Flux Decline Research Articles

Mathematical modeling of the enzymatic hydrolysis of lignocellulosic waste in membrane bioreactor considering transport phenomena

Enzymatic hydrolysis is a crucial step in processing lignocellulosic biomass into biofuels and other valuable products in biorefineries. Applying a membrane reactor to realize this process allows for continuous separation of inhibitory end-products, thus improving process efficiency. Developed so far models have generally been dedicated to describing the reaction kinetics without considering transport phenomena and flux decline prediction. In the present paper, a new mathematical model simulating the hydrolysis process course in membrane bioreactor was established. Compared to previous reports, our study presents a novel approach to modeling the process accounting for the reaction course and permeate flux decline depending on reaction hydrodynamics. A surface renewal theory and empirical reaction kinetic model were implemented to simulate the influences of the operating parameters on the permeate flux and the monosaccharide concentration in the permeate. A procedure to determine the model parameters with experimental data was also presented. The proposed model simulated experimental data with good accuracy (R2>0.97). The total mass of glucose and xylose produced during 10 h of the hydrolysis performed under mixing conditions equaled 2.37 g and 2.39 g for the pressure of 0.4 and 0.6 bar, respectively. They correspond to the high hydrolysis yield, equaled in average to 99.1 %.

Preparation of antifouling reverse osmosis membrane with polyacrylic acid brushes based on polydopamine coating assisted atom transfer radical polymerization

An antifouling polyamide (PA) reverse osmosis (RO) membrane was fabricated in this work by incorporating polyacrylic acid (PAA) brushes onto the membrane surface via polydopamine (PDA)-assisted atom transfer radical polymerization (ATRP). Specifically, a PDA intermediate layer containing the initiator 2-bromoisobutyryl bromide (BIBB) for polymerization was coated on original membrane surface. Then, acrylic acid (AA) was controllably incorporated on the membrane surface in the form of PAA brushes by regulating ATRP reaction time. The PDA-assisted polymerization was mild to the separation layer, and BIBB could be immobilized on the membrane surface with even distribution and controllable density. It was demonstrated that the water contact angle and surface roughness of the RO membranes with PAA brushes was reduced, while the negative charge and hydrophilicity were increased. Simultaneously, the water flux of the membrane was enhanced by 27.8% and the NaCl rejection was maintained compared with that of virgin membrane. Moreover, the modified membrane presented a higher flux recovery ratio and a lower flux decline ratio when lysozyme, bovine serum albumin, humic acid, and sodium alginate were used as model foulants. Besides, the membrane exhibited a satisfactory long-term performance stability. Our work provides a gentle and controllable strategy for the fabrication of antifouling RO membranes with enhanced water permeability and maintained salt rejection, which is crucial for increasing the efficiency of RO processes.

Molecular weight insight into critical component contributing to reverse osmosis membrane fouling in wastewater reclamation

Molecular weight (MW) of organics was one of the important factors influencing membrane fouling propensity. This study identified critical foulants of reverse osmosis (RO) membranes in reclaimed water by MW fractionation. MW > 10 kDa component was identified as the critical fouling contributor (CFC) in secondary effluent (SE), which accounted for only 13 ± 5% of dissolved organic carbon (DOC) but contributed to 86 ± 11% of flux decline. Throughout 12-month monitoring, SE and MW > 10 kDa component showed a similar fouling variation tendency: apparently higher fouling potential in winter and lower in summer, while MW < 10 kDa component presented minor fouling changes. Morphology of membrane fouled by CFC characterized a smooth and thick foulant layer on membrane surface. CFC was mainly composed of proteins and polysaccharides, and a protein-polysaccharide-protein “sandwich” fouling layer structure was preferentially formed on membrane surface. extended Derjaguin–Landau-Verwey–Overbeek (xDLVO) analysis demonstrated that strong attractive interactions between CFC and membrane surface dominated the fouling process. Furthermore, computational fluid dynamics (CFD) simulation revealed strong filtration resistance of CFC, confirming its significant fouling potential. Dual effects including attractive interactions and advantageous ridge-and-valley surface appearance accounted for the significant fouling propensity of MW > 10 kDa component and glean valuable insights into RO fouling mechanisms of reclaimed water in practical application.

