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The low-fouling propensity of commercially available polyethersulfone (PES) membranes was studied after modification of the membrane surface via coating with polymerizable bicontinuous microemulsion (PBM) materials. The PBM coating was polymerized within 1 min using ultraviolet (UV) light exposure. It was detected on the PES membrane surface via attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The PBM coating led to an average 10% increase in the hydrophilicity of the PES membrane surface and an increase in total organic content (TOC) removal by more than 15%. Flux-step tests were conducted with model foulant comprising 100 mg L−1 humic acid (HA) solution to detect the onset of critical fouling, characterized by a rapid and substantial increase in TMP, and to compare the fouling propensity of commercially available PES membranes with PBM-coated membranes. The critical flux was found to be about 40% higher for PBM spray-coated membrane and 20% lower for PBM casting-coated membrane than the commercial PES membrane. This demonstrates the performance advantages of the thin PBM layer spray-coated on PES membrane compared to the thick casting-coated PBM layer. The study showcases the potential of PBM spray-coated membranes over commercial PES membranes for use in membrane bioreactors (MBR) for wastewater treatment systems with reduced maintenance over longer operation periods.

Laboratory membrane fouling studies are often performed with a single foulant. However, studies comparing the behavior of different foulants using a single membrane are rarely reported. In this study, a poly(vinylidene fluoride) (PVDF) microfiltration membrane was challenged with a series of aqueous-based model fouling media, including a suspension of latex beads, as well as soybean, motor and crude oil emulsions, in constant permeate flux fouling experiments. The critical and threshold fluxes were determined for each membrane-foulant pair. Constant permeate flux crossflow fouling experiments were performed at both low and high fluxes. A direct comparison of the fouling propensity of the PVDF membrane to the four fouling media was made. The fouling propensity was evaluated based on threshold flux values and the extent of transmembrane pressure (TMP) increase during constant permeate flux fouling experiments. In this study, the zeta potential of various fouling media correlated with their fouling propensities. The higher the zeta potential, the lower the fouling propensity. The fouling propensity followed the order of: latex beads

Laboratory membrane fouling studies are often performed with a single foulant. However, studies comparing the behavior of different foulants using a single membrane are rarely reported. In this study, a poly(vinylidene fluoride) (PVDF) microfiltration membrane was challenged with a series of aqueous-based model fouling media, including a suspension of latex beads, as well as soybean, motor and crude oil emulsions, in constant permeate flux fouling experiments. The critical and threshold fluxes were determined for each membrane-foulant pair. Constant permeate flux crossflow fouling experiments were performed at both low and high fluxes. A direct comparison of the fouling propensity of the PVDF membrane to the four fouling media was made. The fouling propensity was evaluated based on threshold flux values and the extent of transmembrane pressure (TMP) increase during constant permeate flux fouling experiments. In this study, the zeta potential of various fouling media correlated with their fouling propensities. The higher the zeta potential, the lower the fouling propensity. The fouling propensity followed the order of: latex beads

[Display omitted] • The apple juice can be athermally concentrated up to 5.45-fold by a single stage FO process. • The effects of process parameters on FO flux and fouling control were investigated. • The pectin plays a crucial role in membrane fouling. • Hydraulic flushing showed considerable advantage in membrane cleaning. The athermal concentration as green and sustainable technique is desired for fruit juice concentration to improve product quality and decrease the energy consumption. The emerging forward osmosis (FO) process was employed for apple juice concentration at ambient operational conditions in order to preserve juice nutrition and flavor. The parameters of FO process (membrane property, crossflow velocity of feed solution (FS), type of draw solutes, and concentration of draw solution (DS)) were detailedly investigated for the effects on water flux, membrane fouling control and membrane cleaning. The content of total soluble solids (TSS) in the apple juice was increased from 11°Brix to 60°Brix. The acidity and total phenols were both increased by 4.07-fold and 4.92-fold, respectively. The apple juice can be concentrated up to about 5.45-fold according to TSS by a single stage FO process after 48 h. The membrane fouling mechanism was investigated by the flux change with and without the pectin. Furthermore, different methods of membrane cleaning were further assessed to recover the water flux. Hydraulic flushing could efficiently recover the flux up to 95.2%. The optimization of the FO process parameters could further facilitate FO process for athermal concentration of apple juice, which may have great potentials for the practical applications in the food processing. [ABSTRACT FROM AUTHOR]

Ultrafiltration is a promising, environment-friendly alternative to the current physicochemical-based tannery wastewater treatment. In this work, ultrafiltration was employed to treat the tanning wastewater as an upstream process of the Zero Liquid Discharge (ZLD) system in the leather industry. The filtration efficiency and fouling behaviors were analyzed to assess the impact of membrane material and operating conditions (shear rate on the membrane surface and transmembrane pressure). The models of resistance-in-series, fouling propensity, and pore blocking were used to provide a comprehensive analysis of such a process. The results show that the process efficiency is strongly dependent on the operating conditions, while the membranes of either PES or PVDF showed similar filtration performance and fouling behavior. Reversible resistance was the main obstacle for such process. Cake formation was the main pore blocking mechanism during such process, which was independent on the operating conditions and membrane materials. The increase in shear rate significantly increased the steady-state permeation flux, thus, the filtration efficiency was improved, which resulted from both the reduction in reversible resistance and the slow-down of fouling layer accumulate rate. This is the first time that the fouling behaviors of tanning wastewater ultrafiltration were comprehensively evaluated, thus providing crucial guidance for further scientific investigation and industrial application.

