Model Organic Foulants Research Articles

Membrane distillation of wastewater: comparison of model and real organics.

Fouling behaviour in membrane distillation (MD) processes plays a crucial role in determining their widespread acceptability. Most studies have primarily focused on model organic foulants, such as humic acid (HA) and sodium alginate (SA). This study investigates the fouling of a polytetrafluoroethylene membrane in a direct contact MD (DCMD) using model organics (i.e., HA and SA) and real wastewater. The results indicated that the flux decline (5-60%) was only observed during the initial phase of the operation with model organic foulants. In contrast, real wastewater caused a gradual decline in flux throughout the experiment in both the concentrate (40%) and continuous (90%) modes. The study also found significant differences in the fouling layer morphology, composition, and hydrophobicity between the model organic foulants and real wastewater. Fourier transform infrared spectroscopy findings demonstrated that the fouling layer formed by real wastewater varied significantly from model organics, which primarily comprised of protein-like and polysaccharide-like functional groups. Finally, liquid chromatography-organic carbon detection revealed that the fouling layer of the MD membrane with real wastewater was composed of 40.7% hydrophobic and 59.3% hydrophilic organics. This study suggests that model organics may not accurately reflect real wastewater fouling.

Covalent Organic Framework Membranes and Water Treatment.

Covalent organic frameworks (COFs) are an emerging class of highly porous crystalline organic polymers comprised entirely of organic linkers connected by strong covalent bonds. Due to their excellent physicochemical properties (e.g., ordered structure, porosity, and stability), COFs are considered ideal materials for developing state-of-the-art separation membranes. In fact, significant advances have been made in the last six years regarding the fabrication and functionalization of COF membranes. In particular, COFs have been utilized to obtain thin-film, composite, and mixed matrix membranes that could achieve effective rejection (mostly above 80%) of organic dyes and model organic foulants (e.g., humic acid). COF-based membranes, especially those prepared by embedding into polyamide thin-films, obtained adequate rejection of salts in desalination applications. However, the claims of ordered structure and separation mechanisms remain unclear and debatable. In this perspective, we analyze critically the design and exploitation of COFs for membrane fabrication and their performance in water treatment applications. In addition, technological challenges associated with COF properties, fabrication methods, and treatment efficacy are highlighted to redirect future research efforts in realizing highly selective separation membranes for scale-up and industrial applications.

Short term fouling tests on homogeneous and heterogeneous anion-exchange membranes from food and bio-based industrial streams: Foulant identification and characterization

Electrodialysis is used in food and bio-based industries for selective separation and recovery of target ions and neutral molecules. Anion exchange membranes (AEM) are prone to fouling due to their complex interactions with organics. Currently, research has focussed mainly on fouling tests using model organic foulants. In this study, three different complex industrial feed streams: corn steep liquor (CSL), citric acid by-product (CA), and cheese whey (CW), were used to foul two commercial AEM types: Fujifilm type-10 (homogeneous) and RALEX (heterogeneous). A 1.5 – 2.3 fold higher membrane resistance after fouling was a result of a difference in membrane structure, ion exchange capacity, water uptake, and thickness (depending on the feed used). Liquid Chromatography – Organic Carbon Detection (LC-OCD) analysis of feed revealed highly hydrophilic (CDOC) fractions in CSL (85%), CA (87%), and CW (100%). This analysis was extended to foulant desorption solutions (NaCl (35 g/L) and EtOH-water-H2SO4 mixtures), which revealed that > 90 % of humic substances (HS) and building blocks (BB) desorbed when using NaCl (35 g/L), following a (concentration wise) desorption order: HS > BB > LMWN > BP > LMWA. For the EtOH-water-H2SO4 solution, low molecular weight neutrals and acids (LMW(A + N)) were desorbed majorly (>60%) and followed a desorption order: LMWN > LMWA > BB > BP > HS. Desorption due to the ion-exchange mechanism was dominant for NaCl (35 g/L) solution, while foulant-desorbant polar interactions were prevalent for the EtOH-water-H2SO4 solution. Upon foulant desorption using NaCl (35 g/L) solution, RALEX AEM owing to the presence of nanovoids in them, showed a 1.5 – 4 fold higher concentration difference vs. FF10 AEM, while this difference was not dominantly observed when EtOH-water-H2SO4 mixture was used. This study revealed that LMW fractions could possibly enter into the membrane matrix whereas HS and BB fractions owing to their high molecular weight, majorly adsorbed on surfaces.

