Flux Decline Research Articles

Insights into the alleviation of membrane fouling in AGMBR through thermal/Fe2+-activated persulfate pre-oxidation: Performance and mechanisms

Aerobic granular sludge membrane bioreactors (AGMBRs) are a viable option for municipal sewage reuse; however, the issue of membrane fouling remains a significant obstacle to overcome to achieve large-scale implementation. Therefore, a novel thermal/Fe2+/persulfate (PDS) system was proposed to investigate its alleviation effect on membrane fouling in AGMBR. The findings indicated that the thermal/Fe2+/PDS system demonstrated superior efficacy in eliminating pollutants from raw sewage. Radical scavenging experiments demonstrated that sulfate radicals and coagulation were the primary contributors to mitigating membrane fouling in the thermal/Fe2+/PDS system, effectively reducing fouling resistance and retarding the decline in membrane flux. Analysis of interfacial interaction energy indicated that increasing the electrostatic double-layer repulsion between foulant–membrane and foulant–foulant could mitigate membrane fouling. Additionally, the interfacial characteristics (membrane surface morphology and foulant content) of the fouled membranes were characterized to further validate the efficacy of this system in alleviating membrane fouling. The correlation analysis revealed a positive association between the mitigation of membrane fouling and the substantial elimination of various pollutants, such as chemical oxygen demand, polysaccharides, and suspended solids. This study highlights the exceptional performance of the thermal/Fe2+/PDS system and provides novel insights into alleviating AGMBR membrane fouling.

Surface modification of FeⅢ-juglone coating on nanofiltration membranes for efficient biofouling mitigation

Nanofiltration membranes have increasingly played a vital role in the purification of surface water and the recycling of wastewater. However, the problem of membrane biofouling, which leads to shortened service life and increased energy consumption, has hindered the widespread application of nanofiltration membranes. In this study, we developed functionalized nanofiltration membranes with anti-adhesive and anti-biofouling properties by coordinating FeIII and juglone onto commercial nanofiltration membranes in a facile and viable manner. Due to the hydrophilic nature of the FeⅢ-juglone coating as well as its ultra-thin thickness and minimal impact on the membrane pores, the permeance of the optimally modified membrane even increased slightly (14 %). The outstanding anti-adhesive property of the FeⅢ-juglone coating was demonstrated by a significant reduction in the adsorption of proteins and bacteria. Furthermore, the modified membranes exhibited lower flux decline amplitude and reduced biofilm deposition during dynamic fouling experiment, further supporting the outstanding anti-biofouling performance of the nanofiltration membrane after the modification with FeⅢ-juglone coating. This study presents a novel and feasible approach for simultaneously improving the water permeance, anti-adhesive property and anti-biofouling property of commercial nanofiltration membranes.

Modification of microfiltration membranes by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/n-hydroxy sulfosuccinimide coupling mediated antimicrobial peptides grafting for biofouling mitigation

Microfiltration membrane separation is widely applied for water and wastewater but biofouling is a challenging task in real applications. In this work, we fabricated a novel antibiofouling polyvinylidene fluoride (PVDF) membrane by grafting non-drug-resistant antimicrobial peptides (AMPs) on the membranes via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxy sulfosuccinimide (EDC/Sulfo-NHS) chemistry. Effects of AMPs concentration on the membrane basic properties, antibacterial and antibiofouling behaviors of the modified membranes were systematically investigated. Membrane surface characterization demonstrated that the AMPs were successfully grafted onto the base PVDF membranes. The AMPs modified membrane showed enhanced hydrophilicity, consistent permeability and prominent antimicrobial ability (i.e., >90% of antibacterial efficiency against both Escherichia coli and Staphylococcus aureus). Batch filtration tests exhibited that the modified membranes with the concentration of AMPs less than or equal to 0.7 mg/mL had lower flux decline rate compared to the pristine membrane (M0). According to the images from confocal laser scanning microscopy analysis, less total cells as well as more dead cells were observed on the AMPs modified membrane compared to M0. Furthermore, the grafted AMPs on the membranes also displayed favorable stability suffered from a cycle involving biofouling and chemical cleaning. This grafting protocol for AMPs highlights a robust way to fabricate antibiofouling membranes for water and wastewater treatment.

