Role In Fouling Research Articles

An experimental study of underwater radiated noise from a small vessel with damaged and fouled propellers.

Damage and fouling to a marine propeller can alter underwater noise levels through numerous mechanisms, but there are very few studies where clean propellers are compared to those with realistic levels of damage or fouling. This study presents acoustic data combined with underwater camera footage for a vessel fitted with three propellers: clean, damaged, and fouled. The results show that the fouled propeller is quieter than the clean one due to it reducing the levels of tip vortex cavitation. This work highlights the need for further research into the role of fouling and damage on noise from marine vessels.

The role of feed spacers in membrane technology: 45 years of research

Feed spacers are crucial for enhancing the performance and efficiency of membrane-based technologies. Researchers have long focused on optimizing feed spacer designs and materials to improve fluid mixing and mass/heat transfer across membranes. However, these improvements often increase pressure drops, raising energy requirements. Therefore, innovative designs are sought to balance enhanced mass/heat transfer with reduced pressure drops and improved antifouling properties. This study analyzes patterns and trends in the feed spacer field using bibliometric methods, data analysis, and machine learning. The analysis includes 457 articles from the Scopus database, collected on March 5, 2024, covering publications from 1978 to 2023 across 45 journals. The analysis revealed that reverse osmosis technology emerges as the most studied membrane process, with 153 articles. Furthermore, experimental research in this field is preferred over theoretical evaluations, and the impact of feed spacers on mass transfer and pressure drops is the most explored topic, with 197 articles addressing one or more of these phenomena. Additionally, 204 articles focused on feed spacers’ role in fouling, scaling, and biofouling, with commercial feed spacers being the most frequently studied. The Journal of Membrane Science leads in publication volume with 152 articles, and Vrouwenvelder J.S. is the top author in 4 out of 6 metrics. Sentiment analysis of abstracts shows that authors generally express positive sentiments (385 articles) while maintaining an objective (453 articles) and emotion-free (446 articles) writing style.

Fouling of virus filtration membranes by monoclonal antibody feeds with low aggregate content.

Membrane fouling by monoclonal antibodies (mAbs) is one of the main challenges in virus-filtration processes. Previous publications attributed membrane fouling to the presence of mAb aggregates in the solution, which block the membrane pores. This fouling mechanism can be solved by a prefilter; however, it was shown that there are mAbs that severely foul the membranes (reduce permeability by 90% and more) even after prefiltering the aggregates, while other mAbs foul the membrane weakly (reduce permeability by ~10% and less). Unfortunately, the differences between the fouling- and the nonfouling mAbs have never been convincingly explained. To get a deeper insight on these differences, we measured the fouling of chemically modified Isoprene-Styrene-4-vinylpyridine (ISV) membranes (TeraPore Technologies) by 8 mAbs exhibiting different hydrophobicity and charge. The results show that mAb solutions with low concentration of aggregates foul ISV membranes via an adsorptive mechanism, and the adsorption is driven mainly by hydrophobic forces between the mAb and the membrane. The charge of the mAbs plays a secondary role in fouling. We want to emphasize that the conclusions pertain to ISV membranes; the insights presented in this paper can potentially be used to engineer new surface chemistries to mitigate fouling of other virus-filtration and/or ultrafiltration membranes.

Exposure to stressful conditions alters the properties and fouling behavior of suspended microparticles in anaerobic processes

Microparticles, a type of suspended particles in anaerobic membrane bioreactors (AnMBRs) with a size ranging from 0.45 to 10 µm, play a vital role in fouling. Here, the occurrence, composition, and fouling behavior of microparticles were determined during the cultivation of anaerobic sludge under stressful conditions that included high sulfate (3 g/L), high ammonium (3 g/L), high temperature (55 °C), and high salinity (28 g NaCl/L) tests. The results showed that the total organics in the supernatant of anaerobic sludge liquor increased after exposure to high temperature and high salinity, and the proportion of microparticles decreased significantly compared with that of the control, which could be due to the decreasing ratios of live/dead cells in the microparticles, thereby producing more soluble organics (< 0.45 µm). Accordingly, dead-end filtration tests showed that the supernatants with the same organic concentration in high temperature and high salinity groups had a decreasing fouling potential. Based on Hermia’s model, the cake filtration model fitted the supernatant filtration data under all stressful conditions. Moreover, the high-temperature group also fitted well with the pore-blocking model. The correlation between fouling parameters and the microbial species of microparticles suggested the potential contributions of Bacteroidales, Aminicenantales, Anaerolineales, and Caldisericales to cake/gel fouling, and the positive effects of Ignavibacteriales and Syntrophobacterales on pore blocking. Overall, exposure to stressful conditions considerably altered the production and characteristics of microparticles during the anaerobic digestion, thus leading to different fouling mechanisms in AnMBRs.

