Humic Acid Fouling Research Articles

Molecular-level understanding of membrane fouling formation during ultrafiltration of high-saline organic wastewater: Insights from molecular dynamics simulations

Membrane technology has been prevalently employed to treat high-saline organic wastewater, yet the ongoing hurdle of membrane fouling impedes the advancement and widespread implementation of membrane processes. To date, limited works had been devoted to comprehending the mechanisms of fouling development influenced by high salinity, particularly from the perspective of intermolecular interactions at a deeper level. This work filled the knowledge gap by deciphering the mechanisms underlying humic acid (HA) fouling formation under high salinity mainly using molecular dynamics (MD) simulations, which overcome the spatial scale limitation of traditional experiments and provide new mechanistic insights from the molecular level. The MD results demonstrated that Na+ primarily coordinated and bonded with the carboxyl oxygen and hydroxyl oxygen of HA through Na–O bonds, which reduced the surface charge of HA and solubility in water. Subsequently, HA swiftly migrated and deposited on membrane surface, with the molecular configuration dramatically changed from coiled state to elongated state observed under high salinity. Compared to the scenario without salt, the distribution of HA was found to be more concentrated and closer to the membrane surface, and the position of the lowest free energy decreased significantly from 0.88 nm to 0.5 nm, reflective of complete adsorption occurred. The results of real fouling experiments verified the enhanced fouling formation indeed occurred induced by high salinity, where notable NaCl crystallization appeared on the fouling layer, potentially heightening the porosity and roughness of fouling layer. This work proposed the in-depth HA fouling mechanisms under high-saline conditions from the intermolecular interaction perspective, which should offer theoretical guidance for fouling control when treating high-saline organic wastewater using membrane-based techniques.

In situ polymerization of a poly(3,4-ethylenedioxythiophene):poly(sodium–styrennesulfonate) conductive layer for electro-assisted ultrafiltration and fouling mitigation

Electrification can enhance the antifouling performance of ultrafiltration membranes and improve the sustainability of membrane technologies. The design of high-performance conductive membrane materials remains one of the core technologies in electro-assisted ultrafiltration. Here, conductive PVDF/PEDOT:PSS composite membranes were prepared via in situ chemical oxidation polymerization on a PVDF surface. The PVDF/PEDOT:PSS membranes were subsequently used for electro-filtration to study the effect of the applied potential on humic acid fouling. When a voltage of 3 V was applied, the PVDF/PEDOT:PSS20 membrane was continuously polluted for 5 cycles. The results showed that after simple hydraulic cleaning, the membrane flux recovery rate reached 91 %. Compared with that of the PVDF membrane, the irreversible fouling of the PVDF/PEDOT:PSS20 membrane decreased by 65 %. The modified Poisson Boltzmann equation indicates that applying cathodic potential on the surface of PEDOT:PSS conductive layer increases the cumulative concentration of counter ions on the membrane surface and the thickness of the charged layer, thereby promoting the migration of peak forces on the membrane surface to the bulk solution, changing the fouling behaviour of HA from cake filtration to standard blocking.

Crossflow-induced membrane vibration and its effects on fouling and scaling in direct contact membrane distillation

Membrane distillation (MD) is driven by vapor pressures rather than hydraulic pressures. Consequently, certain regions of the membrane may be in an unrestrained state, which potentially lead to membrane vibrations due to the turbulence caused by crossflow. However, this crossflow-induced membrane vibration has been largely overlooked in the previous studies. Here, we made the first attempt to investigate the crossflow-induced membrane vibration through the observation using optical coherence tomography (OCT), and explore the effect of this vibration on membrane fouling and scaling. The experimental results revealed that the vibration exhibited a self-excited vibration mode, with amplitudes reaching tens of micrometers. Moreover, the amplitude could be readily adjusted through changing crossflow velocity, transmembrane pressure, and the mesh size of spacer. For humic acid (HA) fouling, the membrane vibration could effectively reduce the thickness of HA cake layer, thereby stabilizing the specific flux at a constant level of 0.85, in contrast to the continuous decline of the flux under non-vibration condition. For gypsum scaling, the membrane vibration allowed the MD under low crossflow velocity (5 cm/s) to achieve comparable scaling occurrence concentration and scaling layer thickness as those under high crossflow velocity (10 cm/s). Our findings emphasized the potential of crossflow-induced membrane vibration as an effective strategy to mitigate membrane fouling and scaling in MD and other non-pressure driven membrane systems.

