Pore Blocking Mechanism Research Articles

Investigating the Fouling Models of the Microfiltration Mixed Matrix Membranes-Based Oxide Nanoparticles Applied for Oil-in-Water Emulsion Separation

Membrane fouling is a major problem encountered in the use of microfiltration (MF) processes to separate the emulsified oil from water. This work involves assessing the efficacy of removing oil-in-water emulsion (O/W emulsion), and evaluating fouling resistance by studying the membrane morphology before and after fouling, and after washing with different cleaning solutions via field emission scanning electron microscopy (FESEM) analysis. Also, the fundamental mechanism involved in the flux drop during crossflow MF has been assessed using models such as the Hermia blocking models and the modified model by Field. The standard and intermediate pore blocking models provided the best prediction for experimental behavior when analyzing the decay in the flux with time for the bio silicon oxide/polyvinylchloride (B-SiO2/PVC) membrane and the stannic oxide/polyvinylchloride (SnO2/PVC) membrane. This research established regression equations of the flux for both membranes in which these equations are highly correlated with R2 of 98.33% for B-SiO2/PVC and R2 of 99.52% for SnO2/PVC using the surface response methodology (RSM). The high flux recovery ratio (FRR) is indicative of the improved antifouling feature of the manufactured membranes where it was 96.8% for B-SiO2/PVC and 94.6% for SnO2/PVC. The results obtained by Hermia and Field were in good agreement with RSM analysis supporting the standard pore-blocking mechanism.

Impact of membrane characteristics and chemical ageing on algal protein fouling behaviour of ultrafiltration membranes

Membrane characteristics can exacerbate the prevailing challenges associated with membrane fouling in industry. However, the combined impact of deliberate membrane modifications and the unavoidable effects of chemical ageing on fouling behaviour is still not well understood. In this study, three polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes with different pore size and surface roughness were selected and subject to chemical ageing with 5000 ppm sodium hypochlorite (NaOCl) at pH 10.5, selected to simulate accelerated ageing conditions. The impact of NaOCl on membrane characteristics was assessed for exposure times from 1.2 x 105 to 25.2 x 105 ppm·h using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, contact angle, and clean water resistance analysis. The fouling behaviour of each pristine and aged membrane was compared using 10 mg C·L−1 dissolved organic carbon algal protein feed containing 18 % biopolymeric compounds. The membrane with intermediate pore size presented lower overall filtration resistance compared to the membrane with smaller pores that developed rapid foulant cake layers. It also displayed less susceptibility to fouling via pore blocking mechanisms compared to membranes with larger pores where greater surface area available in pore walls leads to higher foulant adhesion.

Probing the Proton-Gated ASIC Channels Using Tetraalkylammonium Ions.

The action of tetraalkylammonium ions, from tetrametylammonium (TMA) to tetrapentylammonium (TPtA), on the recombinant and native acid-sensing ion channels (ASICs) was studied using the patch-clamp approach. The responses of ASIC1a, ASIC2a, and native heteromeric ASICs were inhibited by TPtA. The peak currents through ASIC3 were unaffected, whereas the steady-state currents were significantly potentiated. This effect was characterized by an EC50 value of 1.22 ± 0.12 mM and a maximal effect of 3.2 ± 0.5. The effects of TPtA were voltage-independent but significantly decreased under conditions of strong acidification, which caused saturation of ASIC responses. Molecular modeling predicted TPtA binding in the acidic pocket of closed ASICs. Bound TPtA can prevent acidic pocket collapse through a process involving ASIC activation and desensitization. Tetraethylammonium (TEA) inhibited ASIC1a and native ASICs. The effect was independent of the activating pH but decreased with depolarization, suggesting a pore-blocking mechanism.

