Fouling Of Low-pressure Membranes Research Articles

Reduced Low-Pressure Membrane Fouling by Inline Coagulation Pretreatment for a Colored River Water.

Drinking water treatment (DWT) using low-pressure membranes (LPM) has become increasingly popular due to their many reported advantages compared to conventional technologies. Productivity decline due to fouling has prevented LPMs from becoming the technology of choice in DWT, however, coagulation pretreatment either with or without particle separation mitigates fouling phenomena. The effectiveness of coagulation/flocculation/sedimentation (CF-S), coagulation/flocculation/dissolved air flotation (CF-DAF), and inline coagulation (CF-IN) as technologies for pretreatment of feed water has rarely been investigated using the same water source. In this study, CF-S, CF-DAF, and CF-IN are directly compared as pretreatment of a tubular multi-channeled ultrafiltration (UF) membrane using the same highly colored river water. Three-day long filtration tests were performed using an automated bench-scale filtration apparatus with an inside-out configuration. Although CF-DAF had the greatest removal of dissolved organic matter (DOM) and hydrophobic organics, CF-S pretreatment resulted in a similar level of total fouling. Compared to CF-DAF and CF-S, CF-IN pretreatment resulted in lower fouling. The hydraulic and chemical reversibility of CF-IN fouling was seen to be strongly influenced by the feed water zeta potential, suggesting the importance of floc electrostatic and morphological characteristics on inline coagulation performance.

Efficacy of selected pretreatment processes in the mitigation of low-pressure membrane fouling and its correlation to their removal of microbial DOM

Membrane fouling by dissolved organic matter (DOM), especially microbially-derived DOM, is a major challenge for ultrafiltration (UF) membranes in water purification. Fouling may be mitigated by pretreating feed waters; however, there are no comprehensive studies that compare the fouling reduction efficacies across different pretreatment processes. Further, there is a limited understanding of the relationship between fouling reduction efficacy and microbially-derived DOM removal from source waters. Accordingly, the objectives of this study were to: (i) evaluate and compare the efficacies of five pretreatment processes in reducing UF membrane fouling by DOM; and (ii) investigate whether a relationship exists between membrane fouling reduction and microbially-derived DOM removal by pretreatment processes. We investigated seven water sources and a polyvinylidene fluoride hollow-fiber UF membrane using bench-scale fouling tests. Dissolved organic carbon content, ultraviolet absorbance and fluorescence excitation-emission matrix spectroscopy were used to assess DOM concentration and composition. Alum and ferric chloride coagulation were the most effective pretreatment processes in reducing membrane fouling, anion exchange was moderately effective, and PAC adsorption and chlorine pre-oxidation were the least effective. Consistent with previous studies, microbially-derived DOM was the major contributor to UF membrane fouling regardless of water source or pretreatment type. Fouling reduction was strongly correlated with the reduction of microbially-derived DOM in foulant layers but not from source waters. This result indicates that a fraction of the total microbially-derived DOM in feed waters was responsible for UF fouling. Overall, pretreatment processes that remove microbially-derived DOM are well-suited for UF membrane fouling reduction.

The combination effect of preozonation and CNTs layer modification on low-pressure membrane fouling control in treating NOM and EfOM

In this study, the combination effect of preozonation and carbon nanotubes (CNTs) layer modification on low-pressure membrane (LPM) fouling control was systematically investigated. To understand the alleviation mechanism of the hybrid process, natural organic matter (NOM) from IHSS and effluent organic matter (EfOM) from actual sewage effluent were both selected as the typical organic foulants presented in actual surface water and wastewater. A dead-end continuous flow model combined with programmable logic control system was used to operate four membrane filtration units and their backwash processes. With a constant permeates flux, the fouling resistant of CNT modified LPM after preozonation could be evaluated according to the increase in transmembrane pressure (TMP). The results revealed that the hybrid approach of preozonation and CNTs modification could significantly improve the anti-fouling ability of LPM, reduce the backwash frequency, and improve the reversibility of membrane fouling. During the filtration of EfOM and NOM, preozonation improved the water treatment capacity of the CNTs modified membranes. The experiment of mass balance revealed that preozonation enhanced the recoverability of CNTs modified membrane and greatly increased its operation time in treating EfOM and NOM. The molecular weight distribution as well as EEM analysis demonstrated the dissimilar characteristics of EfOM and NOM, which caused the different treatment efficiency by preozonation and CNT modification. The mechanism of EfOM/NOM fouling on LPM was summarized as the primary blocking by medium-MW EfOM/NOM. CNTs modification had a better effect on the control of LPM fouling when treating EfOM, as it removed the medium-MW EfOM by adsorption and prevented the pores blockage of the original PVDF membrane. Preozonation had a better effect on the control of LPM fouling when treating NOM, as it greatly changed the MWD of NOM by removing medium-MW NOM. The combination effect of the hybrid preozonation and CNTs modification resulted in the most effective fouling control of LPM by both decreasing the medium-MW and large-MW EfOM/NOM. At the same time, it decreased irreversible fouling related with membrane pore blocking. The hybrid approach demonstrated its promising application for LPM fouling control in actual sewage water and surface water treatment process.