Impact of nanoplastics on membrane scaling and fouling in reverse osmosis desalination process

Nanoplastics (NPs) are a prevalent type of emerging pollutant in marine environment. However, their fouling behavior and impact on reverse osmosis (RO) membrane performance remain unexplored. We investigated the relationship between polystyrene (PS), one of the most abundant NPs, with silica scaling and humic acid (HA) fouling in RO. The results demonstrated that the surface potential of NPs played an important role in the combined scaling and fouling process. Compared with the negatively charged NPs (original PS and carboxyl group modified PS, PS−COOH), the amino-functionalized PS (PS−NH2) with positive surface charge significantly accelerated membrane scaling/fouling and induced a synergistic water flux decline, due to the strong electrostatic attraction between PS−NH2, foulants, and the membrane surface. The amino groups acted as binding sites, which promoted the heterogeneous nucleation of silica and adsorption of HA, then formed stable composite pollutants. Thermodynamic analysis via isothermal titration calorimetry (ITC) further confirmed the spontaneous formation of stable complexes between PS−NH2 and silicates/HA. Our study provides new insights into the combined NPs fouling with other scalants or foulants, and offers guidance for the accurate prediction of RO performance in the presence of NPs.

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.

Enhancing membrane separation performance in the conditions of different water electrical conductivity and fouling types via surface grafting modification of a nanofiltration membrane, NF90

A commercialized and widely applied nanofiltration membrane, NF90, was in-situ modified through a surface grafting modification method by using 3-sulfopropyl methacrylate potassium salt and initiators. The effects of water electrical conductivity (EC) and fouling types on membrane separation efficiency were examined before and after membrane modification. Results reveal that both the pristine membrane (PTM) and surface grafting modification membrane (SGMM) had a declining permeate flux and salt (NaCl) removal efficiency but an increasing trend of pharmaceuticals and personal care products (PPCPs) removal with increasing water EC from 250 to 10,000 μs cm−1. However, SGMM exhibited a slightly declining permeate flux but 13%–17% and 1%–42% higher rejection of salt and PPCPs, respectively, compared with PTM, due to electrostatic repulsion and size exclusion provided by the grafted polymer. After sodium alginate (SA) and humic acid (HA) fouling, SGMM had 17%–26% and 16%–32% higher salt rejection and 1%–12% and 1%–51% greater PPCP removal, respectively, compared with PTM due to the additional steric barrier layer contributed by the foulants. The successful grafting and increasing hydrophilicity of the SGMM were confirmed by contact angle analysis, which was beneficial for mitigating membrane fouling. Overall, the proposed in-situ surface grafting modification of NF90 can considerably mitigate organic and biological fouling while raising the rejection of salt and PPCPs at different background water EC, which is beneficial for practical applications in producing clean and high quality water for consumers.

Impacts of Calcium Addition on Humic Acid Fouling and the Related Mechanism in Ultrafiltration Process for Water Treatment.

Humic acid (HA) is a major natural organic pollutant widely coexisting with calcium ions (Ca2+) in natural water and wastewater bodies, and the coagulation-ultrafiltration process is the most typical solution for surface water treatment. However, little is known about the influences of Ca2+ on HA fouling in the ultrafiltration process. This study explored the roles of Ca2+ addition in HA fouling and the potential of Ca2+ addition for fouling mitigation in the coagulation-ultrafiltration process. It was found that the filtration flux of HA solution rose when Ca2+ concentration increased from 0 to 5.0 mM, corresponding to the reduction of the hydraulic filtration resistance. However, the proportion and contribution of each resistance component in the total hydraulic filtration resistance have different variation trends with Ca2+ concentration. An increase in Ca2+ addition (0 to 5.0 mM) weakened the role of internal blocking resistance (9.02% to 4.81%) and concentration polarization resistance (50.73% to 32.17%) in the total hydraulic resistance but enhanced membrane surface deposit resistance (33.93% to 44.32%). A series of characterizations and thermodynamic analyses consistently suggest that the enlarged particle size caused by the Ca2+ bridging effect was the main reason for the decreased filtration resistance of the HA solution. This work revealed the impacts of Ca2+ on HA fouling and demonstrated the feasibility to mitigate fouling by adding Ca2+ in the ultrafiltration process to treat HA pollutants.

