Degree Of Membrane Fouling Research Articles

Thermodynamic mechanism insights into the dynamic evolution of nanofiltration membrane fouling: Effect of calcium ion on organic fouling

To better control nanofiltration (NF) membrane fouling during mine water treatment, an accurate elaboration of the fouling mechanisms of anionic polyacrylamide (APAM) coexisted with Ca2+ and fulvic acid (FA) is vital. An attractive phenomenon was observed during the membrane fouling tests: When Ca2+ and FA coexist with APAM, increasing Ca2+ concentration at high Ca2+ concentration will alleviate membrane fouling. The degree of membrane fouling is determined by the interaction of the foulant with the membrane and is closely related to the Lewis acid-base (AB) interaction energy. At the shortest separation distance, the AB interaction energy decreased from 3608 kT to −17,386 kT when the Ca2+ concentration was increased from 0 mM to 2 mM, then increased to −14,385 kT when the Ca2+ concentration was further increased to 6 mM. The change in AB interaction energy explains the dynamic evolution of the membrane fouling phenomenon. This work elucidates the effects of high Ca2+ concentrations on organic fouling and will benefit the better understanding of the efficient NF processes when multiple pollutants coexist.

Prediction of membrane purification by membrane fouling based on mathematic and machine learning models combined with image processing technology

Apples have been widely cultivated due to their multiple functional nutrients such as polyphenols. In this study, polyphenol of apple skins were extracted and purified by ultrasound treatment and membrane filtration, respectively. The effects of feed liquid concentration, transmembrane pressure, and rotational speed on the purification of polyphenols by membrane filtration were mainly investigated. The efficiency of polyphenol purification was analyzed based on the particle deposition effect, steric rejection effect, and pectin sieving effect. Single and multi-stage Hermia models were applied to corroborate the aforementioned theory. The degree of membrane fouling was quantitatively analyzed using a self-written image processing program. The study compared the quantitative prediction models between the degree of membrane fouling and polyphenol purification using mathematical models and two machine learning (ML) models, namely Support Vector Machine Regression (SVR) and Back Propagation Artificial neural networks (BPNN). The degree of membrane fouling and the degree of polyphenol purification were used as input parameters and output parameters of the ML prediction model, respectively. The ratio of the training set (98 data points) and the test set (42 data points) was 7:3. The obtained results showed that the prediction efficiency of BPNN model (R2 =0.99968) outperformed the SVR model (R2 =0.97697), which was better than the mathematical model in terms of prediction performance due to the high generalization ability of the ML model and the high robustness of BPNN. The study provided an effective and accurate method for predicting membrane fouling and filtration purification. Thus, the use of ML as an artificial intelligence technique has a promising future in membrane separation and purification.

Effect and degradation pathway of sulfamethoxazole removal in MBR by PVDF/DA modified membrane

To reduce the hazard of sulfamethoxazole (SMX) to the water ecology, the removal mechanism of SMX in wastewater was revealed. This study evaluated the PVDF/DA modified membrane in the membrane bioreactor (MBR) toward the removal and degradation of SMX as a recalcitrant micropollutant. A strategy of dopamine for surface modification of polyvinylidene fluoride (PVDF) membrane was proposed, and PVDF/DA membrane was prepared. Subsequently, PVDF/DA was run in the MBR for 60 days, and the reactor could produce good removal ability for SMX after certain acclimation. When the SMX concentration increased from 0.5 to 2 mg/L, liquid chromatography was used for analysis, and the results showed that the average removal rate was above 85%. The removal effect of COD and NH4+-N and the degree of membrane fouling were also evaluated. By measuring the extracellular polymer (EPS) content, the results showed that after 30 days of operation, the protein and polysaccharide contents in the cake layer on the surface of the PVDF membrane were 1.35 times and 1.49 times that of PVDF/DA membrane, respectively, and the PVDF/DA membrane could alleviate membrane fouling, thereby improving the service life of the membrane and reducing its operating cost. Finally, degradation by-products are evaluated to achieve deeper insight into the degradation mechanisms in the MBR process.

