Irreversible Fouling Rate Research Articles

Constructing quaternized graphene oxide filtration layer on PVDF membrane by a facile strategy via dopamine crosslinking and its performance

The increasing utilization of polyvinylidene fluoride (PVDF) ultrafiltration membranes in water treatment has necessitated the development of membranes with superior separation, antifouling performance and high pure water permeability. As a hydrophilic and antibacterial modifier, quaternized graphene oxide (QGO) has been successfully applied to improve the antifouling and antibacterial properties of the membranes simultaneously. Herein, we proposed a simple and effective strategy to fabricate a nanocomposite ultrafiltration membrane by coating the PVDF membrane surface with QGO and using polydopamine (PDA) as a “bio-glue”. The filtration followed by cross-linking method was utilized to construct a “brick-mud” structure on the membrane surface. The prepared QGO/PDA-PVDF membrane exhibited favorable separation and antifouling properties (79.5% of BSA rejection rate, 15.7% of irreversible fouling rate when filtering 0.5 g/L BSA solution, 97.2% of E. coli and 96.3% of S. aureus antibacterial rate), while maintaining a high pure water permeability of 1105.4 L.m−2.h−1.bar−1. QGO nanosheets were stably coated on the membrane surface, and the QGO/PDA-PVDF membrane prepared by this novel strategy also demonstrated application potential in the field of seawater desalination pretreatment. Besides, the possible mechanisms during modifications were also discussed. This research could serve as a reference for improving the comprehensive performance of PVDF ultrafiltration membrane through surface coating.

Self-cleaning foulant attachment on near-infrared responsive photocatalytic membrane for continuous dynamic removing antibiotics in sewage effluent environment

Bifunctional photocatalytic nanofiltration (PNF) membrane has become a reliable frontier technique for removing refractory organic micropollutants. However, the active mitigated fouling mechanism from the microscopic perspective during its long-term operation of purifying real micro-polluted water is rarely studied. Herein, with an integrated use of QSense Explorer and confocal laser scanning microscope techniques, self-cleaning foulant attachment on an activated and customized near-infrared responsive polymeric PNF (termed as nPNF) membrane with good service performance for continuous dynamic removing antibiotics in sewage effluent environment was firstly elucidated. Time-dependent changes in dissipation oscillation frequency, sensed mass and the visualized foulant spatial distribution all indicated that there were only sporadic foulant attachment, an extremely low fouling layer thickness and irreversible fouling rate on/of the activated nPNF membrane top surface, thereby endowing it with excellent self-cleaning characteristic. This is probably because the reactive oxygen species (mainly •O2− and •OH) concurrently destroys the integrity of fouling layer and its internal adhesion structure, transforming part of the irreversible fouling on nPNF membrane surface into reversible one that is easy to wash off. These new horizons provided useful insight on the fate of selected antibiotics in the to-be-removed stage and self-cleaning foulant attachment of PNF membrane.

Revealing the fouling characteristics in membrane-based primary treatment (MPT) of municipal wastewater and the antifouling mechanism of influent conditioning

Membrane-based technology is becoming an attractive option for primary treatment of municipal wastewater (MW) due to its superior organic retention capacity and footprint savings. However, limited understanding of fouling mechanisms still hampered its practical application. This study aims to investigate the fouling characteristics in MPT and analyze anti-fouling mechanisms of influent conditioning. In the meantime, the differences between microfiltration (MF) and ultrafiltration (UF) are also discussed. Dozens of filtration experiments with different membranes (0.1 μm and 100 kDa), MW conditioning methods (coagulation and adsorption) were conducted. Results indicated that a hallmark of MPT is the protective ability of particulate matters present in the raw MW. The irreversible fouling rate was 2–4 times higher in the absence of particulates. Besides, the main irreversible foulant types and the cake growth patterns differed with different pore sizes. As for influent conditioning, coagulation and adsorption collaborate effectively in regulating cake characteristics. Polymeric aluminum chloride reduces the tendency of binding between foulants and membrane, while activated carbon increases the porosity of the cake layer.

