Development Of Membrane Fouling Research Articles

Impacts of micron-sized aeration bubble on sludge properties and hydraulic dynamics in relation to membrane fouling alleviation

This investigation elucidates the influence of micron-scale aeration bubbles on the improvement of anti-fouling characteristics within submerged membrane bioreactors (sMBRs). A systematic examination of sludge properties, hydraulic dynamics, and fouling tendencies revealed that the application of microbubble aeration, specifically at dimensions of 100 μm, 80 μm, and 30 μm, significantly reduced sludge electrostatic repulsion and augmented particle size distribution, as opposed to the utilization of coarse bubble aeration of 1 mm. Notably, the employment of 100 μm bubbles achieved a significant reduction in the proportion of smaller particles (<10 μm) and sludge viscosity, thereby facilitating a more homogenous and vigorous turbulence at the membrane interface. These optimized conditions were instrumental in the substantial reduction of membrane fouling, which was corroborated by the diminished rate of fouling, reduced resistance accumulation, and lesser foulant deposition. The investigation identified sludge particle size, turbulent kinetic energy, and shear stress as the predominant factors influencing the development of membrane fouling. The findings underscore the pronounced advantages of employing 100 μm-sized bubbles in aeration strategies, providing enhanced understanding for the optimization of aeration parameters to improve sMBR efficiency and maintenance.

Dynamic evolution of ultrafiltration membrane fouling affected by S(IV)–Fe(II)-activated permanganate pretreatment during a long-term operation

ABSTRACT The S(IV)–Fe(II)/PM pretreatment has demonstrated preliminary potential as an effective ultrafiltration (UF) pretreatment technology. However, a comprehensive understanding of its impact on UF membrane fouling control and the dynamic evolution of membrane fouling during prolonged operation is still lacking. In this study, a relatively prolonged fouling experiment was conducted. Results revealed that the S(IV)–Fe(II)/PM pretreatment exhibited superior performance over Al(III) coagulation pretreatment in mitigating the transmembrane pressure difference and addressing both reversible and irreversible membrane fouling. The application of a cluster analysis method to classify membrane fouling evolution stages further confirmed that S(IV)–Fe(II)/PM pretreatment effectively decelerated the rate of membrane fouling evolution. The surface cake layer of UF membranes pretreated with S(IV)–Fe(II)/PM exhibited greater looseness and smoothness. It also showed better results than Al(III) coagulation pretreatment in reducing the accumulation of organic foulants, controlling the Si content and reducing the total microorganisms and live microorganisms in the UF feed water. Variance Partitioning Analysis indicated that the combined contribution of organic, inorganic, and biological foulants was the most significant for UF membranes after S(IV)–Fe(II)/PM pretreatment (50.4%) and UF membranes after Al(III) coagulation pretreatment (70.2%). These findings underscore the efficacy of S(IV)–Fe(II)/PM pretreatment in controlling UF membrane fouling under prolonged operation.

Multistage membrane-integrated zero liquid discharge system for ultra-efficient resource recovery from steel industrial brine: Pilot-scale investigation and spatial membrane fouling

Zero liquid discharge (ZLD) strategy provides significant potential for industrial brine treatment. Still, the application has been constrained by the inadequate water recovery and membrane fouling of its membrane-based brine concentration system. Herein, a pilot-scale system was established that integrated pretreatment, reverse osmosis (RO), nanofiltration (NF), and disk tube reverse osmosis (DTRO), and demonstrated over a 6-month operation for the first application in treating steel industry brine. Meanwhile, novel insights were offered into the spatial evolution of DTRO membrane fouling. The overall ZLD system reached ultra-efficient water recovery at 91% with relatively low energy consumption (7.27 kWh/m3). The RO and NF units concentrated the brine and selectively separated ions of different valences, simultaneously eliminating various contaminants. The DTRO unit enriched the highly saline NF permeate with a remarkable 7.5-fold concentration effect, producing an extremely hypersaline brine salinity (138,472 ± 34,804 mg/L, Cl−/SO42− mass ratio of 56) that ultimately yielded ultra-pure NaCl salt. Additionally, DTRO special fouling patterns revealed a distinctive "W"-shaped fluctuation in humic acid along the device water flow, with concurrent reduction in iron/aluminum oxides leading to their deposition at the outlet. This synergistic fouling, coupled with silicon, coincides with the transformation of silica colloids into silicate compounds. The multistage membrane-based strategy and the spatial membrane fouling evolution pattern proposed and investigated in this work provide a highly efficient and cost-effective solution for industrial brine treatment with ZLD.