Influence of Iron and Magnesium on Fouling Properties of Organic Matter Solution in Membrane Process.

Organic matter has been identified as a significant type of foulant in membrane processes for water treatment. Its fouling tendency is highly affected by the presence of ions and inorganics. While the effects of ions addition on organic fouling have been extensively researched in the past, studies on the effect of positively-charged inorganics, such as Fe2+ and Mg2+, on organic fouling are limited. This study investigates the influence of Fe2+ and Mg2+ addition on fouling properties of the Suwannee River Organic Matter (SROM) solution in the MF process, with and without Ca2+ ions. Results showed that increasing the concentration of Fe2+ and Mg2+ from 0-5 mM promoted SROM fouling, and resulted in an increased flux decline up to 33% and 58%, respectively. Cake layer resistance became more dominant with the addition of Fe2+ and Mg2+, and was counted for more than 60% of the fouling. Mg2+, however, caused higher internal pore blocking, and facilitated the formation of a less permeable cake layer, compared to Fe2+. This was evident in the analysis of the cake layer properties and the visualization of the fouling layer. In all cases, SROM fouling with Fe2+ and Mg2+ worsened with the addition of Ca2+ ions. The results of the study indicated the importance of understanding the interaction between organic matter and Fe2+ and Mg2+, which would provide useful insights on their fouling mechanism and control.

Integration of CaO2/Fe2+ and ultrafiltration acts as multiple-workfunctions pretreatment for seawater desalination during harmful algal blooms

This study employed calcium peroxide/ferrous iron (CaO2/Fe2+) as an innovative pretreatment strategy for seawater reverse osmosis (SWRO) operation during harmful algae blooms (HABs). CaO2/Fe2+ showed improved coagulation performance compared to conventional coagulation (Fe3+ coagulant). The dynamic dominance of foulants between micro-particles and algal organic matters (AOMs), due to the different dosages of CaO2/Fe2+, was found to be crucial in reducing ultrafiltration (UF) fouling. As a result, the optimal dosage of 0.05 mM/0.1 mM of CaO2/Fe2+ achieved a higher reduction of 71.6 % of modified fouling index (MFI) compared to conventional coagulation (38.1 % via 0.1 mM Fe3+). Specifically, CaO2/Fe2+ demonstrated a greater capacity to remove micro-particles across size ranges of 1–5 μm and various AOMs (i.e., biopolymer and humics) in algae-laden seawater compared to conventional coagulation. This resulted in reduced flux decline and less accumulation of algal cells, proteinaceous substances and humics on membrane surfaces, which were validated through Optical-Photothermal Infrared Spectromicroscopy (O-PTIR) with sub-micron resolution. Additionally, CaO2/Fe2+ reduced dissolved Fe3+ in UF permeate, and generated combined chlorine simultaneously with disinfection effects on marine algae (evidenced by O-PTIR and Raman spectroscopy). Thus, it would reduce fouling of subsequent SWRO membranes. Overall, CaO2/Fe2+ presents a multiple-workfunctions pretreatment method for HAB mitigation in seawater desalination plants.

Development of zwitterion-functionalized graphene oxide/polyethersulfone nanocomposite membrane and fouling evaluation using solutes of varying charges