Application of a newly-designed capacitive deionizing membrane distillation (CDIMD) technique for the efficient production of high-quality drinking water from seawater

A newly-designed capacitive deionizing membrane distillation (CDIMD) system which introduced the activated carbon fiber felt (ACFF) electrodes and self-fabricated electrically conductive membranes (CNTs-PTFE) into the convention MD technique for the efficient production of high-quality drinking water from seawater in this work. Two different CDIMD systems of forward-CDIMD (ACFF linking to positive poles) and reversed-CDIMD (ACFF liking to negative poles) were established in this study to investigate the impacts of electric field form on the desalination efficiency. The severe membrane flux decline of MD (83.17%, 168 h) was clearly mitigated in the CDIMD system, which was respectively 52.93% and 69.82% for the forward-CDIMD and reversed-CDIMD group. In terms of the CDIMD system without input voltage, an anabatic flux drop to 8.85% was observed in the later period, implying the necessity of periodic regeneration for ACFF and CNTs-PTFE. The membrane scaling induced by the deposition of CaSO4, as the core drawback of MD application, has been remarkably solved in the CDIMD system, especially in the forward-CDIMD system. Although the ACFF and CNTs-PTFE were periodically regenerated in the forward- and reversed-CDIMD system, an increasing appearance of crystals was observed inside the ACFF and CNTs layer along with the long-term seawater desalination, accordingly degrading their electrochemical performance. Hence, the forward-CDIMD system with an abbreviated time-set of adsorption/desorption phase might be a superior choice for efficient seawater desalination.

A novel approach for sterilization and concentration of traditional functional drinks: Membrane‐based nonthermal processes

AbstractThe applicability of microfiltration (MF) and osmotic membrane distillation (OMD) for sterilization and concentration of traditional functional drink constituents, such as Curcuma xanthorrhiza, ginger, lime, Java tea, and sappan wood extracts, was evaluated in this study. MF showed excellent performance in microorganisms elimination, turbidity reduction, and maintaining antihyperglycemic activity performance. However, a reduction of total phenol and antioxidant activity were observed due to the retention by MF. Fouling in MF was challenging and resulted in rapid flux decline. The concentration of sterilized extracts by OMD operation resulted in a concentration factor of 1.15, 1.13, 1.10, 1.24, and 1.24 for ginger, lime, C. xanthorrhiza, Java tea, and sappan wood, respectively. The active compounds were well preserved, with a maximum of 20% reduction compared to sterilized extracts. Despite insignificant foulant deposition, the OMD flux in tests using C. xanthorrhiza, ginger, and lime as the feed decreased over time, indicating reduced driving force.Practical applicationsThe application of membrane technology for juices and liquid foods sterilization and concentration has been widely researched. In this research, we evaluated the performance of MF and OMD for the sterilization and concentration of traditional functional drinks. The results indicated that the functional drink can be sterilized by MF with excellent preservation of the active compounds, such as those responsible for the antihyperglycemic and antioxidant activities. The OMD could also concentrate the traditional functional drink, even though concentration polarization posed a challenge to flux stability. The degradation of phenolic compounds and antioxidant activity of the concentrated traditional functional drink was at a minimal value, indicating the promising application of MF and OMD. We believe this article provides new and exciting insights to push forward the sterilization and concentration process in industrial scale.

Boosting the performance of reverse osmosis membrane by macrocyclic molecule through interfacial coordination-driven strategy