Pre-chlorination effects on fouling during microfiltration of secondary municipal wastewater effluent

Chlorination-induced changes in the physicochemical characteristics of effluent organic matter (EfOM) and their role in fouling of hollow fiber polyvinylidene fluoride (PVDF) microfiltration membranes during wastewater reclamation was mechanistically investigated. Pre-chlorination strongly influenced pressure rise during constant flux forward filtration as well as hydraulically irreversible fouling by backwashing with low doses exacerbating it and high doses alleviating it. Dose-dependent fouling trends originated from alterations in EfOM size and polarity and consequently its interactions with the membrane based on whether applied chlorine concentrations were above or below a threshold value. Variations in macroscopic phenomena such as sorption tendency, streaming potential, and initial fouling upon exposure to pre-chlorinated EfOM were consistent with favorable adhesion energies calculated using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. Progressive fouling even though XDLVO theory predicted unfavorable EfOM-EfOM cohesive energies under all chlorination conditions demonstrated that hydrodynamics (permeation drag) dominated later stages of fouling. EfOM in the raw wastewater was largely deposited on the membrane surface resulting in compressible cake filtration. In contrast, pre-chlorination fragmented EfOM leading to intrapore fouling (standard blocking) at the beginning stages of filtration later transitioning to surface fouling (intermediate blocking).

Effect of inorganic colloidal water constituents on combined low-pressure membrane fouling with natural organic matter (NOM)

The impact of inorganic colloidal water constituents on fouling in low-pressure membrane systems was evaluated by carrying out ultrafiltration (UF) experiments using synthetic waters containing model foulants. Humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA) were chosen as model natural organic matter (NOM) foulants, and silicon dioxide and α-aluminum oxide were chosen as model inorganic colloidal foulants. The synthetic solutions were filtered using one lab-scale flat sheet UF system (i.e., unstirred filtration cell) and one pilot-scale hollow fiber UF system (i.e., custom made hollow fiber modules), both of which employed polyethersulfone (PES) membranes. Filtering the inorganic colloids by themselves did not result in any significant fouling, as evidenced by the negligible permeability decline and high hydraulic reversibility. However, when combined with NOM, severe permeability decline and hydraulic reversibility reduction were observed. Moreover, the permeability decline and reversibility loss of the combined inorganic colloids and NOM were more severe than the sum of the individual effects from organics and inorganic colloids, suggesting that combining the two acts to enhance fouling (i.e., synergistic fouling effects). Aluminum oxide tended to result in more severe synergistic fouling compared to silicon dioxide, suggesting that the inorganic colloid material character, especially its surface charge, affects the severity of combined fouling. Rejection of TOC and analysis of the fouled membranes by scanning electron microscopy indicated higher NOM adsorption by aluminum oxide colloids, which lead to a larger amount of foulants in the cake layer and a worse reversibility. Both the lab- and pilot-scale systems exhibited similar fouling behavior, thus indicating that the lab-scale system provides a meaningful representation of the pilot-scale system, even though the operating conditions are quite different. This study highlights the importance of interactions between foulants with respect to fouling in low-pressure membrane systems and showed conclusively that inorganic colloids play an important role in fouling of NOM. Moreover, present results underline the impact of colloidal surface charge on the resulting hydraulic and chemical fouling reversibility during ultrafiltration of natural waters containing NOM and inorganic colloids.

Compatibility of Heavy Blends Evaluated by Fouling and Its Relationship With Colloidal Stability

To predict oil compatibility is crucial because incompatibility could cause severe deposition and fouling problems. Therefore, compatibility of heavy oils and blends in different ratios were evaluated by fouling at heat transfer conditions. Thermal resistance and fouling rates were obtained on a fouling loop. Effect of colloidal stability based on asphaltene precipitation and SARA composition on fouling was also discussed. Results showed that different variations of fouling rate versus blending ratio were observed for these blending systems. For oils whose viscosities approach at heat conditions, the lower colloidal stability of blends is the higher fouling rate is. However, for oils with greatly different viscosities, inconsistency was observed between compatibility by the two indicators, which is attributed to remarkable change of flow condition. This indicates that both colloidal stability and flow condition play key roles in fouling. Oil compatibility at heat transfer condition is favored being predicted by fouling instead of correlating with the colloidal stability.