Mechanism study of synergistic effect of organic and inorganic foulants in membrane distillation

In this paper, we investigated the mechanism of membrane fouling during the membrane distillation (MD) process by using humic acid (HA) and calcium carbonate (CaCO3) as the model organic and inorganic foulants respectively. The aggregation induced crystallization theory was introduced to analyze the fouling process. Field emission scanning electron microscopy (FESEM) images and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and variation of foulants on membrane surfaces that treated different feeds at different concentration factors. The interface free energies of the membranes surfaces were calculated based on contact angles and surface tensions between the testing solutions and the membrane surfaces. The results indicated that the aggregations of HA onto the hydrophobic polyvinylidene fluoride (PVDF) membrane surface altered membrane surface properties, which reduced critical nucleus radius (R⁎) and facilitated the heterogeneous nucleation of CaCO3. Furthermore, the presence of calcium ion enhanced the aggregation of HA, which further promoted the crystallization of CaCO3.

Ionic fluid as a novel cleaning agent for the control of irreversible fouling in reverse osmosis membrane processes

While a variety of chemical cleaning strategies has been studied to control fouling in membrane-based water treatment processes, the removal of irreversible foulants strongly bound on membrane surfaces has not been successful. In this study, we firstly investigated the diluted aqueous solutions of ionic fluid (IF, 1-ethyl-3-methylimidazolium acetate) as a cleaning agent for three model organic foulants (humic acid, HA; bovine serum albumin, BSA; sodium alginate, SA). The real-time monitoring of cleaning progress by optical coherence tomography (OCT) showed that fouling layer was dramatically swelled by introducing IF solution and removed by shear force exerted during cleaning. This phenomenon was induced due to the pre-existing interactions between organic foulants were weakened by the intrusion of IF into the fouling layer, which was analyzed by the measurement of adhesion forces using atomic force microscopy (AFM). In the experiments with model foulants and wastewater effluent, IF was added to alkaline cleaning agents (NaOH) to verify the applicability to be supplemented in commercial cleaning agents, and resulted in the significantly enhanced control of irreversible membrane fouling. Implication of utilizing recyclable IF with negligible volatility is that environmental effects of membrane cleaning solutions could be minimized by decreasing usage of cleaning chemicals, while increasing the cleaning efficiency.

A Study on Biofouling and Cleaning of Anion Exchange Membranes for Reverse Electrodialysis.

This study covers the modification, (bio)fouling characterization, use, and cleaning of commercial heterogeneous anion exchange membranes (AEMs) to evaluate their feasibility for reverse electrodialysis (RED) applications. A surface modification with poly (acrylic) acid resulted in an improved monovalent perm-selectivity (decreased sulfate membrane transport rate). Moreover, we evaluated the (bio)fouling potential of the membrane using sodium dodecyl sulfate (SDS), sodium dodecyl benzenesulfonate (SDBS), and Aeromonas hydrophila as model organic foulants and a biofoulant, respectively. A detailed characterization of the AEMs (water contact angle, ion exchange capacity (IEC), scanning electron microscopy (SEM), cyclic voltammetry (CV), and Fourier Transform Infrared (FTIR) spectra) was carried out, verifying that the presence of such foulants reduces IEC and the maximum current obtained by CV. However, only SDS and SDBS affected the contact angle values. Cleaning of the biofouled membranes using a sodium hypochlorite aqueous solution allows for (partially) recovering their initial properties. Furthermore, this work includes a fouling characterization using real surface and sea water matrixes, confirming the presence of several types of fouling microorganisms in natural streams. A lower adhesion of microorganisms (measured in terms of total bacteria counts) was observed for the modified membranes compared to the unmodified ones. Finally, we propose a cleaning strategy to mitigate biofouling in AEMs that could be easily applied in RED systems for an enhanced long-term process performance.