Synergistic effects of microplastics and organic foulants on the performance of forward osmosis membranes

Microplastics (MPs) are emerging contaminants that are abundantly present in the influent and effluent of wastewater treatment plants (WWTPs). Forward osmosis (FO) is an advanced treatment technology with potential applications in WWTPs. The presence of MPs in WWTP effluents can contribute to FO fouling and performance deterioration. This study focuses on FO membrane fouling by MPs of different sizes, and the interactional impacts of MPs and Humic acid (HA) (as the most common organic foulant in WWTPs) on FO membrane performance. The synergistic effect of combined MPs and HA fouling is shown to cause higher flux decline for FO membranes than that of HA or MPs alone. Reverse salt flux increased in the presence of MPs, and decreased when HA was present. Further, full flux recovery was obtained for all fouled membranes after hydraulic cleaning. This indicates the efficiency of FO systems for treating wastewater with high fouling potential. This study highlights the necessity of considering MPs in studying fouling behaviour, and for mitigation strategies of membranes used in WWT. The fundamentals created here can be further extended to other membrane-assisted separation processes.

Preparation of a fouling-resistant Teflon/PVDF composite membrane and its application to treat nanofiltration brine from landfill leachates

Landfill leachates (LFLs) pose a severe environmental threat given their high strength and the slow degradation nature of their organic and inorganic pollutants constituents. Hence, they are challenging to treat by conventional wastewater treatment methods. Although membrane distillation (MD) is promising for wastewater treatment, membrane wetting and scaling that lead to membrane fouling are the bottlenecks in applying this technology to LFLs. In this work, a commercial Teflon emulsion was used to modify the PVDF membrane via a simple dip-coating method, followed by depositing the PTFE particles onto the membrane surface via thermal curing crosslinking reaction. Hence, a Teflon/PVDF composite membrane was successfully prepared with resistance to sodium dodecyl sulfate wetting, CaSO4 scaling, and humic acid fouling. Effects of the Teflon emulsion concentration and dipping time on the composite membrane's chemical composition, surface characteristics, porosity, mechanical properties, liquid entry pressure (LEPW), and direct contact membrane distillation (DCMD) performance were systematically investigated. The results showed that Teflon emulsion modification could improve the membrane surface's hydrophobicity, reduce pore size, and increase mechanical strength. The Teflon/PVDF composite membrane with 100% Teflon emulsion and 10 min dipping time exhibited the highest hydrophobicity and 144.3º water contact angle. The M100-10 membrane also exhibited stable performance for treating nanofiltration (NF) brine collected from the LFL. When concentrating the NF brine, the M100-10 membrane achieved only a 7.1% flux decay rate. Hence, the Teflon/PVDF composite membrane demonstrated excellent wetting, scaling, and fouling resistance. This dip-coating method is simple, low cost, easy to scale up, and has potential in the large-scale production of hydrophobic porous membranes.

Designing of amino silica covalently functionalized carboxylic multi-wall carbon nanotubes-based polyethersulfone membranes for enhancing oily wastewater treatment

The accumulation of oily wastewater is a critical issue that can cause environmental pollution. Membrane technology can play a vital role in the treatment of oily wastewater due to its productivity and economical cost. In this work, the amino silica covalently functionalized carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) nanohybrid was synthesized and blended with polyethersulfone (PES) membranes for oil/water separation to enhance the antifouling property. Membranes were fabricated with various loadings of SiO2-f-MWCNTs nanohybrid (0–2 wt%) using phase inversion technique. The incorporation of nanohybrid resulted in the enhancement of wettability and pore size distribution of nanocomposite membranes. The morphological structure, surface and chemical features of the synthesized membranes were examined using scanning electron microscopy, Fourier transform infrared spectroscopy, water contact angle and X-ray diffraction analyses. Furthermore, the impact of nanohybrid blending with PES membrane on water permeability and oil rejection was investigated. The water permeability enhanced from 188 ± 8 L/m2.h.bar, for the pristine PES membrane, to 293 ± 9 L/m2.h.bar for nanocomposite membrane blended with 2 % SiO2-f-MWCNTs nanohybrid. Similarly, the oil rejection was improved up to 97 ± 0.1 % using the same nanohybrid loading. The results revealed that using 2 % nanohybrid loading has increased the humic acid (HA) flux by 16 %, while the irreversible HA fouling was significantly reduced to 0.9 % compared to 9.9 % for the pristine PES.