Abstract This study explores the functionalization of polyethersulfone (PES) ultrafiltration (UF) membranes using zwitterion-functionalized graphene oxide (GO) and assesses their interactions with solutes of different charges, both neutral and anionic. Initially, PES nanocomposite membranes were synthesized, incorporating varying dosages (ranging from 0-1 % (w/w)) of glycine-functionalized graphene oxide (Gly/GO) and diglycine-functionalized graphene oxide (diGly/GO) through a direct blending method. The physicochemical properties, including hydrophilicity, surface morphology, and porosity of these membranes were characterized using sessile-drop contact angle, tabletop scanning electron microscopy (SEM), and gravimetric methods, respectively. Subsequently, the antifouling performance of these synthesized membranes was assessed by exposing them to a solution containing sucrose as a neutral model foulant and humic acid as an anionic foulant. The incorporation of zwitterion-functionalized graphene oxide nanoparticles improved the surface wettability of the nanocomposite membrane, enhancing its resistance to sucrose fouling. This was supported by a reduction in flux declination ratio (e.g., 40.6 % for pristine PES, 29.7 % for 1.0 % (w/w) Gly/GO PES, and 33.1 % for 1.0 % (w/w) diGly/GO PES) and an increase in flux recovery ratio (67.2 % for pristine PES, 79.7 % for 1.0 % (w/w) Gly/GO PES, and 80.0% for 1.0 % (w/w) diGly/GO PES). The improvement in antifouling characteristics is attributed to the formation of a hydration layer on the membrane surface, which inhibits sucrose deposition. However, zwitterion-functionalized PES nanocomposite membranes displayed a higher affinity for anionic humic acid, resulting in a substantial flux decline and a lower flux recovery ratio. Overall, this research provides insights into the roles of surface wettability and the charge interactions between solutes and the membrane surface, both of which are crucial factors in determining fouling severity and the restorability of spent membranes.

Performance of Chitosan/Carbon Nanotube-Coated Ultrafiltration Membranes for Natural Organic Matter Removal from Drinking Water

The objective of this study is to improve the filtration efficiency of commercially available polyethersulfone (PES) ultrafiltration (UF) membranes, with a specific focus on removing natural organic matter (NOM) and preventing membrane fouling. The modification of UF membranes was accomplished by utilizing chitosan/multi-walled carbon nanotubes (CS/MWCNT-OH) and employing both dip and spin coating techniques. The membrane surface morphologies were evaluated using the Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Energy-Dispersive X-ray Spectroscopy (EDX) techniques. Tests were carried out to assess the effectiveness of the membranes in a laboratory-scale system using two primary water sources from Istanbul, specifically the Melen River and Terkos Lake. Total organic carbon (TOC), UV254 absorbance, turbidity, and trihalomethane formation potential (THMFP) were all measured as part of a thorough analysis. The surface morphology investigations verified the effective deposition of MWCNT-OH nanoparticles onto the membrane surface. This was corroborated by the reduction in the water contact angle, showing an improvement in the hydrophilicity of the membrane. The modified membranes demonstrated much higher TOC removal rates compared to the original membranes. Specifically, the removal efficiencies for Melen River and Terkos Lake were 37.14% and 56.86%, respectively. Nevertheless, the alteration of the surface led to a decline in membrane flux as a result of the concurrent drop in pore size. To summarize, the results of this work highlights the considerable capability of surface modification using CS/MWCNT-OH to improve the performance and antifouling characteristics of commercial PES UF membranes.

Preparation of polysulfone-based nanofiber Janus membrane for membrane distillation containing organic pollutants

Membrane distillation is an emerging wastewater treatment technology that harnesses low-grade heat as an energy source and exhibits potential for complete desalination. Nonetheless, two notable challenges hinder the practical application of this technology: membrane wetting and fouling. To counter these challenges, an innovative anti-fouling Janus membrane with asymmetric wettability was developed through electrospinning. The hydrophobic layer was formed using tetraethyl orthosilicate/polysulfone (PSF), and the superhydrophilic layer was created using polyvinylpyrrolidone (PVP)/PSF. A sensitive adhesion probe was used to assess the anti-fouling performance of the Janus membrane against oil. Molecular dynamics simulation suggested that PVP reduced the adsorption tendency of the membrane for humic acid (HA). Under experimental conditions involving saline water with HA and a saline oil–water emulsion, the non-Janus membrane suffered severe fouling, resulting in rapid water permeate flux decline. However, the Janus membrane demonstrated consistent permeate flux (26.84 LMH and 24.92 LMH) and an impressive salt rejection rate (> 99.99%). This study suggests that the Janus membrane, with its high permeate fluxes and remarkable resistance to fouling and wetting, could be an effective solution for wastewater treatment, with considerable potential for future application.

