As part of sewage treatment,coagulation could remove phosphorus from the effluent of the Anaerobic-Anoxic-Oxic-Anoxic(A^(2)OA)biological process.The importance in investigating the influence of coagulation on Anaerobi...As part of sewage treatment,coagulation could remove phosphorus from the effluent of the Anaerobic-Anoxic-Oxic-Anoxic(A^(2)OA)biological process.The importance in investigating the influence of coagulation on Anaerobic-Anoxic-Oxic-Anoxic Membrane Bioreactor(A^(2)OA-MBR)should be emphasized.In this study,systematic optimization of coagulation parameters for greater pollutant removal was conducted in terms of coagulant dosage,coagulation residence time and stirring hydraulic conditions.Coagulation process could remarkably remove turbidity,phosphorus,chemical oxygen demand,humic-like,protein-like and polysaccharide-like substances from secondary effluent and A^(2)OA sludge-liquid mixture.Furthermore,the influence of coagulation on membrane fouling development during the ultrafiltration of secondary effluent and A^(2)OA sludge-liquid mixture was investigated based on optimum coagulation parameters.Coagulation simultaneously reduced reversible membrane fouling and the irreversible one by 86%and 16%,respectively.According to excitation-emission matrix and attenuated total reflection-fourier transform infrared spectra,membrane fouling was primarily influenced by the cake layer,although pore fouling might be aggravated by A^(2)OA processes.Besides,the feasibility of coagulation-assisted A^(2)OA-MBRwas also assessed using hollowfibermembranes.It exhibited excellent potential in alleviatingmembrane fouling,while regular cleaning twice a day was not enough to suppress transmembrane pressure increase during direct domestic wastewater ultrafiltration.Additionally,both polysaccharide-like and protein-like foulants were vital components for membrane fouling during wastewater treatment.展开更多
Membrane filtration technology has been widely utilized for microalgae harvesting due to its stability and high efficiency.However,this technology faces challenges posed by membrane fouling caused by algal cells and e...Membrane filtration technology has been widely utilized for microalgae harvesting due to its stability and high efficiency.However,this technology faces challenges posed by membrane fouling caused by algal cells and extracellular organic matter(EOM),which are significantly influenced by membrane material and pore size.This study compared the fouling behavior of polyvinylidene fluoride(PVDF)membranes and ceramic membranes with similar pore sizes(0.20 mm and 0.16 mm,respectively)during the filtration of Microcystis aeruginosa.The ceramic membrane exhibited a lower transmembrane pressure(TMP)growth rate and reduced accumulation of surface foulants compared to the PVDF membrane,indicating its greater suitability for filtering algae-laden water.Further investigations employed membranes fabricated from aluminum oxide powders with grain sizes of 1 mm,3 mm,8 mm,and 10 mm,corresponding to membrane pore sizes of 0.08 mm,0.16 mm,0.66 mm,and 0.76 mm,respectively,to assess the impact of pore size on ceramic membrane fouling.The results revealed that increasing membrane pore size significantly lowered the TMP growth rate and reduced the irreversibility of membrane fouling.The extended DerjaguineLandaueVerweyeOverbeek(XDLVO)analysis indicated that large pore sizes enhanced repulsion between the ceramic membrane and algal foulants,further alleviating membrane fouling.This investigation offers new insights into optimizing membrane material and pore size for efficient filtration of algae-laden water.展开更多
Membrane fouling remains the primary economic barrier to the widespread implementation of membrane bioreactors (MBRs), despite the fact that they lead to the production of high-quality effluent. Operational conditions...Membrane fouling remains the primary economic barrier to the widespread implementation of membrane bioreactors (MBRs), despite the fact that they lead to the production of high-quality effluent. Operational conditions are critical factors influencing membrane fouling. This study aimed to investigate the simultaneous impacts of temperature and hydraulic retention time (HRT) variations on membrane fouling. Experiments were conducted at three different temperatures (18°C, 25°C, and 32°C) and HRTs (6 h, 9 h, and 15 h). The results demonstrated that increases in both temperature and HRT contributed to a reduction in membrane fouling. Additionally, a positive interaction between temperature and HRT was observed in the linear slope variation of membrane permeation, with temperature variations exerting a greater influence on membrane fouling than HRT variations. Fouling factor analysis revealed that increases in temperature and HRT led to decreased concentrations of soluble microbial products (SMP) and extracellular polymeric substances (EPS), particularly carbohydrates, in the activated sludge. Analyses of the cake layer of the membrane indicated that increasing temperature and HRT reduced EPS levels, particularly polysaccharides and proteins;altered primary protein structure;and increased the mean particle size distribution. Ultimately, these changes led to reductions in both reversible and irreversible hydraulic resistances. This study highlights the importance of optimizing operational parameters such as temperature and HRT to enhance membrane performance and treatment efficiency in MBR systems while mitigating fouling.展开更多
