Flocculation flotation is the most efficient method for recovering fine-grained minerals,and its essence lies in flotation and recovery of flocs.Fundamental physical characteristics of flocs are mainly determined by t...Flocculation flotation is the most efficient method for recovering fine-grained minerals,and its essence lies in flotation and recovery of flocs.Fundamental physical characteristics of flocs are mainly determined by their apparent particle size and structure(density and morphology).Substantial researches have been conducted regarding the effect of floc characteristics on particle settling and water treatment.However,the influence of floc characteristics on flotation has not been widely studied.Based on the floc formation and flocculation flotation,this study reviews the fundamental physical characteristics of flocs from the perspectives of floc particle size and structure,summarizing the interaction between floc particle size and structure.Moreover,it thoroughly discusses the effect of floc particle size and structure on floc floatability,further revealing the influence of floc characteristics on bubble collision and adhesion and elucidating the mechanisms of interaction between flocs and bubbles.Thus,it is observed that floc particle size is not the only factor influencing flocculation flotation.Within the appropriate apparent particle size range,flocs with a compact structure exhibit higher efficiency in bubble collision and adhesion during flotation,thereby resulting in enhanced flotation performance.This study aims to provide a reference for flocculation flotation,targeting the development of more efficient and refined flocculation flotation processes in the future.展开更多
Natural water bodies mostly contain cations,and the type and content of these cations are the main factors affecting the flocculation of fine-grained cohesive sediments and the floc sedimentation rate at the interface...Natural water bodies mostly contain cations,and the type and content of these cations are the main factors affecting the flocculation of fine-grained cohesive sediments and the floc sedimentation rate at the interface between clear and turbid water.From the microscopic aspect,this study examined the changing patterns of porosity and the fractal dimension of the flocs of fine-grained cohesive sediments.Sedimentation experiments under different sediment contents and electrolyte conditions were conducted,and microscopic images of the flocs were analysed using Image-Pro Plus(IPP)and MATLAB based on the fractal theory.From the macroscopic aspect,this study experimentally investigated the flocculation and sedimentation of fine-grained cohesive sediments and proposed a sedimentation rate equation by introducing an ion concentration-related parameter into an existing sedimentation rate equation(stagnation zone)based on the adsorption isotherm equation.The equation proposed in this study was validated with measured data.The calculated values were in good agreement with the measured values,with a relative error of 16%.The findings of this study provide a reference for further research on the flocculation and sedimentation of fine-grained cohesive sediments in different water bodies.展开更多
Enzymes play essential roles in the biological processes of sludge treatment. In this article, the ultrasound method to extract enzymes from sludge flocs was presented. Results showed that using ultrasound method at 2...Enzymes play essential roles in the biological processes of sludge treatment. In this article, the ultrasound method to extract enzymes from sludge flocs was presented. Results showed that using ultrasound method at 20 kHz could extract more types of enzymes than that at 40 kHz and ethylenediamine tetraacetic acid （EDTA） methods. The optimum parameters of ultrasound extraction at 20 kHz were duration of 10 min and intensity of 552 W/g TSS. Under the optimum condition, ultrasound could break the cells and extract both the extracellular and a small part of intercellular enzymes. Ultrasound intensity was apparently more susceptive to enzyme extraction than duration, suggesting that the control of intensity during ultrasound extraction was more important than that of duration. The Pearson correlation analysis between enzyme activities and cation contents revealed that the different types of enzymes had distinct cation binding characteristics.展开更多
In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters （EMCM） and Laser In Situ Scattering and Transmissometry （LISST-ST） have been deployed withi...In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters （EMCM） and Laser In Situ Scattering and Transmissometry （LISST-ST） have been deployed within a Spartina alterniflora marsh of the Luoyuan Bay in Fujian Province, China, to measure the current velocity, the floc size and the settling velocity between 15 and 22 January 2008. During the observations, the near-bed water was collected in order to obtain the suspended sediment concentration （SSC） and constituent grain size. Data show that： （1） the nearbed current velocities vary from 0.1 to 5.6 cm/s in the central Spartina alterniflora marsh and 0.1–12.5 cm/s at the edge; （2） the SSCs vary from 47 to 188 mg/dm 3 . The mean grain size of constituent grains varies from 7.0 to 9.6 μm, and the mean floc sizes （MFS） vary from 30.4 to 69.4 μm. The relationship between the mean floc size and settling velocity can be described as： w s =ad b , in which w s is the floc settling velocity （mm/s）, a and b are coefficients. The floc settling velocity varies from 0.17 to 0.32 mm/s, with a mean value of 0.26 mm/s, and the floc settling velocity during the flood tide is higher than that during the ebb tide. The current velocity and the SSC are the main factors controlling the flocculation processes and the floc settling velocity.展开更多
