陶瓷膜过滤谷氨酸发酵液过程中的膜污染与对策

用陶瓷膜过滤谷氨酸发酵液以除去其中的细菌等悬浮物具有很好的应用前景,但陶瓷膜的污染是一个必须解决的关键问题。现场的实验发现,膜污染与发酵液的性质有很大关系,也与过滤过程的操作和膜清洗紧密相关。在研究这种关系的基础上,有效地解决了膜污染问题,使陶瓷膜过滤谷氨酸发酵液的操作可以满足工业应用的要求。     

超滤技术用于谷氨酸发酵液中菌体的分离

微生物发酵产物的提取工艺中，几乎都包含着固型物（菌体）和液体的分离过程，而这个过程在很多领域都属于较难解决的大问题。因此，在相当领域范围内，仍采用带菌体的提取工艺。近年来膜过滤技术用于发酵液的菌体和蛋白质大分子脱除，技术日臻成熟，其优势愈见明显。本文通过对膜过滤技术的描述，对超滤技术用于谷氨酸发酵液菌体分离的成本进行分析，并提出一种新的菌体回收工艺。     

无机陶瓷膜错流超滤海水污染机理研究

目前,膜污染已成为制约膜技术在海水淡化领域应用的主要障碍,本文对陶瓷膜在海水预处理过程中的污染机理进行了研究.通过小试试验,分析了不同操作时间膜污染的情况,研究了0.1 μm陶瓷膜过滤阻力的形成,用膜的可逆污染、半可逆污染和不可逆污染取代已有研究结果中的膜表面沉积污染、膜内污染、极化层污染等来研究0.1 μm陶瓷膜各部分占总阻力的比例大小,更具有实际指导意义,并考察了操作条件对膜污染程度的影响,为确定最佳工艺条件和膜清洗方法提供了可靠的依据.     

陶瓷膜在晒制酱油生产中的应用

考察了不同工艺段酱油陶瓷膜过滤的分离效果,并以酱油沉降液为料液,优化陶瓷膜过滤条件。结果表明,陶瓷膜应用在酱油沉降工段后较佳,表现在通量衰减慢、膜污染速度慢等。最佳陶瓷膜过滤操作参数为：选用孔径B陶瓷膜,温度40～50 ℃,跨膜压差280 kPa,膜面流速5.5 m/s,反冲工作压力500～600 kPa,反冲间隔时间4 min,反冲时间3 s,反冲排气5 s,浓缩10倍,平均通量85.7 kg/（h·m2）。陶瓷膜渗透液离心无沉淀,菌落总数低于10 CFU/mL,总酸、氨基酸态氮、总氮、盐分及无机盐固形物透过率均达到98%以上。陶瓷膜技术应用在晒制酱油中值得推广。     

陶瓷膜在谷氨酸发酵液除菌过程中的应用

对陶瓷膜在谷氨酸发酵液除菌过程中的应用进行了实验研究。实现了除菌、洗菌、浓缩过程连续化操作，浓缩倍数达到25倍。选择了合适孔径的陶瓷膜，确定了膜的操作条件和再生方式。当加水量为发酵液量的0.1倍时，水洗后谷氨酸收率＞99．7％。除菌率＞99．98％。     

谷氨酸发酵液除菌过程的超滤膜污染探讨

在谷氨酸发酵液除菌超滤过程中的污染问题是超滤的主要问题。污染的及时消除将使超滤效率提高大于30％并大大减少能耗，从而取得更好的分离效果，提高发酵液谷氨酸的提取率和菌体蛋白等副产品的收率。     

陶瓷膜处理乳酸菌发酵液的膜清洗研究

研究了在不同操作压力下乳酸菌发酵液的渗透通量随时间的变化,以及污染后的陶瓷膜的清洗情况, 同时也考察了用陶瓷膜分离乳酸菌发酵液的效果。结果表明,渗透通量与操作压力、时间有密切关系；清洗过程中,纯水的温度、清洗剂的浓度以及清洗时间等都会影响膜通量的恢复率。     

翘鳞伞胞外多糖无机陶瓷膜分离工艺研究

采用无机陶瓷膜分离提取翘鳞伞胞外多糖,考察不同孔径的膜对膜过滤的影响,优化膜通量影响因素,获得超滤膜分离最佳工艺条件.以微滤处理后的翘鳞伞发酵液为研究对象,测定了5种不同孔径超滤膜的膜通量以及多糖截留率;在5种陶瓷超滤膜中,截留分子量为50kDa的超滤膜最适合于翘鳞伞胞外多糖发酵液分离浓缩,当压力为0.1MPa～0.4MPa,温度为20℃～40℃时,压力和温度的提高均有利于超滤膜通量的增大:选择50kDa的超滤膜在0.3MPa、30℃的操作条件下,膜通量以及多糖截留率最佳.     

