Membrane Fouling Index Research Articles

Research on the removal efficiency and membrane fouling analysis of nanofiltration membranes under the combined pollution of emerging contaminants

Based on the research background of five emerging contaminants (ECs)— sulfadiazine (SD), sulfamethoxazole (SMZ), malathion, hexachlorobenzene (HCB), and bisphenol A (BPA)—which can be detected in trace amounts in a river basin in southern China, a spiking experiment was conducted to effectively address the potential impact risks of these contaminants. The experiment aimed to investigate the removal efficiency and membrane fouling of nanofiltration membranes (NF) under the combined pollution of these ECs. The experimental results show that under the combined pollution of these ECs, the NF exhibits good removal efficiency for all five ECs, with removal rates of approximately 83 ± 2 %, 84 ± 3 %, 76 ± 3 %, 73 ± 6 %, and 80 ± 5 % for SD, SMZ, malathion, HCB, and BPA, respectively. Additionally, NF also has high efficiency in removing other pollutants, with removal rates for chromaticity, CODMn, and total hardness at 80 ± 2 %, 60 ± 3 %, and 62 ± 2 %, respectively, and over 80 % of fluorescent substances were removed. Analysis of the key operating indicators of the NF under the combined pollution of ECs revealed that the membrane flux decreased slightly faster compared to without the combined pollution of ECs, and both the membrane fouling index and membrane resistance increased to a certain extent. Furthermore, the analysis of the NF chemical cleaning solutions showed that these ECs can be detected in both alkaline and acid cleaning solutions. Analysis of membrane dissection on NF revealed that severe cake layer contamination formed on the membrane surface both under and without the combined pollution of ECs, the presence of ECs is worse than the absence of ECs.

Controlling ultrafiltration membrane fouling in surface water treatment via combined pretreatment of O3 and PAC: Mechanism investigation on impacts of technological sequence

In this research, the effects of combined powdered activated carbon (PAC)-ozone (O3) pretreatment on ultrafiltration (UF) performance were comprehensively examined and compared with the conventional O3-PAC pretreatment. The performance of pretreatments on mitigating membrane fouling caused by Songhua River water (SHR) was evaluated by specific flux, membrane fouling resistance distribution, and membrane fouling index. Moreover, the degradation of natural organic matter in SHR was investigated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorescent organic matter. Results showed that the 100PAC-5O3 process was the most effective in improving the specific flux, with 82.89 % and 58.17 % reductions in the reversible fouling resistance and irreversible fouling resistance respectively. Additionally, the irreversible membrane fouling index was reduced by 20 % relative to 5O3-100PAC. The PAC-O3 process also exhibited superior performance in the degradation of UV254, DOC, three fluorescent components, and three micropollutants in the SHR system compared to O3-PAC pretreatment. The O3 stage played a major role in mitigating membrane fouling, while PAC pretreatment enhanced the oxidation in the subsequent O3 stage during the PAC-O3 process. Furthermore, the Extended Derjaguin-Landau-Verwey-Overbeek theory and pore blocking-cake layer filtration model fitting analysis were employed to explain the mechanisms of membrane fouling mitigation and fouling patterns transformation. It was found that PAC-O3 significantly increased the repulsive interactions between the foulants and the membrane, which restrained the formation of the cake layer filtration stage. Overall, this study evidenced the potential of PAC-O3 pretreatment in surface water treatment applications, providing new insights into the mechanism of controlling membrane fouling and improving the permeate quality.

Synergistic mechanism of combined ferrate and ultrafiltration process for shale gas wastewater treatment