Effects of the adsorbate-gas interface at the pore opening on the lower closure point in gaseous adsorption in porous solids

The limit to the lower closure point (LCP) observed experimentally in the desorption isotherm of gases in porous solids has been commonly attributed to the homogeneous cavitation of the condensate in cavities. It was proposed recently that the experimental limit to LCP could be described in simulations with the ink-bottle pore, provided that the length of the uniformly sized conduit connecting the closed cavity to the surrounding is shorter than 2 nm, and the evaporation is by way of pore blocking mechanism, rather than homogeneous cavitation. To substantiate this assertion, that deviates from the commonly belief of homogeneous cavitation, we further investigated in this paper with cavities having wedge-like pore opening, that better mimics real solids, and offer further explanation on the limit of the LCP to the pore blocking as the mechanism of evaporation with simulations of argon and nitrogen adsorption over a range of temperatures that are commonly used experimentally. It was found that simulation results correctly captured the experimental observations for carbon-based materials and silica-based materials in that the limit of LCP shifts to higher reduced pressures for weaker adsorbing silica, compared to stronger adsorbing carbon and for a given adsorbent it also shifts to higher reduced pressure for higher temperatures.

The antimicrobial substance's content influences the membrane blocking mechanism in cross-flow filtration – Flow cytometric assessment of the membrane's activity

The study aims to investigate the antibacterial properties of carvacrol-loaded cellulose acetate membranes in cross-flow filtration using an advanced microbiological flow cytometry method and analyze the influence of carvacrol's presence on the pore-blocking mechanisms. The commercial cellulose acetate microfiltration membranes were impregnated with carvacrol using supercritical carbon dioxide as a solvent and transport medium. This technique enables active substance distribution throughout the whole polymer volume on the molecular level. Carvacrol loadings of up to 30 % were obtainable, whereby the membranes preserved their microstructure and functionality for loadings of up to 25 %. The protocol for flow cytometric assessment of the cell deposition on the membrane surface during the cross-flow filtration was developed. The results showed that the presence of carvacrol considerably decreased Staphylococcus aureus deposition on the membrane (from the order of magnitude 107/(cm2membrane surface·mLpermeate) to 105/(cm2membrane surface·mLpermeate)). The membranes containing 20 % and 25 % carvacrol showed the largest permeate flux and the smallest number of deposited bacteria. The largest fraction of dead bacteria (42 %) was detected in the membrane containing 25 % carvacrol. Mathematical modeling showed that the pore-blocking mechanism changed with the increase in carvacrol content, from the cake filtration phenomenon via the intermediate blocking towards standard and complete blocking mechanisms.

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

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

Generalization and Expansion of the Hermia Model for a Better Understanding of Membrane Fouling

One of the most broadly used models for membrane fouling is the Hermia model (HM), which separates this phenomenon into four blocking mechanisms, each with an associated parameter n. The original model is given by an Ordinary Differential Equation (ODE) dependent on n. This ODE is solved only for these four values of n, which limits the effectiveness of the model when adjusted to experimental data. This paper aims extend the original Hermia model to new values of n by slightly increasing the complexity of the HM while keeping it as simple as possible. The extended Hermia model (EHM) is given by a power law for any n ≠ 2 and by an exponential function at n = 2. Analytical expressions for the fouling layer thickness and the accumulated volume are also obtained. To better test the model, we perform model fitting of the EHM and compare its performance to the original four pore-blocking mechanisms in six micro- and ultrafiltration examples. In all examples, the EHM performs consistently better than the four original pore-blocking mechanisms. Changes in the blocking mechanisms concerning transmembrane pressure (TMP), crossflow rate (CFR), crossflow velocity (CFV), membrane composition, and pretreatments are also discussed.