It is important to understand the evolution of the matter on the polymer membrane surface.The in situ and real-time monitoring of the membrane surface will not only favor the investigation of selective layer formation...It is important to understand the evolution of the matter on the polymer membrane surface.The in situ and real-time monitoring of the membrane surface will not only favor the investigation of selective layer formation but can also track the fouling process during operation.Herein,an aggregation-induced emission(AIE)-active polymer membrane was prepared by the interfacial polymerization of a cyclodextrin-based glycocluster(CD@Glucose)and a tetraphenylethylene derivative modified with boronic acid groups(TPEDB)on the surface of a polyacrylonitrile(PAN)ultrafiltration membrane.This interfacial polymerization method can be stacked layer-by-layer to regulate the hydrophilicity and pore structure of the membrane.With the increase in the number of polymer layers,the separation and antifouling properties of the membrane gradually improved.Owing to the AIE property of the crosslinking agent TPEDB,the occurrence of interfacial polymerization and the degree of fouling during membrane operation can be monitored by the fluorescence distribution and intensity.With the aggravation of membrane fouling,the fluorescence decreased gradually,but recovered after cleaning.Therefore,this AIE effect can be used for real-time monitoring of interfacial polymerization as well as membrane fouling.展开更多
Membrane fouling is the primary resistance to the continuous production of stirred membrane reactors.This work presents a laser-enhanced high-magnification telecentric imaging system(LEHTIS),which uses a high-magnific...Membrane fouling is the primary resistance to the continuous production of stirred membrane reactors.This work presents a laser-enhanced high-magnification telecentric imaging system(LEHTIS),which uses a high-magnification telecentric lens and laser-enhanced illumination to invasively capture the motion of particles on the membrane surface or near the membrane.The problems of working distance and particle interference in the stirred membrane reactor are solved to achieve the purpose of in-situ monitoring of membrane fouling.This method is suitable for high flow rates,high solid holdup,and small particle size systems,and the dynamic motion and accumulation of particles are preliminarily analyzed.It shows that the accumulation and desorption of particles on the membrane surface are related to the physical properties of the membrane surface.There is an intermittent rotational movement in the flow field near the membrane,and it tends to stabilize over time.The filtration process can be assessed by monitoring changes in the overall velocity and acceleration of particles near the membrane.The analysis of forces acting on individual particles is compared and validated with the force balance model to correct and accurately apply it to stirred membrane reactors.The development of LEHTIS provides an effective tool for in-situ monitoring of membrane fouling and optimizing the stirred membrane reactors for industrial applications.展开更多
Membrane fouling is a persistent challenge in membrane-based technologies,significantly impacting efficiency,operational costs,and system lifespan in applications like water treatment,desalination,and industrial proce...Membrane fouling is a persistent challenge in membrane-based technologies,significantly impacting efficiency,operational costs,and system lifespan in applications like water treatment,desalination,and industrial processing.Foul-ing,caused by the accumulation of particulates,organic compounds,and microorganisms,leads to reduced permeability,increased energy demands,and frequent maintenance.Traditional fouling control approaches,relying on empirical models and reactive strategies,often fail to address these issues efficiently.In this context,artificial intelligence(AI)and machine learning(ML)have emerged as innovative tools offering predictive and proactive solutions for fouling man-agement.By utilizing historical and real-time data,AI/ML techniques such as artificial neural networks,support vector machines,and ensemble models enable accurate prediction of fouling onset,identification of fouling mechanisms,and optimization of control measures.This review provides a detailed examination of the integration of AI/ML in membrane fouling prediction and mitigation,discussing advanced algorithms,the role of sensor-based monitoring,and the importance of robust datasets in enhancing predictive accuracy.Case studies highlighting successful AI/ML applications across various membrane processes are presented,demonstrating their transformative potential in improving system performance.Emerging trends,such as hybrid modeling and IoT-enabled smart systems,are explored,alongside a criti-cal analysis of research gaps and opportunities.This review emphasizes AI/ML as a cornerstone for sustainable,cost-effective membrane operations.展开更多
