减压膜蒸馏法咸水淡化的实验研究

以氯化钠水溶液为实验体系 ,采用平板聚丙烯 (PP)膜 ,进行减压膜蒸馏实验研究 ,考察了盐水浓度、进料温度、冷侧真空度对膜渗透通量以及截留率的影响 ;并用聚四氟乙烯 (PTFE)膜进行了冷侧真空度影响的实验。同时利用完全的 (complete)努森 -粘性流(Knudsen -viscous)过渡模型预测减压膜蒸馏的渗透通量。结果表明 ,进料温度和冷侧真空度对膜渗透通量的影响很大 ,而对截留率的影响不大 ;进料浓度在实验范围内对膜渗透通量以及截留率的影响都不大 ;膜的渗透通量随着膜孔径的增大而增加 ;PTFE膜的截留效果优于PP膜。渗透液水质分析说明减压膜蒸馏起到了良好的淡化效果     

减压膜蒸馏法咸水淡化的实验研究

以氯化钠水溶液为实验体系，采用平板聚丙烯(PP)膜，进行减压膜蒸馏实验研究，考察了盐水浓度、进料温度、冷侧真空度对膜渗透通量以及截留率的影响；并用聚四氟乙烯(PTFE)膜进行了冷侧真空度影响的实验。同时利用完全的(complete)努森-粘性流(Knudsen—viscous)过渡模型预测减压膜蒸馏的渗透通量。结果表明，进料温度和冷侧真空度对膜渗透通量的影响很大，而对截留率的影响不大；进料浓度在实验范围内对膜渗透通t以及截留率的影响都不大；膜的渗透通量随着膜孔径的增大而增加；PTFE膜的截留效果优于PP膜。渗透液水质分析说明减压膜蒸馏起到了良好的淡化效果。     

厌氧渗透膜生物反应器的膜污染行为研究

本文主要考察耦合微滤膜(MF)的厌氧渗透膜生物反应器(AnMF-OMBR)处理模拟生活污水时正渗透(FO)膜的运行性能以及膜污染情况。结果表明,MF膜的加入能够有效的控制AnMF-OMBR中的盐度积累,使电导率维持在3 mS/cm左右。聚酰胺材质的FO(TFC-FO)膜对有机物和总磷有优异的截留性能,但对NH_4~+-N的截留效果不好。TFC-FO膜在AnMF-OMBR中运行30 d后,其通量从7.94 LMH下降到2 LMH,这主要是由膜污染造成的。TFC-FO膜的污染由有机污染,生物污染和无机污染组成,且以有机污染和生物污染为主。激光共聚焦显微镜(CLSM)的分析结果表明,有机污染和生物污染的主要组成成分是总细胞、蛋白质及β-D-吡喃多糖。此外,物理反冲洗无法恢复污染的TFC-FO膜的水通量,这说明膜污染主要由不可逆污染造成,进一步证明了膜污染的严重性。     

不锈钢膜超滤澄清甲壳素碱煮废水的研究

不锈钢膜澄清甲壳素碱煮废水,为掌握膜通量衰减规律以及膜对料液中非碱固形物、悬浮固形物的截留规律,用5批次不同浓度的蟹壳碱煮液,全循环模式下进行变跨膜压差(TMP)实验,发现TMP小于3.1 bar时为压差控制区,大于3.1 bar时为浓差极化阻力控制区.在压差控制区内,膜通量随TMP增大而增大.TMP控制在3.1 bar,料液温度控制在70℃,平均膜通量随料液初始浓度减小而增大.分别为108.15、136.65、171.48、187.09、228.57 L·m-2·h-1,非碱固形物的截留率随时间的增加而增大.滤液的悬浮固形物含量均在0.01%以下,证明不锈钢超滤膜技术可以高效澄清甲壳碱煮液,截留全部悬浮固形物.     

