Membrane Fouling Behavior Research Articles

Antifouling mechanism of the additive-free β-PVDF membrane in water purification process: Relating the surface electron donor monopolarity to membrane-foulant interactions

Although the antifouling modification of polyvinylidene fluoride (PVDF) membrane has attracted much attentions recently, the underlying fouling/antifouling mechanism of the PVDF membranes having different polymorphs have rarely been mentioned. In this study, two PVDF membranes with similar pore structure but distinct polymorphs were prepared, and their antifouling performance was systematically investigated by using synthetic solutions containing complex foulants relevant to surface water sources (e.g., humic acid, bovine serum albumin and dextran). A remarkable correlation between PVDF polymorph, membrane surface chemistry and fouling resistance was observed, demonstrating the exceptional ability of β-PVDF phase (i.e., β-PVDF membrane) in fouling mitigations when compared to α-PVDF phase (i.e., α-PVDF membrane). In order to unravel the fouling mechanism of PVDF membrane having different polymorphs, interaction forces between foulant-coated particle probes, simulating foulant molecules, and each membrane surface were measured by AFM and theoretical calculated depended on surface energy components. It is clearly shown that the enhanced fouling resistance of β-PVDF membrane was mainly driven by the reduced adhesion tendency of foulants, which could further attribute to the strong electron donor monopolarity of β-PVDF phase (γAB− = 25.3 mJ/m2) compared to α-PVDF phase (γAB− = 3.3 mJ/m2). Moreover, for each SSW-fouled membrane, depth profiling of the external fouling layer and composition of the extracted internal foulants were carefully investigated by variable angle FTIR and UV–vis spectrometer, respectively, suggesting the strong relationship between membrane fouling behavior and membrane-foulant and foulant-foulant interactions. This work emphasized the selection of proper polymorph of PVDF membrane should be valued so as to mitigate membrane fouling, and we anticipate the advantage of β-PVDF phase in membrane fouling control can boost the development of additive-free and sustainable antifouling strategy in future.

Simultaneous nitritation, anammox, and denitrification (SNAD) process in a membrane bioreactor: start-up, optimization, and membrane fouling behavior

Simultaneous nitritation, anammox, and denitrification (SNAD) process in a membrane bioreactor: start-up, optimization, and membrane fouling behavior

Comparing powdered and granular activated carbon addition on membrane fouling control through evaluating the impacts on mixed liquor and cake layer properties in anaerobic membrane bioreactors

Concerning the lack of comprehensive study on the impact of powdered and granular activated carbon (PAC and GAC) on AnMBR, their impact on treatment performance, mixed liquor and cake layer properties and membrane fouling behaviors were further investigated. High COD removal efficiencies (>90%) and COD converting to CH4 rates (>70%) were achieved. GAC greatly increased extracellular polymeric substances (EPS) production in mixed liquor, but significantly reduced biosolids deposited on membrane surface; while PAC largely increased proteins and polysaccharides on membrane surface. In addition, PAC decreased, whereas GAC increased particle sizes. Fouling rates showed PAC and GAC addition effectively alleviated membrane fouling at HRT 8 h, and GAC remarkably postponed the occurrence of the transmembrane pressure jump and extended membrane service time. This study clarified the roles of GAC and PAC on membrane fouling control over long-term operation, which provides the basis for decision-making in practical application.

Modification of forward osmosis membrane with naturally-available humic acid: Towards simultaneously improved filtration performance and antifouling properties

In this work, a thin-film composite forward osmosis (FO) membrane was fabricated on polyethersulfone substrate by interfacial polymerization with naturally-available humic acid (HA) as a stable membrane additive in the support layer. Compared with the pristine polyethersulfone substrate, the incorporation of HA significantly altered the cross-section structure, increased average pore size and porosity of the substrate, leading to a thinner polyamide layer, further increasing the water flux (permeability). Specifically, the FO membrane showed a higher water flux (~20 L m−2 h−1) with the introduction of HA than the membrane synthesized without HA (~15 L m−2 h−1) in the FO mode with 2 M NaCl as draw solution. Moreover, the selectivity of the membrane was improved ~45% by dosing 0.8 wt% HA into the substrate, in comparation to the pristine membrane without HA doped. Besides, the average roughness of the polyamide layer was reduced by up to 68% when HA was present in the substrate, which mitigated the fouling potential. Thus, a slower flux decline ratio (~60%) was observed for the membrane modified with 0.8 wt% HA than the pristine membrane (~80%). Taken together, our findings shed light on using natural-available HA for effectively and efficiently modifying membrane substrate to simultaneously enhance the permeate-selectivity performance and the anti-fouling behavior in FO membrane process. The fundamental causes of these differences in membrane separation performance and fouling behavior are considered and related to the physical and chemical characteristics of support layer (i.e., porosity and pore size) and polyamide layer (i.e., active layer thickness and roughness) of membranes.