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 activa...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.展开更多
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 ...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.展开更多
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 UV...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.展开更多
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 ...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 ...展开更多
The combined fouling during ultrafiltration（UF） of surface water pretreated to different extents was investigated to disclose the roles of polysaccharides, proteins, and inorganic particles in UF membrane fouling. B...The combined fouling during ultrafiltration（UF） of surface water pretreated to different extents was investigated to disclose the roles of polysaccharides, proteins, and inorganic particles in UF membrane fouling. Both reversible and irreversible fouling decreased with enhanced pretreatment（biologically active carbon（BAC） treatment and sand filtration）. The sand filter effluent fouled the membrane very slowly. The UF membrane removed turbidity to less than 0.1 nephelometric turbidity unit（NTU）, reduced polysaccharides by 25.4%–29.9%, but rejected few proteins. Both polysaccharides and inorganic particles were detected on the fouled membranes, but inorganic particles could be effectively removed by backwashing. The increase of turbidity in the sand filter effluent to 3.05 NTU did not significantly increase the fouling rate, but an increase in the turbidity in the BAC effluent to6.11 NTU increased the fouling rate by more than 100%. The results demonstrated that the polysaccharide, not the protein, constituents of biopolymers were responsible for membrane fouling. Membrane fouling was closely associated with a small fraction of polysaccharides in the feed water. Inorganic particles exacerbated membrane fouling only when the concentration of fouling–inducing polysaccharides in the feed water was relatively high. The combined fouling was largely reversible, and polysaccharides were the predominant substances responsible for irreversible fouling.展开更多
Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration（NF） in this study. The NF performance was optimized, and its fouling characteristics after different operational durations（i.e., 48 a...Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration（NF） in this study. The NF performance was optimized, and its fouling characteristics after different operational durations（i.e., 48 and 169 hr） were analyzed to investigate the applicability of nanofiltration for water reuse. The optimum performance was achieved when transmembrane pressure = 12 bar, p H = 4 and flow rate = 8 L/min using a GE membrane. The permeate water quality could satisfy the requirements of water reclamation for different uses and local standards for water reuse in Beijing. Flux decline in the fouling experiments could be divided into a rapid flux decline and a quasi-steady state. The boundary flux theory was used to predict the evolution of permeate flux. The expected operational duration based on the 169-hr experiment was 392.6 hr which is 175% longer than that of the 48-hr one. High molecular weight（MW） protein-like substances were suggested to be the dominant foulants after an extended period based on the MW distribution and the fluorescence characteristics. The analyses of infrared spectra and extracellular polymeric substances revealed that the roles of both humic- and polysaccharide-like substances were diminished, while that of protein-like substances were strengthened in the contribution of membrane fouling with time prolonged. Inorganic salts were found to have marginally influence on membrane fouling. Additionally, alkali washing was more efficient at removing organic foulants in the long term, and a combination of water flushing and alkali washing was appropriate for NF fouling control in municipal sewage treatment.展开更多
[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...[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.展开更多
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 membra...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.展开更多
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 resi...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.展开更多
