filtration models. Ultimately, recent research reporting the outcome of the hybridization of membrane and adsorption, biosorption, coagulation-flocculation, AOPs, and biological treatment using microorganism were properly reviewed. Overall, this review considerably promotes the findings of those works which mostly revealed positive outcome of the hybrid membrane system contributing to stronger foundation for future research.

Different physio-chemical and biological methods have been applied to reduce membrane fouling and to maintain the flux of membrane bioreactor (MBR). Periodic chemically enhanced backwash (CEB) has been recently developed and displayed good performance to recover the membrane permeability. However, the comparative effect of on-line CEB (using NaOCl and NaOH) on fouling mitigation and the effluent quality of MBR was poorly known. This study aimed to evaluate the changes in membrane resistance, membrane fouling and the effluent quality with and without CEB in MBR to reveal the effect of different NaOCl and NaOH concentrations. Lab-scale MBR treating sewage at high flux were operated for 8 min continuously at a flux of 20 L/(m2.h) followed by a backwash duration of 30 s. In reference MBR permeate (without chemical) was used as a backwash solution. The study found that MBR with CEB has higher operational time and lower fouling rates than reference MBR. Overall, backwash with NaOH increased the run-time by 29% – 45% compared to the control MBR, and backwash with NaOCl increased run-time from 34% to 61% compared to the control MBR. NaOCl was significantly more effective by 7% – 28% compared to NaOH in fouling reduction at different concentrations. CEB has no significant (p > 0.05) effect on the removal efficiencies of different pollutants. The chemical oxygen demand removal efficiencies varied between 82 and 84%. The removals of total kjeldahl nitrogen (50 – 54%) and total phosphorus (45 – 52%) were lower due to the short solids and hydraulic retention time. This study highlights the potential of periodic CEB and concentrations of chemicals on MBR fouling and provides insights into potential approaches for mitigating this issue in MBR systems.

This study investigated the performance of photocatalytic titanium dioxide microfiltration membranes with an average pore size of approximately 180 nm and ultrafiltration membranes with an average pore size of around 40 nm fabricated with the suspension plasma spray process. The membranes were evaluated for their filtration performance using SiO2 particles of different sizes and polyethylene oxide with molecular weights of 20 kDa to 1000 kDa, and the fouling parameters were characterized. The rejection rate was enhanced by increasing the thickness of the membranes. This effect was more pronounced with the ultrafiltration membranes. The rejection rate of the ultrafiltration membrane was improved significantly after filling the larger pores on the surface with agglomerates of titanium dioxide nanoparticles. The self-cleaning performance of the membranes was assessed under visible light. Both ultrafiltration and microfiltration membranes showed a flux recovery under visible light illumination due to the photocatalytic activity of titanium dioxide. The membranes also show a flux recovery of more than 90%.

Nanofibrous membranes for membrane distillation (MD) have demonstrated promising results in treating various water and wastewater streams. Significant progress has been made in recent decades because of the development of sophisticated membrane materials, such as superhydrophobic, omniphobic and Janus membranes. However, fouling and wetting remain crucial issues for long-term operation. This mini-review summarizes ideas as well as their limitations in understanding the fouling in membrane distillation, comprising organic, inorganic and biofouling. This review also provides progress in developing antifouling nanofibrous membranes for membrane distillation and ongoing modifications on nanofiber membranes for improved membrane distillation performance. Lastly, challenges and future ways to develop antifouling nanofiber membranes for MD application have been systematically elaborated. The present mini-review will interest scientists and engineers searching for the progress in MD development and its solutions to the MD fouling issues.