Pectin recovery from apple pomace by forward osmosis – Assisted technology

This study evaluates the performance of forward osmosis (FO) to concentrate and dewater apple pomace extract for subsequent pectin recovery. After pretreatment by sieve filtration and centrifugation, the FO water flux during real apple pomace extract concentration was 7.8 L m−2·h−1 and was comparable to the FO process for a one-component model pectin solution. However, due to fouling, at 75% water recovery, up to 70% flux decline was observed. Osmotic backwashing using a spent draw solution as the osmotic agent was effective and could completely restore the water flux (ca. 100% flux recovery) after multiple filtration cycles. A comprehensive techno-economic assessment was also conducted to demonstrate significant reduction in capital investment and operating cost when applying FO for concentrating apple pomace extract prior to pectin recovery. The investment payback period was shortened from over 5 to 2 years, at 80% water recovery. Results in this study highlight the utility of FO to replace the traditional evaporation method for enhance the economic viability and environmental friendliness of pectin recovery.

Combinational strategy of chemical graft and layer-by-layer assembly of novel nanocomposite membranes fabrication for heavy metal ion capture

Heavy metal ions (HMI), a non-degradable toxic substance, has raised widespread concerns in water purification. Membrane separation is a considerable and promising technology for removing HMIs from water, due to its environmentally friendly, clean and highly effective. This study reported a functional composite ultrafiltration membrane prepared from natural biomolecules ε-Poly-L-lysine hydrochloride (PLL), sodium lingo sulfonate (SLS) or sodium alginate (SA) based on the combination strategy of chemical graft and layer-by-layer assembly. The fabricated membrane exhibited a high pure water flux (2957 L·m−2·h−1), high capture efficiency for Cu2+ (99.1 %) and Pb2+ (98.9 %). Notably, the layer-by-layer assembly strategy provides abundant groups for HMI binding, ensuring the high capture efficiency. The fabricated membrane demonstrated a low flux decline (9 %), along with a high flux recovery ratio (99.2 %). Moreover, it exhibited exceptional stability and reusability across a wide pH range (pH 5–9), meanwhile maintaining a capture efficiency of approximately 99 % under near-neutral condition after undergoing 5 cycle experiments for both Cu2+ and Pb2+. Our work builds a straightforward approach for UF membrane fabricating with excellent HMI capture capacity, displaying the potential application in HMI waste water purification.

Environmentally-friendly calcite scale mitigation: encapsulation of CDs@ MS composite within membranes framework for nanofiltration

Scale formation caused by the precipitation of sparingly soluble salts such as CaCO3 is a major challenge in membrane-based desalination technologies, leading to flux decline and increased energy costs. Surface modification using nanoscale coatings is a promising approach to mitigate membrane fouling. In this work, we demonstrate the antiscalant properties of a MoS2-carbon quantum dot (CDs@MS-NF) composite with a nanoflower-like structure coating for suppressing calcite scale formation. The CDs@ MS-NF coating was synthesized via a solvothermal method and applied to a polyamide reverse osmosis membrane surface using an in-situ growth technique. Characterization revealed uniform coverage of MoS2 nanosheets decorated with CDs@MS-NF on the membrane surface. Static fouling tests simulating calcium sulfate scaling conditions were conducted to evaluate the antifouling performance. The CDs@MS-NF coated membrane exhibited a flux reduction of only 11 %, compared to 34 % for the unmodified membrane after 24 hours. Further analyses showed a calcite nucleation induction time of 5.2 hours and a critical scaling threshold of 1.8 times the solubility for the CDs@ MS-NF coated membrane, indicating significant inhibition of scale formation. We hypothesize that the CDs@ MS-NF nanocomposite layer alters surface charge and wettability while also catalyzing redox reactions to hinder calcite crystal growth. This work demonstrates that multifunctional two-dimensional nanocomposite coatings can effectively mitigate membrane scaling through multiple synergistic mechanisms.

