Complete Pore Blocking Research Articles

Fabrication and application of highly permeable ceramic membranes: Membrane-forming mechanism, pore structure, separation performance and fouling mechanism analyses

High separation efficiency and satisfactory economic benefits are of great importance for ceramic membranes in the field of water treatment. Herein, microfiltration ceramic membrane with high permeability and selectivity was prepared in one-step (dip-coating and sintering) by sacrificial-interlayer method. The membrane-forming mechanism, effect of temperature on the morphology and pore structure, separation performance, fouling mechanism, and regeneration performance of the ceramic membranes were systematically investigated. The results show that membrane-forming mechanism of the membranes largely depends on film-coating filtration. The membrane with a mixture of nanocellulose crystals and graphene oxide as sacrificial interlayer (C1G1) and sintered at 1100–1300 °C possessed smooth surface. The open porosity and average pore size increased, and the pore size distribution became broader as the temperature increased. Moreover, the sacrificial-interlayer membrane sintered at 1300 °C (mA4S-C1G1) possessed suitable porosity (53.4%) and average pore size (200 nm), high permeance (4828 L·m−2·h−1·bar−1), which was larger than that of the membrane without sacrificial interlayer, manifesting that C1G1 could prevent the penetration of membrane-forming particles into support. The final fouling mechanism of mA4S-C1G1 was cake filtration, although complete pore blocking, standard pore blocking, intermediate pore blocking also involved in the initial stage. In addition, the oil rejection rate (∼97%) and steady-state feed flux (810–1154 L·m−2·h−1) of mA4S-C1G1 was high, and it also possessed good regeneration performance.

Fabrication and characterization of ceramic tubular composite membranes using slag waste materials for oily wastewater treatment

In this study, low-cost tubular ceramic membranes were fabricated by using waste slag and natural raw materials in order to decrease the manufacturing carbon footprints. The effects of incorporation of phosphorus slag (PS) and blast furnace slag (BFS) in the mullite-zeolite membrane body were investigated. The structural characteristics of the fabricated membranes were evaluated using X-ray diffraction (XRD), field emission–scanning electron microscopy (FESEM), atomic force microscopy (AFM), contact angle, porosity and average pore size analyses. Thermal and mechanical stability were studied by thermogravimetric analysis (TGA) and three-point bending test, respectively. The oily wastewater treatment tests revealed that an increase in the slag percentage from 0 to 30% leads to enhancing the permeate flux from 99 l m−2 h−1 to 349 l m−2 h−1 for PS-based tubular membrane and to 244 l m−2 h−1 for BFS-based tubular membrane under 1 bar applied. The chemical oxygen demand (COD) removal percentage of all membranes was reported almost 99% for oily wastewater feed with a COD concentration of 612 mg l−1. In addition, the investigation of membrane fouling mechanisms was carried out using Hermia models indicating that the best correlation with the experimental data is observed for the complete pore blocking model. This study presents experimental foundations aimed at enhancing the performance of affordable slag-based membranes, thus fostering their applicability in engineering contexts.

Phenol Removal through Horseradish Peroxidase Immobilization on Ultrafiltration Membranes: Comparative Analysis of Immobilization Methods and Fouling Patterns

This research investigates the removal of phenol using pure peroxidase from horseradish grade I in conjunction with a dead-end ultrafiltration membrane. Various horseradish peroxidase (HRP) immobilization techniques— physical adsorption, covalent bonding, and cross-linking with glutaraldehyde—were applied to a regenerated cellulose (RC) membrane with a surface area of 44 m2 and a molecular weight cut-off of 30 kDa. The investigation examined factors influencing phenol removal, including phenol concentration, membrane fouling, and the reusability of immobilized enzymes. Results indicated that covalent bonding was the most suitable enzyme immobilization technique, achieving a remarkable 90.1% immobilization yield. Phenol removal efficiency reached 100% at 30 min under specific conditions: phenol concentration of 1 mg/L, pH 6.0, hydrogen peroxide concentration of 0.5 mM, and operating pressure set at 3 psig, with temperature maintained at 28 ± 3 °C. Membrane fouling resulted in a decrease in flux. The performance of fouling models was found to be influenced by phenol concentration, with the Cake Formation Model (CFM) proving most effective at low concentrations, while the Complete Pore Blocking Model (CBM) emerged as more suitable at higher concentrations. The immobilized enzyme exhibited reusability for five cycles, maintaining a phenol removal efficiency exceeding 50%. These findings contribute to understanding the enzymatic phenol removal process and the use of appropriate enzyme immobilization techniques for the effective and sustainable treatment of phenol-contaminated water.