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.

Antifouling and chlorine-resistant cyclodextrin loose nanofiltration membrane for high-efficiency fractionation of dyes and salts

Antifouling loose nanofiltration membranes are prepared for effective fractionation of dyes and salts by the construction of a porous cyclodextrin polymer layer on membrane substrate. Octopus-shaped cyclodextrin macromonomers with pendant vinyl groups can be facilely prepared via a union of controlled radical polymerization and esterification reaction, which are then used to fabricate membrane. The surface-initiated photopolymerization of β-cyclodextrin-centered macromonomers could yield a porous polymer layer on the surface of the PVDF substrate. The porous structure could be well-tuned by adjusting the concentration of macromonomers or regulating the polymerization time. The optimal loose nanofiltration membranes have demonstrated high-efficiency separation ability for different dyes and low rejection ability for salts (<10%), owing to the selective layer of porous cyclodextrin polymer. Meanwhile, it maintains a high Congo red (CR) retention (∼99%) in a long-term filtration test. Furthermore, the cyclodextrin polymer layer also endows the membranes with predominant chlorine-resistance performance even after 15 days of immersion in sodium hypochlorite solution. The flux recovery ratio value of optimal membrane towards bovine serum albumin is 97.6% even after 5 antifouling cycles, and the antifouling ability is more than 10 times higher than that of the pristine PVDF membrane depending on the degree of membrane fouling by CR. The proposed strategy could provide helpful guidance in preparing antifouling loose nanofiltration membranes.

Ultrafiltration membrane fouling control by two-stage coagulant dosing with moderate pH adjustment

For the coagulation-ultrafiltration process, it has been recognized that coagulation under acidic condition could greatly alleviate membrane fouling, but the high chemical consumption for pH adjustment and the diminished alkalinity of effluent severely restrict the practical application of this operation. In this study, it was found that two-stage coagulant dosing (separate dosing during rapid mixing and medium speed mixing) with pH adjusted to 6.5 could alleviate membrane fouling as that by one-time coagulant dosing at pH 5.5, which could significantly lower the chemical consumption for pH adjustment. Both the favorable aluminum hydrolysis speciation on the floc surface and the reduced interface interaction between membrane and foulant at pH 6.5 contributed to the effectiveness of this method on membrane fouling control. Compared with the scenarios at pH 5.5 and 7.5, the two-stage dosing at pH 6.5 could promote more aluminum species transformation to amorphous Al(OH)3 on the surface of flocs, resulting in less residual Al in the effluent. The acid-base interaction between foulant and membrane dominated membrane fouling. The degree of membrane fouling by separate dosage ratio of 3:7 at pH 6.5 was as low as that by one-time dosing at pH 5.5 because of the similarly low acid-base interaction energy.

Application of machine learning algorithms in MBR simulation under big data platform

Abstract Membrane bioreactors (MBRs) are a sewage treatment process that combines membrane separation with bioreactor technology. It has great advantages in sewage treatment. Membrane fouling hinders MBR process development, however. Studies have shown that the degree of membrane fouling can be judged using the membrane flux rate. In this study, principal component analysis was used to extract the main factors affecting membrane fouling, then the random forest algorithm on the Hadoop big data platform was used to establish an MBR membrane flux prediction model, which was tested. In order to verify the model's effectiveness, BP neural network and SVM support vector machine models were established using the same experimental data. The experimental results from the different models were compared, and the results showed that the random forest algorithm gave the best MBR membrane flux predictions.

