The Fouling Mechanism of Ceramic Membranes Used for Recovering TS-1 Catalysts

Ceramic ultrafiltration membranes were used to separate titanium silicalite-1 （TS-1） catalysts from the slurry of catalytic ammoximation of cyclohexanone to oxime. Silica was shown to have a great effect on membrane fouling in the alkaline environment of this system. In the ammoximation system, there are three main silica sources, which are residual silica on the catalyst particles surface during preparation, silica dissolved from TS-1 catalyst particles by ammonia solvent, and silica sol added into the reaction slurry to inhibit the dissolution erosion of the TS-1 catalyst. The silica dissolved by ammonia has been proved to influence membrane fouling most among the three silica sources. This was because the amount of silica dissolved by ammonia was the largest, and the polymerization of silica monomers at high concentration caused colloid particles formation, which led to a dense cake layer depositing on the membrane surface. Meanwhile, the size reduction of catalyst particles caused by alkaline dissolution also increased specific resistances of cake layers.

Insight into fouling behavior of poly(vinylidene fluoride)(PVDF)hollow fiber membranes caused by dextran with different pore size distributions

Membrane fouling is the key problem that occurs in membrane process for water treatment. However, how membrane microstructure influences the fouling behavior is still not clear. In this study, fouling behavior caused by dextran was deeply and systematically investigated by employing four poly（vinylidene fluoride） （PVDF） membranes with different pore sizes, ranging from 24 to 94 nm. The extent of fouling by dextran was accurately characterized by pore reduction, flux decline, and the change of critical flux. The result shows that membrane with the smallest pore size of 24 nm experienced the smallest fouling rate and the lowest fouling extent. As the membrane pore size increased, the critical flux ranges were 105-114, 63-73, 38-44 and 34- 43 L. m 2. h t, respectively. The critical flux and fouling resistances indicated that the fouling propensity in- creases with the increase of membrane pore size. Two pilot membrane modules with mean pore size of 25 nm and 60 nm were applied in membrane filtration of surface water treatment. The results showed that serious ir- reversible membrane fouling occurred on the membrane with pore size of 60 nm at the permeate flux of 40.5 L.m 2.h 1. On the other hand, membrane with pore size of 25 nm exhibited much better anti-fouling per- formance when permeate flux was set to 40.5, 48 and 60 L-m 2-h- 1.

Multivariable identification of membrane fouling based on compacted cascade neural network

The membrane fouling phenomenon,reflected with various fouling characterization in the membrane bioreactor(MBR)process,is so complicated to distinguish.This paper proposes a multivariable identification model(MIM)based on a compacted cascade neural network to identify membrane fouling accurately.Firstly,a multivariable model is proposed to calculate multiple indicators of membrane fouling using a cascade neural network,which could avoid the interference of the overlap inputs.Secondly,an unsupervised pretraining algorithm was developed with periodic information of membrane fouling to obtain the compact structure of MIM.Thirdly,a hierarchical learning algorithm was proposed to update the parameters of MIM for improving the identification accuracy online.Finally,the proposed model was tested in real plants to evaluate its efficiency and effectiveness.Experimental results have verified the benefits of the proposed method.

Comparison of membrane fouling during short-term filtration of aerobic granular sludge and activated sludge

Aerobic granular sludge was cultivated adopting internal-circulate sequencing batch airlift reactor. The contradistinctive experiment about short-term membrane fouling between aerobic granular sludge system and activated sludge system were investigated. The membrane foulants was also characterized by Fourier transform infrared （FTIR） spectroscopy technique. The results showed that the aerobic granular sludge had excellent denitrification ability; the removal efficiency of TN could reach 90%. The aerobic granular sludge could alleviate membrane fouling effectively. The steady membrane flux of aerobic granular sludge was twice as much as that of activated sludge system. In addition, it was found that the aerobic granular sludge could result in severe membrane pore-blocking, however, the activated sludge could cause severe cake fouling. The major components of the foulants were identified as comprising of proteins and polysaccharide materials.

