Severe fouling to poly(vinylidene fluoride)(PVDF)membrane is usually caused as filtrating the papermaking wastewater in the ultrafiltration(UF)process.In the paper,fouling behavior and mechanism were investigated,and ...Severe fouling to poly(vinylidene fluoride)(PVDF)membrane is usually caused as filtrating the papermaking wastewater in the ultrafiltration(UF)process.In the paper,fouling behavior and mechanism were investigated,and the low-concentration polyvinyl alcohol(PVA)contained in the sedimentation tank wastewater was found as the main foulant.Consequently,the corresponding cleaning approach was proposed.The experiment and modeling results elaborated that the fouling mode developed from pore blockage to cake layer along with filtration time.Chemical cleaning conditions including the composition and concentration of reagents,cleaning duration and trans-membrane pressure were investigated for their effect on cleaning efficiency.Pure water flux was recovered by over 95% after cleaning the PVDF membrane using the optimal conditions 0.5 wt% NaClO(as oxidant)and 0.1 wt% sodiumdodecyl benzene sulfonate(SDBS,as surfactant)at 0.04MPa for 100 min.In the chemical cleaning method,hypochlorite(ClO−)could first chain-scissor PVA macromolecules to small molecules and SDBS could wrap the fragments in micelles,so that the foulants were removed from the pores and surface of membrane.After eight cycling tests,pure water flux recovery maintained above 95% and the reused membrane was found intact without defects.展开更多
Membrane fouling curtails severely the economical and practical implementation of membrane process. The fundamental principles and mechanisms of membrane fouling as well as factors affecting fouling have been summariz...Membrane fouling curtails severely the economical and practical implementation of membrane process. The fundamental principles and mechanisms of membrane fouling as well as factors affecting fouling have been summarized in this paper. It also has covered three fouling resistance models and four kinds of approaches to improve membrane performance. Membrane cleaning methods are also discussed including physical, chemical, physico\|chemical and biological methods. In the four groups of basic cleaning methods, biological cleaning has considerable advantages and potentials. Extensive research work should be carried out further to explore and develop new ideas and techniques in the field of membrane cleaning and restoration.展开更多
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 ...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.展开更多
In the present study,nano-sized TiO2 /Al2O3 modified PVDF membranes (MM) were fabricated and utilized for anionic polyacrylamide ( APAM) separation. The results showed that,compared with PVDF membrane (OM) ,the contac...In the present study,nano-sized TiO2 /Al2O3 modified PVDF membranes (MM) were fabricated and utilized for anionic polyacrylamide ( APAM) separation. The results showed that,compared with PVDF membrane (OM) ,the contact angle of MM decreases from 83. 64° to 67. 42°,which indicates the increase of the hydrophilicity of MM. The relative flux (RF) decline curve of this ultrafiltration of APAM in water with time shows an obvious two stage properties. The cake filtration models were used to predict the performance of different time over the complete range of filtration times. All the four cake models could simulate this UF process to a certain extent,and the suitability of the two kinds of membranes was: cake filtration > intermediate pore blocking > standard pore blocking > complete pore blocking models. However,they became more and more unsuited to this process with time extending. Surface and cross-sectional morphology of membrane was investigated by SEM to make an advanced certificate of this UF mechanism.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
To improve the hydrophilicity and anti-fouling performance in water treatment,both entrapped method and deposited method were used to modify polyvinylidene fluoride(PVDF)porous membrane with composite Al2O3/TiO2 nano-...To improve the hydrophilicity and anti-fouling performance in water treatment,both entrapped method and deposited method were used to modify polyvinylidene fluoride(PVDF)porous membrane with composite Al2O3/TiO2 nano-particles.Neat PVDF membrane was prepared and its property was also compared with that of the modified membranes.Membrane permeation flux and anti-fouling performance were measured using a membrane cell.The contact angle between water and membrane surface was detected in order to denote the membrane hydrophilicity.Membrane morphology and surface structure were examined by atomic-force microscopy(AFM)and scanning electron microscopy(SEM).Experimental results showed that modified membranes had higher permeation fluxes than that of the neat PVDF membrane.The addition of nano-particles altered membrane surface morphology and increased surface roughness.Due to the hydrophilicity of nano-particles,however,the membrane anti-fouling performance was improved instead of worsened.The entrapped membrane exhibited better anti-fouling performance than the deposited membrane and the neat membrane.展开更多