A cell filtration platform that affords accurate size separation and minimizes fouling was developed. The platform features an ultra-thin porous membrane (UTM) filter, a pumping head filtration with backflush (PHF), and cell size measurement (CSM) software. The UTM chip is an ultrathin free-standing membrane with a large window area of 0.68 mm2, a pore diameter of 5 to 9 μm, and a thickness of less than 0.9 μm. The PHF prevents filter fouling. The CSM software analyzes the size distributions of the supernatants and subnatants of isolated cells and presents the data visually. The D99 particle size of cells of the chronic myeloid leukemia (CML) line K562 decreased from 22.2 to 17.5 μm after passage through a 5-μm filter. K562 cells could be separated by careful selection of the pore size; the recovery rate attained 91.3%. The method was compared to conventional blocking models by evaluating the mean square errors (MSEs) between the measured and calculated filtering volumes. The filtering rate was fitted by a linear regression model with a significance that exceeded 0.99 based on the R2 value. The platform can be used to separate various soft biomaterials and afford excellent stability during filtration.

Due to low sludge production and being a clean source without residuals, hydrogen-based autotrophic denitrification appears to be a promising choice for nitrate removal from agricultural drainage waters or water/wastewater with a similar composition. Although the incorporation of hydrogen-based autotrophic denitrification with membrane bioreactors (MBRs) enabled almost 100% utilization of hydrogen, the technology still needs to be improved to better utilize its advantages. This study investigated the anoxic treatment of both synthetic and real drainage waters using hydrogen gas in a recently developed membrane bioreactor configuration, a venturi-integrated submerged membrane bioreactor, for the first time. The study examined the effects of the inflow nitrate concentration, and the use of a venturi device on the removal efficiency, as well as the effects of the presence of headspace gas circulation and circulation rate on membrane fouling. The study found that using the headspace gas circulation through a venturi device did not significantly affect the treatment efficiency, and in both cases, a removal efficiency of over 90% was achieved. When the inlet NO3−–N concentration was increased from 50 mg/L to 100 mg/L, the maximum removal efficiency decreased from 98% to 92%. It was observed that the most significant effect of the headspace gas circulation was on the membrane fouling. When the headspace gas was not circulated, the average membrane chemical washing period was 5 days. However, with headspace gas circulation, the membrane washing period increased to an average of 12 days. The study found that the headspace gas circulation method significantly affected membrane fouling. When the upper phase was circulated with a peristaltic pump instead of a venturi device, the membrane washing period decreased to one day. The study calculated the maximum hydrogen utilization efficiency to be approximately 96%.

Due to water stress in the world in general desalination technologies are becoming increasingly important. Among the available technologies, reverse osmosis (RO) is the most widespread due to its reliability and efficiency compared to other technologies. The main weakness of RO is the loss of performance due to membrane fouling, which usually affects the water permeability coefficient (A), causing it to decrease. In RO desalination plants, fouling does not affect all spiral wound membrane modules (SWMMs) in the pressure vessels (PVs) in the same way. This will depend on the type of fouling and the position of the SWMM inside the PV. In this study, the impact of A and the position of the SWMM on the performance of the RO system is analyzed. For this purpose, decrements of up to 50% have been assumed for the seven SWMMs in series considering nine commercial SWMM models. The operating point analyzed is that which minimizes the specific energy consumption (SEC), a point obtained in a previous work carried out by the authors. The results show how the impact of A on the SWMM in the first position is more significant than the impact on modules that are in another position for the nine SWRO models studied. A drop of 50% in the coefficient A of the first element produces a permeate loss in the pressure pipe between 0.67 and 1.35 m3 d−1. Furthermore, it was observed that the models with the lowest coefficient A exhibited the highest performance losses in terms of permeate production when A was decreased.

Membrane fouling is a major hurdle to effective pressure-driven membrane processes, such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Fouling refers to the accumulation of particles, organic and inorganic matter, and microbial cells on the membrane’s external and internal surface, which reduces the permeate flux and increases the needed transmembrane pressure. Various factors affect membrane fouling, including feed water quality, membrane characteristics, operating conditions, and cleaning protocols. Several models have been developed to predict membrane fouling in pressure-driven processes. These models can be divided into traditional empirical, mechanistic, and artificial intelligence (AI)-based models. Artificial neural networks (ANNs) are powerful tools for nonlinear mapping and prediction, and they can capture complex relationships between input and output variables. In membrane fouling prediction, ANNs can be trained using historical data to predict the fouling rate or other fouling-related parameters based on the process parameters. This review addresses the pertinent literature about using ANNs for membrane fouling prediction. Specifically, complementing other existing reviews that focus on mathematical models or broad AI-based simulations, the present review focuses on the use of AI-based fouling prediction models, namely, artificial neural networks (ANNs) and their derivatives, to provide deeper insights into the strengths, weaknesses, potential, and areas of improvement associated with such models for membrane fouling prediction.