中空纤维膜分离酵母提取液中活性成分的初步研究

以啤酒废酵母为原料,研究了中空纤维膜(微滤和超滤)分离酵母提取液中活性成分的工艺.基于超滤机理分析了操作压力、温度、pH值和料液浓度对膜通量的影响,得到超滤工艺最佳条件:压力为0.105MPa,温度、pH值和料液浓度分别为24℃、6.0、3.0%.在此条件下,膜通量为18.42 L/m2·h,海藻糖透过率为96.36%,蛋白质截留率为94.50%.经高效液相色谱(HPLC)验证,实现了酵母提取液中活性成分的分离.     

乳清蛋白超滤过程中膜污染机制及监测方法研究进展

尽管乳清蛋白超滤浓缩已经实现工业化应用,但仍存在膜污染严重、生产成本高等问题。该文从pH、温度、跨膜压力、离子强度等方面综述乳清蛋白超滤过程中膜污染的形成机制;介绍了目前描述乳清蛋白超滤过程中膜污染的3种数学模型,用于预测膜污染过程中膜通量随时间变化规律;总结了乳清蛋白超滤过程中的原位监测技术的物理原理、优点和缺点,以预测和控制超滤过程中的膜污染行为,为蛋白超滤过程的实时监测提供有效的动态信息,为膜污染的控制提供理论依据。     

大豆蛋白超滤过程中膜清洗方法的研究

大豆蛋白超滤分离中膜污染主要是蛋白质、糖类、脂类和无机盐在膜面的吸附或沉淀引起的。本文对超滤法生产大豆蛋白过程中膜清洗的方法进行了研究。研究表明,关闭透过液出口,用去离子水冲洗、次氯酸钠的碱溶液清洗污染的膜;透过液出口打开,稀表面活性剂的碱溶液和稀酸液循环清洗超滤膜,能够较好的除去膜污染,恢复膜通量,膜通量恢复率在90%以上。     

正渗透技术浓缩苹果汁过程中反向溶质扩散的研究

反向渗透扩散（RSF）是正渗透技术中的一大挑战,本实验立足于研究正渗透技术浓缩苹果汁性能以及功能性汲取液（乙酸钠、碳酸氢钠、柠檬酸钠溶液）的溶质扩散规律。首先,利用NaCl溶液为汲取液研究正渗透膜的基础特性,通过改变NaCl溶液浓度、进水流速以及膜操作模式,探究正渗透体系的水通量、反向溶质扩散及截留率,分析对去离子水和苹果汁的浓缩能力及溶质扩散规律;其次,对比不同功能性汲取液对苹果汁浓缩的效果和对RSF的影响,以期达到将RSF化弊为利的目的。结果表明,汲取液浓度和膜操作模式影响浓缩效率和RSF;采用压力延迟渗透（PRO）模式,苹果汁浓缩倍数和RSF均比正渗透（FO）模式高,PRO模式下,5 mol·L?1 NaCl汲取液RSF达87.34±6.32 g·m?2·h?1;不同种类功能性汲取液浓缩苹果汁的能力不同,汲水能力:碳酸氢钠>氯化钠>乙酸钠>柠檬酸钠。RSF:乙酸钠>碳酸氢钠>氯化钠>柠檬酸钠。2 mol·L?1柠檬酸钠汲取液的RSF为29.61±2.19 g·m?2·h?1,仅为同浓度NaCl汲取液的一半,与传统的NaCl汲取液相比,柠檬酸钠汲取液可有效控制RSF。     

食醋超滤澄清研究

对食醋进行了超滤澄清研究,考察了不同膜、搅拌速率、透过液通量、料液温度等对食醋超滤过程的影响,并对其中膜污染阻力进行了分级研究.结果表明,截留分子量为100kDa的PVDF超滤膜适合食醋超滤澄清,且效果显著,可使浊度从175 NTU降至0.2 NTU以下,总酸度损失率<6%、葡萄糖和乳酸则基本没有损失;随着搅拌速率的增加、透过液通量的降低以及料液温度的升高,食醋超滤澄清过程的跨膜压力随之降低,而总酸度损失率亦同样有降低趋势;膜污染阻力的分级测定显示,膜表面浓差极化层与滤饼层分别占总膜阻的38.15%和28.95%,而膜内部污染阻力几乎可以忽略;采用浓度为0.05mol/L的NaOH溶液浸泡24h,可有效清除膜污染,清洗后膜阻为新膜膜阻的98%.     