The low-fouling propensity of commercially available polyethersulfone (PES) membranes was studied after modification of the membrane surface via coating with polymerizable bicontinuous microemulsion (PBM) materials. The PBM coating was polymerized within 1 min using ultraviolet (UV) light exposure. It was detected on the PES membrane surface via attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The PBM coating led to an average 10% increase in the hydrophilicity of the PES membrane surface and an increase in total organic content (TOC) removal by more than 15%. Flux-step tests were conducted with model foulant comprising 100 mg L -1 humic acid (HA) solution to detect the onset of critical fouling, characterized by a rapid and substantial increase in TMP, and to compare the fouling propensity of commercially available PES membranes with PBM-coated membranes. The critical flux was found to be about 40% higher for PBM spray-coated membrane and 20% lower for PBM casting-coated membrane than the commercial PES membrane. This demonstrates the performance advantages of the thin PBM layer spray-coated on PES membrane compared to the thick casting-coated PBM layer. The study showcases the potential of PBM spray-coated membranes over commercial PES membranes for use in membrane bioreactors (MBR) for wastewater treatment systems with reduced maintenance over longer operation periods.

This work aimed to characterize the impact of high shear rate generated by crossflow microfiltration on the particles size, the rheological behavior and the overall fouling propensity of fruit juices. To this end, two orange juices, with different characteristics, were circulated during a defined duration (until 120 min) under a high shear rate (22,270 s −1 ) in a side-stream membrane unit, without filtration. Results showed that this shearing condition was likely to induce significant changes concerning at the same time the particles size distribution (with a possible particles fractionation) and the rheological properties of the fruit juices (with a potential increase of energy of cohesion between the particles). The fouling propensity of the juices, estimated through lab-scale filtration test, was also modified by the shear rate, showing that new foulant components could be released during the circulation in the filtration loop. Industrial relevance Crossflow microfiltration is successfully applied to stabilize and clarify fruit juices or to concentrate their pulpy fraction. This work aimed to characterize for the first time the impact of high shear rate applied during crossflow microfiltration on the particles size distribution, the rheological behavior and the overall fouling propensity of fruit juices. This work showed for the first time that it is important to consider the impact of high shear rates on the particles size fractionation and the release of foulant compounds when carrying-out fruit juices microfiltration under high crossflow velocities. Crossflow microfiltration of fruit juices under high crossflow velocity may not be, in some cases, the most appropriate strategy to reduce membrane fouling. According to the juice characteristics, specific industrial strategies such as enzymatic treatment or mechanical actions (e.g. back-pulsing) would be more useful than crossflow velocity to enhance the overall performance of microfiltration. [ABSTRACT FROM AUTHOR]

The effects of inorganic salts and organic hydrocarbons on membrane fouling are often investigated independently. However, in many cases, these foulants are commonly found together, and such mixtures are rarely the subject of fouling studies. In this study, crude oil-in-water emulsions were formulated at three different added NaCl concentrations, 0 , 10 - 3 and 10 − 1 M. Surface properties, such as surface tension and surface charge, of these emulsions and a poly(vinylidene fluoride) (PVDF) microfiltration (MF) membrane were characterized. The Derjaguin-Landau-Verwey-Overbeek (DLVO) model was utilized to simulate membrane-oil droplet and oil layer-oil droplet surface interactions. The DLVO model qualitatively predicted increasing fouling propensity with increasing emulsion salt concentration. The PVDF MF membrane was challenged with crude oil-in-water emulsions in constant permeate flux crossflow fouling tests to characterize the fouling propensity of the various emulsions, and the results were consistent with the model predictions. [ABSTRACT FROM AUTHOR]

