Fouling Mechanisms Research Articles

Leachate treatment by ceramic ultrafiltration membranes: fouling mechanisms identification

Leachate treatment by ceramic ultrafiltration membranes: fouling mechanisms identification

Literature Review on Effect of Sludge Age on Microbial Community Structure in HMBR

The composite membrane biological treatment process has the characteristics of high quality effluent and low membrane pollution, which is widely used in domestic and international water treatment industry. Based on the review of the basic research on membrane fouling mechanism and the comparison of the research results of MBR at home and abroad, from the perspective of microbial ecology, based on the new generation of environmental microbial analysis technology of high-throughput sequencing, this paper expounds the microbial ecological mechanism that sludge age changes the content of microbial metabolites and membrane fouling process by affecting the microbial community structure and physiological characteristics.

Feasibility of hydrophilic polyethylene separator for membrane bioreactor for wastewater treatment: Fouling behaviors and cleaning

The increasing cost of polyvinylidene fluoride has motivated efforts of researchers to seek a cheap membrane material for membrane bioreactors (MBRs). An inexpensive hydrophilic polyethylene (PE) lithium-ion battery separator was used in this study to construct a flat-sheet membrane module for MBRs treating synthetic municipal wastewater (PE-MBR). The PE separator showed an interconnected and open pore structure with a pore size of 50–60 ​nm. Its hydrophilicity was confirmed by the contact angle (77.65°) and relatively high pure water permeability of 412.17 LMH. The operation of the PE-MBR under 15 LMH below the critical flux last more than 50 ​d before the trans-membrane pressure reached 25 ​kPa and the COD removal was higher than 90%. The revised Hermia model fitting suggested that cake formation was the predominant fouling mechanism on the PE separator with polysaccharides as the main organic pollutant. A cleaning efficiency of 76.26% of the PE separator was achieved using 1 ​g/L of Oxalic acid, 3 ​g/L of NaOH, and 100 ​mg/L of EDTA as the cleaning reagents. This study establishes the feasibility of the PE separator in MBRs and provides a new strategy to lower the operation cost and broaden the real applications of MBR in wastewater treatment.

Insight into membrane fouling mechanism and cleaning strategy during selective electrodialysis for metal ions removal from ionic liquid aqueous solutions

Selective electrodialysis (SED) method has been proved to be effective in the process of the removal of mental ions from the ionic liquid (IL) aqueous solution in our previous work. However, the membrane fouling and cleaning strategy have not yet been investigated in IL recovery process, which are essential issues concerning the membrane life and overall cost. Therefore, various operating parameters, i.e. operation time, metal ion concentration, IL concentration, pH and temperature were systematically investigated to reveal the formation of membrane fouling in this work. Then, basing on the analysis results of fouling formation, the ion exchange capacity (IEC), contact angle, resistance, XPS were further adopted to reveal the fouling mechanism. These results showed that the variation of physicochemical properties of membranes with the formation of membrane fouling, and the [Emim]+ cation combined with the fixed groups in MSCM through physical/chemical formation. The EIS further demonstrated that the ion migration path changed as for the formation of [Emim]+, Mg2+, Ca2+ fouling layer. Finally, inspired by this mechanism, a specific cleaning strategy with the order of H2O, 0.1 M HCl, and 0.1 M NaCl was proposed, and the membranes exhibited the steady separation performance and physicochemical properties within 6-times recycle.