聚偏氟乙烯中空纤维气态膜法海水提溴研究

文章以新型高分子材料聚偏氟乙烯(PVDF)为膜,采用中空纤维气态膜分离方法对海水及增浓后海水(卤水)提溴进行了探讨。结果表明:通过改变溴过膜后即膜后侧的真空度来增加膜两边的压强差并不能提高溴的通量J,因此,此传质过程的推动力是浓度差而不是压强差。传质系数k随压强差的增加而略有增大。收率η、传质系数k和通量J均随温度的升高而增大,但收率η和传质系数k随温度变化较通量J显著。通量J随浓度的增加显著增大。由于原料液采用循环方式,因此流速对收率η、传质系数k和通量J的影响可以忽略。     

Synthesis and characterization of novel forward osmosis membranes based on layer-by-layer assembly

Forward osmosis (FO) has received considerable interest for water- and energy-related applications in recent years. FO does not require an applied pressure and is believed to have a low fouling tendency. However, a major challenge in FO is the lack of high performance FO membranes. In the current work, novel nanofiltration (NF)-like FO membranes with good magnesium chloride retention were synthesized using layer-by-layer (LbL) assembly. The membrane substrate was tailored (high porosity, finger-like pores, thin cross-section, and high hydrophilicity) to achieve a small structural parameter of 0.5 mm. Increasing the number of polyelectrolyte layers improved the selectivity of the LbL membranes while reducing their water permeability. The more selective membrane 6#LbL (with 6 polyelectrolyte layers) had much lower reverse solute transport compared to 3#LbL and 1#LbL. Meanwhile, the FO water flux was found to be strongly affected by both membrane water permeability and solute reverse transport. Severe solute reverse transport was observed for the active-layer-facing-draw-solution membrane orientation, likely due to the suppression of Donnan exclusion as a result of the high ionic strength of the draw solution. In contrast, the active-layer-facing-feed-solution orientation showed remarkable FO performance (15, 20, and 28 L/m2.h at 0.1, 0.5, and 1.0 M MgCl?, respectively, for membrane 3#LbL using distilled water as feed solution), superior to other NF-like FO membranes reported in the literature. To the best of the knowledge of the authors, this is the first work on the synthesis and characterization of LbL based FO membranes.     

陶瓷膜超滤净化石灰法制糖清汁

对孔径为0.04?μm的陶瓷超滤膜进一步净化石灰法制糖的清汁进行研究,在跨膜压差0.45～0.50?MPa、膜面流速4.0～4.5?m/s、过滤温度75～97?℃的条件下过滤甘蔗汁30?h,膜渗透通量从350.6?L/（m2·h）降低至160.2?L/（m2·h）,平均通量为177.8?L/（m2·h）,能满足工业化生产的需求。甘蔗汁经陶瓷膜过滤后品质被进一步提升,简纯度可提高2.01?个单位,色素去除率为20.20%,澄清度从79.18%提升至99.98%。研究膜污染形成发现,陶瓷膜过滤甘蔗汁会在膜表面形成一层污染层,膜污染物的主要成分为有机物（多糖、蛋白质、酯类及酚类等物质）,同时还含有少量的Na、Mg、Al、Si、P、Cl、K、Ca及Fe等无机成分。污染膜依次采用工业净水、1%?NaOH-0.5%?NaClO混合溶液、0.5%?HNO3溶液清洗,膜通量恢复率均高于95.5%,重复性较好,是一种有效的膜清洗方法。     