The fractal dimensions in different topological spaces of polyferric chloride-humic acid （PFC-HA） flocs, formed in flocculating different kinds of humic acids （HA） water at different initial pH （9.0, 7.0, 5.0） a...The fractal dimensions in different topological spaces of polyferric chloride-humic acid （PFC-HA） flocs, formed in flocculating different kinds of humic acids （HA） water at different initial pH （9.0, 7.0, 5.0） and PFC dosages, were calculated by effective densitymaximum diameter, image analysis, and N2 absorption-desorption methods, respectively. The mass fractal dimensions （De） of PFC-HA floes were calculated by bi-logarithm relation of effective density with maximum diameter and Logan empirical equation. The Df value was more than 2.0 at initial pH of 7,0, which was 11% and 13% higher than those at pH 9.0 and 5.0, respecively, indicating the most compact flocs formed in flocculated HA water at initial pH of 7.0. The image analysis for those flocs indicates that after flocculating the HA water at initial pH greater than 7.0 with PFC flocculant, the fractal dimensions of D2 （logA vs. logdL） and D3 （logVsphere vs. logdL） of PFC-HA floes decreased with the increase of PFC dosages, and PFC-HA floes showed a gradually looser structure. At the optimum dosage of PFC, the D2 （logA vs. logdL） values of the flocs show 14%-43% difference with their corresponding Dr, and they even had different tendency with the change of initial pH values. However, the D2 values of the floes formed at three different initial pH in HA solution had a same tendency with the corresponding Df. Based on fractal Frenkel-Halsey-HiU （FHH） adsorption and desorption equations, the pore surface fractal dimensions （Ds） for dried powders of PFC-HA flocs formed in HA water with initial pH 9.0 and 7.0 were all close to 2.9421, and the Ds values of flocs formed at initial pH 5.0 were less than 2.3746. It indicated that the pore surface fractal dimensions of PFC-HA floes dried powder mainly show the irregularity from the mesopore-size distribution and marcopore-size distribution.展开更多
Based on the test data in dynamic water and static water, the main factors, which influence the fine sediment flocculation, are analyzed with a gray model method of correlation theory. It is shown that the main influe...Based on the test data in dynamic water and static water, the main factors, which influence the fine sediment flocculation, are analyzed with a gray model method of correlation theory. It is shown that the main influencing factors are water temperature, settling time, salinity, grain size, sediment concentration and current velocity according to the correlation coefficients. Among them, the salinity and the sediment grain size are critical type influencing factors (CrTIF); the settling time, the sediment concentration and the velocity are continuous type influencing factors (CoTIF); and the water temperature has the characteristics of both. When the critical values of CrTIF are reached or exceeded, the fine sediments will be flocculated, but values of CrTIF will not influence the settlement strength of floes. The influence of CoTIF is continuous. The values of the CoTIF will not only influence the occurrence of flocculation but also the settlement strength of the floes.展开更多
This study investigated the floc aggregation, average floc size, floc size variance and floc growth velocity when ferric chloride （FeCl3） and polyferric chloride （PFC） were used to treat the simulated water sample...This study investigated the floc aggregation, average floc size, floc size variance and floc growth velocity when ferric chloride （FeCl3） and polyferric chloride （PFC） were used to treat the simulated water samples. The factors including coagulant dose, ionic strength and solution pH, which affect the floc aggregation, were studied. Experiments were carried out in a bench-scale reactor using photometric dispersion analyzer （ PDA）. Results showed that there were great differences between the floc aggregation of PFC and FeCl3. The average floc size and fioc growth velocity of PFC were much larger than those of FeCl3. Compared with FeCl3, PFC gave a better coagulation performance in wider range of pH, dosage and ionic strength. It was also found that the coagulation efficiency of PFC did not depend on average floc size but on floc growth velocity.展开更多
A series of laboratory investigations are conducted to analyze the effect of flocculant type on the spatial morphology and microstructural characteristics of flocs during the flocculation and settling of tailings.Four...A series of laboratory investigations are conducted to analyze the effect of flocculant type on the spatial morphology and microstructural characteristics of flocs during the flocculation and settling of tailings.Four flocculant types(i.e.,ZYZ,JYC-2,ZYD,and JYC-1)are considered in this study.The fractal characteristics and internal structures of tailings flocs with different flocculant types and settlement heights are analyzed by conducting scanning electron microscopy and X-ray micro-computed tomography scanning experiments based on the fractal theory.Results show that unclassified tailings flocs are irregular clusters with fractal characteristics,and the flocculation effect of the four flocculant types has the following trend:ZYZ>JYC-2>ZYD>JYC-1.The size and average grayscale value of tailings flocs decrease with the increase in settlement height.The average grayscale values at the top and bottom are 144 and 103,respectively.The settlement height remarkably affects the pore distribution pattern,as reflected in the constructed three-dimensional pore model of tailings flocs.The top part of flocs has relatively good penetration,whereas the bottom part of flocs has mostly dispersed pores.The number of pores increases exponentially with the increase in settlement height.By contrast,the size of pores initially increases and subsequently decreases with the increase in settlement height.展开更多