The operational issues of low-pressure ultrafiltration (UF) membrane are associated with its long-term membrane fouling caused by organic and inorganic matters, especially in treating shale gas wastewater (SGW) with complex water compositions. Herein, the effect of ferrate (Fe(VI)) pretreatment on UF membrane fouling and water quality in treating SGW was systematically investigated. Fe(VI) pretreatment significantly mitigated membrane fouling and slightly improved the effluent quality. The hydraulically irreversible fouling index and the total fouling index decreased by 69%–87% and 58%–84%, respectively. The mechanism of membrane fouling mitigation was comprehensively analyzed by the classical pore blocking model, correlation analysis between membrane fouling index and water quality, and the extended Derjaguin-Landau-Verwey-Overbeek theory. The synergistic mechanisms of membrane fouling mitigation were as follows: (i) Macromolecular organic matters (high molecular weight humics and biopolymers) which would block the membrane pores were oxidized into low fractions organics and removed by Fe(VI); (ii) Fe(VI) pretreatment improved interaction free energy of cohesion of foulants-foulants making foulants more hydrophilic and stable, and increased interaction free energy of adhesion of membrane-foulants making it more difficult for foulants to deposit on the membrane surface. Fe(VI) pretreatment had huge potential in alleviating membrane fouling in treating SGW and other complex wastewater.

Detection of dynamic biofouling from adenosine triphosphate measurements in water concentrated from reverse osmosis desalination of seawater

The evaluation of fouling behavior, including biofouling, is crucial to increase efficiency in the reverse osmosis (RO) seawater desalination process (SDP). This paper reports on biofouling behavior in seawater in the SDP, detected by monitoring intracellular, extracellular, and total adenosine triphosphates (ATPs) in the cross-flow RO filtration system as bacterial activity tracers. The first-stage ultrafiltration (UF) treatment of raw seawater reduced the ATP range to approximately 25%, while the ATP concentration in seawater did not decrease significantly on average between the subsequent four stages until the RO membrane treatment. The results demonstrated temporal variation of ∆ATPs, the deference in ATPs between in RO concentrated water and in RO feed water, occurs randomly, as the membrane fouling index, evaluated from pressure measurements, increases to the level of fouling that requires cleaning. The significant increase in ∆ATPs despite a residence time of only approximately fifteen seconds over the RO module reflects bacteria cell detachment from biofilm. The large reduction in ∆ATPs reflects bacteria cell adhesion and biofilm growth on RO membrane surfaces. It is concluded that the temporal increase and decrease in ∆ATP in RO concentrated water capture the dynamic biofouling behavior and the formation process of biofilm on RO membrane surfaces.

Effect of temperature and module configuration on membrane fouling and end-product quality of acidic whey using ceramic ultrafiltration membrane

Ceramic membranes are used in different dairy industry processing owing to their food compatibility, high stability to temperature and pH, and high fractionation efficiency. This work is aiming to optimize the performance of ceramic ultrafiltration membrane for acidic whey processing based on the filtration temperature and module configuration. Disc and tubular membrane modules were used with a ceramic membrane 15kDa molecular weight cut-off and at whey temperature of 40oC and 50oC for both modules. The filtration performance was evaluated with normalized flux and membrane fouling index model. The end-product quality was monitored by analyzing protein, lactose, antibiotics, hormones, and heavy metals. It was found that the module configuration has a great effect on flux behavior and membrane fouling. The tubular module shows better performance with regard to normalized flux and membrane fouling index. However, at a higher temperature, the membrane fouling was higher with the disc membrane module and lower with the tubular one. In terms of end-product quality, the whey temperature is affecting protein and lactose concentration while the module configuration did not show a significant effect. Antibiotics, hormones, and heavy metals were found in concentrations that do not affect human health.

Performance Evaluation of Ceramic Membrane on Ultrafiltration and Diafiltration Modes for Efficient Recovery of Whey Protein

The recovery of high-quality, valuable end products from cheese whey is a very important industrial process. The aim of this study is to improve the recovered protein content of concentrate stream in cheese whey. The experiments were conducted by using ceramic ultrafiltration (UF) membrane followed by diafiltration (DF) process with a 15kDa molecular weight cut-off (MWCO). The volume concentration factor (VCF) was set as 1.4, 2.0 and 3.3 by controlling the permeate and concentrate volume. It was observed that the protein concentration increased from 1.4 g/l in the feed solution to 9.9 g/l in the concentrate stream. After VCF optimization, two intermittent feed diafiltration (IFD) cycles were performed experimentally and a mathematical model with real-time function was applied for DF yield calculation. The maximum yield was found as 88% at the end of the second DF cycle. The protein content reached to 33% in the concentrate stream after applying the IFD process. During the fouling experiments of DF process, the indicative parameters were calculated with three different fouling models. Total resistance (RT), membrane fouling index (MFI), and unified membrane fouling index (UMFI) were found as 5.15x1014 m-1, 25x106, and 344 respectively. IFD process enhanced the overall performance of whey processing compared to normal UF process.