Comprehensive effects of microplastics on algae-laden surface water treatment by coagulation-ultrafiltration combined process: Algae cultivation, coagulation performance and membrane fouling development

In coastal areas, the surface water has been simultaneously exposed to the algae blooms caused by eutrophication and the microplastics (MPs) pollution originating from active human activities. As a practical alternative to address these issues in drinking water plant, coagulation-ultrafiltration combined process is still confronted with the limited understanding about the comprehensive effects of MPs on algae-laden surface water (ASW) treatment. Considering the migration of MPs in nature environment and drinking water treatment process, this study first aims to systematically investigate the influence of MPs on algae cultivation, coagulation performance and membrane fouling development. The results of algae cultivation indicate that MPs stimulated the algae activity by 58 % and then constantly suppressed the secretion of protein-like, humic-like and polysaccharide-like metabolites. The variation of particle size distribution and zeta potential confirm that MPs acted as nuclei to facilitate the development of large coagulation flocs with an increasing average size from 82.6 μm to 107.6 μm, during which the negatively charged pollutants were neutralized and removed from ASW. According to the SEM images, MPs could destroy the structure of fouling layer on 50 kDa membranes during the filtration of ASW coagulation effluent. Its synergistic effect with the enhanced coagulation performance and the suppressed EOM secretion contributed to the alleviation of membrane fouling caused by overlapped large-sized foulants. However, the interaction between the enriched organic foulants by MPs and the deposited coagulants on 300 kDa membranes facilitated the development of cake layer, leading to the deterioration of membrane permeability. This study emphasizes the importance in concerning the existence of MPs during the treatment of ASW by coagulation-ultrafiltration combined process and their exact influence in water purification efficiency.

Construction of synthetic anti-fouling consortia: fouling control effects and polysaccharide degradation mechanisms

The physical states and chemical components of bulk sludge determine the occurrence and development of membrane fouling in membrane bioreactors. Thus, regulation of sludge suspensions can provide new strategies for fouling control. In this study, we used “top-down” enrichment to construct a synthetic anti-fouling consortium (SAC) from bio-cake and evaluate its roles in preventing membrane fouling. The SAC was identified as Massilia-dominated and could almost wholly degrade the alginate solution (1,000 mg/L) within 72 h. Two-dimensional Fourier transformation infrared correlation spectroscopy (2D-FTIR-CoS) analysis demonstrated that the SAC induced the breakage of glycosidic bond in alginates. The co-cultivation of sludge with a low dosage of SAC (ranging from 0 to 1%) led to significant fouling mitigation, increased sludge floc size, and decreased unified membrane fouling index value (0.55 ± 0.06 and 0.11 ± 0.05). FTIR spectra and X-ray spectroscopy analyses demonstrated that the addition of SAC decreased the abundance of the O-acetylation of polysaccharides in extracellular polymeric substances. Secondary derivatives analysis of amide I spectra suggested a strong reduction in the α-helix/(β-sheet + random coil) ratio in the presence of SAC, which was expected to enhance cell aggregation. Additionally, the extracellular secretions of SAC could both inhibit biofilm formation and strongly disperse the existing biofilm strongly during the biofilm incubation tests. In summary, this study illustrates the feasibility and benefits of using SAC for fouling control and provides a new strategy for fouling control.