Experimental study of a 4040 spiral-wound forward-osmosis membrane module

This paper analyzes the structural features of a spiral-wound forward-osmosis (SW FO) membrane module via an experimental approach and presents the relationships between the water flux and operating conditions for design and operation of a large-scale FO process. The SW FO module has four ports: an inlet/outlet for the draw solution and an inlet/outlet for the feed solution. Accordingly, two strongly interacting flow streams existed on either side of the membrane with spatially variable properties. Unlike the operation of a membrane cell device loaded with a small membrane coupon, it was appropriate to operate a housing-type FO unit loaded with a 4040 SW FO module with a lower draw flow rate than feed flow rate. Because of the structural features of the SW FO module, the draw solution flowed inside of the membrane envelope under a considerable pressure in order to overcome the flow resistance. The effect of operating conditions on the water flux in a 4040 SW FO module was investigated. A water flux equation based on a temperature-correction factor (TCF) was proposed to predict the water flux at a given temperature. Our study is a good reference point for designing the FO process and FO membrane module.     

反渗透膜的性能研究及在造纸废水处理中的应用

本文研究了反渗透膜BW30和X-20操作压力对膜通量和脱盐率的影响、离子半径对脱盐率的影响。实验结果表明:当操作压力从0.1MPa升高到0.2MPa时,两种膜对盐溶液的通量分别从0.59 L/(m2·h)上升到1.99 L/(m2·h),从0.34 L/(m2·h)上升到1.36 L/(m2·h),而脱盐率从30%下降到20%左右,随着离子半径的增大,膜的脱盐率依次增大;并研究了反渗透膜在造纸废水处理中的应用。实验结果表明:纳滤膜对小分子有机物有很好的截留、脱盐效果明显,并且对色度、浊度有很好的去除能力。     

Performance of forward (direct) osmosis process: membrane structure and transport phenomenon

The performance of a forward (direct) osmosis (FO) process was investigated using a laboratory-scale unit to elucidate the effect of membrane structure and orientation on waterflux. Two types of RO membrane and a FO membrane were tested using ammonium bicarbonate, glucose, and fructose as the draw solution to extract water from a saline feed solution. The FO membrane was able to achieve higher water flux than the RO membranes under the same experimental conditions while maintaining high salt rejection of greater than 97%. Increasing operating temperature increased the water flux in FO process. To investigate the effect of membrane orientation on water flux, the FO membrane was tested normally (dense selective layer facing draw solution) and reversely (dense selective layer facing feed solution). Explanations on transport phenomenon in FO process were proposed which explain the observation that the FO membrane, when used in the normal orientation, performed better due to lesser internal concentration polarization. This study suggests that an ideal FO membrane should consist of a thin dense selective layer without any loose fabric support layer.     

Boric acid permeation in forward osmosis membrane processes: modeling, experiments, and implications

Forward osmosis (FO) is attracting increasing interest for its potential applications in desalination. In FO, permeation of contaminants from feed solution into draw solution through the semipermeable membrane can take place simultaneously with water diffusion. Understanding the contaminants transport through and rejection by FO membrane has significant technical implications in the way to separate clean water from the diluted draw solution. In this study, a model was developed to predict boron flux in FO operation. A strong agreement between modeling results and experimental data indicates that the model developed in this study can accurately predict the boron transport through FO membranes. Furthermore, the model can guide the fabrication of improved FO membranes with decreased boron permeability and structural parameter to minimize boron flux. Both theoretical model and experimental results demonstrated that when membrane active layer was facing draw solution, boron flux was substantially greater compared to the other membrane orientation due to more severe internal concentration polarization. In this investigation, for the first time, rejection of contaminants was defined in FO processes. This is critical to compare the membrane performance between different membranes and experimental conditions.     