Effects of sludge particles on performance of enhanced backwash for fouling reduction in anaerobic membrane bioreactors

The objectives of this research are to investigate effects of sludge properties in terms of particle size composition on performance of physical and chemical cleaning and to understand fouling mechanisms of the specific feed solutions. The sludge was centrifuged at three rotational speeds to differentiate particle size distributions, and the supernatant and residual flocs were used for microfiltration and cleaning processes. The filtration flux with the flocs was greater than those of the three supernatants, which indicates that fouling was greater with supernatants. Taking into account that the solid concentrations of the raw sludge and the residual flocs were 10 times greater than those of the supernatants, the reduction in flux for the supernatants is significant. The flux was recovered to 64% of the clean water flux at the maximum efficiency by two cleaning of membrane fouled with supernatant treated at 1,000 rpm. In addition, increasing removal of coarse particles by applying higher centrifugal speed (i.e. 1,000 and 1,500 rpm) yielded greater recovery performance by chemical cleaning. Particle composition such as the fine particle concentration played a significant role in fouling and the enhanced backwash cleaning efficiency.

Fouling behaviors of polybenzimidazole (PBI)–polyhedral oligomeric silsesquioxane (POSS)/polyacrylonitrile (PAN) hollow fiber membranes for engineering osmosis processes

This paper investigated the individual effects of reverse salt flux and permeate flux on fouling behaviors of as-spun and annealed polybenzimidazole (PBI)–polyhedral oligomeric silsesquioxane (POSS)/polyacrylonitrile (PAN) hollow fiber membranes under forward osmosis (FO) and pressure retarded osmosis (PRO) processes. Two types of membrane fouling had been studied; namely, inorganic fouling (CaSO4·2H2O gypsum scaling) during FO operations and organic fouling (sodium alginate fouling) during PRO operations. It is found that gypsum scaling on the membrane surface may be inhibited and even eliminated with an increase in reverse MgCl2 flux due to competitive formations of MgSO4° and CaSO4·2H2O. In contrast, the increase of reverse NaCl flux exhibits a slight enhancement on alginate fouling in both FO and PRO processes. Comparing to the reverse salt flux, the permeate flux always plays a dominant role in fouling. Therefore, lesser fouling has been observed on the membrane surface under the pressurized PRO process than FO process because the reduced initial flux mitigates the fouling phenomena more significantly than the enhancement caused by an increase in reverse NaCl flux.

Potassium Retention in Updraft Gasification of Wood

The release of compounds of K with producer gas during biomass gasification is known to play significant roles in fouling and high-temperature corrosion in boilers and high-temperature heat exchangers as well as blades in gas turbines that use producer gas as fuel. These phenomena are a major setback in the application of biomass fuel in combination with advanced process conditions. Updraft gasification provides gas filtering by the fuel bed with a gas cooling effect, conditions anticipated to create an avenue for K retention in the gasifier. The objective of this study was to determine the K retention potential of such gasifiers during wood gasification. Samples for the determination of the fate of K compounds included in the feedstock were collected from the generated producer gas using Teflon filters and gas wash bottles and also from wall deposits and ash residues. Analyses of samples were carried out using inductively coupled plasma–atomic emission spectrometry/mass spectrometry and X-ray diffraction methods. The finding was that about 99% of K was retained in the gasifier. K was found in the ash samples as a crystalline phase of K2Ca(CO3)2(s) (fairchildite). A possible reaction mechanism leading to the formation of K2Ca(CO3)2 is discussed in the paper. The 1% K understood as released, equivalent to 1200 ppbw content of K entrained in the producer gas stream, exceeds a known limit for application of the gas in conventional gas turbines. This would suggest application of the gas in an externally fired gas turbine system, where some limited K and other depositions in the heat exchanger can be relatively easy to handle.