Fruit juice is an essential food product that has received significant acceptance among consumers. Harmonized concentration, preservation of nutritional constituents, and heat-responsive sensorial of fruit juices are demanding topics in food processing. Membrane separation is a promising technology to concentrate juice at minimal pressure and temperatures with excellent potential application in food industries from an economical, stable, and standard operation view. Microfiltration (MF) and ultrafiltration (UF) have also interested fruit industries owing to the increasing demand for reduced pressure-driven membranes. UF and MF membranes are widely applied in concentrating, clarifying, and purifying various edible products. However, the rising challenge in membrane technology is the fouling propensity which undermines the membrane’s performance and lifespan. This review succinctly provides a clear and innovative view of the various controlling factors that could undermine the membrane performance during fruit juice clarification and concentration regarding its selectivity and permeance. In this article, various strategies for mitigating fouling anomalies during fruit juice processing using membranes, along with research opportunities, have been discussed. This concise review is anticipated to inspire a new research platform for developing an integrated approach for the next-generation membrane processes for efficient fruit juice clarification.

This study addressed the fouling issue in membrane distillation (M.D.) technology, a promising method for water purification and wastewater reclamation. To enhance the anti-fouling properties of the M.D. membrane, a tin sulfide (TS) coating onto polytetrafluoroethylene (PTFE) was proposed and evaluated with air gap membrane distillation (AGMD) using landfill leachate wastewater at high recovery rates (80% and 90%). The presence of TS on the membrane surface was confirmed using various techniques, such as Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FT-IR), Energy Dispersive Spectroscopy (EDS), contact angle measurement, and porosity analysis. The results indicated the TS-PTFE membrane exhibited better anti-fouling properties than the pristine PTFE membrane, and its fouling factors (FFs) were 10.4–13.1% compared to 14.4–16.5% for the PTFE membrane. The fouling was attributed to pore blockage and cake formation of carbonous and nitrogenous compounds. The study also found that physical cleaning with deionized (DI) water effectively restored the water flux, with more than 97% recovered for the TS-PTFE membrane. Additionally, the TS-PTFE membrane showed better water flux and product quality at 55 °C and excellent stability in maintaining the contact angle over time compared to the PTFE membrane.

Increased affordability, smaller footprint, and high permeability quality that meets stringent water quality standards have accelerated the uptake of membranes in water treatment. Moreover, low pressure, gravity-based microfiltration (MF) and ultrafiltration (UF) membranes eliminate the use of electricity and pumps. However, MF and UF processes remove contaminants by size exclusion, based on membrane pore size. This limits their application in the removal of smaller matter or even harmful microorganisms. There is a need to enhance the membrane properties to meet needs such as adequate disinfection, flux amelioration, and reduced membrane fouling. To achieve these, the incorporation of nanoparticles with unique properties in membranes has potential. Herein, we review recent developments in the impregnation of polymeric and ceramic microfiltration and ultrafiltration membranes with silver nanoparticles that are applied in water treatment. We critically evaluated the potential of these membranes in enhanced antifouling, increased permeability quality and flux compared to uncoated membranes. Despite the intensive research in this area, most studies have been performed at laboratory scale for short periods of time. There is a need for studies that assess the long-term stability of the nanoparticles and the impact on disinfection and antifouling performance. These challenges are addressed in this study and future directions.