Construction of pseudo-zwitterionic polyamide RO membranes surface by grafting positively charged small molecules

Membrane fouling is the major obstacle to hinder the extensive application of polyamide thin-film composite reverse osmosis (PA TFC RO) membranes in the water purification and reclamation fields. In this study, a series of hydrophilic and charge-tuned antifouling RO membranes were fabricated by grafting three kinds of small molecules of multi-grade amines N,N-dimethylethylenediamine (DMEDA), (2-aminoethyl) guanidine (AEGu) and (2-aminoethyl)triethylenediamine (AEDABCO) via layer-by-layer interfacial polymerization (LbL-IP). Detailed characterizations revealed that the three tailored membranes presented obviously diminished surface negative charge and reduced PA layer thickness, the water permeability increased by 67.4 %, 34.7 % and 75.6 % compared to the pristine membrane, reached 4.05 L m−2 h−1 bar−1, 3.26 L m−2 h−1 bar−1, and 4.28 L m−2 h−1 bar−1, respectively, meanwhile kept high NaCl rejection > 98.5 %. The dynamic fouling tests indicated that the tailored membranes exhibited much improved antifouling performance towards most of the model organic foulants. Meanwhile the membranes assembled with cationic groups exhibited an enhanced antibacterial property against E. coli. These functional small charged molecules and the convenient modification method provide a valuable pattern for designing antifouling PA TFC RO membranes, which is important for sustainable water purification.

Chitosan: Polyvinyl alcohol based mixed matrix sustainable coatings for reusing composite membranes in water treatment: Fouling characterization

This work aims at studying the potential of modifying the surface of used polyamide (PA) reverse osmosis (RO) commercial membranes by coatings made of renewable and biodegradable polymers, chitosan (CS) and polyvinyl alcohol (PVA), filled with Cu-ion-exchange layered AM-4 titanosilicate and UZAR-S3 stannosilicate to provide antifouling properties and enlarging life time of thin-film composite (TFC) membranes. The water permeation and fouling ratios were evaluated as a function of active layer material in the presence of model organic (BSA) and inorganic (NaCl) foulants. The mixed matrix membrane (MMM) coatings added on the active surface of the PA commercial membranes generally decreased the flux decline and increased the permeate flow recovery rate. The CS:PVA based coatings promote the reversible and not the irreversible fouling, especially CuAM-4CS:PVA. Beside, ATR-FTIR confirms the reversible nature of the BSA fouling and the irreversible nature of the NaCl fouling. These results may in the future open the possibility of renewing the useful lifetime of commercial RO membranes by a simple coating method in the light of the circular economy.

Adopting vibration to alleviate the solute buildup and membrane fouling in a forward osmosis system

Forward osmosis (FO) is limited by solute buildup and membrane fouling. Although current solutions (e.g., influent pretreatment and membrane modification) have partially compensated these drawbacks, they are still enslaved to the uncertainties and costs from the complex operational requirements and large use of chemicals. Therefore, developing simply-operated and chemical-free methods is highly required. In this work, a lab-scale vibrating FO device was constructed and its water permeability and anti-fouling capacity were evaluated. The results of flux tests show that the vibration could effectively enhance the water flux and mitigate solute buildup, mainly resulted from changing the flow field on the membrane surface through the computational fluid dynamic simulations. In addition, the vibrating FO was also proven to be effective in controlling the fouling caused by model organic foulants like bovine serum albumin, humic acid, alginate, and biofouling by different ways. The results of anti-fouling tests and fouling characteristics show that the organic fouling was alleviated by disintegrating the fouling layer and reducing the solute buildup, while the biofouling was mitigated through retarding the early microbial attachment and growth. This work provides a feasibility of applying vibration as an effective strategy to control solute buildup and fouling in FO systems.

Comparative analysis of salt cleaning and osmotic backwash on calcium-bridged organic fouling in nanofiltration process

The cleaning efficiency of salt cleaning and osmotic backwash in a nanofiltration (NF) process is evaluated using model organic foulants in the presence of calcium ions (Ca2+). In particular, the organic fouling behavior—which depends on Ca2+ concentration—and cleaning mechanism in both salt cleaning and osmotic backwash are studied. The results show that Ca2+ aggravates organic fouling, and the fouling formation rate is affected by the Ca2+/foulant ratio. Salt cleaning and osmotic backwash effectively clean Ca2+-bridging fouling, and the important cleaning mechanism in both methods is ion-exchange between the monovalent and divalent cations, resulting in the breakup of Ca2+–foulant binding and Ca2+-induced intermolecular bridging. The cleaning efficiency of osmotic backwash is 26% higher than that of salt cleaning, primarily owing to that the backwash flux creates synergy effect with ion-exchange to removes the weakened fouling structure on the membrane surface. In addition, the cleaning efficiency for irreversible fouling is of the order of osmotic backwash > chemical cleaning > salt cleaning, and osmotic backwash exhibited a 7.3% and 20.8% higher cleaning efficiency than chemical cleaning and salt cleaning, respectively. Therefore, osmotic backwash can stably maintain NF membrane performance for organic fouling and potentially replace the traditional chemical cleaning.