On line monitoring local fouling behavior of membrane filtration process by in situ hydrodynamic and electrical measurements

The hollow fiber ultrafiltration (UF) membrane has been widely applied in the water treatment industry, however, the membrane fouling is the core reason and limiting factor in terms of its industrial application. In the constant flux process, hollow fiber membranes (HFM) non-uniform fouling varies along the axis direction, which is the basic mechanism of HFM fouling. In this paper, the local membrane fouling behaviors and verities are investigated using electrical impedance (EI) and zeta potential (ZP) to capture the feedback signals of membrane fouling behaviors. The results are then, integrated with Hermia's model and an equivalent circuit model. As the fitting results show, both the EI and ZP can be employed as indicators of different membrane fouling states. This work defines the different stages of membrane fouling depending on the alternating relationship between EI and ZP in the membrane filtration process. Furthermore, the behavior of cake layer compaction is defined from the perspective of the membrane fouling mechanism. Therefore, this study provides an effective means for accurate identification of membrane fouling behavior. In addition, the EI and ZP exhibit great potential to identify the fouling distributions and proceedings in HFM fouling. Doing so successfully confirms that the characteristics of non-uniform fouling of HFM are reflected in the spatiotemporal difference of the fouling process.

In-situ recovery of bio-butanol from glycerol fermentation using PDMS/ceramic composite membrane

Pervaporation (PV) membranes have been attracted increasing attention in biofuels recovery owing to the higher separation efficiency and less harmful effect on microbes. Herein, we reported polydimethylsiloxane (PDMS) membrane coated on the inner surface of ceramic tube to in-situ recover bio-butanol from glycerol fermentation through PV process. The effects of butanol concentration, intermediates, raw material, inorganic salts and microbes on PV separation property of the PDMS/ceramic composite membranes were systematically discussed. After integrating with the membrane, bio-butanol was successively extracted from the fermentor, thereby remarkably reducing the butanol inhibition effect on microbial growth and thus greatly enhancing the yield and productivity of bio-butanol, from 0.35 to 0.40 g g−1 and 0.09 to 0.17 g L−1 h−1, respectively. Meanwhile, the PDMS composite membrane presented an excellent separation property during the coupled process with 509 g/m2 h for average total flux and 24.7 for butanol/water separation factor. In addition, the membrane fouling behavior was studied by characterizing the membrane microstructure and chemical property before and after using in the coupled process. Compared with the-state-of-the-arts, the PDMS composite membrane coupled with the process of glycerol fermentation presented here shows great potential in application of bio-butanol production.

Deep neural networks for modeling fouling growth and flux decline during NF/RO membrane filtration

Mathematical models have been developed to obtain a better understanding of membrane fouling mechanisms. However, those models could not simulate the membrane fouling behaviors accurately because of the large number of fitting parameters related to feed water quality and flow pattern in a membrane filtration system. In this study, we developed a deep neural network (DNN) to model membrane fouling during nanofiltration (NF) and reverse osmosis (RO) filtration using in-situ fouling image data from optical coherence tomography (OCT). The performance of the DNN model was compared with that of existing mathematical models. In total, 13,708 high-resolution fouling layer images were used to develop the DNN model and validate the model performance. The DNN model was trained to simulate both organic fouling growth and flux decline, and it reproduced two- or three-dimensional images of the organic fouling growth. The DNN model demonstrated better predictive performance than the existing mathematical models. It achieved an R2 value of 0.99 and RMSE of 2.82 μm for the fouling growth simulation and R2 of 0.99 and RMSE of 0.30 Lm−2h−1 for the flux decline simulation. Therefore, the data-driven approach is an alternative way to model the membrane fouling and flux decline processes under high-pressure filtrations.