Characterization of reversible and irreversible foulants in membrane bioreactor (MBR) for eucalyptus pulp and paper mill wastewater treatment using fluorescence regional integration

Abstract Membrane bioreactors (MBRs) are an alternative technology to achieve high quality effluent for water reuse for eucalyptus pulp and paper (P&P) industries, but membrane fouling is still a challenging factor that restricts its application. This study aims to investigate characteristics of reversible and irreversible fouling of the submerged polyvinylidene fluoride (PVDF) MBR for treating eucalyptus P&P wastewater. Six batches of MBR experiments with different mixed liquor suspended solids (MLSS) concentrations were performed. The membrane cleaning protocol included three-steps: backwashing with DI water and subsequently NaOH solution, and then soaking with NaOCl solution, for which achieved 54.6 ± 11 %, 76.6 ± 10 % and 97.8 ± 2 % of flux recovery, respectively. Formation of a cake layer comprised of organic substance and soluble microbial products (SMPs), mostly polysaccharides and proteins, was the main contributor to flux decline of the MBR. Concentration of proteins in the irreversible foulant was found to be positively correlated with degree of membrane fouling. Using fluorescence excitation-emission matrix (EEM) with fluorescence regional integration (FRI) analysis revealed that, during MBR treatment, protein-like substances in the permeate water significantly decreased, simultaneously with the increase in relative proportions of humic-like and fulvic-like substances. Further analysis on the irreversible foulants showed that protein-like substances, including tyrosine-like and tryptophan-like substances, were disproportionately more important to membrane fouling than humic-like substances relative to their respective concentration in raw P&P wastewater.

Study on mitigating membrane fouling based on precursor and flocculant Alb matching in EC/O-UF system.

One of the effective ways to remove halogenated disinfection by-products (DBPs) from drinking water is the application of ultrafiltration technology. However, membrane fouling is an important factor affecting the service life and treatment effect. In this study, the electrocoagulation/oxidation-ultrafiltration (EC/O-UF) process was used to remove the precursor substance that produced DBPs, i.e. dissolved organic matters (DOMs). Operating parameters were optimized from the matching of different flocculant morphology to low concentration DOM. The degree of membrane fouling was characterized by analyzing DOMs concentration and membrane flux. The results showed that the optimal conditions for the production of Alb were: current density 10 A/m2, hydraulic retention time 10 min, and initial pH 5.0-7.0. Under these conditions, the production of flocculant Alb could reach 58-61%, 94-97% DOMs were removed by EC/O-UF.

Energy consumption in a baffled membrane bioreactor (B-MBR): estimation based on long-term continuous operation.

We investigated the operating conditions of a baffled membrane bioreactor (B-MBR) under which long-term stable operation can be achieved through the continuous operation of a pilot-scale B-MBR. Under appropriate operating conditions, the B-MBR was capable of achieving excellent treated water quality in terms of biochemical oxygen demand and concentration of total nitrogen. Excellent removal of total phosphorus was also achieved. In addition, the degree of membrane fouling was acceptable, indicating that stable continuous operation of a B-MBR is possible under the operating conditions adopted in the present study. Estimation of the specific energy consumption in hypothetical full-scale B-MBRs operated under the conditions recommended by the findings was also performed in this study. The results suggest that energy consumption in full-scale B-MBRs would be in the range of 0.20-0.22 kWh/m3. These results strongly suggest that energy consumption in MBR operation can be significantly reduced by applying the concept of a B-MBR.

Surface water biopolymer fractionation for fouling mitigation in low-pressure membranes