Effect of spraying polyvinyl alcohol solution on the surface of liquid film on the structure and antifouling properties of polyvinylidene membrane

Abstract Polyvinylidene fluoride (PVDF) membrane was prepared by a two-step method of surface gelation-immersion precipitation. The surface of the scraping solution film was sprayed with polyvinyl alcohol (PVA) aqueous solution to gel the film surface first, and then the liquid film was immersed in a coagulation bath for phase transformation to obtain the surface modified PVDF membrane. The effects of PVA solution with different mass fraction on the structure and properties of PVDF membrane were studied. The results showed that with the increase of spraying PVA mass fraction, the contact angle of the upper surface of PVDF membranes gradually decreased, the porosity and mean pore size of PVDF membranes gradually increased, and the crystallinity of PVDF membranes gradually decreased. The pores on upper surface of the membranes first increased and then decreased, and the finger-like macropore structure appeared inside the membranes, the water flux first increased and then decreased, and the rejection rate increased. Dynamic cycle filtration experiment of bovine serum protein (BSA) solution showed an increase in membrane flux recovery from 68.31 to 95.08% and a decrease in the irreversible fouling rate from 31.69 to 4.92%, indicating an improvement in the hydrophilicity and antifouling properties of the modified PVDF membrane.

Superhydrophilic membrane with photo-Fenton self-cleaning property for effective microalgae anti-fouling

Membrane filtration is one of the effective approaches to harvest microalgae for industrial biofuel production. However, during the filtration process, microalgae cells and extracellular organic matter (EOM) will deposit on the membrane surface leading to reversible membrane fouling that can be removed by physical methods. When hydrophobic EOM is adsorbed on the membrane surface or inside pores, it will build up a gel layer, causing irreversible membrane fouling. Irreversible fouling can only be removed using chemical methods that will decrease membrane lifespan and increase operational costs. Here, we introduce a versatile superhydrophilic membrane with photo-Fenton self-cleaning property, which can prevent the reversible fouling and remove the irreversible fouling. Tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) were co-deposited on the polyvinylidene fluoride (PVDF) membrane via Schiff base and Michael addition reactions, and β-FeOOH nanorods were inlaid on the membrane surface by in situ mineralization. The water contact angle of the modified membrane is reduced from 120° to 0° Under 60 min visible light, the hydroxyl radical (·OH) generated by the photo-Fenton reaction degraded the irreversible fouling that blocked membrane pores. The irreversible fouling rates of modified membrane was reduced from 39.57% to 3.26%, compared with the original membrane. Microalgae harvesting results illustrated that the membrane has a high flux recovery rate (FRR) of 98.2%, showed excellent passive antifouling and active antifouling performance. We believe this work will spark a novel platform for optimizing energy-efficient microalgae harvesting separation membrane modules. In addition, this method of anti-fouling filtration for microorganisms can be extended to the industrial production of various bioenergy sources and will have very promising practical applications.

Comparison between integrated MIEX/UF and PAC/UF in long-term irreversible membrane fouling reduction: Effectiveness and mechanism analysis

In an integrated adsorption/ultrafiltration process, the choice of adsorbent is key as it affects the effluent water quality in addition to providing membrane fouling control. Magnetic ion-exchange resin (MIEX) and powdered activated carbon (PAC), two of the most used adsorbents in water treatment processes, have similar organic matter removal abilities. However, the corresponding integrated processes exhibited significant differences in terms of irreversible membrane fouling mitigation. Long-term filtration experimental results suggested that the chemical cleaning interval of the MIEX/UF process was 134% longer than that of the PAC/UF process. In addition, MIEX/UF had a 28.8% reduction for the chemically irreversible fouling rate compared to that of PAC/UF. Hydraulically irreversible fouling was effectively alleviated in the MIEX/UF process throughout long-term operation, whereas fouling was exacerbated in the PAC/UF process under the condition of timed chemical cleaning. Further analysis indicated that in the PAC/UF process, irreversible fouling control depended on adsorption; however, fouling mitigation in the MIEX/UF process mainly relied on the enhancement of backwashing by the MIEX dynamic layer. The significant difference in the interfacial forces between the MIEX-pollutants and PAC-pollutants was the fundamental cause for this phenomenon. Therefore, the mitigation of membrane fouling in an integrated adsorption/UF process depends more on the adhesion force between the adsorbent and pollutants than on the adsorption capacity of the adsorbent.