Fouling mechanism identification and analysis in microfiltration of laundry wastewater

Microfiltration (MF) is known as a promising and green technique that can effectively treat domestic and industrial wastewaters. Inevitably, membrane fouling and scaling hinder productivity and large-scale implementation of this process. The aim of the present study is to evaluate the membrane fouling and flux decline behavior during laundry wastewater treatment. The filtration tests were performed using real domestic laundry wastewater at different transmembrane pressures (0.5–1.5 bar) and feed flowrates (30–80 L/h). Several fouling models including the single and multistage Hermia models were fitted to experimental data. The results of the single-stage Hermia model showed that the cake layer formation (with R2 greater than 0.94) was the main contributor to the flux decline regardless of the operating condition. Results also revealed that by increasing the feed pressure, the contribution of the cake formation mechanism enhanced while an opposite behavior was observed when the feed flow rate increased. However, the single stage model could not accurately predict the performance during the entire filtration time. A more detailed analysis indicated that at least a three-stage model (complete pore blocking in early stage, intermediate pore blocking in middle stage, and cake formation in final stage) could model the flux decline during the entire filtration time with acceptable accuracy (with R2 greater than 0.96). Therefore, the multistage Hermia model was used for determining either fouling mechanism, ways for postponing fouling of the membranes, and flux decline behavior during the membrane filtration of laundry wastewater experiments.

Prediction of interfacial interactions related with membrane fouling in a membrane bioreactor based on radial basis function artificial neural network (ANN)

It is of great importance to propose effective methods to quantify interfacial interaction since it directly determines foulant adhesion and membrane fouling process in membrane bioreactors (MBRs). This study developed a radial basis function (RBF) artificial neural network (ANN) to predict the interfacial interactions with randomly rough membrane surface. The interaction data quantified by the advanced extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approach were used as the training samples for the RBF networks. It was found that, the computing time consumption for the RBF network prediction was only about 1/50 of that for the advanced XDLVO approach under same conditions, indicating the high efficiency of the RBF ANN method. Meanwhile, the calculation accuracy of the method was acceptable to get reliable results. This study demonstrated the breakthrough of the fundamental methodology related with membrane fouling. The proposed RBF ANN method has broad application prospects in membrane fouling and interface behavior research.

Evaluating the performance and membrane fouling of an electro-membrane bioreactor treating textile industrial wastewater

This study evaluated for the first time the performance and the membrane fouling behavior of a laboratory-scale electro-membrane bioreactor (EMBR) for the treatment of real textile wastewater. The EMBR was operated initially with no electrocoagulation process (control period) during 30 days (run I), and thereafter, the electrocoagulation was started, using the electrical current density of 10 A m−2 (run II) and 15 A m−2 (run III). The reactor performance on color removal was significantly improved by electrocoagulation process, attaining average efficiency of 50 and 70% in the experimental runs II and III. Similarly, the nitrification performance also was enhanced during the period with electrocoagulation, enabling an average NH4+–N removal efficiencies above 90% in the runs II and III. Activity batch assays have shown that autotrophic biomass exhibited a higher oxygen uptake rate during the electrocoagulation experiments, indicating that nitrifying activity increased in the EMBR over this period. Despite the substantial variation in the influent COD values, the COD removal efficiencies were practically constant (75–77%) throughout experimental period. This behavior indicates that the reactor exhibited a great resistance to shock loading, an important feature for the treatment of industrial wastewaters. Better mixed liquor filterability conditions were found during the electric current application, resulting in a lower membrane fouling rate and demanding a lower frequency of the membrane chemical cleaning process.

Application of Al species in coagulation/ultrafiltration process: Influence of cake layer on membrane fouling

The membrane fouling is a challenge for the application of ultrafiltration, one of which the cake layer is the main influencing factor. However, the pros and cons of cake layer generated in the coagulation-ultrafiltration (C-UF) process needs to be explored. This study was carried out to investigate that the effect of a cake layer on the membrane fouling behavior with three Al species coagulants for different effluents. The results indicated that the fouling mechanisms of cake layer under different effluents conditions were diverse due to the particle characteristics. The Al hydrolysis that accompanied by the interaction between Al species coagulants and the –OH/-COOH functional groups of humic acid were conducted, and the effluents of Ala presented lighter membrane fouling. Meanwhile, the components mainly trapped by the membrane were soluble microbial products, protein, polypeptides and amino acid-like materials during C-UF process, because of the decrease in the proportion of fluorescence response. For the less/compact cake layer (system 2), the average of the external and internal membrane resistances were about 25 × 1010 m−1 and 21 × 1010 m−1, respectively, which caused severe membrane fouling. It was concluded that the poriferous/loose cake layer could effectively alleviate membrane fouling by re-adsorbing some organic matters.