Identification of Membrane Fouling with Greywater Filtration by Porous Membranes: Combined Effect of Membrane Pore Size and Applied Pressure.

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.

Gravity-driven membrane coupled with oxidation technology to modify the surface properties and biofilm formation: Biofouling mitigation

Biofilms caused by biological fouling play an essential role in gravity-driven membranes’ (GDMs) flux decline and rejection rate. The effects of ozone, permanganate, and ferrate (VI) in-situ pretreatment on membrane properties and biofilm formation were systematically studied. Due to the selective retention and adsorption of algal organic matter by biofilms and oxidative degradation, the rejection efficiency of dissolved organic carbon (DOC) in algae-laden water pretreated with permanganate by GDM was up to 23.63%. Pre-oxidation extraordinarily postponed flux decline and biofilm formation of GDM and reduced membrane fouling. The total membrane resistance decreased by 87.22%–90.30% within 72 h after pre-ozonation. Permanganate was more effective than ozone and ferrate (VI) in alleviating secondary membrane fouling caused by algal cells destroyed by pre-oxidation. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that the distribution of electrostatic force (EL), acid-base (AB), and Lifshitz-van der Waals forces (LW) interactions between M. aeruginosa and the released intracellular algogenic organic matter (IOM) and ceramic membrane surface was similar. The membrane and foulants are always attracted to each other by LW interaction at different separation distances. The dominant fouling mechanism of GDM combined with pre-oxidation technology shifts from complete pore blocking to cake layer filtration during operation. After pre-oxidation of algae-laden water by ozone, permanganate, and ferrate (VI), GDM can treat at least 131.8%, 37.0%, and 61.5% more feed solution before forming a complete cake layer. This study provides new insights into the biological fouling control strategies and mechanisms for GDM coupled with oxidation technology, which is expected to alleviate membrane fouling and optimize the feed liquid pretreatment procedure.

Magnetic mining waste based-membranes for trimethoprim removal and fouling mitigation with ozone

The use of ceramic membranes for microfiltration have increased due to their high performance and physical–chemical properties, but their production is still very expensive. For this reason, geopolymeric membranes (GPMs) have been developed with similar characteristics and reduced fabrication costs by incorporating industrial waste. In this study, GPMs were synthesized by incorporating different amounts of magnetic mining waste (MMW), characterized, and used to remove trimethoprim antibiotic from an aqueous solution. Moreover, the presence of high iron oxide content in the membrane composition, ozone could be used as the cleaning agent due to the in situ generation of reactive oxygen species. The porosity of the membranes was widely investigated with micro-CT. MMW incorporation was found to be highly beneficial for increasing the percentage of open pores’ and narrowing the distribution of pore size. The addition of a porogenic agent (H2O2) did not have the expected effects, since a significant number of both closed and very large pores (400–800 µm) were formed. The geopolymeric membranes produced by MMW incorporation up to 50% (w/w) exhibited high hydraulic permeability (6.4–7.0 L·m−2·h−1·bar−1), mechanical strength (30–38 MPa) and open porosity. Yet, rejection rates doubled with the incorporation of 50% (w/w) MMW, despite its high flux decay. Nevertheless, the flux was easily recovered by the reactions between foulant compounds and ozone, which was used as cleaning agent. The filtration performance was evaluated to remove trimethoprim dissolved in aqueous solution and the flux decay was successfully described according to the Hermia’s law, and a complete pore blocking mechanism was used. It is possible that trimethoprim molecules interact between them or with buffer reactants, forming complexes, which can be removed by ozone reactions.