Stable fouling resistance of polyethylene (PE) separator membrane via oxygen plasma plus zwitterion grafting

Low-cost and fouling resistant microfiltration/ultrafiltration membranes for wastewater treatment has been a challenging task when balancing the membrane cost and performance stability. Herein, a low-cost polyethylene (PE) lithium-ion battery separator was explored as a potential solution. To tackle the intrinsic hydrophobic character which incurs severe fouling, a novel cascade process of plasma treatment plus zwitterion grafting was designed: first oxygen plasma to endow oxygen-containing groups for hydrophilicity and supply “grafting sites”, and grafting zwitterion 3-[[3-(trimethoxysilane)-propyl] amino] propane-1-sulfonic acid (TMAPS) for robust fouling resistance. The membranes were analyzed by water contact angle, Fourier-transform Infrared Spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS). Challenged by two typical foulants, e.g., humic acid (HA) and bovine serum albumin (BSA), the zwitterion grafted membrane showed the best antifouling performance. Oxygen plasma treated PE membrane presented a better performance towards HA than to BSA. The Resistance-in-Series model revealed that the plasma-treated membrane showed improvement in reversible resistance but not in irreversible resistance. Migration of hydrophobic PE segment to the surface due to the low glass transition temperature was attributed to the low fouling resistance of the plasma-treated membrane. However, the zwitterion-grafted membrane led to stabilized hydrophilicity and inhibited the hdrophobic-hydrophobic interaction between the membrane and foulant, thus resulting to significantly improved flux recovery and low irreversible fouling rate. This study clarified that oxygen plasma alone is not sufficient to provide sufficient fouling resistance, but grafting with zwitterion provides stable hydrophilicity and fouling resistance.

The synthesis of an amended membrane coated with graphene oxide and dopamine and guanidyl-based modifier and its antifouling properties.

The membrane fouling issue has aroused great concern. To improve their antifouling properties, surface grafting with oxidative deposition were employed to amend a polyvinylidene fluoride (PVDF) membrane. The modifiers were amino-modified graphene oxide (AMGO), dopamine (DPA) and 1,3-diaminoguanidine hydrochloride (DAGH). To take bovine serum albumin (BSA, 1 g/l) as an example of organic materials, BSA interception rate and pure water flux recovery rate increased to 93.65% and 66.74%, respectively, while the corresponding values for the original membrane were much lower (72.82% and 31.72%). The optimum synthesis conditions were found to be 1.5 mg/ml of DPA, 1 wt% of DAGH, 2 mg/ml of AMGO, 4 h of DPA oxidation deposition time and 1 h of AMGO grafting time. Many functional groups like C = N, -NH2, C = O and -OH improved the membrane surface hydrophilicity leading to a higher resistance to organic pollution. Dopamine and guanidyl facilitated the antimicrobial performance of the modified membrane, whose antimicrobial rate was up to 96%, while the raw membrane had no antimicrobial activity. The amended membrane possessed 40% higher mechanical strength than the initial one. It could withstand a high pumping suction force. The noteworthy property was that the irreversible fouling rate decreased by 55%. Therefore, the amended membrane could restore its flux much more easily.