陶瓷超滤膜在乳酸纯化工艺中的应用

把陶瓷超滤膜技术应用于乳酸纯化工艺当中,通过实验,确定了影响膜分离性能的关键参数,并对膜的污染机理及清洗方法进行了研究.结果表明采用孔径为30nm的陶瓷超滤膜,对乳酸钙含量为16%左右,pH为9的乳酸发酵液,采用过膜压差为0.35MPa,膜面流速为5ms-1,在操作温度为80℃下,控制浓缩倍数为8倍的条件下,陶瓷超滤膜的渗透液品质优良,膜过滤通量维持在80～90 L·m-2·h-1.从技术的角度,采用陶瓷超滤膜完全能代替原有的板框及沉淀工序.     

陶瓷超滤膜在乳酸纯化工艺中的应用

把陶瓷超滤膜技术应用于乳酸纯化工艺当中,通过实验,确定了影响膜分离性能的关键参数,并对膜的污染机理及清洗方法进行了研究.结果表明采用孔径为30nm的陶瓷超滤膜,对乳酸钙含量为16%左右,pH为9的乳酸发酵液,采用过膜压差为0.35MPa,膜面流速为5ms-1,在操作温度为80℃下,控制浓缩倍数为8倍的条件下,陶瓷超滤膜的渗透液品质优良,膜过滤通量维持在80～90L·m-2·h-1.从技术的角度,采用陶瓷超滤膜完全能代替原有的板框及沉淀工序.     

微滤膜的污染与清洗保养

微滤是目前所有膜技术中应用最广、经济价值最大的技术。但在微滤过程中存在膜污染现象，极大地影响了微滤技术的实际应用。文章概述了膜污染的定义、膜污染的影响因素、防止膜污染的措施、膜污染的清洗及保养方法。     

膜分离技术在食醋澄清中的应用

膜分离技术具有简单、高效、低能耗等优点,以其分离过程无相变、无化学变化并适用于多种物料分离的特点,而成为了一种新兴的分离技术。文中系统概述了膜在食醋生产过程中膜的选取、过滤过程条件优化、防止膜污染以及膜清洗技术的研究进展。分析了制约我国膜分离技术应用于食醋工业化生产的关键问题并对其应用前景进行了展望。     

中药用膜的污染及防治

分析了膜污染的机理及其影响因素,同时从膜分离过程前、膜分离过程中、膜分离过程后3个阶段采取相应的措施来改善膜的污染。     

陶瓷膜在甘油发酵液除菌中的应用

将陶瓷膜应用于甘油发酵液的除菌操作中,考察了操作参数和清洗方法对膜通量的影响。结果表明,在压差0.1MPa、温度30℃、pH值7.0和错流速度3.5m/s条件下操作,有利于提高膜通量;发酵液过滤后,先以质量浓度为1%的NaOH和质量浓度为0.2%的NaClO混合液清洗膜40min,再以质量浓度为0.5%的HNO3溶液清洗5min,膜通量可迅速恢复。因此,陶瓷膜在甘油发酵液的除菌中是高效可行的。     

Performance assessment of membrane distillation for skim milk and whey processing

Membrane distillation is an emerging membrane process based on evaporation of a volatile solvent. One of its often stated advantages is the low flux sensitivity toward concentration of the processed fluid, in contrast to reverse osmosis. In the present paper, we looked at 2 high-solids applications of the dairy industry: skim milk and whey. Performance was assessed under various hydrodynamic conditions to investigate the feasibility of fouling mitigation by changing the operating parameters and to compare performance to widespread membrane filtration processes. Whereas filtration processes are hydraulic pressure driven, membrane distillation uses vapor pressure from heat to drive separation and, therefore, operating parameters have a different bearing on the process. Experimental and calculated results identified factors influencing heat and mass transfer under various operating conditions using polytetrafluoroethylene flat-sheet membranes. Linear velocity was found to influence performance during skim milk processing but not during whey processing. Lower feed and higher permeate temperature was found to reduce fouling in the processing of both dairy solutions. Concentration of skim milk and whey by membrane distillation has potential, as it showed high rejection (>99%) of all dairy components and can operate using low electrical energy and pressures (<10 kPa). At higher cross-flow velocities (around 0.141 m/s), fluxes were comparable to those found with reverse osmosis, achieving a sustainable flux of approximately 12 kg/h·m² for skim milk of 20% dry matter concentration and approximately 20 kg/h·m² after 18 h of operation with whey at 20% dry matter concentration.     