Membrane fouling remains the major obstacle for development of membrane bioreactors (MBRs). This paper aimed at investigating the effects of carbamazepine (CBZ) present in a discontinuous way at high concentration (peak injection) on fouling propensity of activated sludge from a MBR that treats domestic wastewater. Batch experiments with peak injection of CBZ (100 µg L −1 in sludge for 3 h) were performed for sludges sampled from a MBR operated under different organic loading conditions. HPLC-SEC analysis with a fluorescence detector was employed to study the effects of CBZ on protein-like compounds in supernatant. With addition of CBZ in sludge, a significant increase of sludge fouling propensity was observed when using sludge sampled from the MBR operated under low organic loading rate (0.1 kg COD/kg MLSS/d), which could be attributed to the increase in the quantity of protein-like substances with a 100–1000 kDa molecular size in supernatant. Whereas reduced CBZ effect was found for sludge sampled from the MBR operated under higher organic loading rate (0.2 kg COD/kg MLSS/d). Whatever the sludge, the injection of CBZ induced no significant change of the floc size distribution and of the polysaccharide concentration in supernatant. Moreover, it did not affect the sludge microbial activity. [ABSTRACT FROM AUTHOR]

Abstract: Fouling profiles for reverse osmosis membranes were compared for four municipal and one industrial effluent samples collected from water recycling schemes located on the east coast of Australia. The dissolved organic carbon (DOC) of the four municipal effluents ranged from 5 to 8mgL−1, while the industrial effluent contained 59mgL−1. The hydrophobic/hydrophilic content and molecular size distribution of the effluent organic matter (EfOM), post biological treatment and membrane filtration, were determined using rapid resin fractionation and size exclusion chromatography. Thin film polyamide reverse osmosis (RO) membranes were operated in cross flow to a recovery of 87%. A good correlation was observed between flux decline on the municipal effluent and the overall organic loading (R 2 =0.957 and 0.929) and the percent fraction of hydrophobic acids (HPhoA, R 2 =0.987). A similar correlation was observed for the hydrophilic fraction (HPhi, R 2 =0.912), however, the rate of fouling was independent of the percentage of transphilic acids (TPhiA, R 2 =0.029). Further support for the role of the humic and neutral fractions in membrane fouling was found in changes in the surface chemistry of the polyamide membranes as reflected in change in contact angle and zeta potential. While it is tempting to use EfOM characterisation as a predictor of RO fouling, data from the performance of membranes on the industrial stream suggest that the data should be interpreted cautiously and that consideration should also be given to inorganic fouling. In this case, although the industrial effluent contained more than six times the amount of DOC, which consisted of more than 80% humic substances, scanning electron microscope-energy dispersive X-ray analysis indicated that the dominant foulant on the industrial effluent was inorganic deposits. Consequently, detailed organic characterisation, while useful is site specific and is no substitute for a comprehensive assessment of all potential foulants. [Copyright &y& Elsevier]

Abstract: Microbacterium trichotecenolyticum B4-1, a strain that produces soluble microbial products (SMPs) of protein substances, was employed to investigate SMP production under various substrate levels. This study also estimated the effect of typical operating condition of membrane bioreactor (MBR) under an extremely low substrate level. It was observed that soluble protein production was apparent under a substrate-rich environment, but can be negligible under a normal substrate level. The concentration of soluble protein was directly proportional to initial food to microorganism (F/M) ratio, which the soluble protein can be regarded as utilization-association products (UAPs). Under the extremely low substrate level, soluble protein of possible biomass-associated products (BAPs) was released in correlation with cell decay to 74.0mg/L, which was higher than that under the normal substrate level. In addition, the BAP protein had the highest potential to cause membrane fouling, increasing the total membrane resistance to 89.3×1011 m−1 after 20-h filtration. Excitation–emission matrix (EEM) analysis was also applied to determine the composition of the UAPs and the BAPs. The EEM spectrum of humic-acid and fulvic-acid substances between the UAP and the BAP were different. In this study, it was shown that the fouling potential was more closely related to the SMP composition than the SMP concentration. [Copyright &y& Elsevier]

The effect of adjusting pH on membrane filterability of activated sludge mixed liquor in membrane bioreactors (MBRs) was studied. The properties of the mixed liquor were analyzed to investigate the mechanisms. The results indicated that moderately adjusting pH was effective to improve the membrane filterability of the mixed liquor. HCl addition provided H+, which reduced the zeta-potential of the colloidal particles. NaOH addition at pH of 8.0-9.0 released some extractable extra-cellular polymeric substances (eEPS) to the supernatant. Re-flocculation occurred. The fouling propensity of the mixed liquor was therefore reduced. Microbial activity was not significantly affected within the pH of 6.0-9.0. [ABSTRACT FROM AUTHOR]

