Ultrafiltration recovery of alginate: Membrane fouling mitigation by multivalent metal ions and properties of recycled materials

Recovery of alginate extracted from aerobic granular sludge (AGS) has given rise to a novel research direction. However, these extracted alginate solutions have a water content of nearly 100%. Alternately, ultrafiltration (UF) is generally used for concentration of polymers. Furthermore, the introduction of multivalent metal ions into alginate may provide a promising method for the development of novel nanomaterials. In this study, membrane fouling mitigation by multivalent metal ions, both individually and in combination, and properties of recycled materials were investigated for UF recovery of sodium alginate (SA). The filtration resistance showed a significantly negative correlation with the concentration of metal ions, arranged in the order of Mg²⁺ < Ca²⁺ < Fe³⁺ < Al³⁺ (filtration resistance mitigation), and the moisture content of recycled filter cake showed a marked decrease. For Ca²⁺, Mg²⁺, Fe³⁺, and Ca²⁺+ Fe³⁺, the filtration resistances were almost the same when the total charge concentration was less than 5 mmol⋅L^–1. However, when the total charge concentration was greater than 5 mmol⋅L^–1, membrane fouling mitigation increased significantly in the presence of Ca²⁺ or Fe³⁺ and remained constant for Mg²⁺ with the increase of total charge concentration. The filtration resistance mitigation was arranged in the order of Fe³⁺ > Fe³⁺ + Ca²⁺ > Ca²⁺ > Mg²⁺. Three mechanisms were proposed in the presence of Fe³⁺, such as the decrease of SA concentration, change in pH, and production of hydroxide iron colloids from hydrolysis. The properties of recycled materials (filter cake) were investigated via optical microscope observation, dynamic light scattering, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The results provide further insight into UF recoveries of alginate extracted from AGS.     

乳状液膜技术分离回收金属离子的研究进展

在一些工业生产过程中会产生大量的含铜、汞、锌、铀等重金属的废液,这些废水中的金属一般不能被分解破坏,只能转移其存在位置和转变其物化形态。传统的提取回收金属离子的方法主要有萃取分离、固体吸附、离子交换、共沉淀、电解法、膜分离等。其中膜分离技术因兼有分离、浓缩、纯化和精制的功能,又有高效、节能、环保、分子级过滤及过滤过程简单、易于控制等特征,故目前已广泛应用于食品、医药、生物、环保、化工等领域。文中介绍了常用的处理含金属离子废液的方法及其优缺点,重点介绍了乳状液膜技术的特点和原理,同时,阐述了含铀废液的主要处理方法,并对于乳状液膜技术应用于处理含铀废液进行了展望。     

The synthesis of modified alginate flocculants and their properties for removing heavy metal ions of wastewater

A new flocculant was synthesized through the modification of sodium alginate with thiosemicarbazide. In the preparation, amino thiourea groups which had excellent adsorption properties for heavy metal ions were introduced to the flocculant. The structure of the flocculant was confirmed by elemental analysis, Fourier transform infrared, UV spectrophotometry, nuclear magnetic resonance, and thermal analysis. The flocculation behaviors of the flocculant for three heavy metal ions were investigated. The results showed that the removal rates of the flocculant for Pb²⁺, Cd²⁺, and Cu²⁺ reached up to 97.8%, 86.3%, and 80.0%, respectively, and the flocculation capacities were as high as 489, 215, and 160 mg/g, respectively. The excellent adsorption was ascribed to the double effects of electronic interaction and chelation between the flocculant and heavy metal ions. The flocculant had particular flocculation selectivity for Pb²⁺ in the mixed heavy metal ion solutions containing Cd²⁺or Cu²⁺, respectively. The flocculation process corresponded to Langmuir isotherm model, the flocculation kinetics agree with pseudo second order. The flocculant had potential applications for treatment of wastewater. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46577.     

