Submerged membrane bioreactors （SMBR） are widely used in wastewater treatment. The permeability of a membrane declines rapidly because of the formation of a cake layer on the membrane surface. In this paper, a multi...Submerged membrane bioreactors （SMBR） are widely used in wastewater treatment. The permeability of a membrane declines rapidly because of the formation of a cake layer on the membrane surface. In this paper, a multiple staining protocol was conducted to probe the four major foulants in the cake layer formed on a filtration membrane. Fluorescent images of the foulants were obtained using a confocal laser scanning microscope （CLSM）. The three dimensional structure of the cake layer was reconstructed, and the internal flow was calculated using computational fluid dynamics （CFD）. Simulation results agreed well with the experimental data on the permeability of the cake layer during filtration and showed better accuracy than the calculation by Kozeny-Carman method. B-D-Glucopyranose polysaccharides and proteins are the two main foulants with relatively large volume fractions, while a-D-glucopyranose polysaccharides and nucleic acids have relatively large specific surface areas. The fast growth of B-D-glucopyranose polysaccharides in the volume fraction is mainly responsible for the increase in cake volume fraction and the decrease in permeability. The specific area, or the aggregation/dispersion of foulants, is less important to its permeability compared to its volume fraction.展开更多
A cake layer is formed by coagulation aggregates under certain transmembrane pressure in the coagulation-microfiltration （MF） process. The characteristics of humic acid aggregates coagulated by different iron-based ...A cake layer is formed by coagulation aggregates under certain transmembrane pressure in the coagulation-microfiltration （MF） process. The characteristics of humic acid aggregates coagulated by different iron-based coagulants, such as charge, size, fractal dimension and compressibility, have an effect on the cake layer structure. At the optimum iron dose of 0.6 to 0.8 mmol/L for ferric chloride （FC） and polymer ferric sulfate （PFS） pre-coagulation, at the point of charge neutralization for near zero zeta potential, the aggregate particles produced possess the greatest size and highest fractal dimension, which contributes to the cake layer being most loose with high porosity and low compressibility. Thus the membrane filterability is better. At a low or high iron dose of FC and PFS, a high negative or positive zeta potential with high charge repulsion results in so many small aggregate particles and low fractal dimension that the cake layer is compact with low porosity and high compressibility. Therefore the membrane fouling is accelerated and MF permeability becomes worse. The variation of cake layer structure as measured by scanning electric microscopy corresponds with the fact that the smaller the coagulation flocs size and fractal dimension are, the lower the porosity and the tighter the cake layer conformation. This also explains the MF membrane flux variation visually and accurately.展开更多
To explore the effect of different additive combinations on double-low rapeseed cake （meal） utilization and layer production performance, we randomly divided 756 Roman brown shell layers around 50 weeks age into sev...To explore the effect of different additive combinations on double-low rapeseed cake （meal） utilization and layer production performance, we randomly divided 756 Roman brown shell layers around 50 weeks age into seven groups to detect production performance, of which group 1 was control group supplied with basic diet （added with 9% double-low rapeseed cake）, while groups 2 -7 were experimental groups added with Chinese herbal medicine, enzyme preparation, pro- biotics and peptide antibiotics in basic diet. The results showed that group 4 added with Chinese herbal medicine ＋ enzyme preparation ＋ peptide antibiotics re- ceived the best effect, resulting in significantly increased laying rate （70.50%, P 〈 0.05 ）, significantly reduced feed-egg ratio （2.46, P 〈 0.05 ）, and extremely increased egg Haugh unit （P 〈0.01 ）. This indicated that adding combination of Chinese herbal medicine ＋ enzyme preparation ＋ peptide antibiotics in layer bas- ic diet could improve egg production performance and egg quality of layers.展开更多
Microfiltration membrane technology has been widely used in various industries for solid-liquid separation. However, pore clogging remains a persistent challenge. This study employs (CFD) and discrete element method (...Microfiltration membrane technology has been widely used in various industries for solid-liquid separation. However, pore clogging remains a persistent challenge. This study employs (CFD) and discrete element method (DEM) models to enhance our understanding of microfiltration membrane clogging. The models were validated by comparing them to experimental data, demonstrating reasonable consistency. Subsequently, a parametric study was conducted on a cross-flow model, exploring the influence of key parameters on clogging. Findings show that clogging is a complex phenomenon affected by various factors. The mean inlet velocity