Efficient thickening of tailings is a prerequisite for the metal mine tailings backfill and surface disposal operation.The effective collision of ultrafine tailings particles in suspension with flocculant molecules is...Efficient thickening of tailings is a prerequisite for the metal mine tailings backfill and surface disposal operation.The effective collision of ultrafine tailings particles in suspension with flocculant molecules is essential for flocs aggregates formation and settling.Unreasonable feeding speed and flocculant adding method will lead to the failure of effective dispersion of flocculant and high particle content in thickener overflow.In this work,the effect of turbulence intensity and flocculant adding method on floc size,strength,and movement characteristics are analysed.Aiming to solve the turbidity increased,a pilot-scale continuous thickening test was carried out.Taking a single particle and multiple flocs of full tailings as the research object,the particle iterative settlement model of flocs was established.The influence of turbulence intensity on collision effect is studied by tracking and simulating particle trajectory.The results show that in the process of single particle settlement,chaos appears in the iterative process owing to particle adhesion which caused by micro action.When the turbulence intensity is 25.99%,the maximum particle size of tailings floc is 6.21 mm and the maximum sedimentation rate is 5.284 cm·s^(−1).The tailings floc presents a multi-scale structure of particle-force chain system when hindered settling,and the interweaving of strong and weak force chains constitutes the topological structure of particles.The results are applied to a thicker in plant,the flocculant addition mode and feed rate are optimized,and the flocs settling speed and overflow clarity are improved.展开更多
This study was conducted to evaluate the ef fect of replacing soybean meal(SBM) by low protein ?oc meal(LPFM; 24% CP) in tilapia diets on growth performance, feed utilization and ?sh chemical composition. Three isonit...This study was conducted to evaluate the ef fect of replacing soybean meal(SBM) by low protein ?oc meal(LPFM; 24% CP) in tilapia diets on growth performance, feed utilization and ?sh chemical composition. Three isonitrogenous and isocaloric diets were formulated; control diet(C; without LPFM),FM 25(25% of SBM protein was substituted by LPFM) and FM 50(50% of SBM protein was substituted by LPFM). Nine 55 l circular plastic tanks were stocked by 12 ?sh to form three experimental groups.No dif ferences in tilapia performance were observed between the control and the FM 25 diet. Chemical composition of ?sh did not dif fer signi?cantly among treatments except for protein and selenium contents where the highest values were recorded in the control treatment. The highest mineral content was recorded in ?oc collected from the control tanks, while calcium content showed its highest value in ?oc collected from FM 50 e ? uent. These data indicate that replacing soybean meal with LPFM up to 25%, had no negative ef fect on growth performance and potentially may improve the system sustainability. Meanwhile, the adverse ef fect of more inclusion of LPFM in tilapia diet may be attributed to the higher content of ash. In other word,minerals seem to cause more energy utilization in ?sh fed ?oc meal since it is needed to maintain osmotic homeostasis.展开更多
The study on the criteria used to distinguish floc sedimentation and gel-like network sedimentation of cohesive fine-grained sediment in a turbulent flow has rarely been carried out. In this preliminary study, we deri...The study on the criteria used to distinguish floc sedimentation and gel-like network sedimentation of cohesive fine-grained sediment in a turbulent flow has rarely been carried out. In this preliminary study, we derive three criteria to distinguish these two different sedimentation phases by considering the comparison of the time that a characteristic floc takes to settle through mean distance between characteristic flocs and the time that it takes to move through the same distance under the influence of a turbulent flow. These criteria incorporate physical and chemical factors that have been verified to have some influences on the sediment flocculation in some published literatures, and a simple analysis result is found to be consistent with our qualitative understandings of flocculation phenomenon of cohesive fine-grained sediment.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52174239 and 52204284)。
文摘Flocculation flotation is the most efficient method for recovering fine-grained minerals,and its essence lies in flotation and recovery of flocs.Fundamental physical characteristics of flocs are mainly determined by their apparent particle size and structure(density and morphology).Substantial researches have been conducted regarding the effect of floc characteristics on particle settling and water treatment.However,the influence of floc characteristics on flotation has not been widely studied.Based on the floc formation and flocculation flotation,this study reviews the fundamental physical characteristics of flocs from the perspectives of floc particle size and structure,summarizing the interaction between floc particle size and structure.Moreover,it thoroughly discusses the effect of floc particle size and structure on floc floatability,further revealing the influence of floc characteristics on bubble collision and adhesion and elucidating the mechanisms of interaction between flocs and bubbles.Thus,it is observed that floc particle size is not the only factor influencing flocculation flotation.Within the appropriate apparent particle size range,flocs with a compact structure exhibit higher efficiency in bubble collision and adhesion during flotation,thereby resulting in enhanced flotation performance.This study aims to provide a reference for flocculation flotation,targeting the development of more efficient and refined flocculation flotation processes in the future.