Carbon nanotube-adsorptive dynamic membrane (CNT-ADM) for water purification

Membrane technology plays an important role in water purification, but there are some significant challenges such as membrane fouling and deep purification efficiency. The work proposes a carbon nanotube-adsorptive dynamic membrane (CNT-ADM), including carbon nanotube (CNT) and membrane module, to solve these problems with low operating cost and high removal efficiency. Above all, on the basis of physical adsorption and membrane separation, a CNT-ADM was prepared by applying “forward filtration” of a CNT solution on an ultrafiltration membrane surface. Then, the effects of preparation time, CNT loading amount, transmembrane pressure (TMP) and shear stress on the morphology and permeability were analyzed to evaluate the preparation performance. Pore blocking models were utilized to explain the influence of CNT loading amount on membrane fouling mechanism. The best optimized condition for CNT-ADM preparation was: agitation speed of 50 rpm, TMP of 1 bar, CNT loading amount of 55 g/m2 and preparation time of 10 min. Furthermore, the optimized CNT-ADM was employed to treat the micro-polluted water. The effects of treatment condition on the micropollutant removal rate and flux were investigated with various shear stresses, TMPs, the amounts of micropollutant and CNT. Compared with the new membrane (below 10 %), CNT-ADM displayed a significant improvement for the micropollutant removal (above 95 % for three cycles), due to the synergy of membrane separation (sustaining CNT layer, separating micropollutant and increasing adsorption time) and adsorption removal (forming CNT layer and adsorbing micropollutant). On the other hand, the adsorption behavior also could effectively reduce the direct contact between membrane and micropollutant, then decreasing membrane fouling. Afterwards, the backwash cleaning was also successfully applied to alter the adsorption saturated CNT and generate the new CNT layer. In final, the implications for CNT-ADM application were discussed. Overall, CNT-ADM exhibits the desirable micropollutant removal and strong anti-fouling capacity, and has a great potential application in the sustainable water purification.

Railway ballast fouling, inspection, and solutions - A review

Ballast fouling occurs when the voids of granular particles are wholly or partially filled by fine particles. Railway ballast fouling is always an inevitable issue related to railway performance and safety in ballasted tracks. This paper presents an overview of the railway ballast fouling mechanism, current works, perspective, and innovation. The paper first reviews the fouling mechanism with different fouling sources and their influence, followed by the fouling indices. Then, fouling inspection methods are reviewed, and the ground penetrating radar is highlighted due to its high efficiency and accuracy. The proposed solutions, including rehabilitation, prevention, reinforcement, and stabilization in the ballasted track, are introduced. Additionally, several perspectives and works for the future are mentioned. Ballast cleaning is a thorough and effective treatment. Ground-penetrating radar inspection and proper evaluation can provide a preview and perspective on ballast cleaning determination.

Impact of pre-coagulation on the ceramic membrane process during oil-water emulsion separation: Fouling behavior and mechanism

Coagulation has been evaluated as an economical and effective pre-treatment method for controlling membrane fouling. We investigated the influence of the pre-coagulation of oil-water (O/W) emulsions on the formation of membrane fouling in the ceramic membrane process. The results confirmed that pre-coagulation effectively mitigated the fouling formation on the ceramic membrane surface during the O/W emulsion separation. The mechanism of mitigating membrane fouling by pre-coagulation was proposed, owing to the reduction in the zeta potential value of oil droplets by pre-coagulation, resulting in weak electrostatic attraction between oil droplets and ceramic membrane surfaces, and an increase in the size of the oil droplets by pre-coagulation, leading the formation of a cake layer fouling. In addition, the decrease in the hydrophobicity of oil droplets by pre-coagulation resulted in alleviating the hydrophobic interaction between oil droplets and membrane surface. The proposed fouling mechanism was supported by the characterization of the virgin and fouled membrane surfaces and the analysis of the fouling resistance ability of the membranes. Our study could be indicative of mitigation protocols that can be used to alleviate membrane fouling on ceramic membranes during oily wastewater treatment.

Efficient preparation of ultrathin ceramic wafer membranes for the high-effective treatment of the oilfield produced water

Efficient preparation of ceramic membranes helps to reduce costs and makes them more competitive in the field of wastewater treatment. In this work, an ultrathin Al2O3 ceramic wafer membrane with a thickness of 250 µm and the mean pore size of approximately 200 nm was prepared from the Al2O3/polysulfone slurries via a casting-phase inversion/sintering approach. This ultrathin and hydrophilic ceramic wafer has a fully sponge-like and slightly asymmetric structure and desirable porosity, endowing it with an exceptionally high pure water permeability of ∼ 45,000 L m-2h−1 bar−1, an ultrahigh and stable emulsion flux of 2500 ∼ 3500 L m-2h−1 bar−1, as well as a high oil rejection of 99 % against real oilfield produced water (OPW). In addition, the increased Al2O3 content enhanced the thermodynamic instability of the ceramic slurry, leading to the enhanced interfacial instability, which contributes to the uniform distribution of Al2O3 particles on the precursor membrane surface to some extent during the phase inversion process, thus to reduce the surface defects of ceramic membranes after sintering. The membrane fouling analysis revealed that the dominant fouling mechanism was cake filtration, indicating the formation of a relatively dense and smooth skin layer of the ceramic wafer, which endow it with a high flux recovery ratio of 97.8 % by a simple chemical cleaning after OPW filtration.