Comparative study on treatment performance, membrane fouling, and microbial community profile between conventional and hybrid sequencing batch membrane bioreactors for municipal wastewater treatment.

A sequencing batch conventional membrane bioreactor (SB-CMBR) and sequencing batch hybrid membrane bioreactor (SB-HMBR) were operated in parallel under two different hydraulic retention times (HRTs) (namely 12h and 6h), and their chemical oxygen demand (COD) and nutrient removal performance, membrane fouling behavior, and microbial community characteristics were compared. Both systems exhibited high organic matter (> 95%) and ammonium (> 98%) removal performance regardless of the HRT applied. As the HRT was reduced from 12 to 6h, total nitrogen removal slightly increased in both reactors, being higher in the carrier-based MBR, where anoxic zones may have been established within the biofilm. Conversely, total phosphorus removal improved only in the SB-CMBR at the shorter HRT. Moreover, activity batch assays have shown a faster P uptake rate in the SB-CMBR than in the SB-HMBR, a result likely associated with the lower relative abundance of phosphate-accumulating organisms in both adhered and suspended biomass fractions in the hybrid MBR. The results also revealed that more pronounced increases in the transmembrane pressure and, consequently, in the membrane fouling rate at higher COD loading rates were observed in the SB-CMBR, where the soluble microbial products (proteins, polysaccharides, and especially, transparent exopolymer particles), supernatant turbidity, and filamentous bacteria were more significant. Overall, as compared to the conventional MBR, the plastic media-based SB-HMBR showed a lower fouling propensity at all hydraulic conditions tested.

Effect of Hydraulic Retention Time on Treatment Performance in an Anoxic/Oxic Electro-Membrane Bioreactor

AbstractBacterial profile, nutrients removal performance, and membrane fouling behavior were evaluated in an anoxic/oxic electro-membrane bioreactor (A/O e-MBR) treating municipal wastewater at dif...

Prototype aquaporin-based forward osmosis membrane: Filtration properties and fouling resistance

The trade-off between water permeability and selectivity is considered as the biggest challenge during membrane fabrication for water purification. The aquaporin (AQP)-based biomimetic membrane has been proven to have both enhanced water permeability and improved selectivity due to the unique features of the AQP protein water channel that permits water molecules and rejects all other components. In this study, a prototype forward osmosis (FO) Aquaporin Inside™ membrane (AIM) was evaluated in terms of intrinsic filtration properties, membrane surface chemistry and fouling behaviour, and compared with a commercial FO membrane. The surface of the prototype AIM appeared to be a modified semi-aromatic polyamide layer instead of fully-aromatic as in other conventional FO products. As a result, compared to the commercial FO membrane, the prototype AIM shows higher water flux and comparable reverse salt flux (RSF) when tested under identical conditions. Due to the lower RSF, the AIM had less organic fouling by a sodium alginate solution when calcium chloride (CaCl2) was used as the draw solution (DS). The membrane integrity of the prototype AIM was maintained after repeated cycles of fouling by high concentration of gypsum and physical cleaning tests. This demonstrates the possibility of using the AIM membrane for treating harsh feed solutions.

Functional Determinants of Extracellular Polymeric Substances in Membrane Biofouling: Experimental Evidence from Pure-Cultured Sludge Bacteria.

The aim of this work was to better understand the roles of extracellular polymeric substances (EPS) in membrane biofouling at the single-strain level. In the present study, a total of 23 bacterial strains were isolated from a sludge sample. The EPS extracted from pure-cultured bacteria were assessed for their fouling potentials and were simultaneously analyzed using Fourier transform infrared spectroscopy (FTIR). Further, the impact of calcium on the chemical composition of EPS and membrane fouling behavior was investigated in a strain-dependent manner. The EPS of the 23 bacterial strains exhibited different IR features for protein and polysaccharide regions. In addition, an α-1,4-glycosidic linkage (920 cm-1) and amide II (1,550 cm-1) correlated very well with the fouling potentials of all pure-cultured bacteria. In contrast to low-fouling strains, medium- and high-fouling strains exhibited two distinct peaks at 1,020 cm-1 (uronic acids) and 1,250 cm-1 (O-acetyl), which accelerate membrane fouling given their gelling capacities. In the presence of calcium, the fouling potential of a high-fouling strain (Bacillus sp. strain JSB10) was profoundly reduced (P < 0.0005) due to the binding activity of an α-1,4-glycosidic linkage and amide II with calcium. However, the impact of calcium on a low-fouling strain (Vagococcus sp. strain JSB21) was insignificant. Two-dimensional FTIR correlation spectroscopic (2D-FTIR-COS) analysis further revealed that the susceptibilities of functional groups to calcium largely relied on the composition and abundance of the above-described functional groups in EPS. These findings suggest that bacterial strains with different fouling potentials exhibit varied responses to calcium.IMPORTANCE Membrane biofouling is one of the main challenges for the operation of membrane-based processes used for water and wastewater treatment. This study revealed the functional determinants of EPS in membrane biofouling of 23 bacterial strains isolated from a full-scale membrane bioreactor (MBR) plant. We found that an α-1,4-glycosidic bond, amide II, and uronic acids of EPS significantly correlated with the fouling potentials of bacteria. The roles of these EPS groups in membrane fouling were impacted by calcium resulting from EPS-calcium interactions. In addition, our results also demonstrated that any perturbations in the sludge bacterial community in MBRs can lead to varied filtration potentials of the bulk liquor.