Unlike the role of the membrane in a membrane bioreactor, which is designed to replace a sediment tank, direct sewage membrane filtration（DSMF）, with the goal of concentrating organic matters, is proposed as a pretr...Unlike the role of the membrane in a membrane bioreactor, which is designed to replace a sediment tank, direct sewage membrane filtration（DSMF）, with the goal of concentrating organic matters, is proposed as a pretreatment process in a novel sewage treatment concept. The concept of membrane-based pretreatment is proposed to divide raw sewage into a concentrated part retaining most organics and a filtered part with less pollutant remaining, so that energy recovery and water reuse, respectively, could be realized by post-treatment. A pilot-scale experiment was carried out to verify the feasibility of coagulant/adsorbent addition for membrane fouling control, which has been the main issue during this DSMF process. The results showed that continuous coagulant addition successfully slowed down the increase in filtration resistance, with the resistance maintained below 1.0 × 1013m^（-1） in the first 70 hr before a jump occurred. Furthermore,the adsorbent addition contributed to retarding the occurrence of the filtration resistance jump, achieving simultaneous fouling control and chemical oxygen demand（COD）concentration improvement. The final concentrated COD amounted to 7500 mg/L after 6 days of operation.展开更多
Three-dimensional fluorescence excitation–emission matrix（EEM） coupled with parallel factor analysis（PARAFAC） was performed for a total of 18 water samples taken from three water sources（two lakes and one wastew...Three-dimensional fluorescence excitation–emission matrix（EEM） coupled with parallel factor analysis（PARAFAC） was performed for a total of 18 water samples taken from three water sources（two lakes and one wastewater treatment plant（WWTP） secondary effluent）,with the purpose of identifying the major ultrafiltration（UF） membrane foulants in different water sources. Three fluorescent components（C1, C2 and C3） were identified,which represented terrestrially derived humic-like substances（C1）, microbially derived humic-like substances（C2）, and protein-like substances（C3）. The correlations between the different fluorescent components and UF membrane fouling were analyzed. It was shown that for the WWTP secondary effluent, all three components（C1, C2 and C3） made a considerable contribution to the irreversible and total fouling of the UF membrane.However, for the two lakes, only the C3 exhibited a strong correlation with membrane fouling, indicating that the protein-like substances were the major membrane foulants in the lake waters. Significant attachment of C1, C2 and C3 to the UF membrane was also confirmed by mass balance analyses for the WWTP secondary effluent; while the attachment of C1 and C2 was shown to be negligible for the two lakes. The results may provide basic formation for developing suitable fouling control strategies for sustainable UF processes.展开更多
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...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.展开更多
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(U...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.展开更多
The effects of Ca^(2+) on membrane fouling and trace organic compounds(TrOCs)removal in an electric field-assisted microfiltration system were investigated in the presence of Na^(+) alone for comparison.In the electri...The effects of Ca^(2+) on membrane fouling and trace organic compounds(TrOCs)removal in an electric field-assisted microfiltration system were investigated in the presence of Na^(+) alone for comparison.In the electric field,negatively charged bovine serum albumin(BSA)migrated towards the anode far away from the membrane surface,resulting in a 42.9%transmembrane pressure(TMP)reduction in the presence of Na^(+) at 1.5 V.In contrast,because of the stronger charge shielding of Ca^(2+),the electrophoretic migration of BSA was limited and led to a neglectable effect of the electric field(1.5 V)on membrane fouling.However,under 3 V applied voltage,the synergistic effects of electrochemical oxidation and bridging interaction between Ca^(2+) and BSA promoted the formation of denser settleable flocs and a thinner porous cake layer,which alleviated membrane fouling with a 64.5%decrease in TMP and nearly 100%BSA removal.The Tr OCs elimination increased with voltage and reached29.4%–80.4%at 3 V.The electric field could prolong the contact between Tr OCs and strong oxidants generated on the anode,which enhanced the Tr OCs removal.However,a stronger charge shielding ability of Ca^(2+) weakened the electric field force and thus lowered the Tr OCs removal.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52170070,52400022 and 52200088)the Youth S&T Talent Support Programme of Guangdong Provincial Association for Science and Technology(GDSTA)(No.SKXRC202406)+1 种基金China Postdoctoral Science Foundation(No.2023M740754)“One hundred Youth”Science and Technology Plan,Guangdong University of Technology,China(No.263113906).