Pretreatments to control low-pressure membrane fouling: a review on the coagulant/adsorbent applied and contact modes with the feed

Pretreatments to control low-pressure membrane fouling: a review on the coagulant/adsorbent applied and contact modes with the feed

Biofiltration of feedwater to control organic fouling of low pressure membranes

ABSTRACTThe application of low pressure membrane (LPM) technology, i.e., ultrafiltration and microfiltration, for drinking water treatment and secondary effluent reclamation has increased rapidly over the past two decades. A major drawback in the use and operation of LPM processes is fouling due to the deposition of organic matter present in the feedwater on the membranes which leads to reduced water productivity necessitating membrane cleaning, process downtime and eventual membrane attrition. Pretreatment of feedwater using biological processes (particularly slow sand filtration and biological activated carbon) has been investigated as a simple and cost-effective means to control organic fouling of the membrane. In this paper, membrane fouling by the organic matter in drinking water and secondary effluent, the mechanisms of biological treatment systems, and the effectiveness of biological processes for fouling reduction are reviewed. It has been demonstrated that biological processes have great potential for controlling the organic fouling of membranes.

Investigating the relative contribution of colloidal and soluble fractions of secondary effluent organic matter to the irreversible fouling of MF and UF hollow fibre membranes

Abstract Effluent organic matter (EfOM) matrices were modified by applying physical chemical treatments on biologically treated wastewater effluents in order to identify the EfOM fraction(s) responsible for irreversible fouling of low-pressure membranes. Anion exchange resin (AER) adsorption preferentially removed humic-like structures, while oxidation processes, such as ozonation and H2O2/UV resulted in the breakdown of high molecular weight (MW) structures into lower MW compounds. After re-concentration to the original organic carbon content, the fouling potential of the modified EfOM matrix was investigated using multi-cycle filtration tests performed with commercially available microfiltration (MF) and ultrafiltration (UF) membranes. The pre-oxidized effluents showed low fouling potential regardless of the membrane used. The results confirmed the major role of high MW biopolymers on MF and UF total fouling. Results from MF experiments highlighted that AER treated effluents exhibited similar fouling properties as the untreated effluent indicating that humic-like substances do not significantly affect MF fouling and confirm again that biopolymers is the fraction responsible for fouling. The same tests performed with UF membrane showed a lower irreversible fouling with AER treated effluent suggesting the strong contribution of humic fractions to irreversible fouling. These findings were supported by the results obtained with two different secondary effluent matrices, a conventional activated sludge treated effluent and a membrane bioreactor supernatant.

Minimization of short-term low-pressure membrane fouling using a magnetic ion exchange (MIEX®) resin

Two challenges to low-pressure membrane (LPM) filtration are limited rejection of dissolved organic matter (DOM) and membrane fouling by DOM. The magnetic ion exchange resin MIEX® (Ixom Watercare Inc.) has been demonstrated to remove substantial amounts of DOM from many source waters, suggesting that MIEX can both reduce DOM content in membrane feed waters and minimize LPM fouling. We tested the effect of MIEX pretreatment on the reduction of short-term LPM fouling potential using feed waters varying in DOM concentration and composition. Four natural and two synthetic waters were studied and a polyvinylidene fluoride (PVDF) hollow-fiber ultrafiltration membrane was used in membrane fouling tests. To evaluate whether MIEX removes the fractions of DOM that cause LPM fouling, the DOM in raw, MIEX-treated, and membrane feed and backwash waters was characterized in terms of DOM concentration and composition. Results showed that: (i) the efficacy of MIEX to reduce LPM fouling varies broadly with source water; (ii) MIEX preferentially removes terrestrial DOM over microbial DOM; (iii) microbial DOM is a more important contributor to LPM fouling than terrestrial DOM, relative to their respective concentrations in source waters; and (iv) the fluorescence intensity of microbial DOM in source waters can be used as a quantitative indicator of the ability of MIEX to reduce their membrane fouling potential. Thus, when ion exchange resin processes are used for DOM removal towards membrane fouling reduction, it is advisable to use a resin that has been designed to effectively remove microbial DOM.