Thermodynamic mechanism insights into the dynamic evolution of nanofiltration membrane fouling: Effect of calcium ion on organic fouling

To better control nanofiltration (NF) membrane fouling during mine water treatment, an accurate elaboration of the fouling mechanisms of anionic polyacrylamide (APAM) coexisted with Ca2+ and fulvic acid (FA) is vital. An attractive phenomenon was observed during the membrane fouling tests: When Ca2+ and FA coexist with APAM, increasing Ca2+ concentration at high Ca2+ concentration will alleviate membrane fouling. The degree of membrane fouling is determined by the interaction of the foulant with the membrane and is closely related to the Lewis acid-base (AB) interaction energy. At the shortest separation distance, the AB interaction energy decreased from 3608 kT to −17,386 kT when the Ca2+ concentration was increased from 0 mM to 2 mM, then increased to −14,385 kT when the Ca2+ concentration was further increased to 6 mM. The change in AB interaction energy explains the dynamic evolution of the membrane fouling phenomenon. This work elucidates the effects of high Ca2+ concentrations on organic fouling and will benefit the better understanding of the efficient NF processes when multiple pollutants coexist.

Efficient removal of perfluorinated compounds with the polyamide nanofiltration membrane and membrane fouling resistance analysis

Abstract Perfluorinated compounds (PFCs) are significant pollutants known for their high toxicity and resistance to natural degradation, posing a severe threat to both the global environment and human health. In this study, a polyamide (PA) membrane with an intermediate layer structure of MXene-TiO2 (referred to as MXT-NFM) was utilized for the removal of PFCs. Experimental results confirm that MXT-NFM exhibited remarkable capacity in intercepting PFCs, accompanied by the high water flux. To gain insights into the mechanisms governing membrane fouling induced by PFCs, inorganic ions, and organics, a series of fouling tests were conducted using MXT-NFM under diverse conditions. Additionally, the XDLVO theory was employed to provide a theoretical perspective on the interactions occurring during the fouling process. The findings suggest that the MXene-TiO2 intermediate layer contributed to the exceptional hydrophilicity and rough surface properties, enabling multiple functionalities. These include alleviating membrane pore plugging, improving the physical configuration of the PA layer, and effectively mitigating fouling phenomena in coexisting systems during practical applications. Moreover, the particle size of pollutant colloids and the acid–base interaction were identified as decisive factors influencing the development of membrane fouling.

Effect of superficial gas velocity on membrane fouling behavior and evolution during municipal wastewater treatment

Aerobic granular sludge membrane bioreactor (AGMBR) is a promising technology for wastewater reuse and membrane fouling mitigation. Superficial gas velocity (SGV) plays an important role in the efficient and stable operation of AGMBR. However, the effect of SGV on the membrane fouling behavior and evolution of AGMBR has not been reported, which was systematically investigated in this study. AGMBR with various SGVs was used to treat synthetic municipal wastewater, and more than 94.5% and 60.5% of organics and total nitrogen, respectively, were removed at all SGVs. Further, a larger SGV prolonged the AGMBR overall operation. Contents and physiochemical properties of foulants varied with SGV and transmembrane pressure (TMP). Micro-level analyses revealed that the proportion of pore-blocking resistance in total fouling resistance as well as the microbial community diversity in the sludge mixture or on the membrane surface increased with TMP and SGV. The correlation analyses demonstrated that decreasing the polysaccharide content of soluble microbial products, increasing the protein content of tight extracellular polymeric substances in the sludge mixture, and enhancing the relative abundance of Bacteroidia and Gammaproteobacteria were beneficial for mitigating membrane fouling. This study reveals membrane fouling evolution and provides theoretical guidance for the large-scale application of AGMBR in wastewater reuse.

In Situ Visualization of Membrane Fouling Evolution during Ultrafiltration Using Label-Free Hyperspectral Light Sheet Fluorescence Imaging.