Investigation of the fouling behaviors correlating to water characteristics during the ultrafiltration with ozone treatment

This study investigated the fouling behavior and mechanism of ozone treatment correlating to water characteristics for micro-polluted water during ultrafiltration (UF). The results indicated that pre-ozonation efficiently mitigated membrane fouling of natural organic matter (NOM). The higher ozone doses were, the more the performance transmembrane pressures (TMPs) decreased. Ozone mainly converted macro molecule organics into low molecule organics. Macro molecular biopolymers (BP) can be removed up to 35.5% with an ozone treatment of 9 mg/L, while low molecular weight building blocks of acids and humics (BB) and neutrals (LMWN) increased 7.25% and 14.62%, respectively, with an ozone treatment of 9 mg/L. Analysis of fluorescence excitation emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) indicated that ozone mainly removed soluble microbial organics and fulvic-like and humic-like organics but not tyrosine organics. Hydrophobic organics (HPO) were reduced with an increase of ozone doses, especially macro molecular BP and humic substances (HS), and the neutral hydrophilic fraction (N-HPI) was enhanced. Ozone treatment helped to reduce the interception of BP and HS in HPO and improved the interception of BP and HS in N-HPI, as well as BB and LMWN, in both fractions. Principal component analysis suggested that BP, as well as UV254, had high correlations with a membrane fouling index, which can be used as the fouling indicator during ozone treatment.

Impact of transmembrane pressure (TMP) on membrane fouling in microalgae harvesting with a uniform shearing vibration membrane system

A uniform shearing vibration membrane system can mitigate membrane fouling during algae filtration. In this paper, the effects of transmembrane pressure (TMP) on the membrane filtration performance at 8 kPa, 9 kPa and 10 kPa were investigated. The results of membrane fouling mechanisms predicted by Hermia's model surmised that membrane fouling is principally caused by the cake layer model, and the application of the Unified Membrane Fouling Index for quantitative evaluation of antifouling properties substantiating membranes in sub-critical condition exhibited superior antifouling properties. The reversible membrane fouling was largely dependent on polysaccharides due to size exclusion. Proteins tended to block the membrane pores and to cause irreversible fouling. It was also observed that high-molecular weight (>100 kDa) extracellular organic matters contributed a significant portion of membrane fouling. For greater insight, the CRiteria Importance Through Intercriteria Correlation (CRITIC) method was administered; it could be concluded that the removal of proteins was more responsible for the total fouling resistance than was the removal of polysaccharides, especially for membranes at the TMP of 9 kPa.

CuO nanoparticle–humic acid (CuONP–HA) composite contaminant removal by coagulation/ultrafiltration process: The application of sodium alginate as coagulant aid

In order to remove CuO nanoparticle–humic acid composite contaminant (CuONP–HA) and reduce the membrane fouling in coagulation/ultrafiltraion process, sodium alginate (SA) was used as a coagulant aid of polyaluminum chloride (PAC) to pre-treat CuONP–HA in synthetic water. The effect of SA on floc properties and membrane fouling was investigated by a laser diffraction instrument and ultrafiltration fouling model. The results showed that SA, as coagulant aid, could improve the removal efficiency of CuONP–HA by coagulation/ultrafiltration process. CuONP was completely removed, and the removal efficiency of HA was over 80% at PAC dosage=3.0mg/L and SA dosage≥0.2mg/L. Besides, PAC with SA (PAC+SA) could form larger flocs with better recoverability than PAC alone. The average size of CuONP–HA flocs formed by PAC+SA exceeded 1000um which was about 66% larger than flocs formed by PAC, and the small CuONP–HA aggregation also increased to about 280um. Moreover, membrane fouling was effectively reduced by pre-treating of SA, and membrane fouling index (MFI) was decreased with the dosage of SA increasing.