Development of membrane distillation by dosing SiO2-PNIPAM with thermal cleaning properties via surface energy actuation

This study evaluates the performance and cleaning efficiency of Direct Contact Membrane Distillation (DCMD) by changing its surface energy via thermal actuation. Thermoresponsive SiO2-PNIPAM particles were dosed into the DCMD with different surface energy and its thermal cleaning efficiency was evaluated against the model organic foulants namely Bovine Serum Albumin (BSA) and Sodium Alginate (SA). The impact of SiO2-PNIPAM dosing on the performance of membrane distillation as well as its defouling efficiency were evaluated under thermal actuation effect. Results showed that composite membrane has higher flux recovery (93%–95%) compared to pristine membrane (55%–90%). The composite membranes were analysed for their Surface Free Energy (SFE) to understand their fouling and cleaning behaviour. Based on SFE analysis, it was found that both low and high SFE composite membranes surface that fouled by BSA and SA foulants were able to restore their hydrophobicity after thermal actuation. The stability of the embedded hydrogel could be maintained after thermal actuation which indicated sufficient interactions between the SiO2-PNIPAM with the PVDF membrane matrix.

Interdependence of Contributing Factors Governing Dead-End Fouling of Nanofiltration Membranes.

Cake-enhanced concentration polarization (CECP) has been ascribed as the main cause of flux decline in dead-end filtration. An unfamiliar approach was used to investigate the role of CECP effects in the fouling of a nanofiltration membrane (NF-270) that poorly reject salts. Membrane–foulant affinity interaction energies were calculated from measured contact angles of foulants and membrane coupons based on the van der Waals/acid–base approach, and linked to resistance due to adsorption (Ra). In addition, other fouling mechanisms and resistance parameters were investigated using model organic and colloidal foulants. After selection, the foulants and membranes were characterized for various properties, and fouling experiments were conducted under controlled conditions. The fouled membranes were further characterized to gain more understanding of the fouling layer properties and flux decline mechanisms. Sodium alginate and latex greatly reduced membrane permeate flux as the flux declined by 86% and 59%, respectively, while there was minor flux decline when aluminum oxide was used as model foulant (<15% flux decline). More flux decline was noted when fouling was conducted with a combination of organic and colloidal foulants. Contrary to other studies, the addition of calcium did not seem to influence individual and combined fouling trends. Foulants adsorbed more on the membrane surface as the membrane–foulant affinity interactions became more attractive and pore blocking by the foulants was not important for these experiments. Hydraulic resistance due to cake formation (Rc) had a higher contributing effect on flux decline, while CECP effects were not substantial.

Organic Fouling in Forward Osmosis: A Comprehensive Review

Organic fouling in the forward osmosis process is complex and influenced by different parameters in the forward osmosis such as type of feed and draw solution, operating conditions, and type of membrane. In this article, we reviewed organic fouling in the forward osmosis by focusing on wastewater treatment applications. Model organic foulants used in the forward osmosis literature were highlighted, which were followed by the characteristics of organic foulants when real wastewater was used as feed solution. The various physical and chemical cleaning protocols for the organic fouled membrane are also discussed. The study also highlighted the effective pre-treatment strategies that are effective in reducing the impact of organic fouling on the forward osmosis (FO) membrane. The efficiency of cleaning methods for the removal of organic fouling in the FO process was investigated, including recommendations on future cleaning technologies such as Ultraviolet and Ultrasound. Generally, a combination of physical and chemical cleaning is the best for restoring the water flux in the FO process.

In Situ Electrochemical Generation of Reactive Chlorine Species for Efficient Ultrafiltration Membrane Self-Cleaning.

Reactive membranes based on hydroxyl radical generation are hindered by the need for chemical dosing and complicated module and material design. Herein, we utilize an electrochemical approach featuring in situ generation of reactive (radical) chlorine species (RCS) through anodization of chloride ions for membrane self-cleaning. A hybridized carbon nanotube (CNT)-functionalized ceramic membrane (h-CNT/CM), possessing high hydrophilicity, permeability, and conductivity, was fabricated. Using carbamazepine (CBZ) as a probe, we confirmed the presence of RCS in the electrified h-CNT/CM. The rapid and complete degradation of CBZ in a single-pass ultrafiltration indicates a high localized RCS concentration within the three-dimensional porous CNT interwoven layer. We further demonstrate that the electrogeneration of RCS is a critical prestep for free chlorine (HClO and ClO-) formation. The self-cleaning efficiency of the membrane after fouling with a model organic foulant (alginate) was assessed using an electrified cross-flow membrane filtration system. The fouled h-CNT/CM exhibits a near complete water flux recovery following a short (1 min) self-cleaning with an applied voltage of 3 or 4 V and feed solutions of 100 or 10 mM sodium chloride, respectively. Considering the superior performance of the RCS-mediated self-cleaning compared to conventional membrane chemical cleaning using sodium hypochlorite, our results exemplify an effective strategy for in situ electrogeneration of RCS to achieve a highly efficient membrane self-cleaning.