High propensity of membrane fouling and the underlying mechanisms in a membrane bioreactor during occurrence of sludge bulking

While sludge bulking often occurring in activated sludge processes generally leads to serious membrane fouling in membrane bioreactors (MBR), the underlying causes are still unclear. In this study, fouling behaviors of a MBR operated at stages of normal and sludge bulking were compared, and the fouling mechanisms of the different behaviors were explored. It was found that, the MBR could be stably operated in normal stage without membrane cleaning for about 60 days, whereas, daily membrane cleaning had to be carried out when operated in sludge bulking stage. The bulking sludge possessed a rather high specific filtration resistance (SFR) of about 1.36×1014 m·kg−1, which is over 5.33 times than that of the normal sludge. A series of characterizations demonstrated that the bulking sludge had rather lower dewaterability, smaller particle size, higher fractal dimension, higher viscosity, abundant filamentous bacteria and different functional groups of extracellular polymer sustains (EPS). It was suggested that microbial community transition was responsible for the occurrence of sludge bulking, further affecting membrane fouling. Based on these characterizations, it was reported that adhesion propensity (indicated by the thermodynamic interaction) of the bulking sludge to the membrane surface is about 3.6 times than that of the normal sludge. It was proposed that, extra force should be provided to offset a chemical potential gap caused by foulant layer structure transition during sludge bulking in order to sustain filtration of the bulking sludge, resulting in extremely high SFR. This study offered deep thermodynamic mechanisms of MBR fouling during occurrence of sludge bulking.

Development and Implementation of MBR Monitoring: Use of 2D Fluorescence Spectroscopy.

The monitoring of a membrane bioreactor (MBR) requires the assessment of both biological and membrane performance. Additionally, the development of membrane fouling and the requirements for frequent membrane cleaning are still major concerns during MBR operation, requiring tight monitoring and system characterization. Transmembrane pressure is usually monitored online and allows following the evolution of membrane performance. However, it does not allow distinguishing the fouling mechanisms occurring in the system or predicting the future behavior of the membrane. The assessment of the biological medium requires manual sampling, and the analyses involve several steps that are labor-intensive, with low temporal resolution, preventing real-time monitoring. Two-dimensional fluorescence spectroscopy is a comprehensive technique, able to assess the system status at real-time without disturbing the biological system. It provides large sets of data (system fingerprints) from which meaningful information can be extracted. Nevertheless, mathematical data analysis (such as machine learning) is essential to properly extract the information contained in fluorescence spectra and correlate it with operating and performance parameters. The potential of 2D fluorescence spectroscopy as a process monitoring tool for MBRs is, therefore, discussed in the present work in view of the actual knowledge and the authors' own experience in this field.

Efficient selective methylene blue adsorption by polyurethane/montmorillonite‐based antifouling electrospun composite membranes

AbstractA robust antifouling membrane with pollutant‐removing capacity is in high demand for industrial wastewater treatment. Here, we report a new multifunctional polyurethane/montmorillonite‐oxidized multi‐walled carbon nanotube (PU/MMT) nanofibrous composite membrane, beneficial for both water filtration and selective methylene blue adsorption. It was observed that oxidized multi‐walled carbon nanotube (o‐MWCNT) imparted high flexibility with a high percentage elongation (318%–405%) to the composites, whereas montmorillonite (Mt) improved the hydrophilicity, antifouling property, and dye adsorption capacity of the fibrous PU membrane. The sample with 20 wt% Mt (PU/20‐MMT) showed a minimum water contact angle of 57°. It showed a high water flux, oil rejection, and flux recovery ratio compared to the pristine electrospun PU membrane. The Hermia fouling mechanism suggested that electrospun PU obeyed an intermediate blocking model, whereas PU/20‐MMT was best fitted with a cake formation model. During adsorption, the cationic dye methylene blue (MB) was selectively adsorbed on the sample from a methyl orange/methylene blue (MO/MB) mixture. It showed a maximum adsorption capacity (qm) of 112.35 mg/g. The anionic dye methyl orange, on the other hand, remained unadsorbed. The adsorption kinetics and the adsorption isotherm were pseudo‐second‐order kinetics and the Langmuir adsorption isotherm, respectively. The developed, robust electrospun composite membrane opens a new avenue for the selective adsorption of MB from dye mixtures and contaminated water.