Investigation of Fouling Mechanisms of a Light Crude Oil Using an Alcor Hot Liquid Process Simulator

Fouling mechanisms of a light conventional crude were investigated by characterizing the crude oil, performing fouling tests using a bench-scale Alcor hot liquid process simulator (HLPS) unit and characterizing fouling deposits by means of elemental analysis, scanned electron microscopy (SEM), thermogravimetric analysis (TGA), and photoacoustic infrared spectroscopy (PAS-IR). In addition, a mathematical fouling model was developed under a laminar flow regime following Epstein’s methodology. Fouling tests were conducted at different temperatures and bulk velocities. Although the asphaltene content in the crude oil is low, the asphaltenes are still unstable because of a high saturate content and this crude oil has a high fouling propensity. On the basis of the fouling test results, fouling model analysis, and characterization of fouling deposits, the fouling mechanism of this crude oil can be explained as follows: In a laminar flow regime, unstable asphaltenes transport to the hot surface, become attached to the surface, and then, through chemical reactions, form fouling deposits. Mass transfer of entrained suspended particulates in the crude oil also contributes to fouling, although it is not the main cause. However, under turbulent flow conditions, such as those that prevail in industrial operations, it is expected that suspended particles would play a greater role in fouling.

Fouling of RO membranes by effluent organic matter (EfOM): Relating major components of EfOM to their characteristic fouling behaviors

Effluent organic matter (EfOM) has been considered by many to play an important role in fouling of RO membranes used for wastewater reclamation. However, due to their heterogeneous composition, which is a mixture of structurally complex aquatic humic substances (AHS), soluble microbial products (SMP) or extracellular polymeric substances (EPS) and other poorly defined organic compounds, the fractional component(s) or physical–chemical properties responsible for the fouling phenomenon are still not well understood. This study aims to obtain a better understanding of interactions between fractional components of EfOM and RO membranes and attempts to identify the most influential fraction(s) or physical–chemical properties governing the fouling process. Four EfOM fractions were isolated and fractionated from UF prefiltrated treated effluent based on hydrophobicity and charge characteristics. EPS was extracted from the biological treatment stage to assess their fouling potential on RO membranes via well-controlled laboratory-scale experiments. The individual organic fractions were rigorously characterized in terms of physico-chemical properties. A clear correlation was observed between the physico-chemical properties of EfOM fractions and their fouling potential. Under hydrodynamic and chemical conditions typical of commercial applications, the hydrophilic neutral fraction, mainly composed of small size carbohydrates, resulted in the highest flux decline and exhibited highest affinity towards the membrane. EPS biopolymers, to which great importance has been associated with regard to causing RO organic fouling, resulted in less fouling than hydrophilic carbohydrates. Although EPS biopolymers tended to accumulate on the membrane in much higher quantities, the cake layer formed was found to constitute a much lower resistance towards filtration and has a much lower membrane affinity, probably due to their large molecular sizes. The contribution of AHS and other hydrophilic fractions to membrane fouling was found to be much lower as compared to hydrophilic carbohydrates and EPS biopolymers.

A study of selected phytoestrogens retention by reverse osmosis and nanofiltration membranes - the role of fouling and scaling

AbstractFouling and scaling are common phenomena that accompany membrane filtration and are caused by the presence of organic and inorganic matter in water, which may affect the removal of low-molecular mass organic micropollutants. Comparative filtration of deionized water containing selected phytoestrogens (biochanin A, daidzein, genistein, and coumestrol) was carried out using one new membrane and one contaminated with organic or inorganic matter. Two commercial Osmonics DS membranes were selected for the research, reverse osmosis DS3SE and nanofiltration DS5DK. Filtration was carried out in the dead-end mode. Higher removal of phytoestrogens was caused by reverse osmosis and retention depended on the molar mass of the compound. The decrease in membrane efficiency associated with fouling or scaling brings about an increase in the retention coefficient of phytoestrogens during both reverse osmosis and nanofiltration. The highest increase in phytoestrogen retention was found for the nanofiltraton membrane which was more susceptible to fouling than the osmotic one. This confirms the effect of membrane porosity on the phenomenon studied. The increase in micropollutants removal observed after fouling or scaling was caused by the modification of the membrane surface, hindered diffusion of the compound, and intensified or limited adsorption of micropollutants on the membrane surface.