Effects of physical and chemical aspects on membrane fouling and cleaning using interfacial free energy analysis in forward osmosis.

Natural organic matter (NOM) in micro-polluted water purification using membranes is a critical issue to handle. Understanding the fouling mechanism in the forward osmosis (FO) process, particularly identifying the predominant factor that controls membrane fouling, could have significant effects on exerting the advantages of FO technique. Cellulose triacetate no-woven (CTA-NW) membrane is applied to experiments with a high removal efficiency (> 99%) for the model foulant. Tannic acid (TA) is used as a surrogate foulant for NOM in the membrane fouling process, thus enabling the analysis of the effects of physical and chemical aspects of water flux, retention, and adsorption. The membrane fouling behavior is affected mainly by the combined effects of the osmotic dragging force and the interaction of the pH in the working solution, foulants, and calcium ions, as demonstrated by the water flux loss and the changes of membrane retention and adsorption. The fouled CTA-NW membrane (in PRO mode) could be flux-recovered by > 85% through physical cleaning methods. The interfacial free energy analysis theory was used to analyze the membrane fouling behavior with calculating the interfacial cohesion and adhesion free energies. The cohesion free energy refers to the deposition of foulants (TA or TA combined with calcium ions) on a fouled membrane. In addition, the adhesion free energy could be used to evaluate the interaction between foulants and a clean membrane.

Membrane Fouling Characteristics of a Side-Stream Tubular Anaerobic Membrane Bioreactor (AnMBR) Treating Domestic Wastewater

A lab-scale of a side stream anaerobic membrane bioreactor (AnMBR) equipped with a tubular membrane operated at the mesophilic temperature of 37.0 ± 1.2 °C for treating domestic wastewater was tested to investigate its performance and fouling characteristics at two organic loading rates (OLR) of 0.25 kg COD m−3d−1, and 0.70 kg COD m−3d−1, respectively. The AnMBR was operated for 600 days at sludge retention time (SRT) of 100 days. This AnMBR exhibits excellent chemical oxygen demand (COD) removal of 91% at 0.25 kg COD m−3d−1, and 94% at 0.7 kg COD m−3d−1 respectively, with effluent-soluble COD below 50 mg/L. Chemically-enhanced cleaning method using NaOH, NaOCl, and citric acid solution were introduced for fouling investigation at these two stages. The results showed that sequential chemical cleaning of alkaline and acid were most effective to recover the membrane flux. The alkaline cleaning was effective at removing organic foulants, while citric acid cleaning was effective at removing the scalants. The analyses of the excitation emission matrix, gel permeation chromatography, and extracellular polymeric substances indicated that major components of membrane foulants were proteins, carbohydrates, humic, and fulvic acids. At 0.25 kg COD m−3d−1, organic fouling was more prone to be trapped in the cake layers and responsible for membrane pore blockage, inorganic fouling exhibited marginal contribution to the membrane fouling behavior. However, at 0.70 kg COD m−3d−1, high concentrations of organic and inorganic foulants supported an essential role of organic and inorganic fouling on membrane fouling behavior.