Membrane fouling by lysozyme: Effect of local interaction

Molecular dynamics simulations were performed to understand the adsorption of positive-charged lysozyme onto negative-charged polyvinylidene fluoride membrane at three pH and two ionic strengths. The lysozyme was initialized at six orientations at 10 Å from the membrane and adsorption was deemed to occur when the lysozyme is less than 4 Å from the membrane. Local interactions are clearly important: (i) despite opposite net charges, no adsorption occurs in some cases throughout; (ii) lysozyme-membrane separation distances differ among the initial orientations of lysozyme; and (iii) the correlation between lysozyme-membrane interaction energy and adsorption probability is poor. Correspondingly, seven key local adsorption sites on lysozyme were identified. Of the two most common sites, one anchors due to electrostatics, while the other is not electrostatics-based. Also, different sites are dominant in different feed conditions and have different interaction energies. These results reveal the importance of local interactions in membrane fouling by proteins in different feed conditions.     

Serum Protein Fractionation by Membrane Processes: Centrifugal Ultrafiltration,Osmosedimentation, and Multistage Ultrafiltration

Abstract

Whole sera proteins may be fractionated according to their molecular weights by using three membrane techniques: centrifugal ultrafiltration, osmosedimentation, and multistage ultrafiltration. Ultrafiltration or dialysis cells were mounted in the swinging baskets of a centrifuge in all three cases, with the membranes aligned parallel to the centrifugation radius. As a result, solute accumulated over the membrane was convectively removed from its surface, thus preventing membrane polarization and fouling. During these experiments, smaller proteins migrated across the membrane, leaving behind the larger ones. Multistage filtration experiments were performed using cells fitted with three different membranes of successively narrower pores. Four different fractions were thus obtained and analyzed by gel permeation chromatography; separation factors as high as 2000 were obtained.     

An experimental study of UF membrane fouling by humic acid and sodium alginate solutions: the effect of backwashing on flux recovery

One of the critical issues for the successful application of ultrafitration in water treatment is membrane fouling due to dissolved organic matter, which negatively affects productivity, product quality and process cost. The aim of the present study is to contribute to the understanding of fouling phenomena by organic matter and the efficiency of the backwashing technique, which is applied in practice to restore membrane flux. In this experimental study commercial humic acid and sodium alginate have been used as model substances representative of natural organic matter and extracellular organic matter, respectively. All fouling experiments were carried out in a special single fiber apparatus. An important parameter considered in the study of both model substances is the concentration of calcium ions, which promote their aggregation and influence the rate of flux decline, the reversibility of fouling and rejection. Membrane fouling by humic acid appears to be the outcome of simultaneous action of several fouling mechanisms. Initially, a relatively rapid irreversible fouling takes place due to internal pore adsorption; however, progressively pore blocking becomes important and a fouling layer develops on the membrane. Sodium alginate fouling on the other hand is apparently due to two consecutive mechanisms; i.e. a rapid irreversible fouling due to internal pore constriction, followed by cake development on the membrane surface which becomes the dominant mechanism. Comparing fouling in both cases it can be inferred that even though sodium alginate fouling is more severe than the one caused by humic acids, it is to a large extent reversible by backwashing. On the contrary, fouling caused by humic acid is characterized by greater and increasing with calcium addition irreversibility, which is not remedied by the periodic backwashing. The different fouling propensity of the two types of macromolecules is apparently due to differences of their physical–chemical characteristics.     

超滤和纳滤膜分离提取纳他霉素

为提高纳他霉素(natamycin)生产提取得率,减少溶剂使用,本文采用超滤、纳滤操作对工业生产的纳他霉索发酵液进行处理。实验结果表明:操作压力、操作时间及料液流速对超滤过程有很大影响。通过超滤可将蛋白质等大分子杂质去除,然后再用纳滤膜对超滤渗透液进行浓缩纯化,对纳滤工艺的操作条件如进料压力、料液pH、浓缩倍数等进行了研究。采用超滤、纳滤技术提取纳他霉素,其收率可达62.74%。     

Concentration by Membrane Ultrafiltration of a Shear-Thinning Fluid

Abstract

Many commercial membrane processes involve fluids whose rheological properties are non-Newtonian. However, very little has been published on ultrafiltration of non-Newtonian fluids. The aim of this work is to show some experimental results concerning the concentration by membrane ultrafiltration of fluids whose viscosity is high and shear-thinning. Experiments were performed with xanthan solutions as model shear-thinning fluids. The variations of permeate flux with respect to the operating parameters show the unusual effects of some of these parameters. It is shown that when the feed solution in an ultrafiltration process has shear-thinning properties, those properties have an enormous influence in determining the operation efficiency.     