Mechanism of calcium mitigating membrane fouling in submerged membrane bioreactors

Two parallel membrane bioreactors （MBRs） were operated under different calcium dosages （168.5, 27 mg/L） to gain a better understanding of the mechanism of retarding membrane fouling by adding calcium. The results showed that the particle size of sludge flocs increased and the particle size distribution tended to be narrow at the optimum dosage （168.5 mg/L）. Calcium was effective in decreasing loosely bound extracellular polymeric substances （LB-EPS） in microbial flocs and soluble microbial products （SMP） in the supernatant at the dosage of 168.5 mg/L by strengthening the neutralization and bridging of EPS with flocs. Furthermore, the amount of CODs and CODc decreased in both the mixed liquor and the fouling cake layer on the membrane surface. In order to compare the filtration characteristics of cake layers from the MBRs with the two calcium dosages, the specific cake resistance and the compressibility coefficient were measured. The specific cake resistance from the MBR with optimum dosage （168.5 mg/L） was distinctly lower than that with low dosage （27 mg/L）. The compressibility coefficient of the cake layers under two dosages were respectively attained as 0.65, 0.91. Scanning electron microscopy （SEM） and three-dimensional confocal scanning laser microscope analysis （CLSM） images were utilized to observe the gel layer directly.

Ultrafiltration with in-line coagulation for the removal of natural humic acid and membrane fouling mechanism

Experimental and theoretical analysis were made on the natural humic acid removal and the membrane fouling of ultrafiltration （UF） with in-line coagulation. The results showed dissolved organic carbon （DOC） and UV254 removals by the UF with in-line coagulation at pH 7 were increased from 28% to 53% and 40% to 78% in comparison with direct UF treatment respectively. At the same time, the analysis of high performance liquid chromatography showed that UF with coagulation had significant improvement of removal of humic acid with molecular weights less than 6000 Da in particular. Compared to direct UF, the in-line coagulation UF also kept more constant permeate flux and very slight increase oftransmembrane pressure during a filtration circle. Two typical membrane fouling models were used by inducing two coefficients Kc and Kp corresponding to cake filtration model and pore narrowing model respectively. It was found that membrane fouling by pore-narrowing effect was effectively alleviated and that by cake-filtration was much decreased by in-line coagulation. Under the condition of coagulation prior to ultrafiltration at pH 7, the cake layer formed on the membrane surface became thicker, but the membrane filtration resistance was lower than that at pH 5 with the extension of operation time.

Study on membrane fouling of submerged membrane bioreactor in treating bathing wastewater

A pilot-scale submerged membrane bioreactor (MBR) was used to treat the bathing wastewater for more than 90 d. Several factors a?ecting membrane fouling were studied, including the variation in transmembrane pressure (TMP), changes in extracellular polymeric substance (EPS), and distribution of membrane resistance (R). The relationships between R and EPS concentration were found to be R = 0.00008(EPSS)2.915 in the mixed liquor (EPSS) and R = 0.2853(EPSm) – 0.824 on the membrane surface (EPSm). The constant ...

Research on Influence Factors of Membrane Fouling in A/O-MBR System

[Objective] The aim was to study the influence factors of membrane fouling in A/O-MBR system,so as to control membrane fouling better,prolong the service life of membrane,further reduce the cost of water treatment and promote the popularization of membrane bioreactor(MBR) effectively.[Method] Based on small A/O-MBR device,an orthogonal test with three factors(including aeration intensity,pump-stop ratio and mixed liquor suspended solid) and three levels was designed to optimize three parameters,and the effects of factors on membrane fouling and their mechanisms were studied through single-factor analysis.[Result] The order of operation parameters affecting membrane fouling in A/O-MBR was aeration intensity>pump-stop ratio>mixed liquor suspended solid(MLSS),and the optimum operating parameters were composed of 1.6 m3/h of aeration intensity,4 500 mg/L of MLSS and 9:2 of pump-stop ratio.With the increase of running time,soluble microbial product(SMP) and extracellular polymeric substance(EPS) accumulated gradually in the reactor,and EPS accumulated more rapidly than SMP;meanwhile,membrane fouling was accelerated.Therefore,EPS was the priority factor for membrane fouling compared with SMP.In addition,membrane fouling was accelerated gradually with the increase of protein content in EPS,while the variation of polysaccharides content in EPS had no obvious effect on membrane fouling,so protein content in EPS was the main factor for membrane fouling.[Conclusion] The study could provide theoretical references for the choice of parameters,operation and running in practical engineering.