Evaluation of direct osmosis high salinity (DO-HS) method by nitrate salts as draw solution in fouled RO membrane cleaning

In this study, cleaning of organic-fouled reverse osmosis membranes with direct osmosis high salinity (DO-HS) method by nitrate salts as draw solution was investigated. Synthetic feed water including alginate and natural organic matter were used as model organic foulants. Nitrate salts were selected as draw solution which has not been used for DO-HS cleaning until now. Physicochemical properties of these salts were investigated systematically and related to the DO-HS cleaning performance. The results revealed that the zinc nitrate (1.5 M) draw solution may generate high osmotic pressure more than NaCl. Also, the DO-HS cleaning by zinc nitrate as draw solution was found to be quite effective in cleaning reverse osmosis membranes (cleaning efficiency up to 110%) fouled by gel-forming hydrophilic organic foulants, such as alginate. The effect of physicochemical factors investigated included salt dose, salt type, organic foulants composition and cleaning contact time. It was found that the membrane needed to be cleaned for about 10 min because of the appearance of all foulants on membrane surface. Most importantly, DO-HS cleaning appeared to be an effective cleaning method, and found to be useful for membrane-based advanced wastewater reclamation, where a large fraction of the organic foulants is hydrophilic.

Complexation between dissolved silica and alginate molecules: Implications for reverse osmosis membrane fouling

Dissolved silica and organic matter are major membrane foulants in desalination of brackish water and wastewater by reverse osmosis. However, the interaction between inorganic silica species and dissolved organic molecules and their combined impact on membrane fouling are poorly understood. In this study, we have used sodium silicate and sodium alginate as model inorganic and organic foulants, respectively. Membrane fouling experiments showed a cooperative effect between the dissolved silica and alginate macromolecules, which aggravated membrane fouling. The molecular interactions between sodium alginate and sodium silicate and the properties of the formed complexes were determined by X-ray diffraction and X-ray photoelectron spectroscopy. Results show that the crystallinity of the formed complexes decreased as we increased the ratio of silica in the silica-alginate mixture, indicating the formation of amorphous complexes. Full reflection Fourier transform infrared spectroscopy also confirms new functional groups following the interaction between silica and alginate. Isothermal titration calorimetry was also employed to quantitatively determine the binding parameters by measuring the heat change during the reaction. When binding occurs between silica and alginate, the measured adsorbed or released heat is used to determine the binding constants as well as the enthalpy and entropy changes. Our results suggest that the interaction between silica and alginate is spontaneously exothermic and dominated by noncovalent bonding. Our findings provide fundamental insights into the complexation between silica and alginate in reverse osmosis membrane fouling and highlight the binding mechanism between silica and alginate molecules.

Antifouling electrically conductive membrane for forward osmosis prepared by polyaniline/graphene nanocomposite

Forward Osmosis (FO) has been listed as one of the best strategies to combat growing worldwide water scarcity. Not only FO, but all membrane-based technologies are still suffering from unpleasant fouling propensity, hindering their continuous performance in a long-term application. Using polyaniline (PANI) and graphene, herein, we fabricated a novel electro-conductive membrane (graphene/PANI laminated membrane, GPANILM) through laminating by facile pressure-assisted technique onto polyamide-imide (PAI) support layer. To improve the mechanical stability of the fabricated film via crosslinking of PANI with graphene nanosheetsthe membrane was thermal treated in 140 °C for 3 h (GPANILM-140). Both nanocomposite membranes (GPANILM and GPANILM-140) demonstrated excellent mechanical stability and their performances in terms of water permeation (JW) and reverse salt flux (Js) were verified using a regular FO desalination system. Our results showed that the selectivity ratios (Js/Jw) of GPANILM and GPANILM-140 membranes are 0.79 and 0.69 g/L in FO mode (top active layer of nanocomposite was facing to feed solution (FS)) and 0.67 and 0.58 g/L in PRO mode (PAI support layer was facing to FS), respectively. The anti-fouling behaviors of the electro-conductive membranes were investigated by a FS containing alginate as a model organic foulant. By applying 2 V anodic potential, both flux recovery rate (FRR) and fouling resistance were substantially improved in both membranes.