Understanding ultrafiltration membrane fouling by soluble microbial product and effluent organic matter using fluorescence excitation–emission matrix coupled with parallel factor analysis

Membrane fouling of soluble microbial product (SMP) and effluent organic matter (EfOM) in ultrafiltration (UF) was investigated by using fluorescence excitation–emission matrix coupled with parallel factor analysis (EEM–PARAFAC) as well as dissolved organic carbon (DOC) and polysaccharides measurement. SMP and EfOM samples were generated in bench-scale sequencing batch reactors (SBRs) fed with synthetic wastewater and domestic wastewater under different solid retention times (SRTs). Results showed that EfOM contained more DOC and more sub-fractional components except for tyrosine-like substances compared to SMP, however, SMP caused more severe fouling. The fluorescence intensity of tyrosine-like substances in UF feed showed good correlation with membrane fouling index, suggesting that it can serve as a fouling potential indicator. The mass balance analysis also indicated that the tyrosine-like substances was a major foulant. Membrane fouling was alleviated as SRT increased, which can be associated with the decrease of protein-like (tyrosine-like and tryptophan-like) substances under longer SRT.

Study of the relation between kinematic viscosity and SDI in polyethylene glycol solutions for predicting membrane fouling: preliminary test

Nowadays, membrane technology plays an essential role in water treatment as a method of producing good-quality water. Its success is due to its ease of implementation, high efficiency and low cost. However, fouling of the active layer of the membranes is one of the main problems of this technology because it affects the operation conditions of the process, requires maintenance and limits the useful lifetime of membranes. Several parameters have been developed for the prediction of fouling being the most used Silt Density Index (SDI). However, it has some limitations that have prompted the search for alternative parameters such as Modified Fouling Index, Modified Fouling Index-UF, Mini Plugging Factor Index and Unified Membrane Fouling Index, among others. In this work, a prediction methodology of colloidal fouling is studied by means of a direct, simple and immediate measure of the combination of kinematic viscosity and SDI. To perform the tests, synthetic solutions of polyethylene glycol at a concentration ranging between 0.1 and 0.75 g/l were used. In kinematic viscosity tests, a Cannon–Fenske viscometer was used and SDI measurements were performed using a standard testing system. Results show that there is a linear relationship between the kinematic viscosity values and SDI in the concentration range studied. These preliminary results can be used to introduce a new parameter for predicting fouling potential in membranes based on the measurement of the kinematic viscosity in the feed water.

A study on enhancing physical cleaning effectiveness in microfiltration membrane system

Fouling control is generally taken by selective pre-treatments, proper membrane operation conditions, and various membrane cleaning methods. The compactness and growth of cake layer on the membrane surface should be timely controlled by mechanical force or hydraulic action. In this work, the sequence of physical cleaning method was strategically introduced by changing cross-flow velocity (CFV), backwash intensity, and backwash waste discharge method from membrane housing. Intensive backwash flush was automatically applied when delta TMP obtained after backwash events was more than 2%. It provided higher pressure on the permeate side of the membrane compared to the normal backwashing, resulting in the reduction of sharp increase of TMP during several operation modes. In addition, the variation of CFV from 0 to 16 m/d based on the membrane fouling index caused turbulence on the membrane fiber, resulting in the discharge of particles accumulated on the membrane surface from membrane module. Finally, flushing mode followed by filtration was more effective in maintaining the TMP stable rather than discharging mode. Flushing effect could induce another shear force to the suspended solids in the bulk and remove cleaning wastes effectively from membrane housing. Large particulates and colloidal matters could be controlled by the proper sequence of physical cleaning based on the TMP monitoring. Furthermore, the strategic physical cleaning could sufficiently reduce not only TMP increase but also the damage of membrane, which is resulted from the more frequent and aggressive chemical cleanings.