With the widespread application of liquid chromatography with organic carbon detection (LC-OCD) to investigate membrane fouling in low-pressure membranes such as microfiltration (MF) and ultrafiltration (UF), membrane fouling by macromolecular hydrophilic biopolymer fraction has been recognized. In this study, a drinking water source was intensively investigated over 16 months. Membrane filtration using hollow-fiber MF membranes was carried out in constant flux mode with periodic backwashing, and two pretreatments (aluminum coagulation and anion exchange) were examined in terms of biopolymer removal and fouling mitigation. Higher biopolymer removal rates achieved by anion exchange than coagulation did not cause better control of membrane fouling in MF. Coagulation and anion exchange removed different types of biopolymers, which implied diversity in the biopolymer fraction. A modified set-up of LC-OCD analysis in which two different columns were sequentially connected was examined. It was demonstrated that the biopolymer fraction detected as a single peak with molecular weight of > 10,000 Da with the conventional LC-OCD set-up comprised of molecules with a variety of molecular weights including > 1,000,000 Da. It was found that coagulation removed large-size biopolymers with higher fouling potentials; while anion exchange preferentially removed small-size biopolymers with lower fouling potential. Concentration of large-size biopolymers in the feed water collected on different dates correlated with the degree of membrane fouling. In an attempt to generalize the conclusion drawn from the experiments using the specific drinking water source, batch MF tests filtering biopolymers isolated from different drinking water sources were also carried out. Importance of the large-size biopolymer fraction in the evolution of membrane fouling was also suggested with different drinking water sources.

Effect of mean cell residence time on transmembrane flux, mixed-liquor characteristics and overall performance of a submerged anaerobic membrane bioreactor

ABSTRACTKinetic control of Mean Cell Residence Time (MCRT) was shown to have a significant impact on membrane flux under steady-state conditions. Two laboratory-scale flat-plate submerged anaerobic membrane bioreactors were operated for 245 days on a low-to-intermediate strength substrate with high suspended solids. Transmembrane pressure was maintained at 2.2 kPa throughout four experimental phases, while MCRT in one reactor was progressively reduced. This allowed very accurate measurement of sustainable membrane flux rates at different MCRTs, and hence the degree of membrane fouling. Performance data were gathered on chemical oxygen demand (COD) removal efficiency, and a COD mass balance was constructed accounting for carbon converted into new biomass and that lost in the effluent as dissolved methane. Measurements of growth yield at each MCRT were made, with physical characterisation of each mixed liquor based on capillary suction time. The results showed membrane flux and MLSS filterability was highest at short MCRT, although specific methane production (SMP) was lower since a proportion of COD removal was accounted for by higher biomass yield. There was no advantage in operating at an MCRT <25 days. When considering the most suitable MCRT there is thus a trade-off between membrane performance, SMP and waste sludge yield.

Important fractions of organic matter causing fouling of seawater reverse osmosis (SWRO) membranes

In this study, we investigated the organic matter responsible for reverse osmosis (RO) membrane fouling in seawater desalination. In addition, pretreatments by which fouling organic fractions causing severe membrane fouling can be removed effectively were investigated. The results from continuous operation of a pilot-scale sand filter indicated that the changes in the concentrations of specific organic fractions, such as transparent exopolymer particles (TEP) and biopolymers determined by liquid chromatography with organic carbon detection (LC-OCD), cannot be evaluated by comprehensive water quality indices (e.g., total organic carbon (TOC) or dissolved organic carbon (DOC) concentrations). In addition, the changes in the degree of membrane fouling cannot be explained by the comprehensive TOC and DOC concentrations. Among the water quality indices examined in this study, the concentration of TEP with relatively large particle size (i.e., >1.0μm) and content of protein-like organic matter that can be detected by fluorescence excitation-emission matrix (EEM) spectral analysis were well correlated to RO membrane fouling levels. The results obtained in this study strongly suggest that developing a pretreatment method that can effectively eliminate TEP and proteinaceous compounds contained in seawater is important for the stable operation of a seawater desalination plant utilizing an RO membrane.