Abstract: Soluble microbial products (SMPs) contained in membrane bioreactor (MBR) supernatant have been proved to be main foulants. To obtain a comprehensive understanding of the fouling potential of SMPs on the basis of both hydrophilic/hydrophobic properties and molecular size, MBR supernatant of a pilot-scaled system treating municipal wastewater was partitioned into different hydrophilic/hydrophobic fractions by DAX-8 resins, with joint size partition of hydrophilic fraction also undertaken. A series of stirred dead-end filtration tests were conducted to investigate the flux decline. Hydrophilic fraction was found the dominant foulant responsible for flux deterioration, which was mainly attributed to the subclass of molecular weight above 100kDa. The molecular weight distribution and atomic force microscopy images indicated that large molecules in hydrophilic fraction plugged the membrane pores. The backwash tests showed the flux decline caused by hydrophilic fraction was much less recoverable by hydraulic cleaning. It can be inferred that steric factor, i.e. size exclusion was the primary cause in the initial stage of fouling, while the role of hydrophobic interaction was of less significance. Additional modeling work indicates that the main fouling mechanism was complete blocking, further confirming the predominance of size exclusion contributing to membrane fouling by SMPs in MBR supernatant. [Copyright &y& Elsevier]

Abstract: In membrane bioreactors, mixed liquor properties influence membrane fouling significantly. An effective method was therefore proposed to identify the major factors that affect membrane fouling under identical conditions for direct comparison. First, the membrane filterability of the mixed liquor was measured to evaluate fouling propensity. Forty mixed liquor samples taken from various membrane bioreactors were measured in terms of their membrane filterability and 14 other properties. The correlation of membrane filterability with each mixed liquor property was further analyzed by multivariate statistical analyses. The results showed that supernatant organic concentration was the most significant factor influencing membrane filterability. The soluble organics and polysaccharides in the supernatant contributed to fouling more than the colloidal organics and proteins. Additionally, mixed liquor suspended solid concentration had an effect on filterability at concentrations greater than 10gL−1, which resulted in a great increase in the viscosity of the mixed liquor. Otherwise, mixed liquor with mean floc size greater than 80μm consistently featured good membrane filterability. Extra-cellular polymeric substance content had little effect on membrane filterability. [Copyright &y& Elsevier]

Abstract: Fouled RO membranes from a real water treatment plant were analyzed biochemically to investigate the role of quorum sensing in controlling the rate and the extent of biofilm formation on the membrane surface. The results showed that 60% of bacterial species found on the fouled membrane surface contribute to biofilm formation through the active intraspecies as well as interspecies communication. It was confirmed that N-acylated homoserine lactones (AHL) produced from microorganisms involved in the quorum sensing transferred bacterial signal. In addition, flow field-flow fractionation (Fl-FFF) analyses demonstrated that most microorganisms contributing to biofilm formation through quorum sensing exhibited favorable adsorption on the membrane surfaces. The skewness values of these microorganisms were noticeably greater than those of organic macromolecules (i.e., natural organic matter) and particles. The study suggests that biochemical control of interfering quorum sensing could be an effective alternative to control biofilm formation and, thus, the reduction in biofouling of RO membranes. [Copyright &y& Elsevier]

This paper presents the experimental results on the fouling propensity of five pairs of blended coals (19 coals and blends) tested in the Australian Coal Industry Research Laboratory (ACIRL) furnace. The results showed that the coal D has the highest fouling propensity among tested coals and blends. A parameter, growth rate (mm/h), is used to numerically rank the fouling propensity based on photos of fouling deposits taken over a period of test time. The growth rate correlates the fouling propensity better than the build up rate or the fouling coefficient. Five empirical fouling indices are examined against the fouling propensities of the above 19 coals and blends, and another 10 coals and blends previously tested in the Energy and Environmental Research Cooperation (EER) furnace. The linear correlation between the flue gas exit temperature/initial deformation temperature (FGET/IDT(ox.)), a measure of the overall heat transfer in the furnace, and the Na2O, g/GJ, is proved to be a good tool for predicting the fouling propensity of coals. There is also a relationship between the FGET and the growth rate. [Copyright &y& Elsevier]

Ultrafiltration is a promising, environment-friendly alternative to the current physicochemical-based tannery wastewater treatment. In this work, ultrafiltration was employed to treat the tanning wastewater as an upstream process of the Zero Liquid Discharge (ZLD) system in the leather industry. The filtration efficiency and fouling behaviors were analyzed to assess the impact of membrane material and operating conditions (shear rate on the membrane surface and transmembrane pressure). The models of resistance-in-series, fouling propensity, and pore blocking were used to provide a comprehensive analysis of such a process. The results show that the process efficiency is strongly dependent on the operating conditions, while the membranes of either PES or PVDF showed similar filtration performance and fouling behavior. Reversible resistance was the main obstacle for such process. Cake formation was the main pore blocking mechanism during such process, which was independent on the operating conditions and membrane materials. The increase in shear rate significantly increased the steady-state permeation flux, thus, the filtration efficiency was improved, which resulted from both the reduction in reversible resistance and the slow-down of fouling layer accumulate rate. This is the first time that the fouling behaviors of tanning wastewater ultrafiltration were comprehensively evaluated, thus providing crucial guidance for further scientific investigation and industrial application. [ABSTRACT FROM AUTHOR]