Synthesis, characterization, and application of gravity-driven ceramic microfiltration membranes for surface water treatment

Gravity-driven ceramic microfiltration (MF) disk-shaped membranes were synthesized using kaolin and different alumina contents (0 % wt, 25 % wt, and 50 % wt). The pure water flux, mean pore size, porosity and contact angle of membranes were measured. Their structure and composition were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of alumina content was evaluated for long-term river water filtration in terms of permeate flux, turbidity, dissolved organic carbon (DOC), UV254, pH, and alkalinity removal. The physical characteristics of the biofouling layer, such as thickness and roughness, were studied using optical coherence tomography (OCT) imaging and the concentration of active microorganisms in the biofilm. The results showed acceptable turbidity removal after the flux stabilization period and relatively high performance for DOC, UV, and alkalinity removal during the first three days of filtration. Flux stabilized at 2.5–3 LMH on day 24 of filtration, indicating that the alumina content does not considerably affect the stable flux. As the flux modeling data showed, prior to the flux stabilization time, the fouling was controlled by the pore blocking mechanism. This was confirmed by OCT imaging that showed a very outspread biofilm layer with a low relative roughness; the layer became more compact with a higher relative roughness over time, showing that the cake layer is dominant after the flux stabilization period. Increasing the alumina content of the membranes increased the number of active microorganisms in the biofilm layer; possibly because of an increased adsorption of nutrients in the biofouling layer.

Characterization and Chemical Synthesis of Cm39 (α-KTx 4.8): A Scorpion Toxin That Inhibits Voltage-Gated K+ Channel KV1.2 and Small- and Intermediate-Conductance Ca2+-Activated K+ Channels KCa2.2 and KCa3.1.

A novel peptide, Cm39, was identified in the venom of the scorpion Centruroides margaritatus. Its primary structure was determined. It consists of 37 amino acid residues with a MW of 3980.2 Da. The full chemical synthesis and proper folding of Cm39 was obtained. Based on amino acid sequence alignment with different K+ channel inhibitor scorpion toxin (KTx) families and phylogenetic analysis, Cm39 belongs to the α-KTx 4 family and was registered with the systematic number of α-KTx 4.8. Synthetic Cm39 inhibits the voltage-gated K+ channel hKV1.2 with high affinity (Kd = 65 nM). The conductance-voltage relationship of KV1.2 was not altered in the presence of Cm39, and the analysis of the toxin binding kinetics was consistent with a bimolecular interaction between the peptide and the channel; therefore, the pore blocking mechanism is proposed for the toxin-channel interaction. Cm39 also inhibits the Ca2+-activated KCa2.2 and KCa3.1 channels, with Kd = 502 nM, and Kd = 58 nM, respectively. However, the peptide does not inhibit hKV1.1, hKV1.3, hKV1.4, hKV1.5, hKV1.6, hKV11.1, mKCa1.1 K+ channels or the hNaV1.5 and hNaV1.4 Na+ channels at 1 μM concentrations. Understanding the unusual selectivity profile of Cm39 motivates further experiments to reveal novel interactions with the vestibule of toxin-sensitive channels.

Goat milk concentrated by nanofiltration: flow decline modeling and characterization

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

Experimental Investigation on the Impacts of Fracture Roughness and Fluid Composition on the Formation of Bubble Bridges through the Microbubble Fluid Flow.

The colloidal gas Aphron (CGA) drilling fluids are an alternative to ordinary drilling mud to minimize formation damage by blocking rock pores with microbubbles in low-pressure or depleted reservoirs. Fractured formations usually have different characteristics and behavior in contrast to conventional ones and need to be investigated for Aphron applications. In this research, a series of core flood tests were conducted to understand the factors controlling the pore-blocking mechanisms of microbubbles in fractured formations. For the first time, a synthetic metal plug was used to simulate the fracture walls and eliminate the formation matrix effect. This study analyzed the effects of three fluid compositions, considering the polymer and surfactant concentrations at reservoir conditions, including temperature and overburden pressure. Additionally, fracture surface roughness as one of the parameters affecting the microbubble fluid penetration through the fracture path and bubble blockage were studied. The results indicated that microbubble fluid composition would not affect the bubble size or blockage probability. The different stable microbubble fluids resulted in the same pattern and conditions. Besides, fluid penetration would be more challenging if the fracture roughness decreased. Due to the accumulation of bubbles and the fact that some of them were trapped in the fracture's rough surface, the blockage possibility increased. According to the range of roughness for the steel core in previous studies and compared with the roughness of carbonate reservoir rocks, the roughness of fractured reservoir rocks is much higher than that of the steel surface. Accordingly, the observed trend in the experiments showed that when it is possible to form a bubble bridge in steel cores, then in carbonate rocks, we will definitely see blockage with any roughness, provided that other parameters are acceptable.