A multi-spectral approach to differentiate the effects of adsorbent pretreatments on the characteristics of NOM and membrane fouling

Pretreatment of feed water is widely applied to mitigate NOM-induced fouling of low-pressure membranes. This research investigated the effectiveness of two pretreatment modes for NOM removal by heated aluminum oxide particles (HAOPs) and the associated reductions in membrane fouling and trihalomethane (THM) formation potential. One mode, referred to here as pre-adsorption, is the conventional process in which adsorbent particles are added to and thoroughly mixed with the feed, after which the particles are separated from the water either upstream of or by the membrane. By contrast, in the pre-deposition mode, a thin layer of adsorbent particles is deposited on a support media (which could be the membrane) prior to passing feed through the layer and the membrane.Although both pretreatment methods remove similar amounts of DOC at the same adsorbent dose, pre-deposition is superior with respect to mitigating membrane fouling and reducing DBP formation. UV and fluorescence spectroscopy and HPSEC analysis indicate that a pre-deposited adsorbent layer removes more chromophores and low apparent molecular weight (AMW) material than pre-adsorption does. Based on absorbance ratios at selected wavelengths, a pre-deposited HAOPs layer removes more aromatic moieties than aliphatic carboxyls, especially at higher HAOPs doses. In addition, pre-deposition is more effective than pre-adsorption at reducing the THM formation potential. The results provide new insights into the interactions between HAOPs and NOM molecules and shed light on the significantly different effects of different adsorbent contacting modes on the fouling potential of the pretreated water.

Biopolymer removal in full-scale conventional and advanced drinking water treatment trains at two large adjacent plants

The performance of conventional and advanced processes with regard to the reduction of the biopolymer fraction of natural organic matter (NOM) at two large adjacent full-scale drinking water treatment plants was compared and evaluated. Both plants were fed with the same surface water source, however, they differed in configuration and type of coagulant used. The biopolymer fraction, although of critical importance for low-pressure membrane fouling, is only a relatively small percentage of the overall NOM. Therefore, to provide context and comparison, the removal of humic substances, the largest NOM fraction, was also investigated. It was observed that the plant using aluminum sulfate slightly outperformed the one dosing polyaluminum chloride for biopolymer and humic substance removal when the coagulants were dosed at average concentrations of 0.68±0.23 mg Al/L and 1.10±0.63 mg Al/L, respectively. Under the conditions investigated, coagulation, flocculation, and sedimentation may be a better pre-treatment option for ultrafiltration membranes in terms of biopolymer removal compared to ozonation and biofiltration. However, as confirmed by Liquid Chromatography-Organic Carbon Detection analysis, biopolymer removal through biofiltration with prior ozonation was less than expected, suggesting that the process pairing was not optimized. This research illustrates the value of biopolymer quantification with respect to assessing its impact on membrane fouling.

Mitigating Low-Pressure Membrane Fouling by Controlling the Charge of Precipitated Floc Particles

Fouling presents the most significant obstacle to optimal low-pressure membrane plant performance. The occurrence of fouling tends to decrease production rates (flux), increase chemical usage incurred during clean-in-place (CIP) process, increase energy costs, shorten membrane life and reduce recovery. Fouling may be of organic or inorganic nature, necessitating more frequent dual chemical cleaning procedures. Regardless of the nature of the foulants, particulate loading onto the membrane fiber surface has been identified as a common mechanism of deteriorating performance. Particulates and colloidal materials such as turbidity, natural organic material (NOM), algae and precipitated coagulant floc accumulate on the membrane surface and disrupt the laminar flow of water through the element. Particulates can either attach or adhere to the membrane surface through electrostatic attraction. One method of reducing this fouling mechanism is to employ controlled coagulation as a direct feed or coupled with a clarification step prior to membrane process. Coagulation can attract and retain naturally occurring particulates and colloidal materials via charge neutralization. Then, by controlling the charge of precipitated floc particulates to align with the surface charge of the membrane element, both types of fouling can be mitigated. This Paper summarizes two demonstrations featuring a pressure feed and a submerged vacuum ultrafiltration (UF) system.