Profound understanding of fouling behaviors and underlying mechanisms is fundamentally important for fouling control in membrane-based environmental applications. Therefore, it entails novel noninvasive analytical approaches for in situ characterizing the formation and development of membrane fouling processes. This work presents a characterization approach based on hyperspectral light sheet fluorescence microscopy (HSPEC-LSFM), which is capable of discriminating various foulants and providing their 2-dimensional/3-dimensional spatial distributions on/in membranes in a label-free manner. A fast, highly sensitive and noninvasive imaging platform was established by developing a HSPEC-LSFM system and further extending it to incorporate a laboratory-scale pressure-driven membrane filtration system. Hyperspectral data sets with a spectral resolution of ∼1.1 nm and spatial resolution of ∼3 μm as well as the temporal resolution of ∼8 s/plane were obtained, and the fouling formation and development process of foulants onto membrane surfaces, within the pores and on the pore walls were clearly observed during the ultrafiltration of protein and humic substances solutions. Pore blocking/constriction at short times while cake growth/concentration polarization at longer times was found to have coupled effects for the flux decline in these filtration tests, and yet the contribution of each effect as well as the transition of the governing mechanisms was found distinct. These results demonstrate in situ label-free characterization of membrane fouling evolution with the recognition of foulant species during filtration and provide new insights into membrane fouling. This work offers a powerful tool to investigate dynamic processes for a wide range of membrane-based explorations.

Comparison of membrane fouling during ultrafiltration with adsorption studied by quartz crystal microbalance with dissipation monitoring (QCM-D)

Even though membrane technology is used in numerous industrial applications, membrane fouling is still a major challenge. Valuable information on the formation kinetics and structure of the fouling layer can be obtained by in situ real-time monitoring. Quartz crystal microbalance with dissipation monitoring (QCM-D) enables the study of adsorptive fouling in situ on a model membrane. However, so far, there has been no in-depth investigation as to what extent observations from QCM-D relate to fouling during membrane filtration. This gap is here approached by comparing membrane fouling during ultrafiltration with QCM-D measurements using the same feed (process water from thermomechanical pulping) and the same material in the polymer film as in the membrane (hydrophilized polysulfone). The performance at two temperatures (25 °C and 50 °C) was studied. Fouling was analyzed by flux measurements, changes in frequency and dissipation over time with QCM-D, and surface characterization of the membrane samples and QCM-D sensors. QCM-D revealed an increase in rigidity of the fouling layer at 50 °C with time, which was consistent with a higher irreversible resistance during ultrafiltration. This was presumably caused by structural changes of hemicelluloses and colloidal wood extractive droplets in the process water at the higher temperature. The study shows that findings from QCM-D on the attachment of foulants on polymer films are comparable to membrane fouling. Thus, QCM-D, together with complementary analytical methods, can provide valuable insights on the development of membrane fouling of e.g., industrial wastewater.

Development and Implementation of MBR Monitoring: Use of 2D Fluorescence Spectroscopy.

The monitoring of a membrane bioreactor (MBR) requires the assessment of both biological and membrane performance. Additionally, the development of membrane fouling and the requirements for frequent membrane cleaning are still major concerns during MBR operation, requiring tight monitoring and system characterization. Transmembrane pressure is usually monitored online and allows following the evolution of membrane performance. However, it does not allow distinguishing the fouling mechanisms occurring in the system or predicting the future behavior of the membrane. The assessment of the biological medium requires manual sampling, and the analyses involve several steps that are labor-intensive, with low temporal resolution, preventing real-time monitoring. Two-dimensional fluorescence spectroscopy is a comprehensive technique, able to assess the system status at real-time without disturbing the biological system. It provides large sets of data (system fingerprints) from which meaningful information can be extracted. Nevertheless, mathematical data analysis (such as machine learning) is essential to properly extract the information contained in fluorescence spectra and correlate it with operating and performance parameters. The potential of 2D fluorescence spectroscopy as a process monitoring tool for MBRs is, therefore, discussed in the present work in view of the actual knowledge and the authors' own experience in this field.

Interplay of organic components in membrane fouling evolution: Statistical evidence from multiple spectroscopic analyses