Developing polyamide reverse osmosis (RO) membrane with superior permeability and salt rejection is highly desired for desalination. In this study, we propose an interfacial coordination-driven strategy to promote the incorporation of macrocyclic molecule into the polyamide layer and further improve the performance of RO membrane. To this end, the macrocyclic molecule Noria and transition metal salt Fe(acac)3 are added into the aqueous phase and organic phase respectively. During the interfacial polymerization (IP) reaction of m-phenylenediamine (MPD) with trimesoyl chloride (TMC), Fe3+ as electron acceptor would coordinate with the electron donor Noria to form Noria-Fe3+ complex at the aqueous-organic interface. This effectively promotes the diffusion of Noria and its further incorporation into the resulting polyamide layer. As a result, the RO membrane with Noria-Fe3+ exhibits closely packed band-like surface morphology, obviously different from the traditional leaf-like structure formed by MPD-TMC. Benefitting from the inner cavity of Noria, the permeance of RO membrane is significantly improved from 1.37 Lm−2h−1bar−1 to 3.87 Lm−2h−1 bar−1 at the optimal Noria and Fe(acac)3 concentrations of 0.1 wt%, while the NaCl rejection experiences little change from 98.8 % to 98.2 %. Besides, the flux decline ratio and flux recovery ratio of obtained RO membrane are 21 % and 85 % respectively in the bovine serum albumin fouling test. It exhibits more excellent anti-fouling ability than the nascent membrane due to the better hydrophilicity and smoother membrane surface. This simple strategy may pave a novel way for the application of other molecules with special structures as additives to fabricate high-performance RO membranes.

Sieving and Clogging in PEG-PEGDA Hydrogel Membranes.

Hydrogels are promising systems for separation applications due to their structural characteristics (i.e., hydrophilicity and porosity). In our study, we investigate the permeation of suspensions of rigid latex particles of different sizes through free-standing hydrogel membranes prepared by photopolymerization of a mixture of poly(ethylene glycol) diacrylate (PEGDA) and large poly(ethylene glycol) (PEG) chains of 300,000 g·mol-1 in the presence of a photoinitiator. Atomic force microscopy and cryoscanning electron microscopy (cryoSEM) were employed to characterize the structures of the hydrogel membranes. We find that the 20 nm particle permeation depends on both the PEGDA/PEG composition and the pressure applied during filtration. In contrast, we do not measure a significant permeation of the 100 nm and 1 μm particles, despite the presence of large cavities of 1 μm evidenced by the cryoSEM images. We suggest that the PEG chains induce local nanoscale defects in the cross-linking of PEGDA-rich walls separating the micrometer-sized cavities, which control the permeation of particles and water. Moreover, we discuss the decline of the permeation flux observed in the presence of latex particles compared to that of pure water. We suggest that a thin layer of particles forms on the surface of the hydrogels.

Modification of the distribution of humic acid complexations by introducing microbubbles to membrane distillation process for effective membrane fouling alleviation

Membrane fouling caused by inorganic ions and natural organic matters (NOMs) has been a severe issue in membrane distillation. Microbubble aeration (MB) is a promising technology to control membrane fouling. In this study, MB aeration was introduced to alleviate humic acid (HA) composited fouling during the treatment of simulative reverse osmosis concentrate (ROC) by vacuum membrane distillation (VMD). The objective of this work was to explore the HA fouling inhibiting effect by MB aeration and discuss its mechanism from the interfacial point of view. The results showed that VMD was effective for treating ROC, followed by a severe membrane fouling aggravated with the addition of 100 mg/L HA in feed solution, resulting in 45.7% decline of membrane flux. Analysis using the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and zeta potential distribution of charged particles proved the coexistence of HA and inorganic cations (especially Ca2+), resulting in more serious membrane fouling. The introduction of MB aeration exhibited excellent alleviating effect on HA-inorganic salt fouling, with the normalized flux increased from 19.7% to 37.0%. The interfacial properties of MBs played an important role, which altered the zeta potential distributions of charged particles in HA solution, indicating that MBs adhere the HA complexations. Furthermore, this mitigating effect was limited at high inorganic cations concentration. Overall, MBs could change the potential characteristics of HA complexes, which also be used for other similar membrane fouling alleviation.