Comparison of membrane fouling induced by protein, polysaccharide and humic acid under sodium and calcium ionic conditions

To further compare the effect of sodium and calcium on the membrane fouling mechanism of typical organic matters, the adsorption behavior of sodium alginate, humic acid and bovine serum albumin on PVDF membranes were explored by quartz crystal microbalance and dissipation (QCM-D), while the adhesion force between foulants and between the foulants and membrane were examined by using atomic force microscopy (AFM) detection with foulant-coated probes. Results demonstrated that the adhesion force between organic and membrane had significant impact on the adsorption rate at the initial fouling stage, whereas the interaction force among the organic was connected with the degree of irreversible fouling and the structure of the fouling layer. Ca2+ made organic fouling more severe and irreversible due to the complexation effect under the same ionic strength conditions, which is consistent with the XDLVO theory. Compared to the other two organics, BSA demonstrated deposition more in mass, higher in adsorption rate and irreversibility under both Ca2+ and Na+ conditions, which attributed to stronger interaction forces among BSA molecules and the thus formed denser fouling layer. During the adsorption process the pseudo-second-order agreed well with fouling behavior of SA and BSA, while HA conformed to the pseudo-first order kinetic model.

Interaction mechanisms of fouling and cleaning protocol for A/O-MBR treatment of coal⁃to⁃hydrogen wastewater

The anoxic/aerobic membrane bioreactor (A/O-MBR) was conducted to investigate pollutants removal in coal⁃to⁃hydrogen wastewater at the pilot experiment. Results showed that the system exhibited effective removal of chemical oxygen demand (∼90%), ammonia nitrogen (>95%), and total phenols (>95%). Moreover, the Extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approach was used to predict the MBR system's membrane fouling and chemical cleaning mechanisms in the MBR system. The results indicated that the initial stage dominated membrane fouling by the acid-base (AB) interaction energy. With aggravated membrane fouling, the determinate role was the van der Waals (LW) interaction energy. Furthermore, the cleaning agent NaClO obtained the highest trans-membrane pressure recovery (104.7% of the virgin trans-membrane pressure) in CGW treatment, compared with HCl or NaOH cleaning. It was attributed to the higher LW interaction energy between foulants and the NaClO-cleaned membrane than those between foulants and the HCl-/NaOH-cleaned membrane. Meanwhile, it could effectively restrain AB interaction energy decline between them. The findings of this study confirmed successful development of A/O-MBR for bio-refractory CGW treatment with NaClO chemically enhanced backwash. It also provided an in-depth understanding on the fouling and cleaning mechanisms of the MBR system.

Fouling evolution of extracellular polymeric substances in forward osmosis based microalgae dewatering

Membrane fouling was still a challenge for the potential application of forward osmosis (FO) in algae dewatering. In this study, the fouling behaviors of Chlorella vulgaris and Scenedesmus obliquus were compared in the FO membrane filtration process, and the roles of their soluble-extracellular polymeric substances (sEPS) and bound-EPS (bEPS) in fouling performance were investigated. The results showed that fouling behaviors could be divided into two stages including a quickly dropped and later a stable process. The bEPS of both species presented the highest flux decline (about 40.0%) by comparison with their sEPS, cells and broth. This performance was consistent with the largest dissolved organic carbon losses in feed solutions, and the highest interfacial free energy analyzed by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. The chemical characterizations of algal foulants further showed that the severe fouling performance was also consistent with a proper ratio of carbohydrates and proteins contents in the cake layer, as well as the higher low molecular weight (LMW) components. Compared with the bEPS, the sEPS was crucial for the membrane fouling of S. obliquus, and an evolution of the membrane fouling structure was found in both species at the later filtration stage. This work clearly revealed the fundamental mechanism of FO membrane fouling caused by real microalgal suspension, and it will improve our understanding of the evolutionary fouling performances of algal EPS.