Effect of Fe (III) species in polyferric chloride on floc properties and membrane fouling in coagulation–ultrafiltration process

Impacts of Fe (III) species on floc properties and membrane fouling in coagulation–ultrafiltration (C-UF) hybrid process were investigated. Fulvic acid (FA)-kaolin synthetized water was used to simulate the actual surface water coagulated by polyferric chloride (PFC) with four different basicity (B) values. Four PFC coagulants with B values of 0.5, 1.0, 1.5 and 2.0 were denoted as PFC05, PFC10, PFC15 and PFC20, respectively. The distribution of Fe (III) species in PFC was determined by a timed complexation spectroscopy method. The results implied that the sum of monomeric and polymeric species (Fea and Feb) in PFC decreased as B values of PFC increased. PFC with higher Fea and Feb had better dissolved organic carbon (DOC) removal efficiency and higher zeta potential, which made charge neturalization stronger. Fea and Feb in PFC were beneficial to form larger and looser flocs. The permeate fluxes of PFC with different B values decreased in the following order: PFC05>PFC20>PFC10=PFC15 and membrane fouling index (MFI) had opposite order. PFC05 displayed a flux advantage due to larger and looser flocs formed by it. In addition, cake resistance (Rc) relative to the total resistance was in the order of PFC20<PFC05<PFC10<PFC15.

Impact of enhanced coagulation ways on flocs properties and membrane fouling: Increasing dosage and applying new composite coagulant

Increasing dosage and applying new composite coagulants were common ways to enhance coagulation in removing natural organic matter (NOM). The role of increasing dosage and applying new composite coagulant on flocs properties and ultrafiltration membrane fouling were investigated by examining flocs aggregation process and membrane permeate flux variation of polyferric chloride (PFC) and polyferric chloride–polydimethyldiallylammonium chloride (PFC–PDMDAAC) in traditional and enhanced coagulation regions. The results showed that when PFC dosage was increased to 82mg/L (the second enhanced region), the removal efficiency of DOC was increased by 70%. The application of PFC–PDMDAAC could get 85% UV254 removal efficiency in the traditional coagulation region, which was higher than PFC. The flocs size and fractal dimension of PFC–PDMDAAC was 462um and 2.35 in traditional coagulation region respectively, which were higher than those of PFC. And increasing PFC dosage would result in flocs size decreasing from 414um to 166um, although fractal dimension increased when PFC dosage increased to the first enhanced coagulation region. Membrane fouling index (MFI) of PFC decreased in the following order: the first enhanced coagulation > traditional coagulation > the second enhanced coagulation. And MFI of PFC–PDMDAAC was significantly higher than that of PFC.

Influence of floc size and structure on membrane fouling in coagulation–ultrafiltration hybrid process—The role of Al 13 species

Coagulation application prior to ultrafiltration process was carried out to increase humic acid (HA) removal and membrane permeability. The [Al 13O 4(OH) 24(H 2O) 12] 7+ polycation (Al 13 species) was used in the coagulant process and polyaluminum chloride (PACl) was also used for comparison. Characteristics of aggregates pre-coagulated by Al 13 species and PACl were investigated using a laser diffraction particle sizing device. Additionally, membrane fouling was investigated under different coagulation conditions. The various resistances caused by Al 13 and PACl treatment effluents were determined using the membrane fouling index equation. The results indicated that at dose of 1 and 3 mg/L, Al 13 produced larger flocs than PACl; while when dosage further increased, the PACl-HA flocs were much larger. The flocs formed by Al 13 were strong and compact, and those formed by PACl were weak and loosely structured with the exception of the flocs generated at 1 mg/L. The investigation of membrane fouling demonstrated that Al 13 contributed to the best effluent permeating at 5 mg/L and the corresponding dose for PACl was 7 mg/L. The adsorption resistance of effluent pre-treated by Al 13 accounted for a smaller percentage of the total resistances compared with that by PACl.

Fouling mechanism and resistance analyses of systems containing sodium alginate, calcium, alum and their combination in dead-end fouling of nanofiltration membranes

Fouling of sodium alginate, calcium and alum coagulant in dead-end nanofiltration membranes was systematically investigated in this study. Alginate was used as a model component of polysaccharide, one of the most ubiquitous components of extracellular polymeric substances (EPS) in the secondary wastewater effluent. Fouling mechanism and specific cake resistances were determined using the membrane fouling index (MFI) equation, and the compressibility of cake layer in each system was analyzed. We have found that calcium improved permeate flux and reduced the resistances, in contrary to previous researches. The dominant fouling mechanism in the presence of alginate and/or calcium was cake formation without compression, whereas when alum was present there might exist more than one fouling mechanisms. It is further observed that calcium and alum had synergistic effects in lowering the resistances and changing the characteristics of the cake into more compressible. Based on our findings, a schematic model of fouling mechanisms in these systems was proposed.