There is increasing interest in membrane systems powered by renewable energy sources, including solar and wind, that are suitable for decentralized water supply in islands and remote regions. These membrane systems are often operated intermittently with extended shutdown periods to minimize the capacity of the energy storage devices. However, relatively little information is available on the effect of intermittent operation on membrane fouling. In this work, the fouling of pressurized membranes under intermittent operation was investigated using an approach based on optical coherence tomography (OCT), which allows non-destructive and non-invasive examination of membrane fouling. In reverse osmosis (RO), intermittently operated membranes were investigated by OCT-based characterization. Several model foulants such as NaCl and humic acids were used, as well as real seawater. The cross-sectional OCT images of the fouling were visualized as a three-dimensional volume using Image J. The OCT images were used to quantitatively measure the thickness of foulants on the membrane surfaces under different operating conditions. The results showed that intermittent operation retarded the flux decrease due to fouling compared to continuous operation. The OCT analysis showed that the foulant thickness was significantly reduced by the intermittent operation. The decrease in foulant layer thickness was found to occur when the RO process was restarted in intermittent operation.

Combined cycle power plants (CCPPs) use large amounts of water withdrawn from nearby rivers and generate wastewater containing ions and pollutants. Despite the need for wastewater reclamation, few technologies can successfully convert the wastewater into make-up water for CCPPs. Therefore, this study aimed to apply capacitive deionization (CDI) for wastewater reclamation in CCPPs. Using a bench-scale experimental unit, which included ion exchange membranes and carbon electrodes, response surface methodology (RSM) was used to optimize the operating conditions of the CDI process to increase the total dissolved solids (TDS) removal and product water ratio. The optimal conditions were found to be a voltage of 1.5 V, a flow rate of 15 mL/min, and an adsorption/desorption ratio of 1:0.8. The changes in CDI performance with time were also studied, and the foulants on the membranes, spacers, and electrodes were examined to understand the fouling mechanism. The TDS removal decreased from 93.65% to 55.70% after 10 days of operation due to the deposition of scale and organic matter. After chemical cleaning, the TDS removal rate recovered to 93.02%, which is close to the initial condition.

The wastewater generated as a result of car washes is considered a new source of water. However, recovered water must meet the required quality criteria for reuse. For this purpose, the ultrafiltration (UF) process can be successfully used. The main aim of the present work was to investigate the influence of the membrane’s molecular weight cut-off (MWCO) on the UF performance in terms of the fouling phenomenon and retention degree of car wash wastewater. Moreover, for a better understanding of the fouling mechanisms, Hermia’s model was used. The experimental studies were conducted with the use of two polyethersulfone (PES) membranes (MWCO of 10 kDa and 100 kDa). It has been noted that the used membranes provided a high-quality permeate and excellent turbidity removal, up to 99%. Moreover, it has been noted that the MWCO membrane has a significant impact on the fouling mechanism. Generally, a much greater intensity of fouling for the membrane with MWCO of 100 kDa was observed. Results obtained in the present study showed that both real wastewaters and the clean solutions used for washing cars cause the fouling phenomenon. It has been proven that rinsing the membranes with water is not sufficient to recover the initial membrane’s performance. Hence, periodic chemical cleaning of the membranes was required. Fitting the experimental data to Hermia’s model allowed us to indicate that membranes with MWCO of 100 kDa are more prone to intermediate blocking. To sum up, the findings suggest that for the UF of the car wash wastewater, the use of membranes with MWCO equal to 10 kDa is recommended.

This paper presents an analysis of the fouling of a ceramic membrane by a mixture containing high concentrations of humic acid and colloidal silica during cross-flow ultrafiltration under various operating conditions. Two types of feed water were tested: feed water containing humic acid and feed water containing a mixture of humic acid and colloidal silica. The colloidal silica exacerbated the fouling, yielding lower fluxes (109–394 L m−2 h−1) compared to the humic acid feed water (205–850 L m−2 h−1), while the retentions were higher except for the highest cross-flow rate. For the humic acid feed water, the irreversible resistance prevails under the cross-flow rate of 5 L min−1. During the filtration of an organic–inorganic mixture, the reversible resistance due to the formation of a colloidal cake layer prevails under all operating conditions with an exception. The exception is the filtration of the organic–inorganic mixture of a 50 mg L−1 humic acid concentration which resulted in a lower flux than the one of a 150 mg L−1 humic acid concentration under 150 kPa and a cross-flow rate of 5 L min−1. Here, the irreversible fouling is unexpectedly overcome. This is unusual and occurs due to the low agglomeration at low concentrations of humic acid under a high cross-flow rate. Under lower transmembrane pressure and a moderate cross-flow rate, fouling can be mitigated, and relatively high fluxes are yielded with high retentions even in the presence of nanoparticles. In this way, colloidal silica influences the minimization of membrane fouling by organic humic acid contributing to the control of in-pore organic fouling.