Fouling mechanisms in ultrafiltration under constant flux: Effect of feed spacer design

The impact of feed spacer design on membrane fouling mechanism in ultrafiltration (UF) process under constant flux mode was systematically investigated. Thecombined intermediate pore blocking and cake filtration model was employed,coupled with experimental crossflow UF experiments of dextran and sodium alginate (SA) in aqueous feed solutions. Filtration resultsofthree different spacer geometries, which included two 3D-printed spacers based on triply periodic minimal surfaces (TPMS) (Gyroid and TCLP) and one commercial net-type spacer, were analyzed. Flux-stepping tests were performed to determine the threshold flux (TF) in each case. Experimental data were fitted using the filtration model and the results were evaluated in terms of cake filtration constant (Kc, m−1), rate of cake erosion (S, kg.m−2.s−1), particle resuspension rate (B, s−1), and specific cake resistance (α, m.kg−1), in order to understand the cake formation and erosionbehavior that is influenced by the spacer geometry. A difference in spacer performance was observed when the solute was changed from SA to dextran. The results demonstrated that spacer design has a significant effect on the fouling mechanism in UF separation. The TCLP spacer is able to operate at the intermediate pore blocking mechanism at higher fluxes compared to the net-type spacer for both solutes tested. The flow hydrodynamics induced by the spacer geometry influenced the re-suspension rate of the deposited particles in the filtration cake. Additionally, combination of spacer surface roughness and solute molecular sizes were found to be the significant factors in cake-buildup on the spacer and the membrane.

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

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

General Considerations Related to the Membrane Material Locking Models ‒ A Short Rewiew

Abstract The problem of clogging membrane pores has become an area of interest for the vast majority of researchers in the field, because according to the literature, membrane materials are very sensitive when it comes to clogging and blocking pores. Therefore, this paper briefly describes the problems that occur during the process of obstruction the pores of the membrane. Models and characteristics of pore blocking mechanisms have also been developed. It is essential to mention that the principal purpose of the paper, which which consisted to review the simulations and classical models that were optimized, used in the analysis processes of clogging of membrane materials, was successfully fulfilled. According to those mentioned, the combined mathematical models of pore blocking (methods combined with three blocking mechanisms using Hagen-Poiseuille’s law or standard 0-order blocking) have proven to be very effective in describing membrane clogging problems.

Application of a Pickering Emulsified Polymeric Gel System as a Water Blocking Agent.

The conventional methods for controlling excess water production in oil/gas wells can be classified on the basis of the mechanism (pore-blocking mechanism and relative permeability modification) used. Gel systems developed on the basis of a pore-blocking mechanism completely block the pores and stop the flow of both oil and water, whereas a relative permeability modifier (RPM) only restricts the flow of a single phase of the fluid. The gel working on the basis of the pore-blocking mechanism is known as a total blocking gel. An invert emulsified (PAM–PEI) polymer gel is a relative permeability modifier system. The same invert emulsion system is tested as a total blocking gel system in this research work. The dual-injection technique (1st injection and 2nd injection) was used for this purpose. In this research work, the emulsion system was tested at a temperature of 105 °C. The core sections with drilled holes and fractures were used for the core flooding experiments, representing a highly fractured reservoir. The developed emulsified gel system was characterized using a dilution test, an inverted bottle test, microscopic images, and FTIR images. The emulsified polymer gel was tested using a core flooding experiment. After the 2nd injection, the postflood medical CT and micro-CT images of the core sections clearly showed the presence of two different phases in the core section, i.e., the oil phase and the gel phase. The core flooding experiment result indicates that the gel formed after the 2nd injection of the emulsion system can withstand a very high differential pressure, i.e., above 2000 psi. The gel did not allow any oil or water to be produced. Hence, the developed emulsified polymer gel system with the help of a dual-injection technique can be efficiently used as a total blocking gel for high-temperature reservoirs.

