甘蔗汁中絮凝物产生的影响因素

为了解决甘蔗汁絮凝物沉淀引起的饮料浑浊问题,以甘蔗汁为原料,对膜滤后的甘蔗清汁中影响絮凝物生成的因素进行了研究。通过控制温度、pH来研究二者对絮凝物产生的影响,并对絮凝物中蛋白质、总糖、灰分等成分进行分析,利用傅里叶红外光谱和扫描电镜能谱仪观测絮凝物官能团结构和组成元素。研究发现,温度对生成絮凝物的影响较小。絮凝物的产量随pH的升高而增加,推断氢氧根会促进甘蔗汁中絮凝物的产生。傅里叶红外光谱结果表明,絮凝物主要由多糖、蛋白质以及灰分等物质构成。通过能谱分析电子扫描和红外扫描可以看出,絮凝物中含有铁、钙、磷、硅、锰等无机离子。说明在碱性条件下,糖类与蛋白质分子相互作用产生絮凝结构,铁、钙等金属离子生成的氢氧化铁、氢氧化钙与蛋白质和多糖产生的絮凝结构网络在一起,形成饮料中的絮凝沉淀物。     

Permeability of collapsed cakes formed by deposition of fractal aggregates upon membrane filtration

We have investigated, theoretically, the physical properties of cake layers formed from aggregates to obtain a better understanding of membrane systems used in conjunction with coagulation/flocculation pretreatment. We developed a model based on fractal theory and incorporated a cake collapse effect to predict the porosity and permeability of the cake layers. The floc size, fractal dimension, and transmembrane pressure were main parameters that we used in these model calculations. We performed experiments using a batch cell device and a confocal laser-scanning microscope to verify the predicted specific cake resistances and porosities under various conditions. Based on the results of the model, the reduction in inter-aggregate porosity is more important than that in intra-aggregate porosity during the cake collapsing process. The specific cake resistance decreases upon increasing the aggregate size and decreasing the fractal dimensions. The modeled porosities and specific cake resistances of the collapsed cake layer agreed reasonably well with those obtained experimentally.     

Preparation of titanium dioxide (TiO2) from sludge produced by titanium tetrachloride (TiCl4) flocculation of wastewater

Sludge disposal is one of the most costly and environmentally problematic challenges of modern wastewater treatment worldwide. In this study, a new process was developed, which has a significant potential for lower cost of waste disposal, protection of the environment and public health, and yield of economically useful byproducts. Titanium oxide (TiO2), which is the most widely used metal oxide, was produced from the wastewater sludge generated by the flocculation of secondary wastewater with titanium tetrachloride (TiCl4). Detailed analyses were conducted to compare TiCl4, ferric chloride (FeCl3), and aluminum sulfate (Al2(SO4)3) flocculation. Removal of organic matter and different molecular sizes by Ti-salt flocculation was similar to that of the most widely used Fe- and Al-salt flocculation. The mean size of Ti-, Fe-, and Al-salt flocs was 47.5, 42.5, and 16.9 microm, respectively. The decantability of the settled flocs by TiCl4 coagulant was similar to that by FeC13 coagulant and much higher than that of Al2(SO4)3. The photocatalyst from wastewater (PFW) produced by TiCl4 flocculation was characterized by X-ray diffraction, BET surface area, scanning electron microscopy/energy dispersive X-ray, transmission electron microscopy, photocatalytic activity, and X-ray photoelectron spectroscopy. The resulting PFW was found to be superior to commercial TiO2 (P-25) in terms photocatalytic activity and surface area. The PFW as also found to be mainly doped with C and P atoms. The atomic percentage of the PFW was TiO(1.42)C(0.44)P(0.14).     

The effect of ultrasound waves on the efficiency of membrane clarification of pomegranate juice

Pomegranate juice has a turbid appearance, which poses difficulties in its concentration process. Membrane clarification can be used to clarify pomegranate juice; however, membrane fouling reduces the permeate flux, limiting its effectiveness. Ultrasound at 30 kHz was used to reduce membrane fouling. Results were compared with the data obtained for membrane clarification without ultrasonic treatment at the same temperature. Results showed that permeate flux increased with ultrasonic treatment. Evaluation of different membrane fouling characteristics showed that the total membrane resistance fell due to the reduction in irreversible fouling and cake resistance. However, ultrasound did not affect the thick caking produced in membrane processing at low feed‐flow rates. Evaluation of the physicochemical properties of pomegranate juice showed that ultrasound can decrease antioxidant activity due to the reduction in total anthocyanin content. Also, total soluble solid content and acidity of pomegranate juice changed with ultrasonic treatment.     