Understanding Protein and Polysaccharide Fouling with Silicon Dioxide and Aluminum Oxide in Low-Pressure Membranes.

Humic, protein, and polysaccharide substances have been recognized as significant types of foulants in membrane systems. Despite the remarkable amount of research that has been performed on the interaction of these foulants, particularly humic and polysaccharide substances, with inorganic colloids in RO systems, little attention has been paid to the fouling and cleaning behavior of proteins with inorganic colloids in UF membranes. This research examined the fouling and cleaning behavior of bovine serum albumin (BSA) and sodium alginate (SA) with silicon dioxide (SiO2) and α-aluminum oxide (Al2O3) in individual and combined solutions during dead-end UF filtration. The results showed that the presence of SiO2 or Al2O3 in water alone did not cause significant fouling or a flux decline in the UF system. However, the combination of BSA and SA with inorganics was observed to have a synergistic effect on membrane fouling, in which the combined foulants caused higher irreversibility than individual foulants. Analysis of blocking laws demonstrated that the fouling mechanism shifted from cake filtration to complete pore blocking when the combined organics and inorganics were present in water, which resulted in higher BSA and SA fouling irreversibility. The results suggest that membrane backwash needs to be carefully designed and adjusted for better control of BSA and SA fouling with SiO2 and Al2O3.

Assessment of natural tannin-based coagulant for effective ultrafiltration (UF) of UASB effluent: Fouling mechanisms, pollutant removal and water reclamation feasibility

In this work, tannin coagulant (TANm) was applied at different dosages and compared with a PACl for UASB effluent filterability enhancement during membrane ultrafiltration. The results showed that TANm exhibited the greatest potential to improve UASB effluent filterability. Flux decay, total fouling resistance, and specific cake layer resistance were all reduced by both coagulants. However, the highest flux (55%) and fouling resistance reduction (70%) were obtained with 40 mg.L−1 of TANm, which was caused by an increase in particles larger than 200 μm, facilitating its removal by cross-flow filtration. Protein and carbohydrate reduction in the membrane was only observed at 25 mg.L−1 for both coagulants, with a higher influence of proteins in strongly/very strongly bound for all samples. In addition, fouling irreversibility increases, with a strong correlation between TANm dosage and Rirr and complete and intermediate pore blocking pointed as the main mechanisms responsible for irreversibility for both coagulants. Based on these and other findings, the mechanisms of the fouling layer adhered to the membrane with coagulants included the formation of complexes with proteins that were more strongly adhered (related to UASB effluent zeta potential increase), the density of the cake layer due to the presence of compact aggregates, and action of the coagulants themselves as foulants. Lastly, the economic evaluation revealed that the system without coagulant would have a lower total cost, but payback showed that the application of TANm has a lower investment time of return due to a lesser CAPEX.

Kinetic and mechanistic analysis of membrane fouling in microplastics removal from water by dead-end microfiltration

This study explores and analyses the kinetic and mechanistic aspects of microfiltration cellulose acetate membrane fouling by polyamide (PA) and polystyrene (PS) particles in dead-end configuration and the main interactions between the microplastics and the membrane during the filtration process. First, PA and PS particles were characterised to define the differences in shape (regular and irregular), particle size distribution (10–105 µm and 20–320 µm), and surface charge (neutral and negative). The results showed that the prevailing mechanisms during microplastic filtrations were complete pore blocking followed by cake layer formation in both cases. The mechanisms’ kinetics were positively correlated to MPs load through a power-law relationship which was stronger for PS than for PA particles because of higher steric hindrance effects. On the other hand, increasing the working transmembrane pressure led to an optimum working condition, between 0.3 and 0.5 bar for PA and 0.3 bar for PS filtration. Overall, higher fouling was induced by the PA particles due to the higher PA hydrophobicity and their smaller size, which caused a denser cake layer. Instead, PS particles with higher irregularities and repulsive electrostatic forces formed a more porous layer but induced a high degree of abrasion on the membrane surface. Finally, membrane fouling led to an increase in hydrophobicity and roughness, probably causing further fouling. To conclude, modelling membrane fouling can help predict the best working conditions and the membrane replacement cycles to increase the MPs removal efficiency and reduce secondary MP-based pollution.