and transmembrane flux were found to directly impact clogging, while the confinement ratio and cosine of the membrane pore entrance angle had an inverse relationship with it. Two clog types were identified: internal (inside the pore) and external (arching at the pore entrance), with the confinement ratio determining the type. This study introduced a dimensionless number as a quantitative clogging indicator based on transmembrane flux, Reynolds number, filtration time, entrance angle cosine, and confinement ratio. While this hypothesis held true in simulations, future studies should explore variations in clogging indicators, and improved modeling of clogging characteristics. Calibration between numerical and physical times and consideration of particle volume fraction will enhance understanding.展开更多
A dielectric analysis model for the fouling layer on the polyethersulfone composite ultrafiltration （UF） membrane and solution system, which consists of the solution, concentration polarization layer （CPL）, and ca...A dielectric analysis model for the fouling layer on the polyethersulfone composite ultrafiltration （UF） membrane and solution system, which consists of the solution, concentration polarization layer （CPL）, and cake layer, was established by virtue of the interfacial polarization and the electrostatic field theory. The effect of some important parameters, such as the depth, conductivity of CPL, and cake layer, on the dielectric spectroscopy （or dielectric relaxation properties） of the UF system was discussed by the parameter sensitivity analysis and the dielectric measurement. The simulations indicate that the CPL can be created rapidly and the cake layer formation is the dynamic balance process of growth and erosion in the process of UF. The key factor affecting on the dielectric spectrum of UF system is the electrical properties of the CPL and the cake layer. In comparison to the results of dielectric measurement, the simulations indicate that the model proposed in this work is valid and reliable to some degree for describing and explaining the dielectric relaxation phenomenon in UF system. It is very important to further understand the fouling behavior of membrane surface and optimize the controlling techniques of membrane fouling in the process of UF.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51176090 and 51321002)
文摘Submerged membrane bioreactors （SMBR） are widely used in wastewater treatment. The permeability of a membrane declines rapidly because of the formation of a cake layer on the membrane surface. In this paper, a multiple staining protocol was conducted to probe the four major foulants in the cake layer formed on a filtration membrane. Fluorescent images of the foulants were obtained using a confocal laser scanning microscope （CLSM）. The three dimensional structure of the cake layer was reconstructed, and the internal flow was calculated using computational fluid dynamics （CFD）. Simulation results agreed well with the experimental data on the permeability of the cake layer during filtration and showed better accuracy than the calculation by Kozeny-Carman method. B-D-Glucopyranose polysaccharides and proteins are the two main foulants with relatively large volume fractions, while a-D-glucopyranose polysaccharides and nucleic acids have relatively large specific surface areas. The fast growth of B-D-glucopyranose polysaccharides in the volume fraction is mainly responsible for the increase in cake volume fraction and the decrease in permeability. The specific area, or the aggregation/dispersion of foulants, is less important to its permeability compared to its volume fraction.
基金supported by the National Natural Science Foundation of China (No.50978014)the Fundamental Research Funds for the Central Universities (No.2011JBM077)
文摘A cake layer is formed by coagulation aggregates under certain transmembrane pressure in the coagulation-microfiltration （MF） process. The characteristics of humic acid aggregates coagulated by different iron-based coagulants, such as charge, size, fractal dimension and compressibility, have an effect on the cake layer structure. At the optimum iron dose of 0.6 to 0.8 mmol/L for ferric chloride （FC） and polymer ferric sulfate （PFS） pre-coagulation, at the point of charge neutralization for near zero zeta potential, the aggregate particles produced possess the greatest size and highest fractal dimension, which contributes to the cake layer being most loose with high porosity and low compressibility. Thus the membrane filterability is better. At a low or high iron dose of FC and PFS, a high negative or positive zeta potential with high charge repulsion results in so many small aggregate particles and low fractal dimension that the cake layer is compact with low porosity and high compressibility. Therefore the membrane fouling is accelerated and MF permeability becomes worse. The variation of cake layer structure as measured by scanning electric microscopy corresponds with the fact that the smaller the coagulation flocs size and fractal dimension are, the lower the porosity and the tighter the cake layer conformation. This also explains the MF membrane flux variation visually and accurately.