Membrane fouling is a complex process that can be caused by multiple organic foulants such as polysaccharides, proteins and humic substances. The key mechanisms, especially interactions between coexisting foulant components, have yet to be well understood. This study proposes a combination of spectral and statistical methods to unravel the interactive role of typical organic foulants during microfiltration, taking bovine serum albumin (BSA), humic acid (HA) and sodium alginate (SA) as examples. Results show that the membrane effluent spectra (ultraviolet absorption, fluorescence and circular dichroism) can differentiate the state of foulant interception at the pore adsorption/blocking stage (BSA and HA actively involved) and gel/cake layer stage (SA dominant). Multivariate redundancy analysis revealed interrelations between the spectral characteristics of the effluent and surface fouling layer. Accumulation of proteins and polysaccharides in the fouling layer was detected by infrared spectroscopy while that of humics was more sensitively reflected by Raman spectroscopy, as confirmed by nonnegative linear least square fitting of time-series spectral data during fouling evolution. A variance partitioning analysis nested in multiple linear regression of the infrared or Raman signals offered further statistical evidence for the interplay of organic components by quantifying the single/double/triple-component contributions to the total fouling response. It revealed that ternary BSA × HA × SA interplay is prominent at the initial pore adsorption/blocking stage whereas binary HA × SA interplay prevails at the later gel/cake layer stage. Such role shifting of foulant interactions during the fouling process might provide useful information for a more accurate understanding and control of fouling. The combined spectral and statistical methods, which can effectively trace inter-component relations and link molecular fingerprints to fouling behavior, are particularly promising for exploring fouling mechanisms in complex systems.

Antifouling Conductive Composite Membrane with Reversible Wettability for Wastewater Treatment.

Membrane fouling severely hinders the sustainable development of membrane separation technology. Membrane wetting property is one of the most important factors dominating the development of membrane fouling. Theoretically, a hydrophilic membrane is expected to be more resistant to fouling during filtration, while a hydrophobic membrane with low surface energy is more advantageous during membrane cleaning. However, conventional membrane materials do not possess the capability to change their wettability on demand. In this study, a stainless steel mesh–sulfosuccinate-doped polypyrrole composite membrane (SSM/PPY(AOT)) was prepared. By applying a negative or positive potential, the surface wettability of the membrane can be switched between hydrophilic and relatively hydrophobic states. Systematic characterizations and a series of filtration experiments were carried out. In the reduction state, the sulfonic acid groups of AOT were more exposed to the membrane surface, rendering the surface more hydrophilic. The fouling filtration experiments verified that the membrane is more resistant to fouling in the hydrophilic state during filtration and easier to clean in the hydrophobic state during membrane cleaning. Furthermore, Ca2+ and Mg2+ could complex with foulants, aggravating membrane fouling. Overall, this study demonstrates the importance of wettability switching in membrane filtration and suggests promising applications of the SSM/PPY(AOT) membrane.

Molecular level insights into the dynamic evolution of forward osmosis fouling via thermodynamic modeling and quantum chemistry calculation: Effect of protein/polysaccharide ratios

While forward osmosis (FO) shows broad application prospects in wastewater reuse and desalination, it is still hindered by membrane fouling issues. From the perspective of molecular structure and energy, this work investigated the effects of protein (PN)/polysaccharide (PS) ratios of organic foulants on the dynamic evolution of membrane fouling in FO. Fouling tests showed two interesting membrane fouling phenomena: Ⅰ) when PN content increased from 0.2 to 0.8 g/L with fixed PS content of 0.2 g/L, membrane fouling decreased for filtration of the same volume of foulants; Ⅱ) with the increase of filtration volume, the membrane fouling caused by 1:1 PN/PS foulants increased almost linearly, while the membrane fouling caused by 4:1 PN/PS foulants increased significantly at first, and then rapidly reached a stable fouling state. Thermodynamic analyses and quantum chemical calculations revealed that the attractive interaction energy between 1:1 PN/PS foulants and membrane was 1.90 times greater than that for 4:1 PN/PS foulants, and the protein and polysaccharide molecules with a ratio of 1:1 were more likely to form a tight cross-linked structure. Furthermore, the reverse solute diffusion significantly reduced the electrostatic repulsion energy among the polymer chains for 4:1 PN/PS foulants, which induced the transformation of foulant morphology from gel to floc and reduced the adhesion energy to membrane surface by 61%. As a result, in the later fouling stage, few 4:1 PN/PS foulants were newly attached to the membrane, leading to a pseudo-stable flux. Based on the aforementioned findings, this study reveals a unified thermodynamic framework for the effects of the PN/PS ratios of organic foulants on the dynamic evolution of FO membrane fouling. The proposed mechanism is beneficial in formulating “tailored” fouling mitigation strategies and elucidating the appropriate application fields for FO technology.