This study investigates three types of organic matter, namely algal organic matter (AOM), bacterial organic matter (BOM), and humic organic matter (HOM). These organics are different in properties and chemical composition. AOM, BOM and HOM were compared in terms of organic content, fouling behavior, and removal efficiency in ceramic UF filtration. UF experiments were conducted at a constant flux mode using 5 kDa and 50 kDa ceramic membranes. Results showed that 5 kDa membrane removed more transparent exopolymer particles (TEP)/organics than 50 kDa membranes, but less fouling formation for all the three types of organic matters tested. Membranes exhibited the lowest trans-membrane pressure (TMP) during the filtration of HOM, most probably due to the high porosity of the HOM cake layer, contributed by big HOM aggregates under Ca bridging effect. AOM shows the highest MFI-UF (modified fouling index-ultrafiltration) and TMP (transmembrane pressure) values among the three organics and during all filtration cycles for both membranes. The AOM fouling layer is well known for having high fouling potential due to its compressibility and compactness which increase the TMP and eventually the MFI values. AOM and BOM organics exhibited a similar fouling behavior and mechanism. Furthermore, the divalent cations such as calcium showed a significant impact on membrane fouling. That is probably because calcium ions made the membranes and organic matter less negatively charged and easier to deposit on membranes, thus, enhancing the membrane fouling significantly.

Lignin is a polyphenolic biopolymer present in large amounts in black liquor (BL). This work investigated the recovery of lignin from BL (pre-filtered by ultrafiltration (UF)) by nanofiltration (NF). For the NF tests, laboratory-made mixed matrix membrane (MMM) prepared with 0.1% activated carbon (AC) nanoparticles were used in crossflow filtration mode. The effect of pressure (6–15 bar) and volume reduction (VR) (~65%) were analyzed, and the filtration performance was evaluated in terms of permeate flux, lignin rejection rate, and flux reduction. The lignin rejection rate varied in the range of 67–80% with the pressure, however, the highest increases in flux and rejection were observed at 12 bar, which was found to be the optimum pressure. At a VR of ~65%, the permeate flux decreased by ~55% and the lignin rejection rate increased from 78% to 86%. In addition, an economic evaluation was performed for the preparation of UF and NF MMM. The minimum-to-maximum price range was estimated considering the costs of the laboratory and commercial grade regents. It showed a difference of ~10-fold and ~14-fold for UF and NF membranes, respectively. The results of the laboratory-scale study were used to evaluate the economic feasibility of the process for recovering lignin- and hemicellulose-rich retentate streams.

The alterations in current-voltage and transport characteristics of highly basic and strongly acidic ion-exchange membranes, during the electrodialysis of solutions containing a heterocyclic amino acid and a strong electrolyte, were studied. An increase in the catalytic activity of the water splitting process at the surface of heterogeneous MK-40 and MA-41 membranes upon prolonged contact with proline and tryptophan solutions was found. A significant effect of electroconvection on the components mass transfer through the cation-exchange membrane in the intensive current mode of electrodialysis was revealed for the solution containing a heterocyclic amino acid along with mineral salt (NaCl). This led to a reduction in the length of the “plateau” of the membrane’s current-voltage characteristics, in comparison with the characteristics for an individual sodium chloride solution with the same concentration. The changes in the characteristics of the studied ion-exchange membranes caused by contact with solutions containing heterocyclic amino acids during electrodialysis were reversible when applying electrochemical regeneration (cleaning in place) using the overlimiting current mode, corresponding to the region of facilitated transport for these ampholytes.