Magnetic properties of metal layer deposited by reduction of polymer containing metal ions

Magnetic properties of metal layer deposited by reduction of polymer containing metal ions were investigated. Varying the ratio of the cobalt ion to the nickel ion in the polymer, the coercivity, the maximum flux density and the remanent flux density of the deposited metal layer were changed from 100 to 600 Oe, from 1 000 to 12 600 G and from 500 to 7 600 G, respectively. The X-ray diffraction pattern of the metal layer with excellent magnetic properties gives distinct peaks corresponding to the (101) and (100) planes of the crystal of α-Co. This suggests that such a deposited metal layer has the structure of highly crystalline metal layer.     

浸没式PAC-AMBRs系统中PAC缓解膜污染的研究进展

浸没式粉末活性炭-好氧膜生物反应器(powdered activated carbon-aerobic membrane bioreactors,PAC-AMBRs)是一种利用PAC吸附性、微生物降解性和膜分离特性的新型废水处理技术。本文重点分析了近20年来浸没式PAC-AMBRs系统直接投加PAC缓解膜污染机制的研究成果,探讨了PAC通过对污泥絮体和溶解性有机物的综合影响缓解膜污染的机制,分析了PAC投加量和补充率对膜污染的影响。通过分析可知PAC缓解膜污染是一个综合作用的结果。以PAC为载体形成的污泥絮体在膜表面形成结构疏松和抗压性强的滤饼层,不仅能有效降低滤饼层阻力(cake resistance,R_c),还可以作为自成型动态膜截留溶解性有机物和悬浮微生物等来减少此类污染物造成的膜污染。PAC通过吸附和/或表面附着的微生物降解溶解性有机物的协同作用降低其造成的过滤阻力。定期排出和补充一定量的PAC可以提高缓解膜污染的效率。     

PVC/PU共混超滤膜性能研究

PVC膜对糖类化合物有较强的排斥力,但其亲水性差,而聚氨酯有较强的亲水性,本课题研究聚氯乙烯(PVC)与聚氨酯(PU)的共混膜,探讨相转化法制备PVC/PU共混超滤膜的性能。实验结果表明,当聚合物浓度为16%,PVC/PU以8/2(质量分数)共混时,可制的水通量、截留率较好的多孔膜。     

UF membrane fouling by mixtures of humic acids and sodium alginate: Fouling mechanisms and reversibility

The fouling characteristics of ultrafiltration (UF) hollow fibers are studied in dead-end mode, with and without periodic backwashing, by filtering dilute mixtures of humic acids (HA) and sodium alginate (SA) — a polysaccharide — in the presence and absence of calcium ions. The fouling behaviour of the HA/SA mixtures (regarding reversibility by backwashing and flux recovery) is quite similar to that of polysaccharides alone, even when the SA proportion is relatively small. The organic species rejection in filtration of HA/SA mixtures is greater than that for separate HA or SA filtration, increasing with increased polysaccharides concentration in solution. In the presence of Ca²⁺, the cake filtration mechanism dominates; some deviation, at the start of filtration, especially with HA-rich mixtures, is attributed to membrane pore constriction possibly caused by small molecules, not retained by the developing cake. The specific cake resistances of HA/SA mixtures are relatively high and tend to be much closer to those of SA deposits, than to HA layer resistances. The reversibility of mixed fouling layers and the very high flux recovery by backwashing are attributed to their coherent gel-like structure, which is a typical feature of polysaccharides.     