Antiscalants for mitigating silica scaling in membrane desalination: Effects of molecular structure and membrane process

Silica scaling is a major type of mineral scaling that significantly constrains the performance and efficiency of membrane desalination. While antiscalants have been commonly used to control mineral scaling formed via crystallization, there is a lack of antiscalants for silica scaling due to its unique formation mechanism of polymerization. In this study, we performed a systematic study that investigated and compared antiscalants with different functional groups and molecular weights for mitigating silica scaling in membrane distillation (MD) and reverse osmosis (RO). The efficiencies of these antiscalants were tested in both static experiments (for hindering silicic acid polymerization) as well as crossflow, dynamic MD and RO experiments (for reducing water flux decline). Our results show that antiscalants enriched with strong H-accepters and H-donors were both able to hinder silicic acid polymerization efficiently in static experiments, with their antiscaling performance being a function of both molecular functionality and weight. Although poly(ethylene glycol) (PEG) with abundant H-accepters exhibited high antiscaling efficiencies during static experiments, it displayed limited performance of mitigating silica scaling during MD and RO. Poly (ethylene glycol) diamine (PEGD), which has a PEG backbone but is terminated by two amino groups, was efficient to both hinder silicic acid polymerization and reduce water flux decline in MD and RO. Antiscalants enriched with H-donors, such as poly(ethylenimine) (PEI) and poly(amidoamine) (PAMAM), were effective of extending the water recovery of MD but conversely facilitated water flux decline of RO in the presence of supersaturated silica. Further analyses of silica scales formed on the membrane surfaces confirmed that the antiscalants interacted with silica via hydrogen bonding and showed that the presence of antiscalants governed the silica morphology. Our work indicates that discrepancy in antiscalant efficiency exists between static experiments and dynamic membrane filtration as well as between different membrane processes associated with silica scaling, providing valuable insights on the design principle and mechanisms of antiscalants tailored to silica scaling.

Improving permeability and fouling resistance of GO hydrophilic/hydrophobic Janus membrane by polyether amine crosslinking for membrane distillation of dye wastewater

Graphene oxide (GO) modification is promising to increase vapor flux and antifouling properties of hydrophobic membranes in membrane distillation for wastewater treatment. However, the acid bonding of GO with dyes impedes its wide application in dye wastewater treatment. In this study, polyether amine D400 was used to modify hydrophilic GO layer of Janus membrane. The GD3/PTFE composite membrane (GO and D400 mass ratio of 1:2) demonstrated the best water flux and antifouling performance for methyl orange (MO) containing 3.5 wt% NaCl. The flux was increased by 170.3%− 228.9% compared to PTFE pristine membrane and the flux decline due to fouling was decreased by 41.3%− 60.8% to GO/PTFE membrane. The observed increase in the longitudinal thermal conductivity of the cross-linked GO layer suggests that the enhanced permeability is attributed to improved heat transfer resulting from the higher density of GO nanosheets. Acid bonding of GO layer with dye molecular is weakened and electrostatic repulsion is also increased, leading to the excellent antifouling performance. This study indicate that polyether amine crosslinking is promising method for modification of GO composite membrane for dye wastewater treatment.

Overlooked flocs in electrocoagulation-based ultrafiltration systems: A new understanding of the structural interfacial properties

An integrated ferrate-induced electrocoagulation-ultrafiltration (FECUF) process is proposed to cope with the growing demand for water treatment. Although flocs formed during the electrocoagulation (EC) process are useful for contaminant reduction and mitigation of membrane fouling, few studies have been focused on their structures and properties. Herein, we investigated the formation and structural transformations of flocs and their responses to organic matter, as well as the relationships between their interfacial properties and membrane fouling mitigation. It was found that ferrate contributed to the fast formation of flocs during the ferrate-induced electrocoagulation (FEC) process, which accelerated the FECUF process. Physicochemical analyses indicated that the flocs formed in the FEC process were mainly composed of Fe(III)-(hydr)oxides with abundant hydroxyl groups and poor crystallinity, which allowed complexation with NOM. Therefore, the mobilities of the NOM and the soluble coagulant ions were reduced. The responses of flocs to NOM suggested that the period of 0–20 min resulted in the most efficient NOM removal. In addition, two patterns revealed the relationships between the interfacial properties of the small colloidal particles (SCPs) and the membrane filtration performance: i) the decline in the initial flux was closely related to the composition (gel-type substances or metal-(hydr)oxides) of the SCPs and ii) the steady-state flux was influenced by the energy barrier between the SCPs. However, when the SCPs had the same composition, the interfacial properties influenced both the initial flux and the steady-state flux. This study provides an alternative FECUF process for intensive upgrades of centralized water treatment systems.