Under a constant pressure, a pilot-plant test was conducted through the use of anoxic-aerobic membrane bioreactor （AO-MBR）, and this test operated steadily for 251 days. During the experiment, there were a total of ...Under a constant pressure, a pilot-plant test was conducted through the use of anoxic-aerobic membrane bioreactor （AO-MBR）, and this test operated steadily for 251 days. During the experiment, there were a total of four membrane cleaning processes, for the 90th day, the 150th day, the 210th day and the 240th day, respectively （The cleaning cycle was 90 days, 60 days, 60 days and 30 days, respectively）. From the initial 33.26 L/m^2.b dropped to 20.03 L/m^2.h after the fourth membrane cleaning, membrane flux reduced to 60.22% of the initial flux. During the 180 thd-210 thd of the experiment, the powdered activated carbon （PAC）, the segment size of which is 80-100, was put into anoxic reactor. Membrane flux decreased from 16.02 L/m^2·h to 15.29 L/m^2·h, and then rose to 15.65L/m^2·h. The dosing of PAC had a significant effect on the maintenance of a high membrane flux and extending running time. Before several membrane cleanings, a wire of membrane was intercepted from membrane module. It was found that the membrane surface sediments seemed to the inorganic colloid formed by Fe^2＋, Ca^2＋ and biofilm formed by some micro-organisms after the membrane surface pollutants were analyzed preliminarily with scanning electron microscopy （SEM）.展开更多
基金financially supported by the National Natural Science Foundation of China(21921006).
文摘Severe fouling to poly(vinylidene fluoride)(PVDF)membrane is usually caused as filtrating the papermaking wastewater in the ultrafiltration(UF)process.In the paper,fouling behavior and mechanism were investigated,and the low-concentration polyvinyl alcohol(PVA)contained in the sedimentation tank wastewater was found as the main foulant.Consequently,the corresponding cleaning approach was proposed.The experiment and modeling results elaborated that the fouling mode developed from pore blockage to cake layer along with filtration time.Chemical cleaning conditions including the composition and concentration of reagents,cleaning duration and trans-membrane pressure were investigated for their effect on cleaning efficiency.Pure water flux was recovered by over 95% after cleaning the PVDF membrane using the optimal conditions 0.5 wt% NaClO(as oxidant)and 0.1 wt% sodiumdodecyl benzene sulfonate(SDBS,as surfactant)at 0.04MPa for 100 min.In the chemical cleaning method,hypochlorite(ClO−)could first chain-scissor PVA macromolecules to small molecules and SDBS could wrap the fragments in micelles,so that the foulants were removed from the pores and surface of membrane.After eight cycling tests,pure water flux recovery maintained above 95% and the reused membrane was found intact without defects.
文摘Membrane fouling curtails severely the economical and practical implementation of membrane process. The fundamental principles and mechanisms of membrane fouling as well as factors affecting fouling have been summarized in this paper. It also has covered three fouling resistance models and four kinds of approaches to improve membrane performance. Membrane cleaning methods are also discussed including physical, chemical, physico\|chemical and biological methods. In the four groups of basic cleaning methods, biological cleaning has considerable advantages and potentials. Extensive research work should be carried out further to explore and develop new ideas and techniques in the field of membrane cleaning and restoration.
基金Supported by the National Natural Science Foundation of China(2160060639)the Natural Science Foundation of Jiangsu Province(BK20160984)the Scientific Research Foundation for Returned Overseas Chinese Scholars,State Education Ministry(ZX15511310002)
文摘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.
