The purpose of this study is to understand the effect and mechanism of preventing membrane fouling, by coagulation pretreatment, in terms of fractional component and molecular weight of natural organic matter （NOM）....The purpose of this study is to understand the effect and mechanism of preventing membrane fouling, by coagulation pretreatment, in terms of fractional component and molecular weight of natural organic matter （NOM）. A relatively higher molecular weight （MW） of hydrophobic compounds was responsible for a rapid decline in the ultrafiltration flux. Coagulation could effectively remove the hydrophobic organics, resulting in the increase of flux. It was found that a lower MW of neutral hydrophilic compounds, which could remove inadequately by coagulation, was responsible for the slow declining flux. The fluxes in the filtration of coagulated water and supernatant water were compared and the results showed that a lower MW of neutral hydrophilic compounds remained in the supernatant water after coagulation could be rejected by a membrane, resulting in fouling. It was also found that the coagulated flocs could absorb neutral hydrophilic compounds effectively. Therefore, with the coagulated flocs formed on the membrane surface, the flux decline could be improved.展开更多
A pilot plant study on a polyvinylchloride hollow fiber ultrafiltration membrane process was conducted for treating surface water. The membrane system was operated in the dead-end filtration mode under different const...A pilot plant study on a polyvinylchloride hollow fiber ultrafiltration membrane process was conducted for treating surface water. The membrane system was operated in the dead-end filtration mode under different constant permeate fluxes. The results show that the optimized operation (transmembrane pressure≤0.1 MPa, filtration time≤30 min) with a hydraulic cleaning (30 s) and a chemical cleaning (30 min, the chemical cleaning was performed after 16 cycles of filtration ) ensures a quite steady flux (1 100 L/(m^2·h·MPa)) and good permeate quality (turbidity<0.1 NTU). A full-scale plant can be suggested to operate with a mixed strategy of constant permeate flux mode (transmembrane pressure≤0.1 MPa) and constant transmembrane pressure mode. When the temperature of raw water becomes below 5 ℃, a constant transmembrane pressure mode should be used; otherwise a constant permeate flux mode (transmembrane pressure≤0.1 MPa) can be operated. In this way, irreversible fouling of ultrafiltration membrane can be minimized to keep a stable flux and make the life of membrane longer.展开更多
A numerical model was established to predict and optimise the chemical cleaning process of Polyvinylidene Fluoride(PVDF)Ultra filtration(UF)membranes with the results from the experiment that applied the Response Surf...A numerical model was established to predict and optimise the chemical cleaning process of Polyvinylidene Fluoride(PVDF)Ultra filtration(UF)membranes with the results from the experiment that applied the Response Surface Method(RSM)and Central Composite Design(CCD).The factors considered in the experimental design were sodium hydroxide(NaOH)concentration,sodium hypochlorite concentration(NaClO),citric acid concentration and cleaning duration.The interactions between the factors were investigated with the numerical model.Humic acid(20 mg·L-1)was used as the model foulant,and chemical enhanced back flush(CEB)was employed to simulate the chemical cleaning process.The concentrations of sodium hydroxide,sodium hypochlorite,citric acid and cleaning duration tested during the experiments were in the range of 0.1%–0.3%,100–300 mg·L-1,1%–3%and 0.5–1.5 h,respectively.Among the variables,the sodium hypochlorite concentration and the cleaning duration showed a positive relationship involving the increased ef ficiency of the chemical cleaning.The chemical cleaning ef ficiency was hardly improved with increasing concentrations of sodium hydroxide.However,the data was sharply decreased when at a low level of sodium hydroxide concentration.In total,54 sets of cleaning schemes with 80%to 100%cleaning ef ficiency were observed with the RSM model after calibration.展开更多