Unravelling temperature-dependent fouling mechanism in a pilot-scale anaerobic membrane bioreactor via statistical modelling

Operational temperature is one of the most vital factors that profoundly affect membrane fouling during anaerobic membrane bioreactor operation. This study uncovered the temperature-dependent fouling mechanism in a pilot-scale anaerobic membrane bioreactor treating real municipal wastewater at ambient temperature seasonally fluctuating from 35 to 5 °C. It showed that compared to time accumulation effect of fouling layer, temperature played a more profound role on influencing membrane fouling. Low temperature caused severe membrane fouling by affecting the release of proteinous soluble microbial products (SMP) and extracellular polymeric substances (EPS) and the abundance of related microbial community structure, like Proteobacteria, Firmicutes, Bacteroidetes and Chloroflexi. The path analysis model established in this study, which was statistically significant at 5% level, revealed that temperature could substantially affect SMP and EPS, especially proteinous SMP (β = −0.94, p < 0.01), and thus indirectly influence total fouling rate, since SMP and EPS had significant influence on total fouling rate (p < 0.05). A temperature-based model (R2 > 0.95) was successfully developed in this study for predicting membrane fouling development over the seasons. The output of these two models varied with the type of membrane module. As calculated from the path coefficients, the influence of temperature on the total fouling rate of polymeric membrane (0.70) was greater than that on the total fouling rate of ceramic membrane (0.56). The regression coefficients of the formula obtained from the temperature-based model using the TMP results of polymeric membrane were around twice as large as those obtained from the model using the TMP results of ceramic membrane. These results suggested that ceramic membrane had better anti-fouling property, probably due to its chemical and thermal stability, hydrophilic surface, and well-organized pore structure, as confirmed by the resistance-in-series analysis and excitation-emission matrix (EEM) analysis of the foulant layer.

Direct and indirect effects of membrane pore size on fouling development in a submerged membrane bioreactor with a symmetric chlorinated poly (vinyl chloride) flat-sheet membrane

Membrane bioreactors (MBRs) have been recognized as a promising wastewater treatment technique because of their superior solid–liquid separation performance; however, fouling development remains a concern. In this study, the relationship between membrane pore size and fouling development is investigated using originally prepared chlorinated polyvinyl chloride (CPVC) flat-sheet membranes with different pore sizes in MBRs; further, the mechanism of fouling development is demonstrated. Under the conditions in this study, the optimal membrane pore size for suppressing fouling development was determined to be in the range of 0.31–0.57 µm. It was also demonstrated that irreversible fouling is closely related to the capture of protein-like compounds inside the membrane; in contrast, it was considered that reversible fouling is caused by gel and cake layers formed on the membrane surface. Moreover, it was indicated that the membrane pore size directly and indirectly affected both reversible and irreversible fouling through the mutual relationship with other membrane characteristics such as the surface roughness. Finally, it is concluded that the optimal membrane pore size for suppressing fouling development is determined by the total filtration resistance caused by irreversible and reversible fouling phenomena.

Seasonal shift of water quality in China Yangtze River and its impacts on membrane fouling development during the drinking water supply by membrane distillation system

Membrane distillation (MD) technique is increasingly regarded as a promising process for drinking water supply and wastewater treatment owing to its great water purification and usage of renewable energy. Like other membrane separation processes, the membrane fouling issue is widely considered as the main obstacle for real applications of large-scale MD systems. Feedwater characteristics, as the predominant factors for membrane fouling layer formation, mostly determined the membrane fouling trend of MD. Thus the impacts of seasonal shifts of initial feedwater quality on the MD membrane fouling were detailedly researched in this study, and the biofilm development mechanism was especially explored. The bacterial community structure of membrane biofilms was clearly clarified in MD runs of Yangtze River waters that collected in four seasons. The results revealed that the winter run posed a quite sharp flux drop, while a relatively milder flux decline behaviour was seen for other groups despite of the higher bacteria concentration of initial feedwaters. The poorer water quality in winter induced the establishment of a rather thick biofilm on the MD membrane, in which the biofilm-forming bacteria (Gammaproteobacteria and Alphaproteobacteria) and organic matters (EPS) were remarkably observed. Comparatively, a relatively thin biofilm containing abundant live cells and fewer organics finally formed in summer and autumn runs, causing a mitigated flux decline trend. Hence, it can be inferred that the membrane flux decline of MD was likely to be more sensitive to the organic attachment on the membrane in comparison with the bacteria adhesion. Finally, a three-phase pretreatment method was suggested for MD fouling control, including heating course, sterilization course, and filtration course.