文摘As part of sewage treatment,coagulation could remove phosphorus from the effluent of the Anaerobic-Anoxic-Oxic-Anoxic(A^(2)OA)biological process.The importance in investigating the influence of coagulation on Anaerobic-Anoxic-Oxic-Anoxic Membrane Bioreactor(A^(2)OA-MBR)should be emphasized.In this study,systematic optimization of coagulation parameters for greater pollutant removal was conducted in terms of coagulant dosage,coagulation residence time and stirring hydraulic conditions.Coagulation process could remarkably remove turbidity,phosphorus,chemical oxygen demand,humic-like,protein-like and polysaccharide-like substances from secondary effluent and A^(2)OA sludge-liquid mixture.Furthermore,the influence of coagulation on membrane fouling development during the ultrafiltration of secondary effluent and A^(2)OA sludge-liquid mixture was investigated based on optimum coagulation parameters.Coagulation simultaneously reduced reversible membrane fouling and the irreversible one by 86%and 16%,respectively.According to excitation-emission matrix and attenuated total reflection-fourier transform infrared spectra,membrane fouling was primarily influenced by the cake layer,although pore fouling might be aggravated by A^(2)OA processes.Besides,the feasibility of coagulation-assisted A^(2)OA-MBRwas also assessed using hollowfibermembranes.It exhibited excellent potential in alleviatingmembrane fouling,while regular cleaning twice a day was not enough to suppress transmembrane pressure increase during direct domestic wastewater ultrafiltration.Additionally,both polysaccharide-like and protein-like foulants were vital components for membrane fouling during wastewater treatment.
基金supported by the National Natural Science Foundation of China(Grant No.52370035)the Natural Science Foundation of Hebei Province,China(Grant No.E2023202064)the China Postdoctoral Science Foundation(Grant No.2024M750717).
文摘Membrane filtration technology has been widely utilized for microalgae harvesting due to its stability and high efficiency.However,this technology faces challenges posed by membrane fouling caused by algal cells and extracellular organic matter(EOM),which are significantly influenced by membrane material and pore size.This study compared the fouling behavior of polyvinylidene fluoride(PVDF)membranes and ceramic membranes with similar pore sizes(0.20 mm and 0.16 mm,respectively)during the filtration of Microcystis aeruginosa.The ceramic membrane exhibited a lower transmembrane pressure(TMP)growth rate and reduced accumulation of surface foulants compared to the PVDF membrane,indicating its greater suitability for filtering algae-laden water.Further investigations employed membranes fabricated from aluminum oxide powders with grain sizes of 1 mm,3 mm,8 mm,and 10 mm,corresponding to membrane pore sizes of 0.08 mm,0.16 mm,0.66 mm,and 0.76 mm,respectively,to assess the impact of pore size on ceramic membrane fouling.The results revealed that increasing membrane pore size significantly lowered the TMP growth rate and reduced the irreversibility of membrane fouling.The extended DerjaguineLandaueVerweyeOverbeek(XDLVO)analysis indicated that large pore sizes enhanced repulsion between the ceramic membrane and algal foulants,further alleviating membrane fouling.This investigation offers new insights into optimizing membrane material and pore size for efficient filtration of algae-laden water.
文摘Membrane fouling remains the primary economic barrier to the widespread implementation of membrane bioreactors (MBRs), despite the fact that they lead to the production of high-quality effluent. Operational conditions are critical factors influencing membrane fouling. This study aimed to investigate the simultaneous impacts of temperature and hydraulic retention time (HRT) variations on membrane fouling. Experiments were conducted at three different temperatures (18°C, 25°C, and 32°C) and HRTs (6 h, 9 h, and 15 h). The results demonstrated that increases in both temperature and HRT contributed to a reduction in membrane fouling. Additionally, a positive interaction between temperature and HRT was observed in the linear slope variation of membrane permeation, with temperature variations exerting a greater influence on membrane fouling than HRT variations. Fouling factor analysis revealed that increases in temperature and HRT led to decreased concentrations of soluble microbial products (SMP) and extracellular polymeric substances (EPS), particularly carbohydrates, in the activated sludge. Analyses of the cake layer of the membrane indicated that increasing temperature and HRT reduced EPS levels, particularly polysaccharides and proteins;altered primary protein structure;and increased the mean particle size distribution. Ultimately, these changes led to reductions in both reversible and irreversible hydraulic resistances. This study highlights the importance of optimizing operational parameters such as temperature and HRT to enhance membrane performance and treatment efficiency in MBR systems while mitigating fouling.