Membrane fouling mechanism transition in relation to feed water composition

The impact of secondary effluent wastewater from the Eastern Treatment Plant (ETP), Melbourne, Australia, before and after ion exchange (IX) treatment and polyaluminium chlorohydrate (PACl) coagulation, on hydrophobic polypropylene (PP) and hydrophilic polyvinylidene fluoride (PVDF) membrane fouling was studied. Laboratory fouling tests were operated over 3–5 days with regular, intermittent backwash. During the filtration with PP membranes, organic rejection data indicated that humic adsorption on hydrophobic PP membrane occurred during the first 24h of filtration and contributed to fouling for both raw wastewater and pre-treated wastewaters. However, after the first 24h of filtration the contribution of humic substances to fouling diminished and biopolymers that contribute to cake layer development became more prominent in their contribution to the fouling rate. For PVDF membranes, the per cent removal of humic substances from both raw wastewater and pre-treated wastewaters was very small as indicated by no change in UV254 from the feed to the permeate over the filtration period, even during the early stages of filtration. This suggested that the hydrophobic PP membrane adsorbed humic substances while the hydrophilic PVDF membrane did not. The highest mass of biopolymer removal by each PVDF membrane was from ETP water followed by PACl and IX treated water respectively. This was possibly due to differences in the backwashing efficiency linked to the filter cake contributed by biopolymers. Hydraulic backwashing was more effective during the later stages of filtration for the ETP water compared to IX and PACl treated waters, indicating that the filter cake contributed by ETP biopolymers was more extensively removed by hydraulic backwashing. It was proposed that humic substances may act to stabilise biopolymers in solution and that removing humics substances by coagulation or IX results in greater adhesive forces between the biopolymers and membrane/filter cake. Extended laboratory filtration is required to understand fouling of low pressure membranes as it relates to commercial applications, as the initial rate of fouling for new membranes can include pore constriction mechanisms from humic substances which diminish in significance as filtration continues. Filtration for >24h was required before the HIFI values became constant.

Irreversible membrane fouling abatement through pre-deposited layer of hierarchical porous carbons

In this work, dual-templated hierarchical porous carbons (HPCs), produced from a coupled ice-hard templating approach, are shown to be a highly effective solution to the commonly occurring problem of irreversible fouling of low-pressure membranes used for pre-treatment in wastewater reuse. For the first time, dual-templated HPCs, along with their respective counterparts – single-templated meso-porous carbon (MPCs) (without macropores) – are tested in terms of their fouling reduction capacity and ability to remove different effluent organic matter fractions present in wastewater and compared with a commercially available powdered activated carbon (PAC). The synthesized HPCs provided exceptional fouling abatement, a 4-fold higher fouling reduction as compared to the previously reported best performing commercial PAC and ∼2.5-fold better fouling reduction than their respective mesoporous counterpart. Thus, it is shown that not only mesoporosity, but macroporosity is also necessary to achieve high fouling reduction, thus emphasizing the need for dual templating. In the case of HPCs, the pre-deposition technique is also found to outperform the traditional sorbent-feed mixing approach, mainly in terms of removal of fouling components. Based on their superior performance, a high permeability (ultra-low-pressure) membrane consisting of the synthesized HPC pre-deposited on a large pore size membrane support (0.45 μm membrane), is shown to give excellent pre-treatment performance for wastewater reuse application.

Fouling of low-pressure membranes during drinking water treatment: effect of NOM components and biofiltration pretreatment

Fouling is a major challenge for low-pressure membrane drinking water treatment systems. Previous research has demonstrated that under the right conditions, biofiltration is an effective method to reduce fouling of low-pressure polymeric membranes. This study provides additional insight into the effect of biofiltration as a pretreatment for fouling reduction by using river water with different raw water quality characteristics than has been examined in previous studies. Two parallel pilot-scale dual media (sand/anthracite) biological filters were operated continuously over a period of 14 months. Liquid chromatography–organic carbon detection analysis confirmed that the parallel biofilters performed similarly with both averaging on 21% biopolymer removal. Raw and treated water biopolymer concentrations were correlated, with increased absolute removals occurring at higher raw water concentrations. Ultrafiltration (UF) membrane fouling experiments showed substantial improvement in performance following biofiltration pretreatment by reducing hydraulically irreversible and reversible fouling rates by 14–68% and 8–55%, respectively. The results also reaffirm the importance of biopolymers at concentrations as low as ∼0.1 mg/L on irreversible and reversible UF membrane fouling and a minimal impact of humic substances.