基金Supported by Core Pure Population Breeding and Industry Demonstration Base Construction of Changshun Green-shell Layer(QNYZ[2011]027)Association Study of PRL Gene and PRLR Gene Polymorphisms of Changshun Greenshell Layer with Egg Production Traits(QKHJ[2011]2174)
文摘To explore the effect of different additive combinations on double-low rapeseed cake （meal） utilization and layer production performance, we randomly divided 756 Roman brown shell layers around 50 weeks age into seven groups to detect production performance, of which group 1 was control group supplied with basic diet （added with 9% double-low rapeseed cake）, while groups 2 -7 were experimental groups added with Chinese herbal medicine, enzyme preparation, pro- biotics and peptide antibiotics in basic diet. The results showed that group 4 added with Chinese herbal medicine ＋ enzyme preparation ＋ peptide antibiotics re- ceived the best effect, resulting in significantly increased laying rate （70.50%, P 〈 0.05 ）, significantly reduced feed-egg ratio （2.46, P 〈 0.05 ）, and extremely increased egg Haugh unit （P 〈0.01 ）. This indicated that adding combination of Chinese herbal medicine ＋ enzyme preparation ＋ peptide antibiotics in layer bas- ic diet could improve egg production performance and egg quality of layers.
文摘Microfiltration membrane technology has been widely used in various industries for solid-liquid separation. However, pore clogging remains a persistent challenge. This study employs (CFD) and discrete element method (DEM) models to enhance our understanding of microfiltration membrane clogging. The models were validated by comparing them to experimental data, demonstrating reasonable consistency. Subsequently, a parametric study was conducted on a cross-flow model, exploring the influence of key parameters on clogging. Findings show that clogging is a complex phenomenon affected by various factors. The mean inlet velocity and transmembrane flux were found to directly impact clogging, while the confinement ratio and cosine of the membrane pore entrance angle had an inverse relationship with it. Two clog types were identified: internal (inside the pore) and external (arching at the pore entrance), with the confinement ratio determining the type. This study introduced a dimensionless number as a quantitative clogging indicator based on transmembrane flux, Reynolds number, filtration time, entrance angle cosine, and confinement ratio. While this hypothesis held true in simulations, future studies should explore variations in clogging indicators, and improved modeling of clogging characteristics. Calibration between numerical and physical times and consideration of particle volume fraction will enhance understanding.
基金This work was supported by the Natural Science Foundation of Shandong Province of China （No.Q2007B01）.
文摘A dielectric analysis model for the fouling layer on the polyethersulfone composite ultrafiltration （UF） membrane and solution system, which consists of the solution, concentration polarization layer （CPL）, and cake layer, was established by virtue of the interfacial polarization and the electrostatic field theory. The effect of some important parameters, such as the depth, conductivity of CPL, and cake layer, on the dielectric spectroscopy （or dielectric relaxation properties） of the UF system was discussed by the parameter sensitivity analysis and the dielectric measurement. The simulations indicate that the CPL can be created rapidly and the cake layer formation is the dynamic balance process of growth and erosion in the process of UF. The key factor affecting on the dielectric spectrum of UF system is the electrical properties of the CPL and the cake layer. In comparison to the results of dielectric measurement, the simulations indicate that the model proposed in this work is valid and reliable to some degree for describing and explaining the dielectric relaxation phenomenon in UF system. It is very important to further understand the fouling behavior of membrane surface and optimize the controlling techniques of membrane fouling in the process of UF.