Forward osmosis concentration of high viscous polysaccharides of Dendrobium officinale: Process optimisation and membrane fouling analysis

Polysaccharides of Dendrobium officinale (DOP) need to be dehydrated and concentrated after extraction for further application. They are usually concentrated by thermal evaporation which consumes great energy. However, high viscosity of DOP makes the concentration more difficult even using non-thermal membrane technologies such as nanofiltration (NF) or reverse osmosis (RO). In this study, effects of process conditions, such as membrane orientations, draw solutions and their concentrations, and flowrate on forward osmosis (FO) concentration of viscous DOP were studied. Active layer to feed solution mode, cross flowrate at 240 mL min⁻¹, and draw solution of 3 m NaCl have been found as the optimal conditions. Foulants on the membrane surface with loose structure could be easily cleaned and removed by hydraulic flushing. DOP concentrated by FO achieved almost 1.3 times at the same time compared with that in NF and RO. DOP could be further concentrated for 1.5 folds at longtime without significant decrease in water flux. In addition, slight reverse solutes in FO process could reduce the viscosity of high viscous DOP, which was good for concentration. Accordingly, FO is a potential technology for concentration of high viscous polysaccharides such as DOP.     

Emerging forward osmosis and membrane distillation for liquid food concentration: A review

As emerging membrane technologies, forward osmosis (FO) and membrane distillation (MD), which work with novel driving forces, show great potential for liquid food concentration, owing to their low fouling propensity and great driving force. In the last decades, they have attracted the attention of food industry scientists in global scope. However, discussions of the FO and MD in liquid food concentration advancement, membrane fouling, and economic assessment have been scant. This review aims to provide an up-to-date knowledge about liquid food concentration by FO and MD. First, we introduce the principle and applications of FO and MD in liquid food concentration, and highlight the effect of process on liquid food composition, membrane fouling mechanism, and strategies for fouling mitigation. Besides, economic assessment of FO and MD processes is reviewed. Moreover, the challenges as well as future prospects of FO and MD applied in liquid food concentration are proposed and discussed. Comparing with conventional membrane-based or thermal-based technologies, FO and MD show outstanding advantages in high concentration rate, good concentrate quality, low fouling propensity, and low cost. Future efforts for liquid food concentration by FO and MD include (1) development of novel FO draw solution (DS); (2) understanding the effects of liquid food complex compositions on membrane fouling in FO and MD concentration process; and (3) fabrication of novel membranes and innovation of membrane module and process configuration for liquid food processing.     

Anaerobic fluidized bed membrane bioreactor for wastewater treatment

Anaerobic membrane bioreactors have potential for energy-efficient treatment of domestic and other wastewaters, membrane fouling being a major hurdle to application. It was found that fouling can be controlled if membranes are placed directly in contact with the granular activated carbon (GAC) in an anaerobic fluidized bed bioreactor (AFMBR) used here for post-treatment of effluent from another anaerobic reactor treating dilute wastewater. A 120-d continuous-feed evaluation was conducted using this two-stage anaerobic treatment system operated at 35 °C and fed a synthetic wastewater with chemical oxygen demand (COD) averaging 513 mg/L. The first-stage was a similar fluidized-bed bioreactor without membranes (AFBR), operated at 2.0-2.8 h hydraulic retention time (HRT), and was followed by the above AFMBR, operating at 2.2 h HRT. Successful membrane cleaning was practiced twice. After the second cleaning and membrane flux set at 10 L/m(2)/h, transmembrane pressure increased linearly from 0.075 to only 0.1 bar during the final 40 d of operation. COD removals were 88% and 87% in the respective reactors and 99% overall, with permeate COD of 7 ± 4 mg/L. Total energy required for fluidization for both reactors combined was 0.058 kWh/m(3), which could be satisfied by using only 30% of the gaseous methane energy produced. That of the AFMBR alone was 0.028 kWh/m(3), which is significantly less than reported for other submerged membrane bioreactors with gas sparging for fouling control.