Fourier wavelets from ultrasonic spectra: a new approach for detecting the onset of fouling during microfiltration of paper mill effluent

Nondestructive (NDT) and noninvasive ultrasonic techniques have long been used to evaluate the properties and especially the thickness of thin layers. Here, we use this technique adding a new approach to investigate microfiltration of paper mill wastewater, which gives an unexpected sensitivity in the detection of membrane fouling. In situ ultrasonic reflections data can indicate an early fouling deposition at about 30 s after filtration starts, evident by an initial decline in permeate flux. By producing differential signals, obtained by comparing reference and testwaveforms, the fouling process can be detected and monitored. A linear relationship between fouling resistance and the amplitude of differential signals exists. In the case of fouling layer thickness, the resolution exceeds the theoretical limit of h/lambda +/- 0.25, where h is the layer thickness and lambda is the wavelength. When using differential signals, excellent results for thickness measurements were obtained, down to h/lambda = 0.04. Measurements on wavelet transforms support the findings and add quantitative information on other physical properties such as density and porosity of fouling layers and the fouling process. Measurement of early fouling allows (automated) remedial methods to be applied so as to maintain a high flux and therefore improve the filtration process.     

Characterization of humic substances by environmental scanning electron microscopy

Environmental scanning electron microscopy (ESEM) is a new technique capable of imaging micron and submicron particles. Here, we have applied it to image and quantify natural aquatic organic matter (standard Suwannee River humic acid, SRHA). Uniquely, we have observed the humic aggregate structures as a function of humidity and pH. Large aggregates of tens of micrometers were observed as the dominant material under all conditions, although much smaller material was also observed. Fractal dimensions (D) were calculated between 1.48 and 1.70, although these values were not statistically different under conditions of low humidity. However, D values calculated at high humidities (85%) during the rehydration phase were significantly lower (1.48+/-0.01) than in the initial dehydration phase (1.69+/-0.01). This hysteresis indicated that full rehydration of the HS was either kinetically slow or irreversible after dehydration. Fractal analysis of ESEM images was also performed to probe the change in aggregate structure as a function of pH. Minimum values were calculated at neutral pHs, rising by 0.1-0.2 at both high and low pHs because of a combination of the physical chemistry of HS and the impacts of the drying regime within the ESEM. Thus, ESEM was an important complementary technique to other analytical methods. At present, ESEM cannot be used to image nonperturbed natural samples. However, the method is an ideal method for probing the changes in colloid structure as function of hydration state and has the potential to perform fully quantitative and nonperturbing analysis of colloidal structure.     

Evaluation of the fouling phenomenon in the membrane clarification of black mulberry juice

Mixed cellulose ester (MCE) flat membranes were used to clarify black mulberry juice, the yield of which was limited by fouling. The effects of membrane pore size (0.025, 0.1 and 0.22 μm), transmembrane pressure (0.5, 1, 1.5 and 200 kPa), and cross‐flow velocity (0.1, 0.2, 0.3 and 0.4 m s^?1) on membrane fouling were evaluated; the results showed that fouling increased with increased pore size and pressure, and decreased with increased velocity. Analysis of different resistances showed that both reversible and irreversible fouling resistances have an important role in fouling‐resistance changes. There is no cake resistance in all processes. Microstructure analysis of membrane using scanning electron microscopy confirmed the theory that intermediate blocking was the dominant fouling mechanism in MCE 0.025 μm, and standard blocking was the dominant mechanism in MCE 0.1 and 0.22 μm.     

Study of different fouling mechanisms during membrane clarification of red plum juice

In this study, the flux decline mechanisms were identified during membrane clarification of red plum juice at several processing parameters, including pore size, membrane type, transmembrane pressure, temperature and velocity. The results were used to investigate the effect of changes in operating conditions on the intensity of membrane fouling. Also, scanning electron microscopy (SEM) was used for analysing fouling‐layer morphology. These results showed that the main mechanism responsible for membrane fouling was cake formation (over 95% fitness) occurring in the first stage of the process. Intermediate, standard and complete blockings were formed during most of the runs as filtration proceeded. The results also indicated that increasing the temperature from 30 to 40 °C was the most effective factor in decreasing cake‐layer fouling, reducing it by about 66.7%. Furthermore, an increase in processing velocity of up to 0.5 m s^?1 had the greatest effect on intermediate blocking, reducing it by about 86.1%. Also, increasing pressure up to 2.9 bar completely eliminated standard blocking and complete blocking. Finally, microstructure analysis of membrane using SEM confirmed that cake formation had the greatest impact on membrane fouling.     