Preparation of Co3O4@carbon nanotubes modified ceramic membrane for simultaneous catalytic oxidation and filtration of secondary effluent

To improve the efficiency of wastewater reclamation, a novel Co3O4@carbon nanotubes modified ceramic membrane (Co3O4@CNT-CM) was prepared in this work for simultaneous catalytic peroxymonosulfate (PMS) oxidation and filtration of secondary effluent. The synthesized Co3O4@CNT catalyst showed better dispersibility with more active sites exposed, and Co3O4@CNT-CM exhibited relatively smooth surface, higher permeate flux and excellent catalytic PMS ability. The antifouling and water purification performance of Co3O4@CNT-CM were systematically investigated in secondary effluent purification. With the dual effect of catalytic oxidation and filtration, the organic pollutants were observably reduced. Fluorescent components were also significantly removed, and more macromolecular substances were degraded into small molecular substances. The flux of Co3O4@CNT-CM was significantly improved, with the reversible and irreversible resistances decreased by 82.5% and 78.6%, individually. With respect to the fouling mechanism, the volume entering the stage of cake filtration dramatically increased. The prepared Co3O4@CNT-CM accelerated the generation of various active species for oxidative degradation of pollutants, thus improving the antifouling performance of membrane. These results demonstrated the application potential of Co3O4@CNT-CM for wastewater treatment and reclamation.

Fulvic and alginic acid separation during pressure retarded osmosis: Governing effects and fouling mechanisms

In this study, the performance of model foulant (alginate and fulvic acid) separation by pressure retarded osmosis (PRO) was systematically studied. At the various operating conditions tested, fulvic acid had a greater flux decline and power density loss than alginate. The results of membrane resistance test, SEM-EDX images, and the solute diffusion coefficient K demonstrated that fulvic acid was more likely to clog the inside of the porous support layer of the PRO membrane, which would exacerbate the internal concentration polarization (ICP) phenomena. Although model foulants were successfully removed by PRO (with a retention rate of about 95.0%), the presence of either calcium or magnesium ions was detrimental to the fouling process of PRO membranes. According to the XDLVO theory analysis results, the presence of calcium or magnesium ions increased foulant adhesion to the PRO membrane, thereby resulting in membrane fouling. In addition, Pearson correlation coefficient also showed that the hydrodynamic conditions (effective osmotic pressure difference as well as operating hydraulic pressure acting vertically to the membrane and parallel to the membrane cross-flow shear force) had an important effect on the degree of membrane fouling. This is attributed to the influence of the hydrodynamic conditions on the initial influence water flux and thus on the fouling of the PRO membrane.

Mitigation Mechanism of Membrane Fouling in MnFeOx Functionalized Ceramic Membrane Catalyzed Ozonation Process for Treating Natural Surface Water

In order to efficiently remove NOMs in natural surface water and alleviate membrane pollution at the same time, a flat microfiltration ceramic membrane (CM) was modified with MnFeOX (Mn-Fe-CM), and a coagulation–precipitation–sand filtration pretreatment coupled with an in situ ozonation-ceramic membrane filtration system (Pretreatment/O3/Mn-Fe-CM) was constructed for this study. The results show that the removal rates of dissolved organic carbon (DOC), specific ultraviolet absorption (SUVA) and NH4+-N by the Pretreatment/O3/Mn-Fe-CM system were 51.1%, 67.9% and 65.71%, respectively. Macromolecular organic compounds such as aromatic proteins and soluble microbial products (SMPs) were also effectively removed. The working time of the membrane was about twice that in the Pretreatment/CM system without the in situ ozone oxidation, which was measured by the change in transmembrane pressure, proving that membrane fouling was significantly reduced. Finally, based on the SEM, AFM and other characterization results, it was concluded that the main mitigation mechanisms of membrane fouling in the Pretreatment/O3/Mn-Fe-CM system was as follows: (1) pretreatment could remove part of DOC and SUVA to reduce their subsequent entrapment on a membrane surface; (2) a certain amount of shear force generated by O3 aeration can reduce the adhesion of pollutants; (3) the loaded MnFeOX with a higher catalytic ability produced a smoother active layer on the surface of the ceramic membrane, which was conducive in reducing the contact among Mn-Fe-CM, O3 and pollutants, thus increasing the proportion of reversible pollution and further reducing the adhesion of pollutants; (4) Mn-Fe-CM catalyzed O3 to produce ·OH to degrade the pollutants adsorbed on the membrane surface into smaller molecular organic matter, which enabled them pass through the membrane pores, reducing their accumulation on the membrane surface.