AFM Analysis of Polymeric Membranes Fouling

This work represents a part of a larger work, aimed at evaluating the fouling behavior of different flat polymeric membranes for low-pressure applications when placed in contact with industrial wastewater (IWW). To design and understand the operation of a membrane process it is essential to know the fouling mechanisms. Commercial PVDF and PS membranes were tested under static conditions. The reduction in membrane flux was calculated, before and after the fouling tests. Parameters such as membrane material, pore size, solids concentration, particle size, pH, temperature, flow rate, and pressure were studied to identify the fouling behavior of the membrane. The strong adhesion of organic molecules on the membrane surface develops a resistance to pore blockage which allows a significant decrease in the flow of clean water. It is important to note that membranes of the same material, PVDF, but with different pore size (0.2 and 0.5 mm), and membranes of different materials, PVDF and PS, but with the same pore size (0.2 mm) were tested to study the trend of surface fouling to predict it and/or design surface modifications of the membranes employed. A morphological analysis of the membranes was carried out to understand the fouling mechanism, the fouling times, and the nature of the block that determines the reduction of flow through the membrane itself. Roughness measurements reveal that roughness goes up to 120 minutes of immersing time in wastewater, but after 4 hours it returns to initial value but with a significant decrease of flux to water. Understanding the relationship between flux decline, morphology, and roughness role is key to preventing fouling and studying a valid method to clean the membrane.

Comparison of Coagulation-Integrated Sand Filtration and Ultrafiltration for Seawater Reverse Osmosis Pretreatment.

The removal of dissolved organic matter (DOM) from seawater before the reverse osmosis (RO) processes is crucial for alleviating organic fouling of RO membranes. However, research is still insufficiently developed in the comparison of the effectiveness of integrating coagulation with ultrafiltration (UF) or sand filtration (SF) in the pretreatment stage of seawater reverse osmosis (SWRO) for the removal of DOM. In this study, we investigated the effect of pretreatment technologies on RO fouling caused by DOM in seawater, including the integration of coagulation and sand filtration (C-S pretreatment) and the integration of coagulation and ultrafiltration (C-U pretreatment). Both integrated pretreatments achieved comparable DOM removal rates (70.2% for C-U and 69.6% for C-S), and C-S exhibited enhanced removal of UV-absorbing compounds. Although C-U was more proficient in reducing the silt density index (below 2) compared to C-S (above 3) and improved the elimination of humic acid-like organics, it left a higher proportion of tyrosine-protein-like organics, soluble microbial by-product-like organics, and finer organics in the effluent, leading to the formation of a dense cake layer on RO membrane and a higher flux decline. Therefore, suitable technologies should be selected according to specific water conditions to efficiently mitigate RO membrane fouling.

Purifying surface water contaminated with azo dyes using nanofiltration: Interactions between dyes and dissolved organic matter

In this research, the interactions of two azo dyes, Methyl Orange (MO) and Eriochrome Black T (EBT), with dissolved organic matter (DOM) in surface water were studied, emphasizing their removal using nano-filtration membranes (NF-270 and NF-90). High-Performance Size Exclusion Chromatography (HPSEC) findings indicated that the dyes' molecular weight in deionized (DI) water ranged from 500 to 15k Dalton (Da), adjusting peak intensities with Jingmi River (JM) water Beijing. Notably, when dyes were diluted in JM water, ultraviolet (UV533 &466, and UV254), together with total organic carbon (TOC) parameters, revealed color removal rates of 99.49% (EBT), 94.2% (MO), 87.6% DOM removal, and 86% TOC removal for NF-90. The NF-90 membrane demonstrated a 75% flux decline for 50 mL permeate volume due to its finer pore structure and higher rejection effectiveness. In contrast, the NF-270 membrane showed a 60% decline in flux under the same conditions. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis of dye-treated membranes in JM water revealed that the NF-270 showed a CC bond peak at 1660 cm−1 across various samples, while analyzing NF-90, the peaks at 1400 cm−1, 1040 cm−1, 750 cm−1, and 620 cm−1 disappeared for composite sample removal. The hydrophobicity of each membrane is measured by the contact angle (CA), which identified that initial CAs for NF-270 and NF-90 were 460 and 700, respectively, that were rapidly declined but stabilized after a few seconds of processing. Overall, this investigation shows that azo dyes interact with DOM in surface waters and enhance the removal efficiency of NF membranes.