Modes of natural organic matter fouling during ultrafiltration

The fouling of ultrafiltration membranes by natural organic matter (NOM), isolated from a potable surface water source, was studied with an emphasis on elucidating fouling modes and the role of aggregates. NOM size was related to membrane pore sizes using parallel membrane fractionation and size exclusion chromatography, such analyses confirmed the predominance of low MW species and identified the presence of aggregates in concentrated NOM solutions. Cake formation was the dominant mode of fouling by the unfiltered feed, which contained aggregates. This was identified by a constant rate of increase in membrane resistance with permeate throughput and was independent of pore size over a 10-1000 kDa molecular weight cutoff (MWCO) range. Prefiltration (to remove aggregates) and dilution (to reduce aggregate concentration) reduced the rate of increase in membrane resistance for the low MWCO membranes but did not change the fouling mode. In contrast, such pretreatment prevented cake formation on the larger MWCO membranes and shifted the mode of fouling to pore blockage. The date lend support for the idea that an initial fouling layer of large aggregates can catalyze the fouling by lower MW species. The fouling layer could be removed from the large MWCO membranes by backwashing, but the lower MWCO membranes exhibited some irreversible fouling, suggesting that low MW species penetrated into the pore structure. A combined pore blockage-cake formation model described the data well and provided insight into how fouling modes evolve during filtration.     

剪切力对造纸湿部絮凝作用的影响

本文综述了剪切力对造纸湿部絮凝作用的影响,内容包括造纸过程主要单元操作中的剪切力水平及其对絮凝的影响、剪切力大小的评价、选择性解聚的现象、不同助留体系形成絮体的抗剪切性和可逆转性以及絮凝过程控制.     

Ultrafiltration fouling of amylose solution: Behavior, characterization and mechanism

Applications of ultrafiltration membrane often deal with feed streams containing amylose starch. This paper describes a detailed investigation of amylose fouling during ultrafiltration. Commercial membranes made of polysulfone and fluoro polymer were used. Both adsorptive and ultrafiltration fouling were investigated. Experiments using different membrane characteristics, feed concentrations and trans-membrane pressures were carried out. The resulting fouling was characterized by water flux and contact angle measurements and was visualized by scanning electron microscopy (SEM). The results suggest that solute adsorption has occurred as noticed by significant water flux reductions as well as changes in membrane characteristics. Further, both reversible and irreversible fouling have occurred during ultrafiltration with irreversible fouling was more dominant. Apparently, cake layer formation initiated by either adsorption due to hydrophobic–hydrophobic interactions or pore blocking is the dominant fouling mechanism. However, pore narrowing instead of pore blocking was also observed for the membrane having large and relative uniform pore structure or for the ultrafiltration using low trans-membrane pressure or low solute concentration. Membrane autopsy using SEM confirmed the formation of solute layer on the membrane surface.     

Apple Juice Clarification With the Use of Honey and Pectinase

The clarification of apple juice with the use of honey and enzyme separately and in combinations was studied. The results indicated the existence of a synergistic effect upon the time of initial flocculation when honey was combined with pectinase enzymes. Changes in the rate of flocculation appeared to be an additive effect of enzyme concentration and/or honey concentration. The combined treatment of honey and enzyme was found to induce flocculation very fast as compared to enzyme alone at cold as well as warm temperatures. When used alone, the honey treatment produced a clarified juice with a viscosity similar to cider.     