Fouling control of submerged and side-stream membrane bioreactors based on the statistical analysis of mid-term assays

The response surface methodology has been applied to study reversible and irreversible fouling rates caused by anaerobic sludge in membrane bioreactors, with the aim of controlling membrane fouling by adjusting filtration conditions. The challenge of obtaining statistically significant results of long-term fouling by means of mid-term assays has been addressed. The individual and combined effects of the filtration flux, backwashing intensity, gas sparging and crossflow velocity on membrane fouling, were analyzed in two types of membranes: an external tubular membrane and a submerged hollow fiber membrane. In the external membrane, the reversible fouling rate was as low as 0.27 ± 0.10 mbar/min, depending mainly on the filtration flux and gas sparging. However, the principal control parameter of the irreversible fouling rate was the crossflow velocity, reaching 2.12 ± 1.75 1012 m−2 in terms of increase of resistance per cubic meter filtered by square meter of membrane. In the submerged membrane, the irreversible fouling rate was quite lower, 0.78 ± 0.40 mbar/d, despite the reversible fouling rate was higher, 1.26 ± 0.42 mbar/min. In this case, the irreversible fouling depended mainly on the backwashing frequency despite the reversible fouling was more affected by the filtration flux and gas sparging. Hence, the approach used to control the reversible fouling rate does not involve mitigating irreversible fouling on both submerged and external membranes. This study provides a methodological basis for the selection of site-specific operating conditions, under which sustainable operation of membrane bioreactors could be achieved.

A novel jet-loop anaerobic filter membrane bioreactor treating raw slaughterhouse wastewater: Biological and filtration processes

Results from raw slaughterhouse wastewater treatment in a new jet-loop Anaerobic Filter Membrane Bioreactor (AnFMBR) are presented. The innovation consists in integrating an attached growth anaerobic reactor and a filtration tank as an external loop gas-lift bioreactor, taking advantage of the gas-lift effect caused by the gas sparging used for fouling mitigation. A jet-loop AnFMBR pilot plant was operated for 18 months with a hydraulic retention time of 19.5–21.3 h, a solid retention time of 60d and organic loading rates between 3.5 and 7.4 kgCOD/m3·d, depending on the wastewater concentration, with peaks of up to 10.9 kgCOD/m3·d. Organic matter removal efficiency was maintained between 92 and 97%. Most of the biomass in the jet-loop AnFMBR, 82%, was retained by the carrier material so the membrane was in contact with low concentration biomass suspension.Effects of different backwash scenarios and filtration fluxes on reversible and irreversible fouling rates were studied by short-term and mid-term assays, using Box-Behnken experimental designs. Fouling consolidation due to the fouling layer compression was the main cause of irreversible fouling. Pilot-scale results have shown that jet-loop AnFMBR is a promising technology for real scale complex wastewater treatment.

Comparison of external and submerged membranes used in anaerobic membrane bioreactors: Fouling related issues and biological activity

Anaerobic sludge filtration tests were performed with two experimental set-ups equipped with either submerged hollow-fiber membranes or external tubular membranes operated with low crossflow velocity and gas sparging in a gas-lift mode. Particle size distributions, extracellular polymeric substance concentrations, methanogenic activity, reversible and irreversible fouling rates, and chemical cleaning efficiency were all studied and compared. An increase in the percentage of smaller particles and a decrease in the concentration of volatile suspended solids in the external membrane set-up were observed. Both soluble protein and soluble polysaccharide concentrations were also higher in the external filtration. Operating at 12–15 L/m2 h for 7 days, the total resistance of the external membrane reached 9.3 × 1012 m−1, while the resistance of submerged membrane reached 1.1 × 1012 m−1 despite operating at 15–25 L/m2 h for 12 days. Finally, the type of fouling and the efficiency of chemical cleaning also differed in both configurations.

Membrane fouling mitigation for enhanced water flux and high separation of humic acid and copper ion using hydrophilic polyurethane modified cellulose acetate ultrafiltration membranes