Effect of granular activated carbon adsorption on mitigating microfiltration membrane fouling by algal organic matter

Abstract Algal blooms can seriously affect the operation of water treatment processes including low-pressure (micro- and ultrafiltration) and high-pressure (nanofiltration and reverse osmosis) membranes mainly due to the accumulation of algae-derived organic matter (AOM). This study investigated the effect of granular activated carbon (GAC) pretreatment on PVDF microfiltration performance for the removal of AOM. Dissolved organic matter (DOM) solution of commercial humic acid, extra- and intracellular organic matter from two species of algae, and Cyanobacteria were used for the investigation of the fouling potential of the membrane. A comparison study of different DOM removal and fouling behaviors of microfiltration (MF) after GAC adsorption as pretreatment was evaluated under variable GAC dosage and solution pH. Almost 15–20% improvement in flux and decline in irreversible fouling occurred due to the pretreatment using 1.0 g/L of GAC for an hour. The intracellular material caused higher membrane fouling than humic acid due to the hydrophilic nature of the AOM. Membrane fouling and decline in flux increased with increasing pH in the range of 5.0–8.0. The comparison results might help to provide insights into the real challenge of dealing with the treatment of algal-laden water.

Enrichment of lycopene in watermelon juice by ultrafiltration: technical assessment and fouling analysis

SummaryWatermelon juice is proven to be a potential source of lycopene, but its exploitation and consumption are currently constrained. The research focused on lycopene enrichment in watermelon juice by ultrafiltration (UF) with 1000 Da of molecular weight cut‐off (MWCO). The selectivity of UF membrane for the constituents in watermelon juice was investigated from 2 to 8 bar by dead‐end mode combined with stirring. The 1000 Da UF membrane showed a high potential to recover and separate lycopene from other components. However, membrane deposition and capillary occlusion could occur, affecting the overall efficiency of the enrichment process. To better understand kinetics, phenomena and efficiency, the study was evaluated in cross‐flow mode with full recirculation of retentate. The enrichment efficiency was found to increase the concentration and purity of lycopene by several times. The concentration polarisation was used to describe permeate flux decline, while the Hermia model was developed to explain fouling mechanisms. The utilised models were highly compatible; additionally, pore blocking was thought to be the main mechanism of fouling in lycopene enrichment by 1000 Da UF. The built mathematical model was in good agreement with the experimental observations of permeate flux, and lycopene, TS and ash concentrations. The 1000 Da UF of watermelon juice is a feasible approach for lycopene enrichment.

Covalent codeposition modification of reverse osmosis membranes with Noria and zwitterionic copolymers for antifouling in reclaimed water production

Reverse osmosis (RO) has been recognized as a promising technology to treat municipal wastewater. However, membrane fouling is still an important hurdle in the RO membrane operation. The present work demonstrates the facile and high-effective fabrication of a robust antifouling RO membrane by the codeposition of Noria with zwitterionic copolymers. This modified coating is irreversibly bound to the membrane during typical membrane operational conditions. Compared with the pristine membrane, the modified membrane (that is, the TFC-Co-8 membrane) possesses improved hydrophilicity, reduced roughness, and lower negative charge. Our results illustrate that the TFC-Co-8 membrane displays an excellent antifouling property with milder flux decline and higher flux recovery during protein and alginate filtrations. Additionally, the TFC-Co-8 membrane is applied in the treatment of actual secondary effluent and also exhibits a superior antifouling property, which is consistent with the results of the simulated solution. This work provides a reference for the design of antifouling RO membrane in reclaimed water production.

Enhanced membrane fouling by microplastics during nanofiltration of secondary effluent considering secretion, interaction and deposition of extracellular polymeric substances