PACl: A simulation of the change in Al concentration and Al solubility in RO

Polyaluminium chloride (coagulant) is a very complex compound. The change in the ratio HCO3/CO2 during coagulation cause a change in pH in the subsequent RO unit (because CO2 is not rejected by the RO membrane), and it was found that this change is constant for any given recovery, e.g. at 75% recovery, the pH change between the RO feed water and concentrate water is 0.6. The simulation of aluminium solubility and concentration along RO systems were performed assuming the presence of three aluminium species, Al137+, Al(OH)4−, Al(OH)2+. The simulation of aluminium solubility was performed at two temperatures, 20°C to represent the summer period and 5°C to represent the winter period. Results showed that for winter (5°C) an RO feed water pH of at least 7.2 and for warm weather (20°C), a feed water pH of at least 6.7 are required respectively, to avoid scaling of aluminium on the RO membranes.In conclusion, theoretical simulation of aluminium solubility and results of deposition factor showed that aluminium more than likely plays a role in fouling of the RO membranes and could be a reason for the frequent cleaning.

In Situ Three-Dimensional Characterization of Membrane Fouling by Protein Suspensions Using Multiphoton Microscopy

Fouling of microfiltration membranes leads to severe flux declines and the need to clean or replace the membrane. In situ 3D characterization of protein fouling both on the surface and within the pores of the membrane was achieved using multiphoton microscopy. Time-lapse images of the fouled membrane were obtained for single suspensions and mixtures of fluorescently labeled bovine serum albumin and ovalbumin. Deposited protein aggregates were visible on the membrane and evidently play an important role in fouling. A combination of 3D images and resistance versus time data was used to identify the dominant fouling mechanism. Fouling is initially internally dominated, but after 1 and 15 min for ovalbumin and bovine serum albumin, respectively, the fouling becomes externally dominated. This is in good agreement with two-stage protein fouling models.

Natural organic matter (NOM) fouling of ultrafiltration membranes: fractionation of NOM in surface water and characterisation by LC-OCD

Natural organic matter (NOM) plays a significant role in fouling of ultrafiltration membranes in drinking water treatment processes. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and a hydrophilic PES/PVP hollow fiber ultrafiltration membrane (150–200 kDa). NOM was fractionated into hydrophobic, transphilic and hydrophilic acid fractions according to the XAD-8/4 resin method proposed by Aiken et al. [1]. UF filtration tests were performed with diluted NOM fractions (1.5 mg/l DOC) isolated from surface water (Lake Ijssel). From NOM fractionation results, Lake IJssel water comprised about 53–55% hydrophobic, 20–22% hydrophilic and 25% transphilic NOM acids. Filtration of three NOM fractions (hydrophobic, hydrophilic and transphilic) suggested that the fouling potential was in the order: hydrophilic > hydrophobic > transphilic. The reversibility of fouling due to the hydrophilic fraction was very poor, and decreased from ca. 50% in the first cycle to <30% after 6 cycles. LC-OCD (Liquid Chromatography-Organic Carbon Detection) analyses of UF feed and permeate showed almost no rejection of humic acids (20,000∼1,000 Da), IOW molecular weight acids (< 350 Da) or neutrals/amphiphilic compounds (<350 Da). The absence of a polysaccharide peak (Mw>20,000 Da) in the LC-OCD chromatogram of the UF permeate, suggested that polysaccharides (> 20,000 Da) were rejected by the UF membrane and may have contributed to fouling.

Fouling mechanisms in the integrated system with softening and ultrafiltration

Softening is designed to remove hardness ions, but it can also remove NOM and particles, yielding the possibility to use the process as a pretreatment for ultrafiltration. The objectives of this research were to understand the nature of the fouling mechanisms for ultrafiltration when used for waters that either require softening or have been softened, and to use that understanding to determine promising options for the use of softening as a pretreatment before ultrafiltration. To understand fouling mechanisms in the integrated system with softening and ultrafiltration, three different levels of softening performance in terms of removal of inorganics and organic matter were selected. Experiments were performed with both natural waters and synthetic waters with similar (but separable) inorganic, organic, and particulate characteristics. The synthetic waters were used to distinguish among inorganic fouling by precipitates, organic fouling, particulate fouling, and combined fouling by particles and organic matter. The results showed that organic matter played a major role in fouling, either by itself or by adsorption onto particles, and that softening pretreatment effectively reduced the foulants prior to ultrafiltration.