Tanning Wastewater Treatment by Ultrafiltration: Process Efficiency and Fouling Behavior.

Ultrafiltration is a promising, environment-friendly alternative to the current physicochemical-based tannery wastewater treatment. In this work, ultrafiltration was employed to treat the tanning wastewater as an upstream process of the Zero Liquid Discharge (ZLD) system in the leather industry. The filtration efficiency and fouling behaviors were analyzed to assess the impact of membrane material and operating conditions (shear rate on the membrane surface and transmembrane pressure). The models of resistance-in-series, fouling propensity, and pore blocking were used to provide a comprehensive analysis of such a process. The results show that the process efficiency is strongly dependent on the operating conditions, while the membranes of either PES or PVDF showed similar filtration performance and fouling behavior. Reversible resistance was the main obstacle for such process. Cake formation was the main pore blocking mechanism during such process, which was independent on the operating conditions and membrane materials. The increase in shear rate significantly increased the steady-state permeation flux, thus, the filtration efficiency was improved, which resulted from both the reduction in reversible resistance and the slow-down of fouling layer accumulate rate. This is the first time that the fouling behaviors of tanning wastewater ultrafiltration were comprehensively evaluated, thus providing crucial guidance for further scientific investigation and industrial application.

Structure and Function of the Human Sodium Leak Channel NALCN

The sodium leak channel (NALCN) mediates a persistent depolarising Na+ current in neurons that regulates respiration, locomotion and circadian rhythm. Despite strong clinical evidence supporting its critical role in neurodevelopment and survival, fundamental aspects of NALCN function have remained unexplored due to challenges in heterologous expression. We recently established that the robust function of NALCN in vitro requires three other neuronal proteins, namely UNC79, UNC80 and FAM155A. The resulting channel complex is constitutively active, voltage sensitive, and only conducts small monovalent cations. Moreover, extracellular divalent cations inhibit NALCN directly via a pore-blocking mechanism. These data corroborate the notion that the NALCN channel complex is directly responsible for the increased neuronal excitability in reduced extracellular Ca2+. We also determined the structure of NALCN in complex with FAM155A using cryo-electron microscopy, which revealed several unique features. For instance, FAM155A forms an extracellular dome that sterically hinders neurotoxin access to the selectivity filter. Together with occluded lateral fenestrations that typically serve as entryways for lipophilic drugs, these features provide a simple explanation for the lack of NALCN pharmacology. Structural mapping of disease mutations highlighted the intracellular activation gate as a hotspot for gain-of-function mutations. Our findings suggest these residues participate in intra- and interdomain interactions, and even subtle, conservative substitutions may disrupt these networks to elevate channel activity. Together, we have performed the first in-depth biophysical characterisation of the NALCN channel complex, and provided unprecedented glimpses into the architecture of this physiologically important protein.

Combined alginate-humic acid fouling mechanism and mitigation during microfiltration: Effect of alginate viscosity