Fouling and natural organic matter removal in adsorbent/membrane systems for drinking water treatment

Adsorbent particles added to ultrafiltration (UF) systems treating drinking water can remove natural organic matter (NOM) and some other contaminants from the water, but their effect on membrane fouling is inconsistent-in some cases, fouling is reduced, and in others, it is exacerbated. This research investigated the behavior of UF systems to which powdered activated carbon (PAC), heated iron oxide particles (HIOPs), or (nonadsorbent) SiO2 particles were added. On a mass basis, the PAC removed the most NOM from solution, the HIOPs removed less, and the SiO2 removed essentially none. However, in the case of both PAC and SiO2, increasing the dose of solids led to a steady increase in fouling, whereas the opposite trend applied when HIOPs were added. In the absence of NOM, none of the solids fouled the membrane significantly. Thus, even though NOM is a causative agent for fouling, removing it from solution does not necessarily reduce fouling; the mechanism of removal can be just as important as the absolute amount removed, if the removal occurs in a cake layer near the membrane surface. Scanning electron microscopy images of the cake layers formed in the three systems suggest that the NOM binds PAC or SiO2 particles to one another and to the membrane surface, so that the particles become part of the foulant in the system. By contrast, the NOM appears to bind HIOPs to one another but not to the membrane. This process leaves enough pore space in the cake layer for water to reach the membrane with minimal resistance, and it reduces the tendency for either the NOM or the HIOPs to foul the membrane surface.     

鸡蛋蛋壳超微结构与呼吸强度的相关关系

鸡蛋品质变化原因众多,其中一个主要影响因素是其自身的呼吸作用,而蛋壳超微结构又与呼吸作用息息 相关。为了揭示蛋壳各层超微结构与鸡蛋呼吸强度之间的关系,通过扫描电子显微镜获得蛋壳的超微结构图像, 利用MATLAB软件获取相关参数,并用SPSS 19.0软件得出蛋壳厚度、有效层厚度、乳突层厚度、平均乳突大小以 及孔隙度与鸡蛋呼吸强度的相关关系。结果表明：鸡蛋的呼吸强度与蛋壳厚度（R＝－0.36,P＜0.05）、有效层厚 度（R＝－0.47,P＜0.05）之间存在显著性负相关关系;鸡蛋的呼吸强度与平均乳突大小（R＝0.57,P＜0.01）、 孔隙度（R＝0.66,P＜0.01）之间存在极显著性正相关关系;与乳突层厚度的相关性较低,同时得出呼吸强度大的 鸡蛋蛋壳表面比呼吸强度小的蛋壳表面粗糙。总之,蛋壳厚度、有效层厚度、平均乳突大小以及孔隙度对鸡蛋呼吸 强度影响较大。     

开膜法养殖淡水珍珠的表面微形貌演化特征

为了解淡水珍珠的成珠过程,采用环境扫描电子显微镜对开膜法养殖异形淡水珍珠样品的表面微形貌特征进行了观察。结果显示,在异形淡水珍珠样品珍珠层中,成层排列的文石板块形状各异,具有多层和有序的特点;在珍珠层的生长初期,形成于成核小片上的有机质为三角帆蚌外套膜细胞所分泌,其为后期矿物提供进一步沉淀的局限空间和成核作用的基底,具有确定矿物成核大小、空间排列、结晶取向和离子堆积是否出现同质多象的功能。同时,珍珠样品表面出现了与在海水珍珠和以淡水池蝶蚌为母贝的淡水珍珠中类似的螺旋生长纹,这可能是其在生长过程中受有机质的调控作用,使文石晶体在不同部位上的堆积具有差异性,也使文石晶体在特定面网方向上生长,控制了其成核结晶取向和堆叠方式,导致其螺旋堆积,形成类似螺旋纹的生长外观。     

Chicory juice clarification by membrane filtration using rotating disk module

Clarification is the first step of inulin production from chicory juice, and membrane filtration as an alternative can greatly simplify this process, increase juice yield, improve product quality, and reduce the cost and waste volume. In this study, a rotating disk module (RDM) was used to investigate the clarification of chicory juice by four micro- and ultrafiltration membranes. Compared with dead end filtration, the RDM had a much higher permeate flux and product quality. High rotating speeds produced high permeate fluxes and reduced flux decline, because of the strong back transport of foulant from fouling layer to feed solution. At high rotating speeds of 1500–2000 rpm, the permeate flux increased with membrane pore size and transmembrane pressure (TMP), while at low rotating speeds (<1000 rpm), permeate flux was independent of membrane type and TMP due to a thick deposited fouling layer as a dominant filtration resistance, while carbohydrate transmission decreased at higher TMP because of denser cake layer as an additional selective membrane. The highest carbohydrate transmission (∼98%) and desirable permeate turbidity (2.4 NTU) was obtained at a TMP of 75 kPa and a rotating speed of 2000 rpm for FSM0.45PP membrane. With the RDM, the Volume Reduction Ratio (VRR) could reach 10 with a high permeate flux (106 L m⁻² h⁻¹) in the concentration test, and permeate was still rich in carbohydrate and well clarified. Chemical cleaning with 0.5% P3-ultrasil 10 detergent solution was able to recover 90% water flux of fouled membrane.     