Goat milk concentrated by nanofiltration: flow decline modeling and characterization

The skimmed goat milk was submitted to the nanofiltration process using a volume reduction factor (VRF) equal to 2. It was verified a rapid decrease of the permeate flux at a low time, with a continuous flux, caused by the reversible resistance, which is characterized by the standard and complete blocking. The combined fouling model was evaluated, including complete pore blocking and cake filtration mechanism, which described the skimmed goat milk nanofiltration behavior. For the VRF equal to 2 was determined the total solids, protein, lactose, ash, mineral fraction content, which increased successfully with the nanofiltration process. The Power Law and Herschel-Buckley models were fitting to describe the flow behavior for retentate, which presented the higher apparent viscosity.

Global pore blockage - cake filtration model including pressure effects on protein fouling in virus filtration

Virus removal filtration is a key step in the manufacture of monoclonal antibodies and serum-derived products. There is significant interest in developing continuous biomanufacturing processes for these products, requiring operation at much lower operating pressures/fluxes than those used in batch operations. The objective of this study was to examine the effect of low operating transmembrane pressure (TMP between 0.2 and 5 psi) on the fouling rate and fouling mechanisms during filtration of human serum Immunoglobulin G (hIgG) through the Viresolve® Pro membrane. At equal throughput, the extent of flux decline increased with increasing pressure, with the greatest flux decline observed at TMP ≈ 5 psi, before decreasing at higher pressures. A flux decline model based on fouling by intermediate pore blockage followed by cake formation was developed and shown to be in good agreement with the experimental data. The data at low pressures were combined with previously published results at high TMP (10–60 psi) to develop a global fouling model that was valid at all TMP. The rate of pore blockage decreased with increasing TMP, whereas the cake filtration parameter increased with increasing TMP, with the latter likely reflecting the compressibility of the fouling deposit. The observed transition between intermediate and complete pore blocking occurred around a Péclet number equal to one, corresponding to TMP between 5 and 10 psi, suggesting the importance of protein diffusion on membrane fouling. These results provide important insights into the effects of pressure on both the rate and mechanisms controlling protein fouling during virus removal filtration.

Fouling mechanisms in anoxic-aerobic sequencing batch membrane bioreactor based on adapted Hermia models and main foulant characteristics

Various derivatives of Hermia models (complete pore blocking, intermediate pore blocking, cake layer formation, and standard pore blocking) and different assessments of foulant characteristics have long been used to determine the membrane fouling mechanisms. Accordingly, this study aims to adapt Hermia models and their combination according to the operating conditions of an anoxic-aerobic sequencing batch membrane bioreactor (A/O-SBMBR). In addition, fouling mechanisms of the A/O-SBMBR were assessed using these models along with the main foulant characteristics. Models fitting with the transmembrane pressure (TMP) data indicated that the intermediate-standard model was accounting for the increased fouling during the whole regular operating period, with the residual sum of squares (RSS) of 58.3. A more detailed study on the distinct stages of TMP curve showed that the intermediate-standard model had the best fit in stages of 2 and 3, with the RSS equal to 2.6 and 2.8, respectively. Also, the complete-standard model provided the best description of the fouling mechanism in stage 4, with the RSS of 12.5. Different analyzes revealed how the main foulant characteristics affect the occurrence of intermediate, complete and standard fouling mechanisms in the A/O-SBMBR, which is consistent with the fitting results of the adapted Hermia models. The modeling and experimental methods used in the presented study provided a valuable basis to prevent and control membrane fouling in membrane bioreactors.

Effect of ultrasound, centrifugation, and enzymatic pretreatments on phytochemical properties and membrane fouling during microfiltration of Sohiong (Prunus nepalensis L.) juice.