Treatment of Coking Wastewater by a Submerged Membrane Bioreactor with Suspended Carriers

A renovated hybrid membrane bioreactor (HMBR) was investigated for its capability of coking wastewater treatment. The HMBR combined biofilm process and membrane filtration process. The system was efficient in degrading COD and phenol in coking wastewater and controlling membrane. It was found that the coking wastewater could be effectively treated with 88.6% of COD removal efficiency and 98.3% of phenol removal efficiency at hydraulic retention time (HRT) of 16 h. The removal efficiency of COD and phenol decreased gradually down to 83.2% and 97.7% when HRT decreased to 8 h. The long term experiments indicated that the degree of membrane fouling for HMBR was far lower than that for MBR. The scrubbing effect of suspended carrier in HMBR was observed to be capable of reducing the cake fouling of membrane. The operation time of HMBR was 8.4-fold longer than that with MBR.

Osmosis-based pressure generation: dynamics and application.

This paper describes osmotically-driven pressure generation in a membrane-bound compartment while taking into account volume expansion, solute dilution, surface area to volume ratio, membrane hydraulic permeability, and changes in osmotic gradient, bulk modulus, and degree of membrane fouling. The emphasis lies on the dynamics of pressure generation; these dynamics have not previously been described in detail. Experimental results are compared to and supported by numerical simulations, which we make accessible as an open source tool. This approach reveals unintuitive results about the quantitative dependence of the speed of pressure generation on the relevant and interdependent parameters that will be encountered in most osmotically-driven pressure generators. For instance, restricting the volume expansion of a compartment allows it to generate its first 5 kPa of pressure seven times faster than without a restraint. In addition, this dynamics study shows that plants are near-ideal osmotic pressure generators, as they are composed of many small compartments with large surface area to volume ratios and strong cell wall reinforcements. Finally, we demonstrate two applications of an osmosis-based pressure generator: actuation of a soft robot and continuous volume delivery over long periods of time. Both applications do not need an external power source but rather take advantage of the energy released upon watering the pressure generators.

Influence of membrane properties on physically reversible and irreversible fouling in membrane bioreactors

This study aimed to examine the impact of membrane properties on membrane fouling in membrane bioreactor (MBR). Membrane fouling was divided into two categories: physically reversible and irreversible fouling. Membrane properties related to each type of membrane fouling were investigated separately. Five microfiltration (MF) and one ultrafiltration (UF) membranes with different properties (pore size, contact angle, roughness, zeta potential, and pure water permeability) were examined with a laboratory-scale MBR, fed with synthetic wastewater. Two separate experiments were conducted: the first to examine physically reversible fouling, and the second to examine physically irreversible fouling. The correlation between the degree of each type of fouling and membrane properties was studied. High correlation was observed between the degree of physically reversible fouling and roughness (R(2)=0.96). In contrast, with regard to physically irreversible fouling, strong correlation between roughness and degree of membrane fouling can only be found in the case of MF membranes. Except for the membrane with the highest roughness, the degree of physically irreversible fouling can be well correlated with pure water permeability (lower pure water permeability results in higher degree of physically irreversible fouling) including UF membrane. On the basis of the results obtained in this study, it can be concluded that roughness is an important factor in determination of physically reversible fouling regardless of the types of membrane (i.e. MF or UF membranes) and evolutions of physically irreversible fouling can be mitigated when an MBR is operated with membranes with smooth surface and high pure water permeability.

Effects of various backwash scenarios on membrane fouling in a membrane bioreactor

The main objective of this work was to determine the impact of various backwash scenarios on fouling in a pilot-scale submerged membrane bioreactor (MBR) aerobically treating domestic wastewater. A total of seven different backwash scenarios were tested. The degree of membrane fouling was determined employing the flux-step method and using the resistance-in-series model for each backwash scenario. Fouling rates and total membrane resistances generally decreased with more frequent backwashing; decreasing of filtration duration improved fouling control. A higher rate of fouling was observed above critical flux for all scenarios. As the backwashing scenarios approached “no-backwash-continuous filtration”, permeabilities deviated more from linearity indicating a higher degree of fouling. At a flux of 20 L/m 2-h, fouled membrane resistance was reduced by 1.63-fold with 9 min 45 s of filtration followed by 15 s of backwash compared to continuous filtration. The negative impacts of filtration duration on total membrane resistances were more pronounced than the positive impacts of backwash duration, i.e., as the ratio of filtration/backwash duration increased resistances also increased linearly ( R 2: 0.96). The strong correlation found among this ratio and the total membrane resistance suggests that the use of this ratio may be an effective tool in the optimization of fouling control in submerged MBRs employing routine backwashing. Scenarios 4 (9 min 55 s of filtration followed by 5 s of backwash) and 5 (9 min 45 s of filtration followed by 15 s of backwash) were found to be optimum based on fouling control and net daily volume of permeate production. The reversible fouling caused mainly by pore blocking and cake layer was effectively removed by these filtration/backwash scenarios as long as the operating flux was less than the critical flux.