Impact of effluent organic matter on low-pressure membrane fouling in tertiary treatment

This study aims at comparing low-pressure membrane fouling obtained with two different secondary effluents at bench and pilot-scale based on the determination of two fouling indices: the total fouling index (TFI) and the hydraulically irreversible fouling index (HIFI). The main objective was to investigate if simpler and less costly bench-scale experimentation can substitute for pilot-scale trials when assessing the fouling potential of secondary effluent in large scale membrane filtration plants producing recycled water. Absolute values for specific flux and total fouling index for the bench-scale system were higher than those determined from pilot-scale, nevertheless a statistically significant correlation (r2 = 0.63, α = 0.1) was obtained for the total fouling index at both scales. On the contrary no such correlation was found for the hydraulically irreversible fouling index. Advanced water characterization tools such as excitation–emission matrix fluorescence spectroscopy (EEM) and liquid chromatography with organic carbon detection (LC-OCD) were used for the characterization of foulants. On the basis of statistical analysis, biopolymers and humic substances were found to be the major contribution to total fouling (r2 = 0.95 and r2 = 0.88, respectively). Adsorption of the low molecular weight neutral compounds to the membrane was attributed to hydraulically irreversible fouling (r2 = 0.67).

Fouling mechanisms in low-pressure membrane filtration in the presence of an adsorbent cake layer

Fouling of low-pressure membranes treating natural waters can be substantially mitigated by pre-depositing a thin layer of micron-size adsorbent particles on the membrane, a process we refer to as microgranular adsorptive filtration (μGAF). The role of adsorbent particle size, adsorbent surface loading, and membrane pore size in fouling of μGAF systems by natural surface water has been investigated. μGAF tests using heated aluminum oxide particles (HAOPs) and powdered activated carbon (PAC) reveal that fouling in such systems occurs both on the membrane and in the cake layer. Fouling on the membrane is primarily caused by soluble NOM and is exacerbated by the use of larger adsorbent particles and smaller-pore membranes. Such fouling is mitigated by removal of foulants in the pre-deposited layers, so the extent of mitigation is proportional to the adsorbent surface loading (i.e., the thickness of the cake layer). By contrast, fouling in the cake layer is caused by larger foulants such as colloids and particulate matter. Such fouling is insensitive to the layer's thickness. Use of smaller adsorbent particles improves the capture of colloids and particles but also exacerbates such fouling. In these cases, increasing the membrane pore size decreases the rate of fouling on the membrane, but does not affect the cake layer fouling.

Identification of effluent organic matter fractions responsible for low-pressure membrane fouling

Anion exchange resin (AER), powder activated carbon (PAC) adsorption and ozonation treatments were applied on biologically treated wastewater effluent with the objective to modify the effluent organic matter (EfOM) matrix. Both AER and PAC led to significant total organic carbon (TOC) removal, while the TOC remained nearly constant after ozonation. Liquid Chromatography–Organic Carbon Detection (LC-OCD) analysis showed that the AER treatment preferentially removed high and intermediate molecular weight (MW) humic-like structures while PAC removed low MW compounds. Only a small reduction of the high MW colloids (i.e. biopolymers) was observed for AER and PAC treatments. Ozonation induced a large reduction of the biopolymers and an important increase of the low MW humic substances (i.e. building blocks).Single-cycle microfiltration (MF) and ultrafiltration (UF) tests were conducted using commercially available hollow fibres at a constant flux. After reconcentration to their original organic carbon content, the EfOM matrix modified by AER and PAC treatments exhibited higher UF membrane fouling compared to untreated effluent; result that correlated with the higher concentration of biopolymers. On the contrary, ozonation which induced a significant degradation of the biopolymers led to a minor flux reduction for both UF and MF filtration tests. Based on a single filtration, results indicate that biopolymers play a major role in low pressure membrane fouling and that intermediate and low MW compounds have minor impact. Thus, this approach has shown to be a valid methodology to identify the foulant fractions of EfOM.