基金supported by the Fundamental Research Funds for Central Universities(No.30922010811).
文摘It is important to understand the evolution of the matter on the polymer membrane surface.The in situ and real-time monitoring of the membrane surface will not only favor the investigation of selective layer formation but can also track the fouling process during operation.Herein,an aggregation-induced emission(AIE)-active polymer membrane was prepared by the interfacial polymerization of a cyclodextrin-based glycocluster(CD@Glucose)and a tetraphenylethylene derivative modified with boronic acid groups(TPEDB)on the surface of a polyacrylonitrile(PAN)ultrafiltration membrane.This interfacial polymerization method can be stacked layer-by-layer to regulate the hydrophilicity and pore structure of the membrane.With the increase in the number of polymer layers,the separation and antifouling properties of the membrane gradually improved.Owing to the AIE property of the crosslinking agent TPEDB,the occurrence of interfacial polymerization and the degree of fouling during membrane operation can be monitored by the fluorescence distribution and intensity.With the aggravation of membrane fouling,the fluorescence decreased gradually,but recovered after cleaning.Therefore,this AIE effect can be used for real-time monitoring of interfacial polymerization as well as membrane fouling.
基金Financial support from the National Key Research and Development Program(2022YFB3504000)the National Natural Science Foundation of China(22421003,22478391,22178345)the Youth Innovation Promotion Association CAS(Y2023012,2022045,2023052)。
文摘Membrane fouling is the primary resistance to the continuous production of stirred membrane reactors.This work presents a laser-enhanced high-magnification telecentric imaging system(LEHTIS),which uses a high-magnification telecentric lens and laser-enhanced illumination to invasively capture the motion of particles on the membrane surface or near the membrane.The problems of working distance and particle interference in the stirred membrane reactor are solved to achieve the purpose of in-situ monitoring of membrane fouling.This method is suitable for high flow rates,high solid holdup,and small particle size systems,and the dynamic motion and accumulation of particles are preliminarily analyzed.It shows that the accumulation and desorption of particles on the membrane surface are related to the physical properties of the membrane surface.There is an intermittent rotational movement in the flow field near the membrane,and it tends to stabilize over time.The filtration process can be assessed by monitoring changes in the overall velocity and acceleration of particles near the membrane.The analysis of forces acting on individual particles is compared and validated with the force balance model to correct and accurately apply it to stirred membrane reactors.The development of LEHTIS provides an effective tool for in-situ monitoring of membrane fouling and optimizing the stirred membrane reactors for industrial applications.
文摘Membrane fouling is a persistent challenge in membrane-based technologies,significantly impacting efficiency,operational costs,and system lifespan in applications like water treatment,desalination,and industrial processing.Foul-ing,caused by the accumulation of particulates,organic compounds,and microorganisms,leads to reduced permeability,increased energy demands,and frequent maintenance.Traditional fouling control approaches,relying on empirical models and reactive strategies,often fail to address these issues efficiently.In this context,artificial intelligence(AI)and machine learning(ML)have emerged as innovative tools offering predictive and proactive solutions for fouling man-agement.By utilizing historical and real-time data,AI/ML techniques such as artificial neural networks,support vector machines,and ensemble models enable accurate prediction of fouling onset,identification of fouling mechanisms,and optimization of control measures.This review provides a detailed examination of the integration of AI/ML in membrane fouling prediction and mitigation,discussing advanced algorithms,the role of sensor-based monitoring,and the importance of robust datasets in enhancing predictive accuracy.Case studies highlighting successful AI/ML applications across various membrane processes are presented,demonstrating their transformative potential in improving system performance.Emerging trends,such as hybrid modeling and IoT-enabled smart systems,are explored,alongside a criti-cal analysis of research gaps and opportunities.This review emphasizes AI/ML as a cornerstone for sustainable,cost-effective membrane operations.
基金Project supported by the University Doctorial Research Foundation.Ministry of Education of China(No.20030141022).