The presence of both copper ion (Cu (II)) from industry and humic acid (HA) in natural waters may generate Cu (II)–HA complex, which is a non-biodegradable and toxic organic pollutant in the water. Removal of such toxic substance is of great importance and environmental significance. Although membrane technology provides a solution for the removal via the filtration, fouling still presents a major challenge for the effective separation. In this study, polyurethanes endcapped with β-cyclodextrin and lactic acid were synthesized and used as additives to be blended with cellulose acetate membranes, which possessed enhanced hydrophilicity, permeability and antifouling property for the removal of Cu (II) and HA. As an example, the polyurethane endcapped with lactic acid (LPU-CA) membrane exhibited high pure water flux (PWF) of 648 L m−2 h−1, as well as high flux recovery ratios (FRRs) of 97.8% and 92% and low irreversible fouling rate (Fir) of 2.2% and 7.8% for the ultrafiltration (UF) of HA and Cu (II)–HA complex, respectively, showing excellent anti-fouling performance. In addition, the Cu (II) and HA rejection was greatly enhanced by the HA enhanced complexation process. These results indicated that the polyurethanes modified cellulose acetate membrane provided enhanced separation with good antifouling property, which can be potentially used for the cleaning of the toxic metal-organic pollutants in wastewaters.

Highly hydrophilic poly(vinylidene fluoride) ultrafiltration membranes modified by poly(N-acryloyl glycinamide) hydrogel based on multi-hydrogen bond self-assembly for reducing protein fouling

Reducing protein fouling in membrane separation and purification process is still a great challenge to the widespread application of ultrafiltration (UF) membranes. In this context, polyvinylidene fluoride (PVDF) UF membranes with enhanced hydrophilicity were modified by grafting hydrophilic poly (N-acryloyl glycinamide) (PNAGA) hydrogel formed through multi-hydrogen bond self-assembly via ultraviolet (UV)-initiated radical graft polymerization. Fourier transform infrared spectra (FTIR) and X-ray photo electron spectroscopy (XPS) reveal that PNAGA gel has been grafted onto the surface of the hydrophobic PVDF membranes. Water contact angle of PNAGA modified membranes reduces from 55.2° ± 1.1 to 0° within 11 s, illustrating a superior hydrophilicity. Ultrasonic 30 min and 7 days pure water filtration tests indicate that the PNAGA hydrogel layer has good stability. The results from anti-fouling test show that, when the pH is 7.0, the flux recovery rate of modified membrane maintains at 99%, the total fouling rate is as low as 30%, and the irreversible fouling rate is only 1.2%. Furthermore, the fouling mechanism investigation shows that fouling layers are not easy to form on the anti-protein-fouling PNAGA hydrogel grafted membranes. This work provides new insights for anti-fouling membrane design and application in protein purification, bio-separation and so on.

Characterization of UF foulants and fouling mechanisms when applying low in-line coagulant pre-treatment

Fluorescence spectroscopy was used as a characterization method to examine organic fouling of single ultrafiltration (UF) fibres at bench-scale. Low doses of coagulant were applied to modify organic properties, without significant formation of precipitates. This approach compliments previous studies investigating coagulation as a pre-treatment method for UF fouling control, which have principally focused on reduction of foulant concentrations. Using a continuous system, short time-scale fluorescence results demonstrated significant adsorption of humic components to virgin membrane fibres. Following an initial adsorption phase, protein-like material was the only organic component to be significantly removed by UF. Low doses of coagulant (<1 mg/L as alum; < 0.043 mg/L as Al3+) were observed to significantly reduce irreversible fouling rates for two different surface waters. Paralleling reduced irreversible fouling, surface tryptophan fluorescence resulting from material adsorbed to the fouled membrane increased, as measured using a fibre optic probe. Analysis of peak shifts in the protein-like component revealed a red-shift at low coagulant dose, possibly indicative of greater exposure of tryptophan residues resulting from conformational changes in the protein structure. It is hypothesized that low coagulant doses modified membrane-foulant interactions, resulting in increased adsorption of protein-like matter to the surface. Subsequent interactions of bulk foulants with the adsorbed organic monolayer discouraged further adsorption and reduced irreversible fouling potential.