Exploring the use of ultrafiltration-diafiltration for the concentration and purification of mealworm proteins

This work aimed to study the performance of the UF-DF process, in terms of the permeation flux and membrane resistance, to produce a mealworm protein isolate. Moreover, a detailed characterization of the UF-DF retentates and permeates was performed. The results showed that the UF performances was reduced during the concentration phase, with a total flux decline close to 40 %. The membrane fouling was mainly reversible, and the flux was totally recovered during the DF. As expected, the ash content was drastically reduced in the retentate, but interestingly, low effects on the soluble sugars and lipids contents were noticed. The UF permeates were mainly composed of free amino acids and low molecular weight peptides, which confirms a high protein rejection of the UF membrane. Finally, compared to the protein concentrate before the UF-DF (57.29 %), the protein content increased by 26.4 % to reach 72.40 % which validates the feasibility of producing mealworm protein isolates using filtration parameters described in this work. This study demonstrated the potential of using UF-DF to produce a mealworm protein isolate with a complete amino acid profile rich in essential amino acids.

Unraveling the intricate fouling behaviors of landfill leachate components during membrane distillation concentration toward zero liquid discharge

Membrane distillation (MD) holds promise for cost-effectively concentrating wastewater toward zero liquid discharge (ZLD), while membrane fouling problems still hinder its practical application, especially for high-strength wastewater containing complex constituents. This study investigated the effects of different foulant components in actual landfill leachate (LFL) on MD deep concentration performances. The fouling behaviors of LFL components were revealed by comprehensively characterizing and analyzing the physicochemical properties of the fouling layers and membrane-foulant interactions. Results illustrated that suspended solids (SS) and macromolecular organics (MO) played significant yet distinct roles in fouling layer formation. SS (>0.45 μm, ∼24 % TOC) possessed strong adhesion energies with membrane surfaces and constructed the main skeleton of the fouling layer at the preliminary concentration stage; while MO (>20 kDa, 0.36 % TOC) deposition resulted in a densely packed fouling layer, influencing the salt crystallization potential and interfering with water and ammonia transport. In contrast, the low-molecular organics with the highest content (<20 kDa, ∼75 % TOC) were mainly electron-donor monopolar substances weakly adsorbed on the nonpolar membrane surface. Removing SS and MO from LFL notably prevented fouling layer formation and maintained high membrane efficacies (water flux decline mitigated from ∼50 % to ∼15 % and ammonia rejection increased from 71 % to 88 %), even as water recovery increased to 95 %. The findings of this work imply conventional anti-fouling strategies (e.g., complete removal or degradation of organic components) may have gone beyond what is necessary, and will inspire the development of simpler and greener methods to maintain membrane efficacy during high-strength wastewater treatment toward ZLD.

Constructing superhydrophilic/superhydrophobic Janus membrane assisted by dual-interface-confined strategy for on-demand oil-in-water and water-in-oil emulsions separation

Janus membranes with asymmetric wettability have attracted much attention because they can solve the problem that a single wettable material cannot effectively separate complex oil/water emulsions. Here, a dual-interface-confined strategy combining single-side interface-confined floating and single-side interface-confined spraying methods is provided to fabricate a robust Janus membrane with superwettability. The controllable single-side interface-confined floating method introduces a superior stable hydrophobic-superhydrophilic Janus interface, and the single-side interface-confined spraying method guarantees a robust superhydrophobic-superhydrophilic Janus interface. The Janus membrane featured both superhydrophilicity and superhydrophobicity with the outstanding stable interface and remarkable chemical stability could separate not only surfactant-stabilized water-in-oil emulsions by gravity alone, but also handle the surfactant-stabilized oil-in-water emulsions under low separation pressure through simple operation process. Moreover, this superwettable Janus membrane can achieve long-term on-demand oil/water emulsion separation with low flux decline and near 100% flux recovery. Overall, this work develops a new avenue for Janus membrane and provides a new application for a variety of oily wastewater treatment problems.