Unraveling Membrane Fouling Induced by Chlorinated Water Versus Surface Water:Biofouling Properties and Microbiological Investigation

Chlorine is usually applied in the urban water treatment process to deactivate pathogens and prevent waterborne diseases.As a pre-treatment,it remains unclear whether chlorinated water can effectively alleviate membrane fouling during ultrafiltration(UF).In this study,tap water was investigated for its effect on biofilm formation and biofouling in a gravity-driven membrane(GDM)filtration system.For comparison,biofilm/biofouling with untreated surface(lake)water was studied in parallel.It was found that more severe membrane fouling occurred with the filtration of tap water than lake water,and larger quantities of polysaccharide and extracellular DNA(eDNA)were present in the tap-water biofilm than in the lake-water biofilm.The tap-water biofilm had a densely compact morphology.In contrast,a porous,spider-like structure was observed for the lake-water biofilm,which was assumed to be associated with the bacteria in the biofilm.This hypothesis was verified by 16S ribosomal RNA(rRNA)sequencing,which demonstrated that Xanthobacter was the dominant taxon in the tap-water biofilm.Additionally,membrane hydrophobicity/hydrophilicity played a minor role in affecting the membrane fouling properties and microbial community.This study revealed the significant role of chlorine-resistant bacteria in biofouling formation and provides a deeper understanding of membrane fouling,which can potentially aid in searching for effective ways of controlling membrane fouling.

Effects of a novel bimetallic catalytic biofilter-based pretreatment technique on the form of ultrafiltration membrane fouling

Pretreatments of influents using bimetallic catalytic biofilter(BC-biofilter)can help reduce transmembrane pressures.For ultrafiltration membranes coupled with a conventional biofilter pretreatment,the cake layer resistance accounts for 25.0%of the total resistance.However,for those coupled with BC-biofilter pretreatment,the cake layer resistance accounts only for 12.5%of the total resistance.Confocal laser scanning microscopy is employed to determine the porosity of cake layer.It is found that ultrafiltration membranes with BC-biofilter pretreatment show a cake layer porosity of up to 0.56 or greater,whereas those with a conventional biofilter pretreatment exhibit a cake layer porosity of only 0.36.This is because micro-flocculation occurs in the effluents of BC-biofilter.The flocs generated through flocculation deposit on membrane surfaces to create highly porous cake layer.Moreover,catalytic reduction can increase the zeta potentials of the biofilter effluents.This makes the deposition of colloidal particles and flocs on membrane surfaces difficult under electrostatic repulsion.Simultaneously,micro-flocculation after BC-biofilter pretreatment can remove colloidal particles with particle sizes of200–350 nm in water.This can effectively prevent the blockage of ultrafiltration membrane pores.Furthermore,compared to conventional biofilter,BC-biofilter pretreatment can more effectively reduce the number of colloidal particles and the van der Waals forces of ultrafiltration membranes.They can also change the action directions of electric double layers and thereby mitigate ultrafiltration membrane fouling.

Characteristics of Membrane Fouling in an Anaerobic-(Anoxic/Oxic)~n-MBR Process

The characteristics of membrane fouling and cleaning, in a hybrid MBR process, was investigated. Under the condition of sub-critical flux operation, a characteristic three-stage trans-membrane pressure （TMP） profile is observed as time passes. The initially extended period of slow pressure rise, followed by a somewhat faster rise, is then sup- planted by a sudden transition to rapid pressure rise. Membrane cleaning experiments and SEM examination make it apparent that the rapid TMP rise is mainly caused by the accumulation of a surface cake layer, which is a reversible fouling that can be removed by tap water washing. Fouling caused by a gel layer, which is an irreversible fouling, can be removed efficiently by chemical cleaning. NaC10 can oxidize the gel layer, which is formed mainly of macromo-lecular organic substances. The HC1 can remove inorganic particles formed by Ca^2＋, Mg^2＋ ions etc. The sequence of chemicals used in membrane cleaning has an influence on the cleaning result. The effect of the NaC1O＋HC1 cleaning procedure is superior to that of the HCI＋NaC1O one. Particle size distribution measurements （PSD） reveal that fine particles are inclined to deposit or attach on the membrane surface, or in the membrane pores, and caused rapid fouling.

Ultrafiltration recovery of alginate: Membrane fouling mitigation by multivalent metal ions and properties of recycled materials