Evaluation of fouling mechanisms for humic acid molecules in an activated biochar-ultrafiltration hybrid system

Activated biochar (AB), produced by incomplete biomass combustion of waste or byproducts, was found to be an effective adsorbent in an ultrafiltration (UF) hybrid system. Three different adsorbents, powdered activated carbon (PAC) and oxygen-/nitrogen-based AB (O-/N-AB), were characterized and quantified by elemental composition and aromatic carbon fractions. Based on the results, the economical O-/N-AB could be used as an alternative to coal-based commercially available PAC due to their enhanced inner pore site density. In particular, the adsorption capacity of N-AB (1.306 (mg/g)(mg/L)1/n) for hydrophobic humic acid (HA) molecules was significantly higher than those of PAC (1.208 (mg/g)(mg/L)1/n) and O-AB (1.230 (mg/g)(mg/L)1/n). Although the UF hybrid system with all adsorbents showed a higher reversible fouling rate (11.1%) than a UF membrane system alone, due to the added adsorbents for HA filtration, the adsorbents adsorbed relatively small HA molecules, leading to a significantly lower feed-HA concentration in the membrane system, resulting in a decrease in the irreversible fouling rate (38.1%). Consequently, N-AB in the UF hybrid system showed better performance than PAC in terms of flux decline (12.9%) and HA rejection (4.1%), due to higher hydrophilicity and polar interactions with polar functional groups.

Effects of Pretreatment on Hydraulic Irreversible Membrane Fouling During Ultrafiltration Short Process: A Pilot Study

Pilot-scale performances for ultrafiltration of Dongjiang river water without and with micro-coagulation and coagulation-adsorption-sedimentation pretreatments were conducted to investigate the effects of pretreatments on hydraulic irreversible fouling of ultrafiltration short processes. Scanning electron microscope (SEM) imaging, high performance size exclusion chromatography (HPSEC) and fluorescence excitation-emission matrix (EEM) were employed to identify foulants responsible for irreversible fouling during ultrafiltration with and without pretreatments. The results showed that the hydraulic irreversible fouling rate was 0.16 kPa·d-1 with micro-coagulation pretreatment at 10 L·(m2·h)-1, while the rate without pretreatment was 0.32 kPa·d-1 at the same flux. Meanwhile, the fouling rate with coagulation-adsorption-sedimentation pretreatment was almost zero at the same flux. Furthermore, when the flux increased to 17 L·(m2·h)-1, the irreversible fouling was not observable with coagulation-adsorption-sedimentation pretreatment (backwashing every 24 hours). Properties of foulants from external membrane and internal membrane after backwashing showed that the protein-like and fulvic-like substances were responsible for irreversible fouling in Dongjiang river water. Furthermore, structural alteration of cake layer resulted in less cake resistance and higher backwash efficiency after micro-coagulation pretreatment, leading to less irreversible fouling. Coagulation-adsorption-sedimentation pretreatment decreased irreversible fouling with higher removal efficiency of protein-like and fulvic substances, which were the foulants responsible for irreversible fouling during ultrafiltration. Both micro-coagulation and coagulation-adsorption-sedimentation pretreatments decreased irreversible fouling during ultrafiltration short process.

Identification of irreversible UF membrane foulants by fluorescence excitation–emission matrix coupled with parallel factor analysis

In this work, a total of nine water samples were taken from different water sources at different seasons for UF membrane fouling experiments, with the purpose to find out if there were common foulant components responsible for the irreversible membrane fouling. It was found that the increase in DOC and UV254 in raw water caused a corresponding increase in the developing rate of irreversible membrane fouling, demonstrating NOM as the major membrane foulants. Using the fluorescence excitation–emission matrices coupled with parallel factor analysis, four fluorescence components in NOM were identified, i.e. microbial-derived and terrestrial-derived humic-like substances (C1 and C3), tryptophan-like and tyrosine-like proteins (C2 and C4). The C2 exhibited a strong correlation with the irreversible fouling of UF membrane, while no correlation between C4 and irreversible membrane fouling was observed. The humic-like substances were shown to be weakly correlated to the irreversible membrane fouling. By multivariate linear regression, synergistic fouling effect was identified between the C2 and C3, but a comparison of their coefficients revealed that C2 made a considerably larger contribution to the irreversible membrane fouling than C3. The results may provide insights into the development of appropriate fouling control strategies for sustainable UF operation.