Investigation of scaling inhibition and biofouling potential of different molecular weight fractions of a PAA antiscalant

This study investigates the scale inhibition performance of a commercial polyacrylic acid-based (PAA) antiscalant used for drinking water production and its molecular weight fractions (≤ 500 Da, ≥ 500 Da). The investigated antiscalant is used to prevent sulfate and carbonate scaling in treatment of drinking water sources by reverse osmosis or nanofiltration (RO/NF). Based on two complementary tests involving determination of induction time in a batch test and rate of flux decline in a lab-scale RO/NF plant, concordant results were obtained, proving that the overall performance of commercial PAA was controlled almost entirely by the higher molecular weight fraction. The low molecular weight fraction, which is potentially more permeable through the NF/RO membrane, showed poor inhibition against both sulfate and carbonate scalants. Furthermore, measurements on the assimilable organic carbon (AOC) by flow cytometry reveals that the low molecular weight PAA fraction has low biological stability, as its potential transport into the permeate of a NF270 nanofiltration membrane was inferred by elevated AOC values in the NF-permeate. These results are crucial information for water utilities, plant engineering, regulatory bodies and public authorities with respect to the possible operation of RO/NF especially in drinking water production.

New insights into antifouling property and interfacial mechanism in photo-Fenton membrane distillation

Membrane distillation (MD), boasting high interception efficiency and low operational pressures, emerges as an innovative membrane technology. However, the occurrence of membrane fouling due to interaction between natural organic matter (NOM) and inorganic ions during the MD process curtails water purification efficiency, thereby constraining its potential applications. To address this quandary, this study integrates sulfate radical-based advanced oxidation processes (SR-AOPs) into MD technology to bolster membrane fouling control. A straightforward hydrothermal method coupled with vacuum filtration was employed to synthesize a Co3O4/Nitrogen-modified carbon quantum dots (NCDs)/PVDF (CN-PVDF) membrane for the first time, which was utilized in the MD treatment of simulated humic acid (HA) wastewater. Under visible light irradiation (1.9 kW/m2), CN-PVDF membrane activation of peroxymonosulfate (PMS) effectively altered the chemical attributes of the MD feed solution and reduced organic matter concentration. Moreover, it dismantled the carboxyl sites on HA that interact with Ca2+, consequently attenuating the formation of organic–inorganic complex pollutants. The XDLVO analysis showcased that photo-Fenton oxidation led to a diminishment in pollutant hydrophobicity, correlating with a 17.59 kT reduction in pollutant-membrane adsorption and a 7.47 kT amplification in adhesion barriers. This strategy transformed the initial two-stage fouling mode into a singular one, which significantly decreased the flux decline and the fouling layer thickness. Furthermore, the CN-PVDF membrane demonstrated self-cleaning capabilities via photo-Fenton. This study advances an innovative approach to bolster the fouling resistance of MD membranes and provides substantial theoretical support for the integration of SR-AOPs and MD technologies.

Concentration polarizations of PEG and silica colloids in ceramic nanofiltration

A large decrease in permeability is often observed during the filtration of nano-sized colloids, while fouling is widely regarded as the main explanation for this phenomenon. The osmotic pressure or concentration polarization (CP) of colloids can also contribute to the flux decline. However, the contribution of CP to flux loss cannot be determined by the traditional CP model. In this study, the effect of fouling and CP/osmotic pressure on flux was distinguished. The CP values of polyethylene glycol (PEG) and silica-colloids were determined by the osmotic pressures near the membrane surface and in the feed. The CP induced by colloids accounted for 43–95% of the flux loss in our experiments. Silica exhibited higher CP values (127–460), compared to 7–71 for PEG. This was attributed to the slower back diffusion caused by the larger colloids, as evidenced by the diffusion coefficients of 4.30 × 10−11 m2/s for silica (10 nm) and 1.45 × 10−10 m2/s for PEG (2.9 nm). Although the CP was mitigated by increasing the cross-flow velocity, CP values of 31 and 250 were observed for PEG and silica at high Reynolds number of 7317, respectively. The experimentally obtained CP values were also compared with those calculated by the film diffusion model.