Attribution of photocatalysis of fluorescent natural organic matter fractions to the alleviation of ceramic membrane ultrafiltration fouling

In this study, a novel composite functioned as adsorption-photocatalysis based on bismuth oxide (Bi2O3), reduced graphene oxide and titanium dioxide (TiO2) (labelled as BRGT) was applied in combination with ceramic membrane ultrafiltration to removal natural organic matter (NOM) and to mitigate membrane fouling. The mechanisms of NOM removal and of membrane fouling were investigated. The dual action of adsorption and photocatalysis by the BRGT effectively degraded NOM, giving a removal efficiency of 22.2 % for dissolved organic carbon and 73.0 % for UV absorbance at 254 nm. ·O2− radicals were mainly involved in the degradation of humic and protein/polyphenol-containing fluorescent components of NOM. BGRT had a high adsorption affinity for protein-like components, whose removal depended more on h+. The fouling behavior of the ceramic membrane was the result of pore blocking combined with cake filtration formation. BRGT mainly adsorbed hydrophobic components, which exacerbated the reversible fouling resistance and transformed the fouling mechanism from standard blocking into complete blocking. With increase of photocatalytic time, the hydrophobic fraction was converted into hydrophilic and transphilic fractions, and large and medium molecular weight organics were degraded into small molecules. In this case, the cake filtration formation occurred much earlier, with reversible membrane resistance reduced by 95.5 % and irreversible membrane resistance reduced by 90.4 % at 60 min. From the results we concluded that NOM can be effectively treated with adsorption-photocatalysis by BRGT, especially its fluorescent fractions, which has great potential in alleviating ceramic ultrafiltration membrane fouling.

Research on the mechanism of bed agglomeration and superheater fouling in CFB boiler fired pure petroleum coke

AbstractCirculating fluidized bed combustion is an effective method for the clean and efficient utilization of high‐sulphur petroleum coke. In the actual production and operation process, there are serious problems of bed agglomeration and superheater fouling. The chemical and mineral compositions of the deposition were analyzed by X‐ray diffraction (XRD) and X‐ray fluorescence spectroscopy (XRF), and the effects of CaO sulphation and V2O5 on bed agglomeration and superheater deposits were studied through targeted experiments. The research results show that the sulphation process of CaO is the cause of bed agglomeration, and the superheater fouling is the result of the combined action of K2SO4 condensation and CaO sulphation; V2O5 in petroleum coke ash catalyzes the oxidation reaction of SO2 to accelerate the sulphation of CaO, thereby accelerating the development of bed agglomeration and superheater fouling.

Treatment of dairy wastewater with tubular ceramic membrane

This work illustrates the fabrication of tubular ceramic membrane with extrusion machine using low cost clay materials such as kaolin, quartz, CaCO3, boric acid, feldspar and carboxymethyl cellulose. The raw membrane was kept at ambient temperature for 24 hrs. It is sintered at 950 °C at a heating rate of 0.5 °C per minutes for 6 hrs in stepwise muffle furnace. The fabricated membrane is characterized with pure water permeability and porosity measurement. The pore size of 1.49 µm and permeability of 5.438 × 10−8 m/s.kPa are obtained from pure water permeability test. The tubular membrane was tested for dairy wastewater at different pressure (13.79–55.16 kPa) on a microfiltration range. With increase in the applied pressure the removal rate of chemical oxygen demand (COD) decreases showing optimum removal of 52.08 % at a low pressure of 13.08 kPa. Along with the COD determination, various parameters of the dairy wastewater were also measured like pH, conductivity and turbidity. The obtained pH, conductivity and turbidity of feed are 7.11, 2 mS/cm and 45 NTU respectively. Moreover, the prepared tubular membrane was examined for the fouling mechanism using four conventional pore blocking models.