The monitoring of a membrane bioreactor (MBR) requires the assessment of both biological and membrane performance. Additionally, the development of membrane fouling and the requirements for frequent membrane cleaning are still major concerns during MBR operation, requiring tight monitoring and system characterization. Transmembrane pressure is usually monitored online and allows following the evolution of membrane performance. However, it does not allow distinguishing the fouling mechanisms occurring in the system or predicting the future behavior of the membrane. The assessment of the biological medium requires manual sampling, and the analyses involve several steps that are labor-intensive, with low temporal resolution, preventing real-time monitoring. Two-dimensional fluorescence spectroscopy is a comprehensive technique, able to assess the system status at real-time without disturbing the biological system. It provides large sets of data (system fingerprints) from which meaningful information can be extracted. Nevertheless, mathematical data analysis (such as machine learning) is essential to properly extract the information contained in fluorescence spectra and correlate it with operating and performance parameters. The potential of 2D fluorescence spectroscopy as a process monitoring tool for MBRs is, therefore, discussed in the present work in view of the actual knowledge and the authors’ own experience in this field.

Membrane performance optimization is a critical preparation step that ensures optimum separation and fouling resistance. Several studies have employed additives such as carbon and inorganic nanomaterials to optimize membrane performance. These particles provide excellent results but are rather costly, unstable and toxic to several biological organs. This study demonstrated that performance enhancement can also be achieved through delayed solvent–nonsolvent demixing during phase inversion membrane preparation. The rate of solvent–nonsolvent demixing was delayed by increasing the concentration of the solvent in the coagulation bath. This study employed synthetic and real water samples and several analytical techniques to compare optimized performances and properties of membranes prepared in this study with that of nanoparticle-embedded membranes in the literature. Pure water flux and BSA rejection of the membranes prepared in this study were comparable to those of nanoparticle embedded membranes. This study also shows the influence of delayed solvent–nonsolvent demixing on membrane properties such as morphology, wettability, surface roughness and porosity, thereby showing the suitability of the technique in membrane optimization. Furthermore, fouling studies showed that membranes prepared in this study have high flux recovery when fouled by humic acid feed water (>95%) and above 50% flux recovery with real water samples.

During electrodialysis the ion exchange membranes are affected by such factors as passage of electric current, heating, tangential flow of solution and exposure to chemical agents. It can potentially cause the degradation of ion exchange groups and of polymeric backbone, worsening the performance of the process and necessitating the replacement of the membranes. This article aims to review how the composition and the structure of ion exchange membranes change during the electrodialysis or the studies imitating it.

Fouling on submerged surfaces is a major limiting factor for membranes, heat exchangers, and marine vessels as it induces mass and heat transfer resistances that increase operating costs and lead to system failures. While the role of surface roughness on fouling has been extensively studied, the specific effect of surface roughness on fouling is debated in literature. In this study, we employed force spectroscopy based on atomic force microscopy with two model colloidal probes to elucidate the role of surface roughness on foulant-surface interactions. Specifically, we quantified the strength and characteristic lengths of the interactions between the colloidal probes and hydrophilic and hydrophobic surfaces with and without surface texture. We found that hydrophilic surfaces are generally less prone to foulant adhesion than hydrophobic surfaces and that increasing roughness of a hydrophilic surface mitigates foulant adhesion. In comparison, we found that increased roughness of a hydrophobic surface increases the attractive foulant-surface interaction, and thus, its fouling propensity. Based on the results from this study, the implications for developing surfaces with fouling resistance are also examined.

Electrodialysis (ED) is an attractive method of tartrate stabilization of wine due to its rapidity and reagentlessness. At the same time, fouling of ion-exchange membranes by the components of wine materials is still an unsolved problem. The effect of ethanol, polyphenols (mainly anthocyanins and proanthocyanidins) and saccharides (fructose) on the fouling of aliphatic ion-exchange membranes CJMA-6 and CJMC-5 (manufactured by Hefei Chemjoy Polymer Materials Co. Ltd., Hefei, China) was analyzed using model solutions. It was shown that the mechanism and consequences of fouling are different in the absence of an electric field and during electrodialysis. In particular, a layer of colloidal particles is deposited on the surface of the CJMA-6 anion-exchange membrane in underlimiting current modes. Its thickness increases with increasing current density, apparently due to the implementation of a trap mechanism involving tartaric acid anions, as well as protons, which are products of water splitting and “acid dissociation”. A successful attempt was made to clean CJMA-6 in operando by pumping a water-alcohol solution of KCl through the desalination compartment and changing electric field direction. It has been established that such a cleaning process suppresses the subsequent biofouling of ion-exchange membranes. In addition, selective recovery of polyphenols with high antioxidant activity is possible.