基金funded by The Nature Foundation of Inner Mongolia Autonomous Region 2021MS05042The National Natural Science Foundation of China project 51969021,52169016The Major Science and Technology Projects of Inner Mongolia Autonomous Region 2021ZD0008.
文摘Natural water bodies mostly contain cations,and the type and content of these cations are the main factors affecting the flocculation of fine-grained cohesive sediments and the floc sedimentation rate at the interface between clear and turbid water.From the microscopic aspect,this study examined the changing patterns of porosity and the fractal dimension of the flocs of fine-grained cohesive sediments.Sedimentation experiments under different sediment contents and electrolyte conditions were conducted,and microscopic images of the flocs were analysed using Image-Pro Plus(IPP)and MATLAB based on the fractal theory.From the macroscopic aspect,this study experimentally investigated the flocculation and sedimentation of fine-grained cohesive sediments and proposed a sedimentation rate equation by introducing an ion concentration-related parameter into an existing sedimentation rate equation(stagnation zone)based on the adsorption isotherm equation.The equation proposed in this study was validated with measured data.The calculated values were in good agreement with the measured values,with a relative error of 16%.The findings of this study provide a reference for further research on the flocculation and sedimentation of fine-grained cohesive sediments in different water bodies.
基金supported by the Hi-Tech Research and Development Program (863) of China (No.2006AA06Z384).
文摘Enzymes play essential roles in the biological processes of sludge treatment. In this article, the ultrasound method to extract enzymes from sludge flocs was presented. Results showed that using ultrasound method at 20 kHz could extract more types of enzymes than that at 40 kHz and ethylenediamine tetraacetic acid （EDTA） methods. The optimum parameters of ultrasound extraction at 20 kHz were duration of 10 min and intensity of 552 W/g TSS. Under the optimum condition, ultrasound could break the cells and extract both the extracellular and a small part of intercellular enzymes. Ultrasound intensity was apparently more susceptive to enzyme extraction than duration, suggesting that the control of intensity during ultrasound extraction was more important than that of duration. The Pearson correlation analysis between enzyme activities and cation contents revealed that the different types of enzymes had distinct cation binding characteristics.
基金The National Natural Science Foundation of China under contract No. 40606012the Scientific Research Foundation of Third Institute of Oceanography, State Oceanic Administration under contract No. 2009015
文摘In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters （EMCM） and Laser In Situ Scattering and Transmissometry （LISST-ST） have been deployed within a Spartina alterniflora marsh of the Luoyuan Bay in Fujian Province, China, to measure the current velocity, the floc size and the settling velocity between 15 and 22 January 2008. During the observations, the near-bed water was collected in order to obtain the suspended sediment concentration （SSC） and constituent grain size. Data show that： （1） the nearbed current velocities vary from 0.1 to 5.6 cm/s in the central Spartina alterniflora marsh and 0.1–12.5 cm/s at the edge; （2） the SSCs vary from 47 to 188 mg/dm 3 . The mean grain size of constituent grains varies from 7.0 to 9.6 μm, and the mean floc sizes （MFS） vary from 30.4 to 69.4 μm. The relationship between the mean floc size and settling velocity can be described as： w s =ad b , in which w s is the floc settling velocity （mm/s）, a and b are coefficients. The floc settling velocity varies from 0.17 to 0.32 mm/s, with a mean value of 0.26 mm/s, and the floc settling velocity during the flood tide is higher than that during the ebb tide. The current velocity and the SSC are the main factors controlling the flocculation processes and the floc settling velocity.