文摘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.
基金supported by the National Natural Science Foundation of China (No. 50578024)
文摘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.
基金The National Natural Science Foundation of China (No. 50138020)
文摘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.
基金the Special Funding forShanghai Expo 2010 (No. 07DZ05814)the New CenturyExcellent Talent Scholarship of China (No. NCET-05-0387)the Doctorial Unit Scholarship of China (No.20050247016)
文摘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 ...
基金supported by the China Major Science and Technology Program for Water Pollution Control and Treatment (No. 2012ZX07404-002)
文摘The combined fouling during ultrafiltration（UF） of surface water pretreated to different extents was investigated to disclose the roles of polysaccharides, proteins, and inorganic particles in UF membrane fouling. Both reversible and irreversible fouling decreased with enhanced pretreatment（biologically active carbon（BAC） treatment and sand filtration）. The sand filter effluent fouled the membrane very slowly. The UF membrane removed turbidity to less than 0.1 nephelometric turbidity unit（NTU）, reduced polysaccharides by 25.4%–29.9%, but rejected few proteins. Both polysaccharides and inorganic particles were detected on the fouled membranes, but inorganic particles could be effectively removed by backwashing. The increase of turbidity in the sand filter effluent to 3.05 NTU did not significantly increase the fouling rate, but an increase in the turbidity in the BAC effluent to6.11 NTU increased the fouling rate by more than 100%. The results demonstrated that the polysaccharide, not the protein, constituents of biopolymers were responsible for membrane fouling. Membrane fouling was closely associated with a small fraction of polysaccharides in the feed water. Inorganic particles exacerbated membrane fouling only when the concentration of fouling–inducing polysaccharides in the feed water was relatively high. The combined fouling was largely reversible, and polysaccharides were the predominant substances responsible for irreversible fouling.
基金supported by the Major Science & Technology Projects for Water Pollution Control and Management of China (Nos. 2012ZX07203-002 2015ZX07203-005)
文摘Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration（NF） in this study. The NF performance was optimized, and its fouling characteristics after different operational durations（i.e., 48 and 169 hr） were analyzed to investigate the applicability of nanofiltration for water reuse. The optimum performance was achieved when transmembrane pressure = 12 bar, p H = 4 and flow rate = 8 L/min using a GE membrane. The permeate water quality could satisfy the requirements of water reclamation for different uses and local standards for water reuse in Beijing. Flux decline in the fouling experiments could be divided into a rapid flux decline and a quasi-steady state. The boundary flux theory was used to predict the evolution of permeate flux. The expected operational duration based on the 169-hr experiment was 392.6 hr which is 175% longer than that of the 48-hr one. High molecular weight（MW） protein-like substances were suggested to be the dominant foulants after an extended period based on the MW distribution and the fluorescence characteristics. The analyses of infrared spectra and extracellular polymeric substances revealed that the roles of both humic- and polysaccharide-like substances were diminished, while that of protein-like substances were strengthened in the contribution of membrane fouling with time prolonged. Inorganic salts were found to have marginally influence on membrane fouling. Additionally, alkali washing was more efficient at removing organic foulants in the long term, and a combination of water flushing and alkali washing was appropriate for NF fouling control in municipal sewage treatment.
基金Supported by Science and Technology Key Project of Water Pollution Control and Management(2008ZX07314-003)
文摘[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.
基金financially supported by the Key Research and Development Plan of the Ministry of Science and Technology,China(2019YFD1100104 and 2019YFC1906501)。
文摘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.
基金financially supported by the National Natural Science Foundation of China(No.51638011,No.51678410,No.51878448,No.51578374)National Program on Key Research Project[No.YS2017YFGH000386]+1 种基金Tianjin Science and Technology Plan Project[No.16PTGCCX00070]the support of Tianjin Education Council,the Key of Science and Technology Plan Project(No.2019ZD06)。
文摘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.