Microplastic (MP) has been found to influence membrane fouling during microfiltration/ultrafiltration processes in direct and indirect ways by acting as fouling components and changing microbial activities, respectively. However, there is no relevant research about the contribution of MPs to nanofiltration membrane fouling. In this study, for the first time, the impacts of MPs on membrane fouling during the nanofiltration of secondary effluent (SE) were systematically investigated from the perspective of bacterial extracellular polymeric substances (EPS) secretion, their interaction with coexisting pollutants and also deposition. Membrane flux behaviors indicate that MPs simultaneously aggravated the short-term and long-term membrane fouling resistance of nanofiltration by 46 % and 27 %, respectively. ATR-FTIR, XPS and spectrophotometry spectra demonstrate that the deteriorated membrane fouling by MPs directly resulted from the increased accumulation of protein-like, polysaccharides-like and humic-like substances on membranes. EEM spectra further confirmed that MPs preferred to induce serious cake layers, which dominated membrane flux decline but hindered pore fouling. According to CLSM and SEM-EDS mappings, MPs in SE could stimulate microbial activities and then aggravate EPS secretion, after which their interaction with Ca2+ was also enhanced in bulk solution. The cross-linker nets could promote the deposition of other unlinked pollutants on membranes. Besides, MPs could weaken the rejection of certain dissolved organic matters (from 57 % to 52 % on the 50th day of filtration) by aggravating cake-enhanced concentration polarization (CECP), but improved the average removal of inorganic salts from 58 % to 63 % by improving their back diffusion through cake layers. Based on these analyses, the mechanisms of MP-enhanced membrane fouling during the nanofiltration of SE can be thoroughly revealed.

An accretion disc with magnetic outflows triggered by a sudden mass accretion event in changing-look active galactic nucleus 1ES 1927+654

ABSTRACT 1ES 1927+654 was known as a type 2 Seyfert galaxy, which exhibited drastic variability recently in ultraviolet (UV)/optical and X-ray bands. An UV/optical outburst was observed in the end of 2017, and it reached the peak luminosity ∼50 d later. The high-cadence observations showed a rapid X-ray flux decline with complete disappearance of the power-law hard X-ray component when the soft X-ray thermal emission reached its lowest level about 150 d after the UV/optical peak. The power-law X-ray component reappeared with thermal X-ray emission brightening from its lowest flux within next ∼100 d. We assume an episodic accretion event taking place in the outer region of the disc surrounding a central black hole (BH), which is probably due to a red giant star tidally disrupted by the BH. The inner thin disc with corona is completely swept by the accretion event when the gas reaches the innermost circular stable orbit. The field threading the disrupted star is dragged inwards by the disc formed after the tidal disruption event, which accelerates outflows from the disc. The disc dimmed since a large fraction of the energy released in the disc is tapped into the outflows. The accretion rate of the episodic accretion event declines, and ultimately, it turns out to be a thin disc, which is inefficient for field advection, and the outflows are switched off. A thin disc with corona reappears later after the outburst.

Adsorption and cake layer fouling in relation to Fenton cleaning of ceramic nanofiltration membranes

Catalytic ceramic nanofiltration (NF) is a promising technology for direct wastewater reclamation, given its high separation selectivity and reactive surfaces for oxidative removal of fouling. A better understanding of the relation between fouling types and oxidative cleaning efficacy under high organic loading conditions is of practical importance for realizing stable filtration/cleaning performance in long-term water reclamation operations. In this work, Fenton cleaning, using a hydrogen peroxide solution and an iron oxychloride catalyst pre-coat layer on top of commercially available ceramic NF membranes, was studied with respect to high organic loaded fouling, simulated by a concentrated sodium alginate solution in the presence of calcium. Adsorption (in the absence of a permeate flow) and constant-pressure filtration (with a permeate flow) experiments were performed to distinguish between permeance decreases as a result of either adsorptive or cake layer fouling. The results show that the flux evolution could be divided into an initial sharp flux decline, due to rapid adsorption of the foulants, and a subsequent gradual flux decrease, resulting from progressive cake build-up on the membrane. The two-stage flux decrease was enhanced during the constant-pressure filtration experiments, because they start at a high flux with a high fouling rate, while the flux gradually decreases as fouling proceeds. During multiple adsorption/cake filtration/Fenton cleaning cycles, the cake layer fouling was sufficiently removed by Fenton cleaning in contrast to the adsorptive fouling. However, the total permeate production during ceramic NF was not influenced by the remaining adsorptive fouling (after cleaning), since the adsorptive fouling always only occurs at the beginning of each cycle. The findings provide new insights into the criteria for evaluating and optimizing the efficacy of oxidative (Fenton) cleaning during ceramic NF in water treatment.