In membrane-based water and wastewater treatment processes, understanding the interactive effect of various types of organic components on membrane fouling is crucial in order to identify effective fouling mitigation strategies. In this study, the effect of humic acid on alginate filtration was examined under both dead-end and crossflow constant flux microfiltration conditions using low viscosity and medium viscosity alginate as model foulants. The presence of humic acid (100 mg/L) appeared to accelerate alginate fouling under both dead-end and crossflow filtration conditions, following cake layer filtration mechanism (dead-end) and a combined intermittent pore blocking and cake layer filtration mechanism (crossflow) respectively. Under the crossflow filtration condition, the fouling mechanism of the alginate-humic acid mixture was dependent with the permeate flux and alginate nature, e.g., less pore blocking with more cake layer fouling were present at a higher permeate flux during filtration medium viscosity alginate-humic acid mixture. When intermittent relaxation was employed during crossflow filtration, the presence of humic acid could alleviate medium viscosity alginate fouling. This was attributed by a significant shift of irreversible fouling to reversible cake layer fouling, which was readily removed by shear force during relaxation. A comparison of membrane performance during intermittent filtration with periodical flushing using clean water, NaClO (5%), and persulfate (100 mg/L) at 50 °C indicates that high temperature clean water flushing was effective in maintaining membrane performance during filtrating alginate-humic acid complex, which majorly contributed to a reduction of reversible cake layer fouling.

Fingerprint ridges allow primates to regulate grip

Fingerprints are unique to primates and koalas but what advantages do these features of our hands and feet provide us compared with the smooth pads of carnivorans, e.g., feline or ursine species? It has been argued that the epidermal ridges on finger pads decrease friction when in contact with smooth surfaces, promote interlocking with rough surfaces, channel excess water, prevent blistering, and enhance tactile sensitivity. Here, we found that they were at the origin of a moisture-regulating mechanism, which ensures an optimal hydration of the keratin layer of the skin for maximizing the friction and reducing the probability of catastrophic slip due to the hydrodynamic formation of a fluid layer. When in contact with impermeable surfaces, the occlusion of the sweat from the pores in the ridges promotes plasticization of the skin, dramatically increasing friction. Occlusion and external moisture could cause an excess of water that would defeat the natural hydration balance. However, we have demonstrated using femtosecond laser-based polarization-tunable terahertz wave spectroscopic imaging and infrared optical coherence tomography that the moisture regulation may be explained by a combination of a microfluidic capillary evaporation mechanism and a sweat pore blocking mechanism. This results in maintaining an optimal amount of moisture in the furrows that maximizes the friction irrespective of whether a finger pad is initially wet or dry. Thus, abundant low-flow sweat glands and epidermal furrows have provided primates with the evolutionary advantage in dry and wet conditions of manipulative and locomotive abilities not available to other animals.

SMP Production in an Anaerobic Submerged Membrane Bioreactor (AnMBR) at Different Organic Loading Rates.

Anaerobic membrane bioreactors (AnMBRs) have demonstrated an excellent capability to treat domestic wastewater. However, biofouling reduces membrane permeability, increasing operational costs and overall energy demand. Soluble microbial products (SMPs) that build up on the membrane surface play a significant role in the biofouling. In this study, the production of SMPs in a 32 L submerged AnMBR operated at three different organic loads (3.0, 4.1 and 1.2 kg chemical oxygen demand (COD)/m3d for phases 1, 2 and 3, respectively) during long-term operation of the reactor (144, 83 and 94 days) were evaluated. The samples were taken from both the permeate and the sludge at three different heights (0.14, 0.44 and 0.75 m). Higher production of SMPs was obtained in phase 2, which was proportional to the membrane fouling. There were no statistically significant differences (p > 0.05) in the SMPs extracted from sludge at different heights among the three phases. In the permeate of phases 1, 2 and 3, the membrane allowed the removal of 56%, 70% and 64% of the SMP concentration in the sludge. SMPs were characterized by molecular weight (MW). A bimodal behavior was obtained, where fractions prevailed with an MW < 1 kDa, associated with SMPs as utilization-associated products (UAPs) caused fouling by the pore-blocking mechanism. The chemical analysis found that, in the SMPs, the unknown COD predominated over the known COD, such as carbohydrates and proteins. These results suggest that further studies in SMP characterization should focus on the unknown COD fraction to understand the membrane fouling in AnMBR systems better.