Coagulation optimization for DOC removal: pilot-scale analysis of UF fouling and disinfection byproduct formation potential

A pilot-scale study was performed to evaluate a coagulant dose which had been optimized for biopolymer (i.e., foulant) removal on subsequent ultrafiltration (UF) fouling, as well as disinfection by-product (DBP) precursor removal. Polyaluminum chloride (PACl) dosages were selected based on a point of diminishing returns for biopolymer removal (0.5 mg/L) and directly compared to that applied at full-scale (6 mg/L). Membrane fouling (reversible and irreversible) was measured as resistance increase over a 48 hour filtration period. DBP formation potential (total trihalomethanes (TTHMs), haloacetic acids (HAA9) and total adsorbable organic halides (AOX)) were measured in both raw and treated waters. Results of the study indicate that application of a PACl dose optimized for biopolymer reduction (0.5 mg/L) resulted in 65% less irreversible UF fouling when compared to 6 mg/L. The addition of PACl prior to the membrane resulted in up to a 14% reduction in DBP precursors relative to the UF membrane alone. A similar level of DBP precursor reduction was achieved for both 0.5 and 6 mg/L dosages. The results have implications for cost savings, which may be realized due to decreased chemical use, as well as increased membrane life associated with lower irreversible fouling rates.

Threshold flux and limiting flux for micellar enhanced ultrafiltration as affected by feed water: experimental and modeling studies

Micellar enhanced ultrafiltration is a promising technology for removing trace amounts of organic pollutants in wastewater, but membrane fouling caused by Gemini micelles is a significant problem restricting its industrial application. In this study, a flat sheet ultrafiltration membrane with four types of Gemini surfactant systems and various feed concentrations was used to treat phenol wastewater, while the flux behavior and fouling mechanism were investigated. The optimal permeate flux of phenol decreased in the sequence as follows: CG12 > CG16 > CG12 − Brij35 > CG16 − Brij35. In order to study the rate of membrane fouling, a developed liner regression method was utilized to help determine the threshold flux, as well the degree of concentration polarization and membrane fouling. Furthermore, limiting flux was investigated to avoid extensive cake layer formation. Threshold flux and limiting flux strongly depended on the feed concentration and the type of micelles. The threshold flux reduced gradually with feed concentration, due to the increased fouling rate and presence of irreversible fouling. Owing to the effect of charge density and hydrophobicity of micelles, CG12 exhibited the highest threshold flux and limiting flux. Flux-TMP relation was divided into three regions for analyzing the corresponding changes of permeate flux, filtration resistance and conceptual particle deposition model. Besides, fouling mechanism of MEUF was discussed. This study provides a guideline for analyzing membrane fouling and seeking an optimum operation strategy for controlling fouling in membrane water treatment.

The effect of fine bubble aeration intensity on membrane bioreactor sludge characteristics and fouling

While most membrane bioreactor (MBR) research focuses on improving membrane filtration through air scour, backwashing and chemical cleaning to physically counteract fouling, relatively few studies have dealt with fouling prevention, e.g. minimizing the impact of operational settings that negatively impact sludge filterability. To evaluate the importance of those settings, the effects of bioreactor aeration intensity variations on membrane fouling have been studied in a lab-scale MBR setup while simultaneously monitoring a unique set of key sludge parameters. In particular, this paper focuses on the impact of shear dynamics resulting from fine air bubbles on the activated sludge quality and flocculation state, impacting membrane fouling. When augmenting the fine bubble aeration intensity both the total and irreversible fouling rate increased. Major indications for sludge filterability deterioration were found to be a shift in the particle size distribution (PSD) in the 3–300 μm range towards smaller sludge flocs, and increasing concentrations of submicron particles (10–1000 nm), soluble microbial products and biopolymers. When lowering the aeration intensity, both the sludge characteristics and fouling either went back to background values or stabilized, respectively indicating a temporary or more permanent effect, with or without time delay. The shift in PSD to smaller flocs and fragments likely increased the total fouling through the formation of a less permeable cake layer, while high concentrations of submicron particles were likely causing increased irreversible fouling through pore blocking. The insights from the performed fouling experiments can be used to optimize system operation with respect to influent dynamics.