Irreversible membrane fouling in microfiltration membranes filtering coagulated surface water

Chemical coagulation has been widely used as a method to mitigate membrane fouling in MF/UF membranes used for drinking water treatment. Optimization of coagulation as pre-treatment of membrane processes has not been achieved yet: the optimum condition of coagulation for conventional treatment systems is not necessarily applicable to membrane-based treatment systems. This study investigated (physically) irreversible membrane fouling in an MF membrane used with pre-coagulation by aluminum salt. In a series of bench-scale filtration tests, feed water containing commercially available humic acid or organic matter isolated from surface water was coagulated with polyaluminum chloride (PACl) under various conditions and subsequently filtered with an MF membrane with the nominal pore size of 0.1 μm. It was found that coagulation conditions had great impacts on the degree of physically irreversible fouling. Acidic conditions improved the quality of treated water but generally caused greater physically irreversible fouling than did neutral or alkaline conditions. Also, dosage of coagulant was found to be influential on the degree of membrane fouling: high dosage of coagulant frequently caused more severe irreversible fouling. Sizes of flocs seemed to become small under acidic conditions in this study, which was indicated by high concentrations of aluminum in the permeate under acidic conditions. It is thought that small flocs produced under acidic conditions could migrate into micropores of the membrane and caused physically irreversible fouling by plugging or adsorption. These findings obtained in the bench-scale tests were verified in a long-term pilot-scale test.

Biofouling development and rejection enhancement in long SRT MF membrane bioreactor

This study was conducted to investigate the development and extracellular polymeric substances (EPS) distribution in biofouling layer and biofouling effect on permeate quality. The experimental results suggested that formation of biofouling layer was started by the attachment of polysaccharides and formed a biogel like layer on top of membrane surface (adhesive attachment). It further induced the attachment of protein, polysaccharides and bioparticles, and formed cake layer (cohesive attachment). As evidenced in SEM photos and permeates quality, the formed biofouling layer had changed the properties of membrane surface such as the pore and porosity, and hence produce the better permeates quality. A great enhancement of rejection performance occurred at the early filtration period, and followed by a slight enhancement in rejection throughout the entire filtration. This enhancement of rejection performance by biofouling layer can be mathematically expressed by the logarithm function with the degree of membrane fouling.

Microfiltration of activated sludge wastewater—the effect of system operation parameters

Membrane or hollow fiber microfiltration is increasingly used with the activated sludge process in conventional wastewater treatment to produce a higher quality effluent. The major problem of such applications is membrane fouling, which has generally been attributed to the high contents of suspended solids in the wastewater. In this study, the operation of an integrated activated sludge bioreactor–membrane microfiltration system was investigated. It was found that the airflow rate of aeration, the mechanical mixing of the bioreactor and the circulation flow of the wastewater through the cross-flow microfiltration unit all affected the size distribution of the particles in the wastewater to be filtered, which consequently affected the performance of the microfiltration unit. The degree of membrane fouling by different size fractions of particles in the activated sludge wastewater was examined. The results reveal that the smaller particles played a more important role in membrane fouling. A relatively simple model is presented to predict cake growth and permeation flux decline in a cross-flow microfiltration.