Characterization of cake layer in submerged membrane bioreactor

Cake layer formation on the membrane surface has been a major challenge in the operation of membrane bioreactors (MBRs). In this study, the cake layer formation mechanism in an MBR used for synthetic wastewater treatment was investigated. The major components of cake layer were systematically examined by particle size analyzer (PSA), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray fluorescence (XRF), energy-diffusive X-ray analyzer (EDX), and Fourier transform infrared (FTIR) spectroscopy. The results indicate that the small particles in sludge suspension had a strong deposit tendency on the membrane surface. The SEM and CLSM analysis exhibited that bacterial clusters and polysaccharides were significant contributors to membrane fouling. The main components of biopolymers were identified as proteins and polysaccharide materials by the FTIR. The examination by EDX and XRF demonstrated that Mg, Al, Ca, Si, and Fe were the major inorganic elements in fouling cake. Furthermore, the results suggest that bridging between deposited biopolymers and inorganic compounds could enhance the compactness of fouling layer. During the operation of MBRs, the biopolymers and inorganic elements in the bioreactor should be controlled to minimize membrane fouling.     

Effect of Fouling on Flux and on Energy Requirements in Reverse Osmosis of Skim Milk

The effects of fouling on the permeate flux and on the power and energy required in the process of concentrating skim milk by a plate and frame type reverse osmosis unit with 990 type cellulose-acetate membranes were investigated. The permeate flow characteristics indicate that the fouling layer is rapidly formed and that its resistance is nearly constant over reasonable processing intervals. These fouling properties permit the correlation of permeate flow, overall mass transfer coefficient, and osmotic pressure difference in terms of the energy required per permeate volume versus time. This correlation shows a decrease in energy required per permeate volume with increasing mass transfer coefficient and time. These flow characteristics permit the estimation with confidence of the permeate flow energy requirements and the capacity of a full scale plant. Mass transfer coefficients were estimated for the membrane, the polarized layer, and the fouling layer. The overall mass transfer coefficient was then calculated. The polarized and fouling layers are films of components from the skim milk. Fouling was the controlling resistance.     

Examination of cottage cheese whey proteins by scanning electron microscopy: relationship to membrane fouling during ultrafiltration.

Deposits formed on the membrane during ultrafiltration of aqueous solutions of individual whey proteins were examined under a scanning electron microscope. Gamma-globulin formed granules which agglomerated and stacked into layers to form a porous matrix on the membrane. Beta-lactoglobulin and bovine serum albumin both formed sheets on the membrane and formed multimers which were identified by sodium dodecyl sulfate gel electrophoresis. Beta-lactoglobulin also formed strands where deposits were not thick. Alpha-lactalbumin formed smooth spherical particles which did not hinder water permeation greatly. Studies of ultrafiltration rate indicated that beta-lactoglobulin and gamma-globulin were most significant in causing permeation flux decline by surface fouling.     

利用FBRM研究阳离子聚丙烯酰胺对高岭土的动态絮凝过程

利用聚焦光束反射测量仪（FBRM）研究了阳离子聚丙烯酰胺（CPAM）对高岭土颗粒体系的动态絮凝过程,结合浊度仪、激光衍射粒度仪、显微摄像等表征手段,探讨了絮凝剂用量对絮凝性能和絮体结构的影响。同时基于分形理论对絮凝过程中絮体分形维数的变化进行了考察,基于Smoluchowski模型研究了CPAM作用下高岭土粒子的絮凝动力学。结果表明,随着药品用量的增加,体系中粒子的平均弦长和粒径逐渐增大,体系达到稳定的时间延长,浊度不断下降。在絮凝过程中,随着作用时间的延长,絮体结构发生变化,分形维数增加,形成相对致密的絮体。增加絮凝剂的用量,絮凝作用增强,絮体尺寸变大,絮凝速率较快,需较长的絮凝反应时间才能达到平衡。