基金supported by the National Natural Science Foundation of China (No. 20407004, 50578012, 50178009)the High-Tech Research and Development Program (863) of China (No. 2007AA06Z301)+2 种基金the Fok Ying Tung Education Foundation of National Education Ministry of China (No. 91078)the Beijing Municipal Commission of Education Project, Program for New Cen- tury Excellent Talents in University (No. NCET-06-0120)the Beijing Nova of Science and Technology, Beijing Key Subject (No. XK100220555).
文摘The fractal dimensions in different topological spaces of polyferric chloride-humic acid （PFC-HA） flocs, formed in flocculating different kinds of humic acids （HA） water at different initial pH （9.0, 7.0, 5.0） and PFC dosages, were calculated by effective densitymaximum diameter, image analysis, and N2 absorption-desorption methods, respectively. The mass fractal dimensions （De） of PFC-HA floes were calculated by bi-logarithm relation of effective density with maximum diameter and Logan empirical equation. The Df value was more than 2.0 at initial pH of 7,0, which was 11% and 13% higher than those at pH 9.0 and 5.0, respecively, indicating the most compact flocs formed in flocculated HA water at initial pH of 7.0. The image analysis for those flocs indicates that after flocculating the HA water at initial pH greater than 7.0 with PFC flocculant, the fractal dimensions of D2 （logA vs. logdL） and D3 （logVsphere vs. logdL） of PFC-HA floes decreased with the increase of PFC dosages, and PFC-HA floes showed a gradually looser structure. At the optimum dosage of PFC, the D2 （logA vs. logdL） values of the flocs show 14%-43% difference with their corresponding Dr, and they even had different tendency with the change of initial pH values. However, the D2 values of the floes formed at three different initial pH in HA solution had a same tendency with the corresponding Df. Based on fractal Frenkel-Halsey-HiU （FHH） adsorption and desorption equations, the pore surface fractal dimensions （Ds） for dried powders of PFC-HA flocs formed in HA water with initial pH 9.0 and 7.0 were all close to 2.9421, and the Ds values of flocs formed at initial pH 5.0 were less than 2.3746. It indicated that the pore surface fractal dimensions of PFC-HA floes dried powder mainly show the irregularity from the mesopore-size distribution and marcopore-size distribution.
基金The study was supported by the National Natural Science Foundation of China under contract No. 49976023 the Natural Science Foundation of Zhejiang Province under contract No. N29985.
文摘Based on the test data in dynamic water and static water, the main factors, which influence the fine sediment flocculation, are analyzed with a gray model method of correlation theory. It is shown that the main influencing factors are water temperature, settling time, salinity, grain size, sediment concentration and current velocity according to the correlation coefficients. Among them, the salinity and the sediment grain size are critical type influencing factors (CrTIF); the settling time, the sediment concentration and the velocity are continuous type influencing factors (CoTIF); and the water temperature has the characteristics of both. When the critical values of CrTIF are reached or exceeded, the fine sediments will be flocculated, but values of CrTIF will not influence the settlement strength of floes. The influence of CoTIF is continuous. The values of the CoTIF will not only influence the occurrence of flocculation but also the settlement strength of the floes.
文摘This study investigated the floc aggregation, average floc size, floc size variance and floc growth velocity when ferric chloride （FeCl3） and polyferric chloride （PFC） were used to treat the simulated water samples. The factors including coagulant dose, ionic strength and solution pH, which affect the floc aggregation, were studied. Experiments were carried out in a bench-scale reactor using photometric dispersion analyzer （ PDA）. Results showed that there were great differences between the floc aggregation of PFC and FeCl3. The average floc size and fioc growth velocity of PFC were much larger than those of FeCl3. Compared with FeCl3, PFC gave a better coagulation performance in wider range of pH, dosage and ionic strength. It was also found that the coagulation efficiency of PFC did not depend on average floc size but on floc growth velocity.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51974012 and 51804017)the National Key Research and Development Program of China(No.2018YFC0604602)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.FRF-BD-19-005A)the Opening Fund of State Key Laboratory of Nonlinear Mechanics(No.LNM202009).