Fouling Mitigation in Membrane Distillation Using Pulsation Flow Technique

The main obstacles to scaling up membrane distillation (MD) on a commercial level are membrane fouling and temperature polarization. Therefore, in this study, the significance of the pulsation feed flow phenomenon was used for membrane distillation (DCMD) polarization, and comparisons were made using steady-state feed flow. Two different Hertz and amplitudes of pulsation feed flow trends were used in DCMD using different sources of water, including distilled water, seawater, and wastewater. Compared to steady-state feed flow, the results revealed that flux was enhanced for seawater once the operating flow became turbulent, and it enhanced even more once the flow rate was increased and the turbulence flow was moved. For wastewater, pulsation in the feed flow had an impact on delaying the beginning of the flux decline point and enhancing the overall freshwater recovery. In both pulsation feed flows (1 and 2 Hertz), the results also revealed a deficiency in fouling and an improvement in the temperature distribution in the feed channel for seawater desalination and wastewater running under typical operational conditions. Taking this value into consideration, an enhancement in mass flux (~5–10%) was observed compared to steady-state feed flow. Moreover, the pulsation feed channels were found to reduce CPC by about 10–15%, proving the role of turbulence in mixing the flow and mitigating the reduction in concentration polarization.

Ballasted flocculation pretreatment for mitigating ultrafiltration membrane fouling: Role of differently charged polyacrylamides at typical coagulant dosages

In this work, ballasted flocculation (without sedimentation) was suggested as a potential pretreatment for ultrafiltration to improve cake layer microstructure and mitigate membrane fouling. First, three representative aluminum sulfate (AS) coagulant dosages (including 1.0, 2.5 and 8.0 mg Al/L) were determined during preliminary testing to produce microfloc aggregates with negative, zero and positive zeta potentials at the coagulation stage of ballasted flocculation. Regardless of the applied coagulant dosage, not only ballasted floc size but also their strength and recovery abilities (following breakage) were dependent upon the selection of differently charged polyacrylamides (PAMs), likely due to the effect of PAM selection on polymer bridging and associated flocculation mechanisms. Second, comparisons of membrane flux decline and resistance distribution were performed to evaluate the importance of coagulant dosage and PAM type to cake layer formation and membrane fouling potential in the ballasted flocculation and ultrafiltration integrated process. The results demonstrated that the ballasted floc aggregates formed by ballasted flocculation pretreatment contributed to diverse structural characteristics of the fouled layer during their accumulation on the membrane surface, thereby affecting the degree of membrane fouling for various combinations of AS dosage and PAM type. Besides, the microsand particles involved in the formed layer could act as a skeleton of the cake layer structure, so their spatial distribution within the layer interior played a critical role in cake layer microstructure improvement, ultrafiltration efficiency enhancement and membrane fouling mitigation. In other words, the extent of steric-hindrance effects by ballasted floc aggregates should be emphasized in the formation of cake layer.

The role of intermolecular interactions on monoclonal antibody filtration through virus removal membranes.

The removal of viruses by filtration is a critical unit operation to ensure the overall safety of monoclonal antibody (mAb) products. Many mAbs show very low filtrate flux during virus removal filtration, although there are still significant uncertainties regarding both the mechanisms and antibody properties that determine the filtration behavior. Experiments were performed with three highly purified mAbs through 3 different commercial virus filters (Viresolve ® Pro, Viresolve® NFP, and Pegasus™ SV4) with different pore structures and chemistries. The flux decline observed during mAb filtration was largely reversible, even under conditions where the filtrate flux with the mAb was more than 100-fold smaller than the corresponding buffer flux. The extent of flux decline was highly correlated with the hydrodynamic diameter of the mAb as determined by dynamic light scattering. The mAb with the lowest filtrate flux for all 3 membranes showed the largest attractive intermolecular interactions and the greatest hydrophobicity, with the latter determined by binding to a butyl resin in an analytical hydrophobic interaction chromatography column. These results strongly suggest that the flux behavior is dominated by reversible self-association of the mAbs, providing important insights into the design of more effective virus filtration processes and in the early identification of problematic mAbs / solution conditions. This article is protected by copyright. All rights reserved.