基金supported by the Major Science and Technology Program for Water Pollution Control and Treatment of China (No. 2012ZX07205-002)the Tsinghua University Initiative Scientific Research Program (No. 20121087922)the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT1152)
文摘Unlike the role of the membrane in a membrane bioreactor, which is designed to replace a sediment tank, direct sewage membrane filtration（DSMF）, with the goal of concentrating organic matters, is proposed as a pretreatment process in a novel sewage treatment concept. The concept of membrane-based pretreatment is proposed to divide raw sewage into a concentrated part retaining most organics and a filtered part with less pollutant remaining, so that energy recovery and water reuse, respectively, could be realized by post-treatment. A pilot-scale experiment was carried out to verify the feasibility of coagulant/adsorbent addition for membrane fouling control, which has been the main issue during this DSMF process. The results showed that continuous coagulant addition successfully slowed down the increase in filtration resistance, with the resistance maintained below 1.0 × 1013m^（-1） in the first 70 hr before a jump occurred. Furthermore,the adsorbent addition contributed to retarding the occurrence of the filtration resistance jump, achieving simultaneous fouling control and chemical oxygen demand（COD）concentration improvement. The final concentrated COD amounted to 7500 mg/L after 6 days of operation.
基金supported by the National Natural Science Foundation of China(No.51208140)the National Water Pollution Control and Treatment Science and Technology Major Project of China(No.2012ZX07201002)
文摘Three-dimensional fluorescence excitation–emission matrix（EEM） coupled with parallel factor analysis（PARAFAC） was performed for a total of 18 water samples taken from three water sources（two lakes and one wastewater treatment plant（WWTP） secondary effluent）,with the purpose of identifying the major ultrafiltration（UF） membrane foulants in different water sources. Three fluorescent components（C1, C2 and C3） were identified,which represented terrestrially derived humic-like substances（C1）, microbially derived humic-like substances（C2）, and protein-like substances（C3）. The correlations between the different fluorescent components and UF membrane fouling were analyzed. It was shown that for the WWTP secondary effluent, all three components（C1, C2 and C3） made a considerable contribution to the irreversible and total fouling of the UF membrane.However, for the two lakes, only the C3 exhibited a strong correlation with membrane fouling, indicating that the protein-like substances were the major membrane foulants in the lake waters. Significant attachment of C1, C2 and C3 to the UF membrane was also confirmed by mass balance analyses for the WWTP secondary effluent; while the attachment of C1 and C2 was shown to be negligible for the two lakes. The results may provide basic formation for developing suitable fouling control strategies for sustainable UF processes.
基金Projects 200457 supported by the Planning Foundation of Hebei Water Conservancy Bureau in ChinaOP4476 by the Youth Foundation of China Univer- sity of Mining & Technology
文摘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.
基金partially supported by the Beijing Outstanding Talents TrainingScience and Technology Programs of the Beijing Municipal Education Commission(SQKM201710016001)+1 种基金the BUCEA Post Graduate Innovation Projectthe Beijing Advanced Innovation Center for Future Urban Design。
文摘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.
基金supported by the National Key Research and Development Program of China(No.2016YFC0401107)。
文摘The effects of Ca^(2+) on membrane fouling and trace organic compounds(TrOCs)removal in an electric field-assisted microfiltration system were investigated in the presence of Na^(+) alone for comparison.In the electric field,negatively charged bovine serum albumin(BSA)migrated towards the anode far away from the membrane surface,resulting in a 42.9%transmembrane pressure(TMP)reduction in the presence of Na^(+) at 1.5 V.In contrast,because of the stronger charge shielding of Ca^(2+),the electrophoretic migration of BSA was limited and led to a neglectable effect of the electric field(1.5 V)on membrane fouling.However,under 3 V applied voltage,the synergistic effects of electrochemical oxidation and bridging interaction between Ca^(2+) and BSA promoted the formation of denser settleable flocs and a thinner porous cake layer,which alleviated membrane fouling with a 64.5%decrease in TMP and nearly 100%BSA removal.The Tr OCs elimination increased with voltage and reached29.4%–80.4%at 3 V.The electric field could prolong the contact between Tr OCs and strong oxidants generated on the anode,which enhanced the Tr OCs removal.However,a stronger charge shielding ability of Ca^(2+) weakened the electric field force and thus lowered the Tr OCs removal.