Forward osmosis treatment of algal-rich water: Characteristics and mechanism of membrane fouling

Membrane fouling is an inevitable problem in forward osmosis (FO) treatment of algal-rich water (ARW). Natural ARW has a complex composition. Therefore, the coexisting components (Ca2+, natural organic humic acid [HA], and inorganic particulate kaolinite) in the influence of ARW on FO membrane fouling were studied. The analysis of extended Derjaguin–Landau–Verwey–Overbeek theory and the confocal laser scanning microscopy revealed that the addition of coexisting components increased the attraction between pollutants and membranes, as well as among pollutants to varying degrees, and promoted the development of membrane fouling. Furthermore, Ca2+ and HA aggravated irreversible membrane fouling. All coexisting components changed the distribution and thickness of the fouling layer, and the addition of Ca2+ increased the content of extracellular organic matter (proteins and polysaccharides). The present results enhance the understanding of the mechanism through which natural ingredients affect microalgal membrane fouling and provide a basis for membrane fouling control to treat ARW.

Real-time fouling monitoring and membrane autopsy analysis in forward osmosis for wastewater reuse

Forward osmosis process in emerging technology which can applicable in wastewater reuse and desalination simultaneously. In this study, the development of fouling on the FO membrane surface was monitored in real-time. The investigation of fouling layer physical and chemical characteristics was assessed by performance evaluation and in-depth analysis of fouling layer. Non-invasive visual monitoring and in-depth autopsy, combined with the performance and image analyses provided a better understanding of fouling phenomena. The relative roughness of the fouling layer was correlated with water flux decrease while the fouling layer thickness decreased rapidly when fouling was stabilized. From 66-day operation using the primary wastewater as the feed, membrane fouling development was classified into 4 phases: virgin performance, initial deposition, stabilization and aggregation. With the growing fouling layer and with aggregation, the removal rate of organic matter was reduced from 99 to 70%. Conversely, the removal rate of inorganic matter was maintained at a level higher than 90%. The fractionation of physical and chemical extraction had the following characteristics: TPI>HPI>HPO and HPI>TPI>HPO respectively. Also, low molecular weight and building blocks like organic matter were observed with a high composition ratio of fouling layer. Through the correlation between the process performance, real-time monitoring of fouling layer formation and deep-layer fouling analysis, it was possible to identify the major membrane contaminants and propose process optimization guidelines.

Deep learning model for simulating influence of natural organic matter in nanofiltration

Controlling membrane fouling in a membrane filtration system is critical to ensure high filtration performance. A forecast of membrane fouling could enable preliminary actions to relieve the development of membrane fouling. Therefore, we established a long short-term memory (LSTM) model to investigate the variations in filtration performance and fouling growth. For data acquisition, we first conducted lab-scale membrane fouling experiments to identify the diverse fouling mechanisms of natural organic matter (NOM) in nanofiltration (NF) systems. Four types of NOMs were considered as model foulants: humic acid, bovine-serum-albumin, sodium alginate, and tannic acid. In addition, real-time 2D images were acquired via optical coherence tomography (OCT) to quantify the cake layer formed on the membrane. Subsequently, experimental data were used to train the LSTM model to predict permeate flux and fouling layer thickness as output variables. The model performance exhibited root mean square errors of <1 L/m2/h for permeate flux and <10 µm for fouling layer thickness in both the training and validation steps. In this study, we demonstrated that deep learning can be used to simulate the influence of NOMs on the NF system and also be applied to simulate other membrane processes.