介孔金属有机框架材料吸附水中重金属离子研究进展

介孔金属有机框架材料（介孔MOFs）相较于传统吸附剂具有孔径大、孔隙率可调、比表面积大、官能团丰富,便于功能化改性修饰等优点,可高效地吸附水体中重金属污染物。本文介绍介孔MOFs的特性、合成策略及四种合成介孔MOFs的方法,重点分析四种方法的介孔形成机理及其所面临的问题,并将四种合成方法的优劣进行了比较。详述介孔MOFs吸附去除水中重金属离子、类重金属阴离子以及放射性金属离子的研究进展;介绍了介孔MOFs在吸附去除重金属离子方面的可重复利用性;阐述介孔MOFs吸附去除水中重金属污染物的作用机理。对介孔MOFs成本高昂、合成条件苛刻、回收利用难等问题提出了优化方向,指出提高介孔MOFs的水稳定性、易回收利用、简便绿色合成技术以及痕量去除将是未来的研究方向。     

Membrane fouling in electrodialysis: a model and experiments

Membrane fouling is a common cause for poor performance in electrodialysis systems, usually because it reduces the limiting current. Fouling may be caused by deposits of either neutral matter or colloidal matter with ion exchange properties. In the present paper a model for membrane fouling is developed and expressions are derived for the reduction in limiting current caused by both neutral fouling films and films having ion exchange properties. The effect of fouling is shown to depend not only on the properties of the fouling film, but also on the hydrodynamic conditions in the channels and in the case of ion exchange fouling films on the salt concentration in the dialysate channel. Ion exchange fouling films are shown to be much more effective in reducing the limiting current than neutral films. Some experimental data are presented which confirm the trend of the theory for fouling with ion exchange films.     

反渗透膜与超滤膜的过滤性能分析

以反渗透膜与超滤膜为研究对象,通过计算跨膜压差、膜通量、渗透系数,对这两种滤膜的过滤性能进行比较分析。     

超滤技术及其应用与发展

简要介绍了超滤分离的基本原理、特点及其在食品生产和环境保护中的应用。超滤是一种流体切向流动和压力驱动的过滤过程并按分子量大小来分离颗粒。超滤膜是一种孔径范围为0.001～0.02微米的一种微孔过滤膜。超滤膜采用压力差为推动力的膜过滤方法为超滤膜过滤。最后对超滤膜污染的预防和避免提出了解决的意见。     

膜生物反应器中的膜污染及其再生

作为21世纪最具潜力的水处理技术之一,膜生物反应器受到越来越多的重视,在污水处理与回用中有着良好的应用前景,但膜污染和膜再生技术已成为制约其发展的瓶颈.介绍了膜污染的分类和机理,并从膜的性质、混合液的性质以及操作条件等方面对形成膜污染的影响因素及膜污染的防治进行了综述,同时阐述了几种常用的膜污染再生方法.     

聚醚砜超滤膜的制备与优化

为了给复合膜制备提供理想的支撑基膜,采用L-S相转化法制备聚醚砜超滤膜。通过正交实验设计,系统研究了各种因素对聚醚砜超滤膜性能的影响,并采用回归分析得到了模型方程。结果表明:所制备的聚醚砜超滤膜的水通量为246. 9L·m-2·h-1 (操作压力0. 1MPa),该膜对浓度为500mg/L的聚乙烯醇(PVA80 000)截留率达95%以上。     

Removal and recovery of heavy metal ions in fixed and semi-fluidized beds

Uptakes of heavy metal ions such as Pb²⁺ and Ni²⁺ were studied experimentally in fixed and semifluidized beds packed with a strong cation exchange resin, Amberlite 200. Single and binary aqueous solutions of lead and nickel ions were passed through ion exchange columns, and the exit concentrations were measured to get the breakthrough behavior of the ions. From the exit concentration profiles, the breakthrough time and the ion exchange capacity were evaluated. After removal of heavy metal ions from binary solution of lead and nickel ions until the breakthrough time, two metal ions were recovered by precipitation and resolubilization of lead. In this paper, the recovery yield and separation efficiency are rigorously discussed.