Recovery of alginate extracted from aerobic granular sludge(AGS)has given rise to a novel research direction.However,these extracted alginate solutions have a water content of nearly 100%.Alternately,ultrafiltration(UF)is generally used for concentration of polymers.Furthermore,the introduction of multivalent metal ions into alginate may provide a promising method for the development of novel nanomaterials.In this study,membrane fouling mitigation by multivalent metal ions,both individually and in combination,and properties of recycled materials were investigated for UF recovery of sodium alginate(SA).The filtration resistance showed a significantly negative correlation with the concentration of metal ions,arranged in the order of Mg^2+<Ca^2+<Fe^3+<Al^3+(filtration resistance mitigation),and the moisture content of recycled filter cake showed a marked decrease.For Ca^2+,Mg^2+,Fe^3+,and Ca^2++Fe^3+,the filtration resistances were almost the same when the total charge concentration was less than 5 mmol·L^–1.However,when the total charge concentration was greater than 5 mmol·L^–1,membrane fouling mitigation increased significantly in the presence of Ca^2+or Fe^3+and remained constant for Mg^2+with the increase of total charge concentration.The filtration resistance mitigation was arranged in the order of Fe^3+>Fe^3++Ca^2+>Ca^2+>Mg^2+.Three mechanisms were proposed in the presence of Fe^3+,such as the decrease of SA concentration,change in p H,and production of hydroxide iron colloids from hydrolysis.The properties of recycled materials(filter cake)were investigated via optical microscope observation,dynamic light scattering,Fourier transform infrared,X-ray photoelectron spectroscopy(XPS),and scanning electron microscopy.The results provide further insight into UF recoveries of alginate extracted from AGS.

Membrane Fouling Alleviation by Chemically Enhanced Backwashing in Treating Algae-Containing Surface Water: From Bench-Scale to Full-Scale Application

Ultrafiltration(UF)has been increasingly implemented in drinking water treatment plants;however,algae and their secretions can cause severe membrane fouling and pose great challenges to UF in practice.In this study,a simple and practical chemically enhanced backwashing(CEB)process was developed to address such issues using various cleaning reagents,including sodium hypochlorite(NaClO),sodium chloride(NaCl),sodium hydroxide(NaOH),sodium citrate,and their combinations.The results indicate that the type of chemical played a fundamental role in alleviating the hydraulically irreversible membrane fouling(HIMF),with NaClO as the best-performing reagent,followed by NaCl.Furthermore,a CEB process using a combination of NaClO with NaCl,NaOH,or sodium citrate delivered little improvement in the alleviation of membrane fouling compared with NaClO alone.The optimized dosage and dosing frequency of NaClO were 10 mg·L^(-1) two times per day.Long-term pilot-scale and full-scale experiments further verified the feasibility of the CEB process in relieving algae-derived membrane fouling.Compared with the conventional hydraulic backwashing without chemical involvement,the CEB process can effectively remove the organic foulants including biopolymers,humic substances,and proteinlike substances by means of oxidization,thereby weakening the cohesive forces between the organic foulants and the membrane surface.Therefore,the CEB process can efficiently alleviate the algae-related membrane fouling with lower chemical consumption,and is proposed as an alternative to control membrane fouling in treating the algae-containing surface water.

Effect of components in activated sludge liquor on membranefouling in a submerged membrane bioreactor

By a membrane bioreactor with a settle tank in long-term operation and batch experiments, the effects of floes, soluble microorganism products （SMPs） and metal ions in activated sludge liquor on membrane fouling were investigated. The results showed that foulants absorbed each other and formed a fouling layer as a ＂second membrane＂ influencing the permeability of the membrane. The ＂gel layer＂ caused by SMPs and ＂cake layer＂ by floes showed great differences in morphology by analysis of scanning electron microscope and atomic force microscope. The ＂gel layer＂ was more compact and of poor permeability. When the membrane flux was 40 L/（m^2·h）, the rate of membrane fouling caused by supernatant （0.011 MPa/h） was greater than that by sludgc liquor （0.0063 MPa/h）. SMPs played very important roles on membrane fouling. In the bulking sludge, with SMPs increasing, the rate of membrane fouling （0.0132 MPa/h） was faster. While after flocculation of the SMPs, the rate of fouling decreased to 0.0034 M Pa/h. Floes could keep holes in their overlaps. They could alleviate membrane fouling by preventing the SMPs directly attaching on membrane surface.

Filtering Surface Water with a Polyurethane-based Hollow Fiber Membrane: Effects of Operating Pressure on Membrane Fouling

Membrane fouling seriously restricts applications of membrane technology. A novel strategy was applied in this study to retard membrane fouling by changing operating pressure with the pressure responsibility membrane. A polyurethane-based hollow fiber membrane was used to treat surface water for evaluating the effect of operating pressure on membrane fouling. Some bench-scale tests in dead-end mode were carried out. In the experiments without backwashing, as operating pressure increased, severe membrane fouling occurred on membrane surface, while the permeate quality was improved obviously, which is considered to be due to shrinkage deformation. The total resistance, irreversible resistance and reversible resistance under different backwash pressures were determined in filtration/backwashing test. With the increase of backwash pressure, the total resistance decreased, and more importantly, the irreversible resistance also decreased, which implies that small particles deposited inside membrane pores and cake layers on membrane surface are effectively removed. Similar results could be obtained in mass balance tests. The results of the present study indicate that the application of pressure responsibility membrane in surface water treatment may be an effective strategy for reducing membrane fouling.