Reverse osmosis (RO) is the most popular technology for brackish, seawater and wastewater desalination. An important drawback of RO is membrane fouling, which reduces filtration effectiveness and increase the cost of produced water. This study addresses two important topics of membrane fouling: (i) the impact of different divalent ions on the formation of organic fouling and (ii) online monitoring and prediction of fouling formation. In the absence of divalent ions, dissolved organic matter had little effect on fouling formation, even at 3.5 mgC/L, in the upper range of groundwater concentration. Calcium, strontium and iron enhanced (organic) fouling formation, whereas barium had negligible effect. However, while iron affected fouling throughout the entire tested range (0–0.5 mg/L), calcium and strontium enhanced organic fouling only at high concentrations: more than 140 mg/L and 10 mg/L for calcium and strontium, respectively. An online system was developed for monitoring the formation of organic fouling, consisting of (i) an ex-situ RO cell with a transparent cover, (ii) a video camera continually monitoring the surface of the membrane and (iii) an algorithm which automatically identified changes in the color of the membrane caused by fouling, using a specially designed membrane spacer with colored reference dots. Changes in the color of the membrane surface were normalized to the reference colors, to eliminate all non-fouling related interference. The system was used to record and analyze changes in membrane color during numerous filtration tests. The data was successfully correlated to changes in specific flux (and subsequently to fouling formation rate) and can be applied to monitor and predict the formation of membrane fouling during desalination.

Furfural, acetic acid, and sulfates are found in the hemicellulose (HMC) fraction of lignocellulosic biomass. Separation of furfural, acetic acid, and sulfates from monosaccharides by four nanofiltration (NF) membranes was evaluated with a model solution of glucose, xylose, furfural, acetic acid, and sulfates. Results showed that Alfa Laval NF99HF is the most promising membrane to purify monosaccharides, with the retentions of xylose (85%), glucose (95%), and with the minimum sulfate retention. pH has the highest impact on the retention of all solutes and there is no significant effect of temperature on the retentions of sulphates and acetic acid. Lower pH and temperature are favored to maximize the monosaccharide retention and to remove acetic acid while retaining more furfural with the monosaccharides. Moreover, fouling tendency is maximized at lower pH and higher temperatures. According to the statistical analysis, the retentions of glucose, xylose, furfural, sulfates, and acetic acid are 95%, 90%, 20%, 88%, and 0%, respectively at pH 3 and 25 °C. The presence of sulfates favors the separation of acetic acid and furfural from monosaccharides.

The increase in industry and population, together with the need for wastewater reuse, makes it necessary to implement new technologies in the circular economy framework. The aim of this research was to evaluate the quality of the effluent of an algae membrane photobioreactor for the treatment of the effluent of an urban wastewater treatment plant, to characterise the ultrafiltration membranes, to study the effectiveness of a proposed cleaning protocol, and to analyse the performance of the photobioreactor. The photobioreactor operated under two days of hydraulic retention times feed with the effluent from the Los Vados wastewater treatment plant (WWTP) (Granada, Spain). The microalgae community in the photobioreactor grew according to the pseudo-second-order model. The effluent obtained could be reused for different uses of diverse quality with the removal of total nitrogen and phosphorus of 56.3% and 64.27%, respectively. The fouling of the polyvinylidene difluoride ultrafiltration membrane after 80 days of operation was slight, increasing the total membrane resistance by approximately 22%. Moreover, the higher temperature of the medium was, the lower intrinsic resistance of the membrane. A total of 100% recovery of the membrane was obtained in the two-phase cleaning protocol, with 42% and 58%, respectively.