In recent years, membrane ultrafiltration （UF） of surface water for drinking water treatment has become a more attractive technology worldwide as a possible alternative treatment to conventional clarification. To ev...In recent years, membrane ultrafiltration （UF） of surface water for drinking water treatment has become a more attractive technology worldwide as a possible alternative treatment to conventional clarification. To evaluate the performance of ultrafiltration membranes for treatment of surface water in North China, a 48-m^2 low pressure hollow fiber membrane ultrafiltration pilot plant was constructed. Ultrafiltration was operated in cross-flow and with powdered activated carbon （PAC） adsorption. Turbidity was almost completely removed to less than 0.2 NTU （below Chinese standard 1 NTU）. It was found that PAC addition enhanced organic matter removal. The combined process of PAC/UF allowed to 41% removal of CODMn, 46% removal of DOC and 57% decrease in UV254 absorbance. The elimination of particles, from average 12000/ml in the raw water to approximately 15/ml in the permeated, was observed. When PAC concentration was below 30 mg/L, backwashing could recovery the membrane flux with backwash interval/backwashing duration of 1/30.展开更多
The membrane fouling caused by extracellular organic matter (EOM) and algal cells and organic matter removal of two typical cyanobacteria (M.aeruginosa and Pseudoanabaena sp.)during ultrafiltration (UF) process were s...The membrane fouling caused by extracellular organic matter (EOM) and algal cells and organic matter removal of two typical cyanobacteria (M.aeruginosa and Pseudoanabaena sp.)during ultrafiltration (UF) process were studied in this work.The results showed that EOM had a broad molecular weight (Mw) distribution and the irreversible membrane fouling was basically caused by EOM.Moreover,humic acid and microbial metabolites were major components of EOM of two typical cyanobacteria.Since EOM could fill the voids of cake layers formed by the algal cells,EOM and algal cells played synergistic roles in membrane fouling.Fourier transform infrared spectroscopy analysis indicated that the CH2and CH3chemical bonds may play an important role in membrane fouling caused by EOM.Interestingly,the cake layer formed by the algal cells could trap the organic matter produced by algae and alleviate some irreversible membrane fouling.The results also showed that although the cake layer formed by the algal cells cause severe permeate flux decline,it could play a double interception role with UF membrane and increase organic matter removal efficiency.Therefore,when using UF to treat algae-laden water,the balance of membrane fouling and organic matter removal should be considered to meet the needs of practical applications.展开更多
基金Project supported by the Hi-Tech Research and Development Project(863) of China (No. 2002AA601130)the National Science and Technology Research Project (No, 2003BA808A17)
文摘The purpose of this study is to understand the effect and mechanism of preventing membrane fouling, by coagulation pretreatment, in terms of fractional component and molecular weight of natural organic matter （NOM）. A relatively higher molecular weight （MW） of hydrophobic compounds was responsible for a rapid decline in the ultrafiltration flux. Coagulation could effectively remove the hydrophobic organics, resulting in the increase of flux. It was found that a lower MW of neutral hydrophilic compounds, which could remove inadequately by coagulation, was responsible for the slow declining flux. The fluxes in the filtration of coagulated water and supernatant water were compared and the results showed that a lower MW of neutral hydrophilic compounds remained in the supernatant water after coagulation could be rejected by a membrane, resulting in fouling. It was also found that the coagulated flocs could absorb neutral hydrophilic compounds effectively. Therefore, with the coagulated flocs formed on the membrane surface, the flux decline could be improved.
文摘A pilot plant study on a polyvinylchloride hollow fiber ultrafiltration membrane process was conducted for treating surface water. The membrane system was operated in the dead-end filtration mode under different constant permeate fluxes. The results show that the optimized operation (transmembrane pressure≤0.1 MPa, filtration time≤30 min) with a hydraulic cleaning (30 s) and a chemical cleaning (30 min, the chemical cleaning was performed after 16 cycles of filtration ) ensures a quite steady flux (1 100 L/(m^2·h·MPa)) and good permeate quality (turbidity<0.1 NTU). A full-scale plant can be suggested to operate with a mixed strategy of constant permeate flux mode (transmembrane pressure≤0.1 MPa) and constant transmembrane pressure mode. When the temperature of raw water becomes below 5 ℃, a constant transmembrane pressure mode should be used; otherwise a constant permeate flux mode (transmembrane pressure≤0.1 MPa) can be operated. In this way, irreversible fouling of ultrafiltration membrane can be minimized to keep a stable flux and make the life of membrane longer.