Effect of Solid Retention and Hydraulic Retention Times on Membrane Fouling in Membrane Bioreactor

In this bench scale submerged membrane bioreactor, effect of solid retention time and hydraulic retention time on membrane fouling propensity has been studied. This experiment is carried out at different solid retention time of 5, 10, 30, 70 and 98 days; and fouling behavior of membrane bioreactor is investigated. Average effluent quality is found to be 88.14%-94.38%. The experiment with different hydraulic retention is carried for 3 to 4 days and fouling behavior has been investigated. The effluent quality at different hydraulic retention time of 1, 2, 3, 5, 10 and 24 hours has been investigated. This paper aims to search optimal values of solid and hydraulic retention times at which lower fouling and higher organic removal efficiency can be obtained. This study has been mainly focused on operating parameters rather than microbial structure, effect and analysis of activated sludge to membrane fouling.

Fouling evaluation on membrane distillation used for reducing solvent in polyphenol rich propolis extract

Membrane distillation(MD) has not been widely studied in the concentrate of phenolic rich solution in comparison to osmotic distillation. In this work, the potential of MD to reduce solvent in the polyphenol rich propolis extract was further investigated. Polyvinylidene fluoride(PVDF) membranes were engineered with the smaller pore size for the less hydrophobic surface in order to avoid wetting, allowing only the solvent vapor to be transferred from the warm feed into the cold permeate. All the membranes exhibited more than 95% rejection of phenolic and flavonoid compounds. Although the hydrophilic membranes exhibited less fouling, they displayed a lower flux than the hydrophobic membrane due to the hindrance in the wetted pores. The hydrophobic membrane was seriously fouled by the phenolic acid as shown in the Fourier transform infrared spectroscopy spectrum. Pore plugging occurred on these hydrophobic membranes as confirmed in the scanning electron microscope images.

Effects of operative conditions on membrane fouling of jet loop membrane bioreactor

The orthogonal experiments, which involves three factors： aeration intensity, suction time and suction suspended time, were designed to research membrane fouling of jet loop membrane bioreactor （JLMBR）. Experimental results indicate that increasing aeration intensity, reducing suction time and increasing suction suspended time all could mitigate membrane fouling effectively. However excessive aeration intensity, too short suction time and excessive suction suspended time were bad for bioreactor running. The optimal aeration intensity, suction time and suction suspended time were 0.75 1.00 m3/（m2.h）, 8 -10 min and 4 -5 min, respectively. The three factors all had effect on membrane pollution rate, while the suction time was the most important one and followed by aeration intensity and suction suspended time. It also indicates that, comparing with traditional submerged membrane bioreactors, JLMBR had lower membrane pollution rate.

Membrane fouling characteristics analysis of high concentration powdered activated carbon-microfiltration integrated system

The membrane fouling characteristics of high concentration powdered activated carbon-microfiltration (HCPAC-MF) integrated process are studied by comparing them with those of direct microfitration system using the particle counter,scanning electron microscope (SEM) and atomic force microscope (AFM). The results indicate that the specific flux of HCPAC-MF is 3 times better than that of the direct filtration process after the system is stabilized. The addition of HCPAC changes the particle distribution of raw water and influences the structure of surface fouling layer. The PAC with irregular shapes aggregating on the membrane surface makes the cake layer structure loose and increases the roughness of membrane surface,and this decreases the thickness of hydrodynamic boundary layer and the membrane resistance. After the physical cleaning,the membrane surface and pores are clean without any fouling matters aggregation,which illustrates that the cake layer of PAC can be formed quickly in this HCPAC environment and prevent the occurrence of irreversible fouling.

Fouling Characteristics and Prevention Techniques for Membrane Bioreactor

Membrane fouling is the main problem of membrane bioreactors (MBR), which seriously influ- ences its wastewater treatment effect and running. The characteristics of microbiology and hydrodynamics concerning membrane fouling were investigated and the measure was put forward for optimum operation of MBR. The measure is that 1) the parameters of activated sludge concentration (X) and membrane flux should be lower than the critical values of X and membrane flux respectively, and 2) the activated sludge should be discharged periodically. The experimental results show that the combination backwashing of gas and perme- ated effluent is better than single gas backwashing or single permeated effluent backwashing. This technique can remove the cake layer deposited on the membrane surface, decrease the membrane fouling, and recover the membrane flux effectively. So it is effective for prevention of membrane fouling.