Effects of pre-oxidant (KMnO4) on structure and performance of PVDF and PES membranes

The structure and performance of membrane materials are very important to the efficient and stable operation in membrane drinking water purification technology. Potassium permanganate (KMnO4), which can change the characteristics of organic matters and control membrane surface fouling, has been widely used as pre-oxidant in the front of membrane drinking water process. This study investigates the evolution of membrane surface structure and performance when polyvinylidene fluoride (PVDF) and polyethersulfone (PES) were exposed to 10, 100 and 1000 mg·L− 1KMnO4 solution for 6 and 12 d, respectively. The aged membrane physicochemical characteristics such as membrane surface morphology, chemical composition, hydrophilicity, porosity and zeta potential were evaluated by modern analytical and testing instruments. The anti-fouling property of membrane surface was also investigated by the filtration-backwash experiment. The results indicated that the different concentrations and exposure time of KMnO4 led to a different variation on PVDF and PES membrane surface structure and performance, which could further affect the membrane separation performance and the membrane fouling behaviors. The membrane surface pore size and porosity increased due to the dislodgment and degradation of membrane additive (PVP), which improved membrane permeability and enhanced the adsorption and deposition of pollutants in the membrane pores. With the increase of exposure time, the membrane surface pore size and porosity reduced for the reactions of chain scission and crosslinking on membrane materials, and the backwashing efficiency declined, leading to a more serious irreversible fouling. Compared with PVDF membranes, the formation of sulfonic group for PES membranes increased the negative charge on membrane surface due to the oxidation of KMnO4. The present study provides some new insights for the regulation of the pre-oxidant dose and the selection of the membrane materials in KMnO4 pre-oxidation combined with membrane filtration system.

Membrane fouling of forward osmosis in dewatering of soluble algal products: Comparison of TFC and CTA membranes

Forward osmosis (FO) has increasingly penetrated into traditional process, i.e. microalgae dewatering, to become one of the new energy saving technologies. However, FO membranes can be fouled by soluble algal products (SAP) and fouling behavior of the membrane is not clear due to the variety of SAP composition. In this work, two types of membranes including a self-made TFC and a commercial CTA, and three kinds of draw solutions including NaCl, MgCl2 and CaCl2 were adopted to investigate the dewatering of SAP from microalgae of Chlorella vulgaris. The dependence of permeate flux and foulants composition on the membranes, membrane orientation and reverse salt diffusion were then compared for membrane fouling behavior. The results showed that TFC membrane exhibited higher water permeability but more loss of water flux in comparison with CTA. The SAP was inclined to be adsorbed by TFC membrane while adsorbate was easier to be removed by physical cleaning. By contrast, the pollutants accumulated on the membrane surface of CTA were much more irreversible. The interaction between SAP from feed solution and calcium cations from draw solution induced the formation of cake layer on the surface of TFC membrane while irreversible granular deposits of SAP were found accumulated on CTA membrane surface. Possible membrane fouling mechanism was finally discussed for better fabrication of anti-fouling forward osmosis membranes, thus to propel the integration of forward osmosis with traditional field of microalgae dewatering.

Sunlight irradiation triggers changes in the fouling potentials of natural dissolved organic matter

Sunlight-initiated photodegradation has a great impact on the composition and properties of natural dissolved organic matter (DOM) in aquatic environments, which potentially changes the behavior and roles of DOM in water treatment facilities. Here, we explored the effect of sunlight irradiation on membrane fouling behavior of two natural DOM (i.e., Aldrich humic acid (AHA) and Suwannee River DOM (SRNOM)), particularly in the presence of calcium ion (Ca(II)). Results showed that a long-term exposure (3 months) to sunlight during the summer led to decreases in the chromophores and molecular size of both DOM. The characterization by UV–vis spectral parameter DSlope350–400 (the slope of the log-transformed absorbance spectra in the range of 350–400 nm) indicated that sunlight-exposed DOM had a weaker Ca(II)-binding ability than unirradiated DOM, which could be attributable to the photochemically induced loss of carboxyl and phenolic groups. Additionally, AHA was found to be more susceptible to sunlight irradiation and Ca(II) addition than SRNOM, likely due to its higher aromaticity. Crucially, dead-end ultrafiltration tests showed that sunlight exposure of both AHA and SRNOM can reduce their fouling potential in the absence of Ca(II) and the presence of low Ca(II) (0.4 mM). In contrast, the addition of higher Ca(II) concentrations (2 and 3.6 mM) led to an increase in their fouling propensities. Overall, sunlight exposure can greatly alter the fouling behavior of natural DOM. This study provides a nexus between the naturally occurring transformation of DOM and its behavior (i.e., membrane fouling) in water treatment facilities.