Organic fouling of nanofiltration membranes: Evaluating the effects of humic acid, calcium, alum coagulant and their combinations on the specific cake resistance

Fouling of nanofiltration (NF) membranes by pre-treated Aldrich humic acid (PAHA), alum coagulant, calcium, and their combinations was systematically investigated in a dead-end filtration system in conjunction with analysis of the specific cake resistance. The severity of flux decline was greatly decreased when alum coagulant was added regardless the presence of calcium. Cake compressibility and fouling mechanism were found to be different in each system: non-compressible for system with only PAHA, compressible for system with PAHA and calcium, and in the presence of alum more than one fouling mechanisms co-existed. Specific cake resistances of these systems were determined using the membrane fouling index (MFI) curve, and the values were compared with the empirical ones. A correlation between foulant attachment and specific cake resistance was observed. Finally, a new attachment coefficient in the fouling index was proposed. With this new coefficient, the foulant attachment is accounted for in the determination of specific cake resistance using the MFI curve.

The effects of soluble organic matters on membrane fouling index

This study investigated the effects of soluble organic matters on membrane fouling characteristics, using silt density index (SDI) and modified fouling index (MFI) to evaluate the fouling potential. Experimental results demonstrated that humic acid had significant effects on membrane fouling indexes. When its concentration was in the range of 0.01–0.05 mg/L, the SDI 15 and MFI were 2.9–3.9 and 5.4–13.8 s/L 2, respectively. According to the linear equations of MFI measurements, the fouling potential was in the order of humic acid > nucleic acid ≒ protein > glucose. Moreover, the molecular weight of dextran played an important role in membrane fouling indexes. Furthermore, a mathematical analysis of filtration experiments based on saturation curve was developed in this study. The maximum accumulated filtrate ( V max ) and the constant of filtration ( k f ) could be obtained to improve the precision of membrane fouling prediction.

Analysis of fouling potential in the electrodialysis process in the presence of an anionic surfactant foulant

Fouling of ion exchange membranes in an electrodialysis process is highly sensitive to the concentration of a surfactant. To investigate the influence of the fouling on the process performance, an anion exchange membrane was characterized by electrochemical properties as well as physical and chemical properties. The fouling potential was then quantitatively analyzed using the membrane fouling index as a function of the surfactant concentration. It was observed that the fouling mechanism is initiated by the micelle formation. That is, most of SDBS molecules form a fouling layer on the membrane surface at a higher concentration than the critical micelle concentration. Also the SDBS fouling mechanisms caused by the fouling layer were examined by the electrochemical impedance spectroscopy. The equivalent circuits show that the fouling potential of the system was increased by an additional layer, simultaneously increasing the electrical resistance to permeation of ions through the membrane. However, the SDBS fouling on the membrane was a reversible process.

Unified Membrane Fouling Index for Low Pressure Membrane Filtration of Natural Waters: Principles and Methodology

Membrane filtration is considered an important technology that can contribute to the sustainability of water supplies. However, its continued development necessitates the establishment of proper techniques for the assessment of membrane fouling. Unified Membrane Fouling Index (UMFI) was developed in this study in order to quantify and assess the fouling of low-pressure membranes (LPM) observed at various scales of water treatment. The foundation of UMFI is a revised Hermia model applied to both constant pressure and constant flux filtration. The adoption of UMFI makes it possible to simplify and standardize the bench-scale testing of membrane fouling potential by directly using the commercial LPM of interest. This approach can overcome a major challenge to fouling assessment, i.e., the membrane-specificity of fouling potential, which has not been wholly addressed by existing fouling indices. The fundamentals of UMFI are presented in this paper, together with the methodology for bench-scale testing. The application of UMFI to the assessment of the fouling of a LPM by a natural surface water is also discussed. Good agreement between bench-scale UMFI and pilot-scale UMFI was found, suggesting the validity of this new scientific concept for environmental applications.