In-situ radical graft modification of NF270 to improve membrane separation: Effects of water salinity and fouling types

This study used the concentration–polarization method to perform the radical-graft-modification of a commercial NF membrane (NF270) for enhancing membrane separation performance and mitigating membrane fouling. Influencing factors including different background water salinity and fouling types were systematically evaluated using humic acid (HA) and sodium alginate (SA) for simulating organic and biological fouling, respectively. Increasing water salinity caused decreasing permeate flux as well as the rejection of salt and pharmaceuticals and personal care products (PPCPs) of the pristine and grafted membranes, especially at high electrical conductivity (EC) = 10,000 μs cm−1. In comparison with the clean pristine membrane, the grafted membrane exhibited 19%–26% higher NaCl rejection and 3%–48% higher PPCP rejection, and remained relatively stable permeate flux, especially at low and medium EC (500–5,000 μs cm−1). Compared with the fouled pristine membranes, the fouled grafted membranes at EC=250–10,000 μs cm−1 exhibited 1%–30% and 1%–12% higher PPCP rejection with HA and SA fouling, respectively, especially for TRI and CBZ with high hydrophobicity. The grafted layer displayed a synergistic effect on membrane separation by adding an additional barrier along with enhancing the electrostatic repulsion between the solutes and membrane surface. The mitigation of HA and SA fouling was confirmed using scanning electron microscopy with fewer deposits and smoother surface on the grafted membrane surface. In sum, the results evidenced successful achievement and application of the in-situ radical graft modification technology to improve salt and PPCP rejection as well as mitigate organic and biological fouling with different water salinity.

In Situ Chemical Modification with Zwitterionic Copolymers of Nanofiltration Membranes: Cure for the Trade-Off between Filtration and Antifouling Performance.

Breaking the trade-off between filtration performance and antifouling property is critical to enabling a thin-film nanocomposite (TFC) nanofiltration (NF) membrane for a wide range of feed streams. We proposed a novel design route for TFC NF membranes by grafting well-defined zwitterionic copolymers of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) and 2-aminoethyl methacrylate hydrochloride (AEMA) on the polyamide surfaces via an in situ surface chemical modification process. The successful grafting of a zwitterionic copolymer imparted the modified NF membranes with better surface hydrophilicity, a larger actual surface area (i.e., nodular structures), and a thinner polyamide layer. As a result, the water permeability of the modified membrane (i.e., TFC-10) was triple that of the pristine TFC membrane while maintaining high Na2SO4 rejection. We further demonstrated that the TFC-10 membrane possessed exceptional antifouling properties in both static adsorption tests and three cycles of dynamic protein and humic acid fouling tests. To recap, this work provides valuable insights and strategies for the fabrication of TFC NF membranes with simultaneously enhanced filtration performance and antifouling property.

Membrane capacitive deionization model including fouling indexes obtained via real-time fouling layer measurements

For the application of Membrane capacitive deionization (MCDI), it is essential to investigate how MCDI performance deteriorates owing to natural organic matter (NOM) fouling during operation. However, the difficulty in obtaining real-time fouling layer information has hindered this understanding. Herein, we investigated the effect of fouling with a model using humic acid (HA) as NOM with two background electrolytes (NaCl and CaCl2) in different ratios. To quantify the effect of the fouling, fouling thickness was monitored in real-time through optical coherence tomography. We found that feed water containing more Ca2+ quickly formed more neutrally charged complexes with HA, which increased the rate of fouling thickness and significantly decreased the salt removal rate. The reduction in salt adsorption capacity exhibited high correlation with the observed fouling thickness (≥0.89). Using the experimental values of fouling thickness and newly added parameters that specifically considered fouling, the MCDI transport model was revised to simulate the effluent salt concentration under HA fouling conditions. The modified model showed superior prediction performance than the original model: R2 improved from 0.728 to 0.977 when the ratio of Na+ to Ca2+ was 3:7. Therefore, the developed MCDI transport model will pave the way for the practical application of MCDI.

Reduction and Elimination of Humic Acid Fouling in Air Sparged Membrane Distillation Using Nanocarbon Immobilized Membrane.