膜技术在L-丙氨酸提纯工艺中的应用研究

采用陶瓷膜和纳滤膜工艺从发酵液中提取L-丙氨酸。经试验研究,确定了陶瓷膜过滤的料液经过80 ℃高温灭菌20 min,膜面流速控制在5 m/s;并对纳滤膜进行选型,最终确定UA60纳滤膜对料液进行脱色、脱盐,透光率提高43.6%,磷酸盐去除率为59.8%,对丙氨酸的截留率为10.5%。使用膜过滤提纯后,L-丙氨酸的总收率为85.9%。     

Filtration of milk fat globule membrane fragments from acid buttermilk cheese whey

The proteins and polar lipids present in milk fat globule membrane (MFGM) fragments are gaining attention for their technological and nutritional properties. These MFGM fragments are preferentially enriched in side streams of the dairy industry, like butter serum, buttermilk, and whey. The objective of this study was to recover MFGM fragments from whey by tangential filtration techniques. Acid buttermilk cheese whey was chosen as a source for purification by tangential membrane filtration because it is relatively rich in MFGM-fragments and because casein micelles are absent. Polyethersulfone and cellulose acetate membranes of different pore sizes were evaluated on polar lipid and MFGM-protein retention upon filtration at 40°C. All fractions were analyzed for dry matter, ash, lipids, proteins, reducing sugars, polar lipid content by HPLC, and for the presence of MFGM proteins by sodium dodecyl sulfate-PAGE. A fouling coefficient was calculated. It was found that a thermocalcic aggregation whey pretreatment was very effective in the clarification of the whey, but resulted in low permeate fluxes and high retention of ash and whey proteins. By means of an experimental design, the influence of pH and temperature on the fouling and the retention of polar lipids (and thus MFGM fragments), proteins, and total lipids upon microfiltration with 0.15 μM cellulose acetate membrane was investigated. All models were highly significant, and no outliers were observed. By increasing the pH from 4.6 to 7.5, polar lipid retention at 50°C increased from 64 to 98%, whereas fouling of the filtration membrane was minimized. A 3-step diafiltration of acid whey under these conditions resulted in a polar lipid concentration of 6.79 g/100 g of dry matter. As such, this study shows that tangential filtration techniques are suited for the purification of MFGM fragments.     

Fouling of microfiltration and ultrafiltration membranes by natural waters

Membrane filtration (microfiltration and ultrafiltration) has become an accepted process for drinking water treatment, but membrane fouling remains a significant problem. The objective of this study was to systematically investigate the mechanisms and components in natural waters that contribute to fouling. Natural waters from five sources were filtered in a benchtop filtration system. A sequential filtration process was used in most experiments. The first filtration steps removed specific components from the water, and the latter filtration steps investigated membrane fouling by the remaining components. Particulate matter (larger than 0.45 microm) was relatively unimportant in fouling as compared to dissolved matter. Very small colloids, ranging from about 3-20 nm in diameter, appeared to be important membrane foulants based on this experimental protocol. The colloidal foulants included both inorganic and organic matter, but the greatest fraction of material was organic. When the colloidal fraction of material was removed, the remaining dissolved organic matter (DOM), which was smaller than about 3 nm and included about 85-90% of the total DOM, caused very little fouling. Thus, although other studies have identified DOM as a major foulant during filtration of natural waters, this work shows that a small fraction of DOM may be responsible for fouling. Adsorption was demonstrated to be an important mechanism for fouling by colloids.     

Membrane fouling during filtration of milk––a microstructural study

The surface morphology and internal microstructure of a membrane are the result of membrane manufacturing processes and subsequent use during fluid processing in industry. Both these structural factors have a great effect on fouling and filtration performance.

In this study, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy were used to comprehensively characterise the surface of unused microfiltration and ultrafiltration membranes, the fouled layer on the surface of membranes used for milk filtration and the internal fouling within the used membranes.

A simple and effective sample preparation method was developed to study the internal membrane structure using high-resolution field emission SEM with low-accelerating voltage. Various methods of structural characterisation were compared and the results showed that for flat sheet membranes AFM is an appropriate and convenient technique for examining the surface topography of membranes. In contrast SEM is a very appropriate technique for examining the cross-sectional and internal structure of a membrane, either unused or fouled.

Using these complimentary techniques it has been shown that internal fouling, during filtration of skim milk, proceeds by protein–polymer and protein–protein interactions. A gel layer forms on the surface of the membrane and has been imaged using SEM. This layer is slightly compressible and densifies as it grows. Fouling initiation commences after a very short filtration time.