文摘A series of laboratory investigations are conducted to analyze the effect of flocculant type on the spatial morphology and microstructural characteristics of flocs during the flocculation and settling of tailings.Four flocculant types(i.e.,ZYZ,JYC-2,ZYD,and JYC-1)are considered in this study.The fractal characteristics and internal structures of tailings flocs with different flocculant types and settlement heights are analyzed by conducting scanning electron microscopy and X-ray micro-computed tomography scanning experiments based on the fractal theory.Results show that unclassified tailings flocs are irregular clusters with fractal characteristics,and the flocculation effect of the four flocculant types has the following trend:ZYZ>JYC-2>ZYD>JYC-1.The size and average grayscale value of tailings flocs decrease with the increase in settlement height.The average grayscale values at the top and bottom are 144 and 103,respectively.The settlement height remarkably affects the pore distribution pattern,as reflected in the constructed three-dimensional pore model of tailings flocs.The top part of flocs has relatively good penetration,whereas the bottom part of flocs has mostly dispersed pores.The number of pores increases exponentially with the increase in settlement height.By contrast,the size of pores initially increases and subsequently decreases with the increase in settlement height.
基金funded by the National Natural Science Foundation of China (No. 51834001)
文摘Efficient thickening of tailings is a prerequisite for the metal mine tailings backfill and surface disposal operation.The effective collision of ultrafine tailings particles in suspension with flocculant molecules is essential for flocs aggregates formation and settling.Unreasonable feeding speed and flocculant adding method will lead to the failure of effective dispersion of flocculant and high particle content in thickener overflow.In this work,the effect of turbulence intensity and flocculant adding method on floc size,strength,and movement characteristics are analysed.Aiming to solve the turbidity increased,a pilot-scale continuous thickening test was carried out.Taking a single particle and multiple flocs of full tailings as the research object,the particle iterative settlement model of flocs was established.The influence of turbulence intensity on collision effect is studied by tracking and simulating particle trajectory.The results show that in the process of single particle settlement,chaos appears in the iterative process owing to particle adhesion which caused by micro action.When the turbulence intensity is 25.99%,the maximum particle size of tailings floc is 6.21 mm and the maximum sedimentation rate is 5.284 cm·s^(−1).The tailings floc presents a multi-scale structure of particle-force chain system when hindered settling,and the interweaving of strong and weak force chains constitutes the topological structure of particles.The results are applied to a thicker in plant,the flocculant addition mode and feed rate are optimized,and the flocs settling speed and overflow clarity are improved.
基金Supported by the Science&Technology Development Fund(STDF)in Egypt under title of "Development of biofloc technology for high intensive and organic production of tilapia,mullet and freshwater shrimp under desert conditions"(No.5671)
文摘This study was conducted to evaluate the ef fect of replacing soybean meal(SBM) by low protein ?oc meal(LPFM; 24% CP) in tilapia diets on growth performance, feed utilization and ?sh chemical composition. Three isonitrogenous and isocaloric diets were formulated; control diet(C; without LPFM),FM 25(25% of SBM protein was substituted by LPFM) and FM 50(50% of SBM protein was substituted by LPFM). Nine 55 l circular plastic tanks were stocked by 12 ?sh to form three experimental groups.No dif ferences in tilapia performance were observed between the control and the FM 25 diet. Chemical composition of ?sh did not dif fer signi?cantly among treatments except for protein and selenium contents where the highest values were recorded in the control treatment. The highest mineral content was recorded in ?oc collected from the control tanks, while calcium content showed its highest value in ?oc collected from FM 50 e ? uent. These data indicate that replacing soybean meal with LPFM up to 25%, had no negative ef fect on growth performance and potentially may improve the system sustainability. Meanwhile, the adverse ef fect of more inclusion of LPFM in tilapia diet may be attributed to the higher content of ash. In other word,minerals seem to cause more energy utilization in ?sh fed ?oc meal since it is needed to maintain osmotic homeostasis.
文摘The study on the criteria used to distinguish floc sedimentation and gel-like network sedimentation of cohesive fine-grained sediment in a turbulent flow has rarely been carried out. In this preliminary study, we derive three criteria to distinguish these two different sedimentation phases by considering the comparison of the time that a characteristic floc takes to settle through mean distance between characteristic flocs and the time that it takes to move through the same distance under the influence of a turbulent flow. These criteria incorporate physical and chemical factors that have been verified to have some influences on the sediment flocculation in some published literatures, and a simple analysis result is found to be consistent with our qualitative understandings of flocculation phenomenon of cohesive fine-grained sediment.