Thermal performance of seawater desalination systems

This work describes a steady-state mathematical model developed to analyze both the multi-stage and multi-effect desalination systems. For MSF the model accounts for the geometry of the stages, the mechanism of heat transfer, and the variation of the physical properties of seawater with temperature and salinity. In addition, the model takes into consideration the role of fouling and its effect on the plant performance ratio. Relationships among the parameters controlling the product water cost to other operating and design parameters are presented. These parameters include plant performance ratio, specific flow rate of recirculating brine, top brine temperature, and specific heat transfer area. These relationships are used for studying a typical operating plant. The results obtained by the model are compared with data from the Sidi-Krir plant in west Alexandria, which contains 17 recovery and three rejection stages. There is good agreement between the calculated results and the plant data. The model results are also used to study the different operating conditions such as part load; for example, the effect of decreasing the recirculated flow rate and/or the top brine temperature on the unit performance ratio. In addition, the effect of decreasing the seawater temperature below the design value shows an increase in the unit production rate, while increasing the fouling factor reduces the plant production rate. For WD, the effect of the process variables on the performance of a “forward type” multi-effect boiling falling film is carried out. This includes the effect of number of effects and top brine temperature on performance ratio. In addition, the influence of these factors on the specific heat transfer area and the effect of seawater inlet temperature on the performance ratio are investigated. The effect of the top brine temperature and the temperature difference per effect on the performance ratio, the specific heat transfer area, and the cooling brine flow rate are also investigated. The study results indicate that the performance ratio is completely dependent on the number of effects and slightly dependent on the top brine temperature.

Fouling characteristics of wastewater effluent organic matter (EfOM) isolates on NF and UF membranes

Wastewater effluent organic matter (EfOM) was isolated into different fractions including colloids, and hydrophobic (HPO) and transphilic (TPI) fractions. The EfOM isolates were characterized by different techniques, for example, size exclusion chromatography (SEC) with on-line UVA and DOC detectors, Fourier transform infrared (FTIR), specific UVA (SUVA), and total sugars analysis. The colloidal fraction is primarily composed of polysaccharides, proteins, and/or aminosugars, providing a hydrophilic character. The HPO and TPI fractions possessed characteristics of humic substances, i.e. high aromaticity and carboxylic functional groups. A superimposition of the EfOM isolates reflects characteristics of bulk wastewater effluents, consisting of refractory natural organic matter (NOM) conveyed from the drinking water source and soluble microbial products (SMP) derived during biological processes of wastewater treatment. Each EfOM isolate exhibited different characteristics in fouling of NF and UF membranes due to their distinct characters. The colloidal fraction showed high flux decline and fouling on NF and UF membranes primarily due to the effects of pore blockage. The HPO and TPI fractions exhibited less fouling and flux decline than the colloids due to their molecular size as well as electrostatic repulsion between organic acids and the membrane surface. However, hydrophobic interactions play a significant role with hydrophobic membranes, causing a reduction of permeate flux. Membrane autopsies using FTIR identified functional groups of organic foulants, supporting the evidence of flux decline by each EfOM isolate. Polysaccharides and/or aminosugars from the colloids in wastewater effluent were found to play an important role in fouling of NF and UF membranes.

Nanofiltration of natural organic matter: Removal, fouling and the influence of multivalent ions

The presence of calcium and humic substances or natural organic matter (NOM) in surface waters can cause severe fouling of nanofiltration (NF) membranes. Conditions of fouling were studied using a stainless steel stirred cell of volume 185 ml and a membrane area of 21.2×10 −4 m 2 at a transmembrane pressure of 5 bar. Deposition of organic matter was determined by mass balance in feed and concentrate samples. Electron microscopy and X-ray photoelectron spectroscopy (XPS) were used to study the morphology and composition of the fouling layer. During permeate recycle experiments, which were used for fouling studies, it was found that calcium concentration (as a representative of multivalent ions) and the type of organic play a major role in fouling. The calcium forms complexes with some of the organics and deposits on the membrane surface. Depending on the solution conditions the organic or calcite (on which organics adsorb) precipitate. Factors, which influence the concentration of organics and ions at the membrane surface such as stirring, flux and transmembrane pressure, influenced the deposition of organic matter significantly. Irreversible fouling occurred with all membranes at high calcium concentrations, although the cellulose acetate membrane showed an overall better performance, possibly due to its low salt rejection and smooth surface. IHSS humic acid is the organic which deposits most easily and comparison of UV absorbance and DOC data showed that the fraction which absorbs UV strongest, and is more hydrophobic, deposits preferentially on the membranes. These substances also have the lowest solubility stressing the importance of concentration polarisation effects.