Antifouling Double-Skinned Forward Osmosis Membranes by Constructing Zwitterionic Brush-Decorated MWCNT Ultrathin Films.

Pressure retarded osmosis (PRO) process is hindered by severe fouling occurring within the porous support of the forward osmosis (FO) membranes. We designed a novel double-skinned FO membrane containing a polyamide salt-rejecting layer and a zwitterionic brush-decorated, multiwalled carbon nanotube (MWCNT/PSBMA) foulant-resisting layer on the back side. Our results demonstrated that the coating of the MWCNT/PSBMA layer on the porous polyketone (PK) support imparted enhanced hydrophilicity and smaller membrane pore size, thereby providing excellent resistance toward both protein adhesion and bacterial adsorption. We also further evaluated this resultant double-skinned membrane (i.e., TFC-MWCNT/PSBMA) in dynamic PRO fouling experiments using protein and alginate as model organic foulants. Compared to the pristine TFC-PK and hydrophobic TFC-MWCNT membranes, the TFC-MWCNT/PSBMA membrane exhibited not only the lowest water flux decline but also the highest water flux recovery after simple physical flushing. These results shed light on fabrication of antifouling PRO membranes for water purification purposes.

Roles of membrane–foulant and inter/intrafoulant species interaction forces in combined fouling of an ultrafiltration membrane

To explore better the combined organic–inorganic fouling mechanisms of ultrafiltration (UF) membranes, SiO2 and bovine serum albumin (BSA), humic acid (HA) were chosen as model inorganic and organic foulants, respectively. Fouling experiments with single and combined foulants, corresponding fouling layer structure, and the membrane–foulant and inter/intrafoulant species interaction forces were investigated. The results showed that the addition of SiO2 particles led to opposite fouling phenomena for BSA and HA, which could be explained by the membrane–foulant and interfoulant species interaction forces. In the initial filtration stage, the combined fouling behavior was related to the relative strength of the interaction forces of membrane with both inorganic and organic foulant. Specifically, when the SiO2–membrane interaction force>organic–membrane interaction force, the combined fouling would be enhanced with the addition of SiO2 particles; otherwise, it would be mitigated. In the later filtration stage, the combined fouling was related to the inorganic–organic interaction forces. Thus, the stronger SiO2–BSA interaction force led to the formation of large SiO2–BSA aggregates, which resulted in a more porous fouling layer and higher hydraulic permeability. In contrast, the negligible SiO2–HA interaction forces caused the SiO2 particles to fill uniformly in or between the HA molecules, which resulted in a more compact fouling layer and more serious membrane fouling.

Comparison of fouling propensity between reverse osmosis, forward osmosis, and membrane distillation

Resistance to fouling is often cited as an advantage of emerging desalination technologies such as forward osmosis and membrane distillation over the widely-used reverse osmosis process. However, the nature and magnitude of differences in fouling behavior between these three processes are not well characterized. This study directly compares the fouling and scaling behavior of reverse osmosis (RO), forward osmosis (FO), and direct contact membrane distillation (MD) in the same membrane module under identical hydrodynamic conditions (flux and cross-flow velocity). Fouling experiments were conducted using calcium sulfate as a model inorganic foulant and alginate as a model organic foulant. Although all three processes tolerated some degree of feed supersaturation for 36 h without inorganic fouling (scaling), FO exhibited the greatest scaling resistance, withstanding a feed of 33± 2 mM CaSO4 (approximately twice saturation) without significant flux decline. Scaling occurred at similar concentrations at the membrane between MD and RO; however, while MD tolerated a more concentrated bulk feed due to reduced concentration polarization, flux decline after fouling was considerably more severe in MD. In contrast, MD tolerated organic fouling much better than FO or RO: despite accumulating a similar quantity of alginate gel over 18 h of operation, flux declined only 14% in MD versus 46–47% in RO and FO. These results are explained with respect to differences in temperature, membrane materials, and transport mechanisms between the three processes. Although FO and MD each exhibited superior resistance to one type of foulant, neither process outperformed RO in resistance to both organic and inorganic fouling. These findings inform a more nuanced approach to process selection for the treatment of complex water sources.