The study aimed to investigate the effects of various pretreatment methods on sohiong fruit juice during the microfiltration process. The ultrasound, centrifugation, and enzymatic pretreatment processes were used before the microfiltration process of the juice. The highest total phenolic content, anthocyanin content, and antioxidant activity of sohiong fruit juice were observed after enzymatic pretreatment. However, the browning index and color of the sohiong juice deteriorated with enzyme pretreatment. The fouling behavior of the microfiltration process for the pretreated sohiong juice was well explained by the complete pore-blocking model as the coefficient of determination (R 2 ) varied from 0.821 to 0.971. All pretreatment methods significantly (p ≤ 0.05) increased the initial flux of the microfiltration process, and the highest flux was observed for the enzyme pretreated juice. Furthermore, as compared to alternative pretreatments following microfiltration, the enzyme pretreated fruit juice had a high sensory acceptance. The work manifested a way to develop high-quality sohiong fruit juice with a low fouling tendency.

Enhancement of pozzolanic clay ceramic membrane properties by niobium pentoxide and titanium dioxide addition: Characterization and application in oil-in-water emulsion microfiltration

Pozzolanic clay was mixed with niobium pentoxide (Nb2O5) and titanium dioxide (TiO2) to improve the filtering properties of disk-type ceramic membranes, in 0.1 g L−1 oil-in-water emulsion. The effect of sintering temperatures of 1000 °C, 1100 °C and 1150 °C was evaluated. The newly formed hydrophilic membranes were fully characterized in terms of porosity, mechanical strength, X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric analysis (TGA), water contact angle, scanning electron microscopy (SEM), atomic force microscopy (AFM), and hydraulic permeability. The applicability of the developed membranes was evaluated using crossflow microfiltration (MF) of an oil-in-water emulsion. The results demonstrated that the membranes could offer higher permeate fluxes with low permeate TOC contents that were compliant with that reported in the literature. The niobium pentoxide increased the hydraulic permeability and initial permeate flux by up to 118% and 72%, respectively, compared with the pure clay membranes. The pore blocking models were adjusted to the MF data of the membranes sintered at 1100 °C, revealing that the intermediate pore blocking was the major fouling mechanism for pure clay and niobium pentoxide enriched membranes, while complete pore blocking was best fitted to the titanium dioxide containing membrane. Overall, the results demonstrated that the mixing of pozzolanic clay and niobium pentoxide has great potential.

Casein-dextran complexes subjected to microfiltration: Colloidal properties and their corresponding processing behaviors

In this work, protein-polysaccharide complexes were subjected to microfiltration, a typical multi-force process. Particle and flow properties of casein-dextran complexes were analyzed in various solution conditions, and their processing behaviors of microfiltration, elucidated by resistance, fouling propensity and interaction with porous polymer surface, were also investigated. Results suggested that the medium pH and the casein/dextran ratio had significant influences on particle and rheological properties of such complexes, and then led to notable different processing behaviors of microfiltration. Being subjected to the process of microfiltration, casein-dextran complexes of monomodal particle size distribution formed a compact and smooth cake layer on the membrane surface, which was resistant, and later-coming particles were easy to deposit on previously settled ones. Therefore, the growth rate of fouling was high and the transition of complex/membrane interaction regime was quite fast from complete pore blocking to cake formation mechanism. On the contrary, the complex of multimodal particle size distribution may easily form a loose and rough layer on the membrane surface while partially blocked the membrane pore entrance, which was less resistant. Consequently, the growth of such fouling layer was hindered, which then resulted in the slow-down of the transition from one regime to another (from complete pore blocking to standard pore blocking then to intermediate pore blocking mechanism). This work provides generalized and pertinent guidance for microfiltration of protein-polysaccharide complexes.

Influence of Solute Size on Membrane Fouling during Polysaccharide Enrichment Using Dense Polymeric UF Membrane: Measurements and Mechanisms.