In this paper, we present the treatment of humic acid solution via carbon nanotube immobilized membrane (CNIM) distillation assisted by air sparging (AS). Carbon nanotubes offer excellent hydrophobicity to the modified membrane surface and actively transport water vapor molecules through the membrane to generate higher vapor flux and better rejection of humic acid. The introduction of air sparging in the membrane distillation (MD) system has changed the humic substance fouling by changing the colloidal behavior of the deposits. This modified MD system can sustain a higher run time of separation and has enhanced the evaporation efficiency by 20% more than the regular membrane distillation. The air sparging has reduced the deposition by 30% in weight and offered lesser fouling of membrane surface even after a longer operating cycle. The water vapor flux increased with temperature and decreased as the volumetric concentrating factor (VCF) increased. The mass transfer coefficient was found to be the highest for the air sparged—carbon nanotube immobilized membrane (AS-CNIM) integrated membrane distillation. While the highest change in mass transfer coefficient (MTC) was found for polytetrafluoroethylene (PTFE) membrane with air sparging at 70 °C.

Characterization of humic substances isolated from a tropical zone and their role in membrane fouling

Humic substances (HS) are heterogeneous organic polymers that show monotonous properties. HS are present at different proportions in the terrestrial environment, and they implicate the performance of water desalination plants. Recently electrodialysis self-reversal (EDR) technology has been used to treat excess salinity, hardness and fluoride in HS rich groundwater in Sri Lanka (~3 mg L−1, dissolved C). Due to the high organic content of HS in groundwater, the EDR ion exchange membranes are prone to fouling. To unravel the fouling mechanisms, humic acid (HA) and fulvic acid (FA) fractions were isolated and fractionated from the groundwater and characterized spectroscopically. All membrane fouling experiments were conducted for HA and FA contaminated water using a lab-scale EDR setup operated under batch mode. Sequential desorption experiments were carried out using distilled water, 2% (w/w) NaCl, and 0.3% (w/w) sodium dodecyl sulfate to probe variations among two fouling mechanisms. Similarities were found in aromatic and aliphatic carbon contents, humification degree, and molecular weight of humic substances. Higher proportions of carboxylic and phenolic groups were found in FA compared to HA. Ester groups in HA facilitate P, S, and Si migration within organic moieties. The molecular environs in the vicinity of carboxyl functional groups led different fouling mechanisms. HA fouling was found irreversible compared to FA fouling. The subtle differences between fouling mechanisms will help implement appropriate pretreatments to ensure the durability of EDR membranes.

Modification of polyetersulfone (PES) membrane by using jernang (daemonorops draco blume) as a natural additive on humic acid fouling

This paper reports on the effect of adding Jernang additives on the performance of PES membranes. The membrane was made by mixing PES 16.5%, Jernang 1%, and NMP 82.5%, using the Non-solvent Induced Phase Separation (NIPS) method. The chemical group of Jernang has been studied in this paper. The addition of Jernang additives has succeeded in improving the performance of PES membranes. Pure water flux increases to 18.77 LMH from the initial flux of 1.66 LMH. Humic acid removal showed reasonable results up to 77.52%. Moreover, this membrane has good antifouling properties, but less stable under strong acid and alkaline solution.

Colloidal fouling in electrodialysis: A neural differential equations model

The attachment of colloids to the ion-exchange membranes in electrodialysis is an important hurdle when processing bio-based process streams. Previous research showed that fouling strongly depends on the crossflow velocity, the current and the salt concentration of the medium. Predicting the influence of these variables on the fouling rate is challenging due to the complex physics at play and optimising the process conditions to reduce fouling remains a challenge. The objective of this study is the development of a model to predict the dynamic behaviour of electrodialysis fouling under varying process settings to facilitate this optimisation. A neural differential equation is fit to experimental data of an electrodialysis pilot undergoing humic acid fouling. We show that this model can predict the fouling rate even when using a limited set of experimental data. The robustness of the model is demonstrated by a simulation study and a sensitivity analysis indicates that the crossflow velocity is the most important variable influencing the fouling rate (≈40%). Both the effect of the current (≈20%), the salt concentration (≈13%) and their interaction effects are considerable. With the model, the evolution of the stack resistance as a result of membrane fouling can be simulated, facilitating process control or decision-making.