Characterization of secondary treated effluents for tertiary membrane filtration and water recycling

This study evaluates the impacts of water quality from three different secondary effluents on low pressure membrane fouling. Effluent organic matter (EfOM) has been reported by previous studies as responsible for membrane fouling. However, the contribution of the different components of EfOM to membrane fouling is still not well understood. In order to improve and optimize treatment processes, characterization and quantification of the organic matter are important. The characterization methods used in this study are liquid chromatography coupled with an organic detector (LC-OCD) and excitation emission matrix fluorescence spectroscopy (EEM). A bench-scale hollow fibre membrane system was used to identify the type of fouling depending on the feed water quality. Results showed no measurable dissolved organic carbon removal by the membranes for the three secondary effluents. Biopolymers and humic-like substances found in different proportions in the three effluents were partially retained by the membranes and were identified to contribute significantly to the flux decline of the low pressure membranes. The observed fouling was determined to be reversible by hydraulic backwashing for two effluents and only by chemical cleaning for the third effluent.

Variability and limits of the unified membrane fouling index: application to the reduction of low-pressure membrane fouling by ozonation and biofiltration

Abstract The impacts of ozone (0–8 mg O3 L−1) and filtration with biological activated carbon on membrane fouling by surface waters were investigated using three low-pressure membranes (two ceramics—UF or MF—and one polymeric—UF). The unified membrane fouling index (UMFI) was used to quantify the reversibility and irreversibility of membrane fouling. Minimum UMFI were calculated and repeatability assays were performed in order to evaluate the analytical detection limit and the precision of the method, respectively. The lowest ozone dose tested (1 mg O3 L−1) reduced the total fouling by 44, 63, and 41% for the polymeric membrane, the UF ceramic membrane, and the MF ceramic membrane, respectively. Further increase of the dose led to minor or no improvement, except for the ceramic MF membrane. For the ceramic membranes, a similar trend to that observed for total fouling was observed for hydraulically irreversible fouling. For the polymeric membrane, the hydraulically and chemically irreversible fouling were ...

NOM Fractionation and Fouling of Low-Pressure Membranes in Microgranular Adsorptive Filtration

Membrane fouling by natural organic matter (NOM) was investigated in microgranular adsorptive filtration (μGAF) systems, in which a thin layer of adsorbent is predeposited on low-pressure membranes. The adsorbents tested included heated aluminum oxide particles (HAOPs), ion exchange (IX) resin, and powdered activated carbon (PAC). Size exclusion chromatography (SEC) separated the NOM into four apparent MW fractions with significant UV₂₅₄. HAOPs and the IX resin performed almost identically with respect to removal of these fractions, and differently from PAC. However, while HAOPs and PAC reduced fouling substantially, IX resin did not, indicating that fouling could not be attributed to the NOM fractions detected by SEC. Rather, the key foulants appear to comprise a very small fraction of the NOM with almost no UV₂₅₄ absorbance. Alginate, a strongly fouling surrogate for natural polysaccharides, is adsorbed effectively by HAOPs, but not by IX resin or PAC, suggesting that polysaccharides sometimes play a key role in membrane fouling by NOM.

The significance of interactions between organic compounds on low pressure membrane fouling

Fouling of hollow fibre microfiltration and ultrafiltration membranes by solutions of pure organic compounds and mixtures of these compounds was studied with a backwashable membrane filtration apparatus. Small molecular weight compounds resulted in little fouling, while their polymeric analogues resulted in more severe fouling. Neutrally charged dextran resulted in minor, irreversible fouling, that was considered to be associated with blocking of small pores. Cationically charged chitosan produced gross fouling for which the extent of reversibility increased with salt addition. Anionically charged alginic acid resulted in gross irreversible fouling, except when being filtered by a hydrophilic membrane in the absence of calcium where a high degree of flux recovery was observed. Calcium addition to the alginic acid solutions resulted in gross fouling of all membranes and calcium bridging was considered to be responsible for this behaviour. Greater fouling occurred on the hydrophilic membrane compared to the hydrophobic membranes for bovine serum albumin (BSA) solutions, and this was considered to be due to physical blocking of pores, because addition of calcium resulted in lower flux declines. Addition of BSA and calcium to alginic acid solutions resulted in lower flux recoveries for the alginic acid system, consistent with the proposition that interactions between polysaccharide and other compounds are required for irreversible fouling on hydrophilic membranes.