Fouling mechanisms associated with membrane-based polysaccharide enrichment were determined using a dense ultrafiltration (UF) membrane. Dextran with different molecular weights (MWs) was used as a surrogate for polysaccharides. The influence of dextran MW on fouling mechanisms was quantified using the Hermia model. Flux data obtained with different dextran MWs and filtration cycles were plotted to quantify the more appropriate fouling mechanisms among complete pore blocking, standard pore blocking, intermediate pore blocking, and cake filtration. For 100,000 Da dextran, all four mechanisms contributed to the initial fouling. As the filtration progressed, the dominant fouling mechanism appeared to be cake filtration with a regression coefficient (R2) of approximately 0.9519. For 10,000 Da, the R2 value for cake filtration was about 0.8767 in the initial filtration. Then, the R2 value gradually decreased as the filtration progressed. For 6000 Da, the R2 values of the four mechanisms were very low in the initial filtration. However, as the filtration progressed, the R2 value for cake filtration reached 0.9057. These results clearly show that the fouling mechanism of dense UF membranes during polysaccharide enrichment can be quantified. In addition, it was confirmed that the dominant fouling mechanism can change with the size of the polysaccharide and the duration of filtration.

Unrevealing the role of in-situ Fe(II)/S2O82- oxidation in sludge solid–liquid separation and membrane fouling behaviors of membrane bioreactor (MBR)

Membrane bioreactor (MBR) has received continuous attention in waste activated sludge treatment, however, membrane fouling still remains a big and inevitable challenge to its wide applications. Ferrous-persulfate (Fe(II)/S2O82–) oxidation possesses the outstanding oxidizing capability and high-efficiency in degrading refractory organics and enhancing sludge solubilization. In this study, in-situ Fe(II)/S2O82- oxidation was coupled for pretreating sludge, and the effect on the subsequent filtration performance and membrane fouling behaviors in MBR was investigated. Fe(II)/S2O82- oxidation had an outstanding effect on enhancing filterability of mixed sludge liquor and alleviating membrane fouling. Under the optimal pretreatment condition of 1.5/1.2 mmol-Fe(II)-S2O82-/g-VS, the membrane flux of reactor reached 20.6 mL/s/m2, and a 46.6% decrease in trans-membrane pressure (TMP) was obtained compared to the raw sludge without pretreatment. Correlation analysis reveal that polysaccharides in extracellular polymeric substances was the decisive factor affecting the membrane fouling behavior. The strong oxidizing ability of in-situ Fe(II)/S2O82- pretreatment could effectively break the glutinous and pilotaxitic biopolymer matrix deposited on the membrane surface, and rupture the hydrophilic bonds of proteins and polysaccharides. The high molecular weight biopolymers were brought down, with the water bounded inside the flocs released into liquid phase. Iron-mediated coagulation was also conductive to the re-aggregation of the fine particles and subsequent membrane fouling control. For raw sludge, the predominated fouling mechanisms were intermediate pore blocking and cake layer formation, while complete pore blocking and standard pore blocking occurred more frequently for pretreated sludge. This work provides a promising approach based on Fe(II)/S2O82- oxidation processes for efficient abatement of membrane fouling and sludge treatment.

Insights into the role of concentration polarization on the membrane fouling and cleaning during the aerobic granular sludge filtration process