Scaling, or inorganic fouling, is a major factor limiting the performance of membrane-based water treatment processes in long-term operation. Over the past few decades, extensive studies have been conducted to control the scale growth found in membrane processes and to develop sustainable and greener processes. This study details the role of CO2 in scale inhibition in membrane processes. The core concept of CO2 utilization is to reduce the influent pH and to minimize the risk of scale formation from magnesium or calcium salts. Three reverse osmosis (RO) units were operated with a control (U1), CO2 (U2), and a commercial antiscalant, MDC-220 (U3). The performances of all the units were compared in terms of change in transmembrane pressure (TMP). The overall efficiency trend was found as U1 > U3 > U2. The membrane surfaces were analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) for the morphological and elemental compositions, respectively. The surface analysis signified a significant increase in surface smoothness after scale deposition. The noticeable reduction in surface roughness can be described as a result of ionic deposition in the valley region. A sludge-like scale layer was found on the surface of the control membrane (U1) which could not be removed, even after an hour of chemical cleaning. After 20–30 min of cleaning, the U2 membrane was successfully restored to its original state. In brief, this study highlights the sustainable membrane process developed via CO2 utilization for scale inhibition, and the appropriate cleaning approaches.

It is estimated that Reverse Osmosis (RO) desalination will produce, by 2025, more than 2,000,000 end-of-life membranes annually worldwide. This review examines the implementation of circular economy principles in RO technology through a comprehensive analysis of the RO membrane life cycle (manufacturing, usage, and end-of-life management). Future RO design should incorporate a biobased composition (biopolymers, recycled materials, and green solvents), improve the durability of the membranes (fouling and chlorine resistance), and facilitate the recyclability of the modules. Moreover, proper membrane maintenance at the usage phase, attained through the implementation of feed pre-treatment, early fouling detection, and membrane cleaning methods can help extend the service time of RO elements. Currently, end-of-life membranes are dumped in landfills, which is contrary to the waste hierarchy. This review analyses up to now developed alternative valorisation routes of end-of-life RO membranes, including reuse, direct and indirect recycling, and energy recovery, placing a special focus on emerging indirect recycling strategies. Lastly, Life Cycle Assessment is presented as a holistic methodology to evaluate the environmental and economic burdens of membrane recycling strategies. According to the European Commission’s objectives set through the Green Deal, future perspectives indicate that end-of-life membrane valorisation strategies will keep gaining increasing interest in the upcoming years.

Microalgae have attracted great interest recently due to their potential for nutrients removal from wastewater, renewable biodiesel production and bioactive compounds extraction. However, one major challenge in microalgal bioremediation and the algal biofuel process is the high energy cost of separating microalgae from water. Our previous studies demonstrated that forward osmosis (FO) is a promising technology for microalgae harvesting and dewatering due to its low energy consumption and easy fouling control. In the present study, two FO module configurations (side-stream and submerged) were integrated with microalgae (C. vulgaris) photobioreactor (PBR) in order to evaluate the system performance, including nutrients removal, algae harvesting efficiency and membrane fouling. After 7 days of operation, both systems showed effective nutrients removal. A total of 92.9%, 100% and 98.7% of PO4-P, NH3-N and TN were removed in the PBR integrated with the submerged FO module, and 82%, 96% and 94.8% of PO4-P, NH3-N and TN were removed in the PBR integrated with the side-stream FO module. The better nutrients removal efficiency is attributed to the greater algae biomass in the submerged FO-PBR where in situ biomass dewatering was conducted. The side-stream FO module showed more severe permeate flux loss and biomass loss (less dewatering efficiency) due to algae deposition onto the membrane. This is likely caused by the higher initial water flux associated with the side-stream FO configuration, resulting in more foulants being transported to the membrane surface. However, the side-stream FO module showed better fouling mitigation by simple hydraulic flushing than the submerged FO module, which is not convenient for conducting cleaning without interrupting the PBR operation. Taken together, our results suggest that side-stream FO configuration may provide a viable way to integrate with PBR for a microalgae-based treatment. The present work provides novel insights into the efficient operation of a FO-PBR for more sustainable wastewater treatment and effective microalgae harvesting.