基金Supported by State Key Laboratory of Urban Water Resource and Environment(2016DX01)the Fundamental Research Funds for the Central University(NSRIF.2014096)Science and Technology Planning Project of Chancheng District(2013A1044)
文摘A numerical model was established to predict and optimise the chemical cleaning process of Polyvinylidene Fluoride(PVDF)Ultra filtration(UF)membranes with the results from the experiment that applied the Response Surface Method(RSM)and Central Composite Design(CCD).The factors considered in the experimental design were sodium hydroxide(NaOH)concentration,sodium hypochlorite concentration(NaClO),citric acid concentration and cleaning duration.The interactions between the factors were investigated with the numerical model.Humic acid(20 mg·L-1)was used as the model foulant,and chemical enhanced back flush(CEB)was employed to simulate the chemical cleaning process.The concentrations of sodium hydroxide,sodium hypochlorite,citric acid and cleaning duration tested during the experiments were in the range of 0.1%–0.3%,100–300 mg·L-1,1%–3%and 0.5–1.5 h,respectively.Among the variables,the sodium hypochlorite concentration and the cleaning duration showed a positive relationship involving the increased ef ficiency of the chemical cleaning.The chemical cleaning ef ficiency was hardly improved with increasing concentrations of sodium hydroxide.However,the data was sharply decreased when at a low level of sodium hydroxide concentration.In total,54 sets of cleaning schemes with 80%to 100%cleaning ef ficiency were observed with the RSM model after calibration.
基金Project supported by the Hi-Tech Research and Development Program (863) of China (No. 2002AA601140)the Science and Technology Commission of Shanghai Municipality (No. 052312008)the National Eleven Five-Year Scientific and Technical Support Plans (No. 2006BAJ08B06, 2006BAJ08B02).
文摘In recent years, membrane ultrafiltration （UF） of surface water for drinking water treatment has become a more attractive technology worldwide as a possible alternative treatment to conventional clarification. To evaluate the performance of ultrafiltration membranes for treatment of surface water in North China, a 48-m^2 low pressure hollow fiber membrane ultrafiltration pilot plant was constructed. Ultrafiltration was operated in cross-flow and with powdered activated carbon （PAC） adsorption. Turbidity was almost completely removed to less than 0.2 NTU （below Chinese standard 1 NTU）. It was found that PAC addition enhanced organic matter removal. The combined process of PAC/UF allowed to 41% removal of CODMn, 46% removal of DOC and 57% decrease in UV254 absorbance. The elimination of particles, from average 12000/ml in the raw water to approximately 15/ml in the permeated, was observed. When PAC concentration was below 30 mg/L, backwashing could recovery the membrane flux with backwash interval/backwashing duration of 1/30.
基金supported by the National Natural Science Foundation of China(No.51808532)the Key Research and Development Plan of Shandong Province(No.2019GSF110013)+1 种基金the Major Science and Technology Program for Water Pollution Control and Treatment(No.2017ZX07108-002)。
文摘The membrane fouling caused by extracellular organic matter (EOM) and algal cells and organic matter removal of two typical cyanobacteria (M.aeruginosa and Pseudoanabaena sp.)during ultrafiltration (UF) process were studied in this work.The results showed that EOM had a broad molecular weight (Mw) distribution and the irreversible membrane fouling was basically caused by EOM.Moreover,humic acid and microbial metabolites were major components of EOM of two typical cyanobacteria.Since EOM could fill the voids of cake layers formed by the algal cells,EOM and algal cells played synergistic roles in membrane fouling.Fourier transform infrared spectroscopy analysis indicated that the CH2and CH3chemical bonds may play an important role in membrane fouling caused by EOM.Interestingly,the cake layer formed by the algal cells could trap the organic matter produced by algae and alleviate some irreversible membrane fouling.The results also showed that although the cake layer formed by the algal cells cause severe permeate flux decline,it could play a double interception role with UF membrane and increase organic matter removal efficiency.Therefore,when using UF to treat algae-laden water,the balance of membrane fouling and organic matter removal should be considered to meet the needs of practical applications.