Application of sodium percarbonate activated with Fe(II) for mitigating ultrafiltration membrane fouling by natural organic matter in drinking water treatment

It remains challenging to efficiently mitigate membrane fouling caused by natural organic matter (NOM) for the widespread application of ultrafiltration process. In this study, sodium percarbonate activated with Fe(II) (Fe(II)/SPC) was proposed as a feedwater pretreatment strategy for membrane fouling control. Typical NOM fractions, i.e., humic acid (HA), bovine serum albumin (BSA) were employed as membrane foulants, as well as natural surface water. The results showed that Fe(II)/SPC pretreatment apparently alleviated membrane fouling by BSA and HA-BSA, and the performance outperformed Fe(II) pre-coagulation and SPC pre-oxidation alone. Considering HA fouling, more severe flux decline and increased reversible fouling resistance were obtained, while irreversible fouling was slightly mitigated. The filtration of HA-BSA was well fitted to intermediate blocking followed by cake filtration, and Fe(II)/SPC noticeably increased the filtration volume corresponding to the formation of cake filtration. With Fe(II)/SPC pretreatment, a sparser and more homogeneous foulant layer with lower resistances was observed on membrane surface, and Fourier transform infrared spectroscopy indicated that the peak intensities of major functional groups for organic pollutants were significantly decreased. In surface water treatment, Fe(II)/SPC could effectively improve membrane filtration behavior and pollutants removal, with a distinct decrease of both fluorescent fractions and different molecular weight organic compounds. It seemed that hydroxyl radical oxidation and coagulation with in-situ formed Fe(III) were the main mechanisms of contaminants removal and membrane fouling control. Overall, this combined process exhibited a great potential for actual application during drinking water treatment.

Toward enhancing the separation and antifouling performance of thin-film composite nanofiltration membranes: A novel carbonate-based preoccupation strategy

High-performance nanofiltration (NF) membranes with simultaneously improved antifouling and separation performance are of great significance for environmental water purification. In this work, a high-performance thin-film composite (TFC) NF membrane (TFC-Ca) was constructed through in-situ incorporation of calcium bicarbonate during interfacial reaction. The surface morphology and chemical structure of the TFC-Ca membrane were systematically investigated by FTIR, XPS, AFM, and SEM. The results indicated that the surface characteristics of the pristine NF membrane were greatly changed by the incorporation of calcium bicarbonate. The TFC-Ca membrane exhibited improved hydrophilicity, narrowed pore size, declined negative charge, and increased surface area. Compared to the control membrane, the TFC-Ca membrane possessed a much greater water permeability and higher molecule rejections. For the TFC-Ca membrane, an optimized water permeance of 13.4 ± 0.3 L m−2 h−1 bar−1 with 99.9% Na2SO4 rejection was obtained. Impressively, the TFC-Ca membrane exhibited excellent antifouling performance during 5 cycles of humic acid fouling tests. A satisfactory flux recovery up to 90.0% was achieved after physical cleaning for the optimized membrane. Furthermore, the TFC-Ca membrane also presented superior performance stability when treated with strong acid and chelating agents for 7 days. Overall, this facile preoccupation strategy via in-situ incorporation of calcium bicarbonate allows the fabrication of high-performance TFC membranes with outstanding separation and antifouling properties.

Characteristics of organic fouling, reversibility by physical cleaning and concentrates in forward osmosis membrane processes for wastewater reclamation.

Numerous advantages of forward osmosis (FO) include operation at low or no hydraulic pressure, high rejection of a wide range of contaminants, and low irreversible fouling. The FO has been investigated to reduce effluent discharge in wastewater reclamation. The application of wastewater effluent as a feed stream to FO yields fouling on the active layer of the FO membrane. Fouling was examined using two compounds (i.e., alginate and humic acid) with distinguished hydrophobic properties. The repeated filtration and surface wash were applied and flux decline and reversibility of physical cleaning were evaluated. In addition, the characteristics of fouling cakes and concentrates were also analyzed. The foulants showed different behaviors in flux decline. The thick cake layer of alginate was obvious and the cake enhanced concentration polarization was also observed. The recovery results along with the FTIR spectra and FE-SEM images proved that the surface cleaning was not effective to detach foulants, especially for alginate fouling. The osmotic backwash showed greater flux recovery for alginate fouling than humic acid fouling, which indicated that restoring membrane pores or disturbing cake layers by osmotic backwash might be successful for the foulants for strong interactions between foulants and foulants. The concentrates were mostly composed of humic substances and low-molecular weight neutrals. The differences in the relative portions of the major components were occurred in the concentrates implying that the organic properties of the feed water and also interactions of foulants and membranes should be evaluated prior to determination of disposal options for concentrates.