The aerobic granular sludge (AGS) effectively mitigates the membrane fouling of a membrane bioreactor. However, the role and effects of the concentration polarization (CP), induced during the AGS filtration process on the membrane fouling and membrane cleaning efficiency, remain unclear. In the present study, the AGS resulted in a higher CP proportion (>50%) and a lower CP resistance (<3 × 1012 m−1), compared with the flocculent sludge, owing to the synergistic effect of the hydraulic shear and AGS scouring development, which improved the AGS in suspension and also minimized its deposition on the membrane. High-frequency interactions (contact and collision) between the AGS and membrane enhanced the CP resistance by returning more granular sludge from the cake layer to the CP, which proportionally increased the fouling resistance. Based on the correlation of CP and fouling resistance, the CP resistance was divided into 3 categories: high-intensity (2.76 × 1012 m−1), medium-intensity (1.74 × 1012 m−1), and low-intensity (0.62 × 1012 m−1). At the high-intensity CP, most membrane pores were “sealed” (complete pore blocking [R2 > 0.9015]) and the pore blocking condition was the most serious (K-value = 0.0622 s−1), while the membrane surface became denser and rougher. As a result, the permeability loss after the long-term filtration increased. In the chemical cleaning investigation, the alkaline detergents yielded an enhanced membrane cleaning efficiency to recover permeability. By reducing the CP, the membrane cleaning efficiency was marginally improved. The present study reveals the quantitative role of CP and offers insights into the mechanisms that govern membrane fouling in a membrane bioreactor.

The role of PAC adsorption-catalytic oxidation in the ultrafiltration performance for treating natural water: Efficiency improvement, fouling mitigation and mechanisms

Powdered activated carbon (PAC) has turned out to be an efficient adsorbent in drinking water treatment, whereas its application integrated with membrane filtration is still controversial because of the combined fouling effect between organic pollutants and PAC. To this end, an integrated process of combining PAC adsorption-catalytic oxidation and membrane filtration was proposed for natural surface water treatment. The synergistic effect of PAC and peroxymonosulfate (PMS) was confirmed through the generation of reactive oxidation species, and both radical oxidative pathways (•OH, SO4•− and O2•−) and nonradical (1O2 and PMS) pathways involved in the process. The removal efficiency of DOC and UV254 was significantly strengthened by PAC/PMS, with removal rates of 56.1% and 64.9%, respectively. The integration of PAC and PMS could significantly enhance the reduction of fluorescent organics, and pollutants with varying molecular weights. The fouling condition of membrane was dramatically alleviated, with the flux increased by 38.9%, and the reversible and irreversible resistances declined by 79.7% and 48.3%, respectively. The major fouling mechanism was significantly changed, and complete pore blocking always played a dominant role, rather than cake filtration. The effectiveness of PAC/PMS was further verified by the characterization of membrane surface morphologies and functional groups. Moreover, the attractive interactions between foulants and membrane were converted to repulsive interactions with the pretreatment of PAC/PMS. The proposed synergistic process was efficient and convenient, which could significantly improve the purification efficiency of conventional PAC-UF system in drinking water treatment.

Technical assessment of reverse osmosis for concentration of fresh tea leaf extract

AbstractThis paper focused on the concentration of waste fresh tea leaf extract, byproduct of tea processing, by application of reverse osmosis. The concentration was carried out by plate and frame crossflow system equipped HR98PP membrane, operating as concentration mode with full recirculation of retentate. Results show that permeate flux increased with increase in operating pressure. Modeling of permeate flux based on osmotic pressure model at 30 and 40 bar of operating pressure was proposed. Hermia's model was applied for analyzed the membrane fouling in operation process. Good agreement between complete pore blocking model and experimental data was found. The recovery yields and contents of total solid (TS), total polyphenols (PPs) and antioxidant capacity (AC), consequently effectiveness, at 40 bar of operating pressure were higher than those at 30 bar. At 40 bar of operating pressure and 7.57 of concentration factor, the recovery yields of TS, PPs, and AC were 83.7, 85.1, and 79.6%, respectively. Contents of TS, PPs, and AC in retentate and permeate were 64.62 and 1.91 g/L; 25.82 and 0.61 g GAE/L; 97.87 and 3.35 mM TEAC, respectively. Maximum theoretical content of TS at 40 bar was estimated as 341 g/L. Results imply that it is potential to apply reverse osmosis for concentration of waste fresh tea leaf extract to produce instant powder with high content of polyphenols.Practical applications The concentration of waste fresh tea leaf extract by reverse osmosis membrane Modeling of permeate flux in reverse osmosis Fouling mechanism was analyzed by Hermia's model. Recovery yields and contents of total solid, total polyphenols and antioxidant capacity in concentrate against concentration factor were estimated.