基金Sponsored by the National Natural Science Foundation of China (Grant No.50978068)International Cooperation Program (Grant No.2010DFA92460)+1 种基金National High Technology Research and Development Program of China (863 Program,Grant No.2008AA06Z304)Tianjin Key Laboratory of Aquatic Science and Technology
文摘In the present study,nano-sized TiO2 /Al2O3 modified PVDF membranes (MM) were fabricated and utilized for anionic polyacrylamide ( APAM) separation. The results showed that,compared with PVDF membrane (OM) ,the contact angle of MM decreases from 83. 64° to 67. 42°,which indicates the increase of the hydrophilicity of MM. The relative flux (RF) decline curve of this ultrafiltration of APAM in water with time shows an obvious two stage properties. The cake filtration models were used to predict the performance of different time over the complete range of filtration times. All the four cake models could simulate this UF process to a certain extent,and the suitability of the two kinds of membranes was: cake filtration > intermediate pore blocking > standard pore blocking > complete pore blocking models. However,they became more and more unsuited to this process with time extending. Surface and cross-sectional morphology of membrane was investigated by SEM to make an advanced certificate of this UF mechanism.
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Sponsored by the National High Technology Research and Development Program of China(863 Program)(Grant No.2006AA06Z303)the National Natural Science Foundation of China(Grant No.50778050)+2 种基金the Key Projects in the National Science & Technology Pillar Program in the Eleventh Five-year Plan Period(Grant No.2006BAJ08B09)the National Creative Research Groups(Grant No.50821002)the Key Scientific and Technological Project of Heilongjiang Province(Grant No.GB06C20403)
文摘To improve the hydrophilicity and anti-fouling performance in water treatment,both entrapped method and deposited method were used to modify polyvinylidene fluoride(PVDF)porous membrane with composite Al2O3/TiO2 nano-particles.Neat PVDF membrane was prepared and its property was also compared with that of the modified membranes.Membrane permeation flux and anti-fouling performance were measured using a membrane cell.The contact angle between water and membrane surface was detected in order to denote the membrane hydrophilicity.Membrane morphology and surface structure were examined by atomic-force microscopy(AFM)and scanning electron microscopy(SEM).Experimental results showed that modified membranes had higher permeation fluxes than that of the neat PVDF membrane.The addition of nano-particles altered membrane surface morphology and increased surface roughness.Due to the hydrophilicity of nano-particles,however,the membrane anti-fouling performance was improved instead of worsened.The entrapped membrane exhibited better anti-fouling performance than the deposited membrane and the neat membrane.
文摘Under a constant pressure, a pilot-plant test was conducted through the use of anoxic-aerobic membrane bioreactor （AO-MBR）, and this test operated steadily for 251 days. During the experiment, there were a total of four membrane cleaning processes, for the 90th day, the 150th day, the 210th day and the 240th day, respectively （The cleaning cycle was 90 days, 60 days, 60 days and 30 days, respectively）. From the initial 33.26 L/m^2.b dropped to 20.03 L/m^2.h after the fourth membrane cleaning, membrane flux reduced to 60.22% of the initial flux. During the 180 thd-210 thd of the experiment, the powdered activated carbon （PAC）, the segment size of which is 80-100, was put into anoxic reactor. Membrane flux decreased from 16.02 L/m^2·h to 15.29 L/m^2·h, and then rose to 15.65L/m^2·h. The dosing of PAC had a significant effect on the maintenance of a high membrane flux and extending running time. Before several membrane cleanings, a wire of membrane was intercepted from membrane module. It was found that the membrane surface sediments seemed to the inorganic colloid formed by Fe^2＋, Ca^2＋ and biofilm formed by some micro-organisms after the membrane surface pollutants were analyzed preliminarily with scanning electron microscopy （SEM）.
