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膜分离技术在废水处理和蛋白质回收中的应用研究
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摘要
膜分离技术是一门独立的学科,属高新技术领域。国外20世纪初就已开始了对微孔滤膜的研究,至60年代,继早期开发的醋酸纤维素滤膜之后,又开发出许多新品种,如聚砜、聚酯、聚芳酰胺、聚四氟乙烯等。70年代初,美国首先实现微孔滤膜商品化,为精密过滤提供理想的过滤介质。膜分离技术逐渐成为提高产品质量,改善研究方法,缩短生产周期和提高工效的重要手段。随着精密过滤技术在工业及科研中的重要性日益提高,膜分离技术的应用得到更迅速的发展。
    目前常见的几种膜分离技术主要有:微孔过滤(Micro filtration,简称MF)、超过滤(Ultra filtration简称UF)、反渗透(Reverse Osmosis,简称RO)、电渗析(Electro dialysis,简称ED)、渗透蒸发(Pervaparation,简称PV)、液膜(Liquid Membrane,简称LM)等。
    随着工业化的发展,大量的生活和工业废水排入水体,使人们赖以生存的水源日益受到污染。膜分离技术作为高科技领域中一门新兴的学科,其潜在的应用领域被逐渐认识发现并应用于越来越多的领域。近年来膜技术在环保领域中的应用已受到广泛的关注。
    吉林省是我国重要的粮食产地,先后建立了许多大型粮食深加工企业,在加工过程中产生大量富含蛋白质的废水,蛋白质是非常重要的营养物质,也是引起COD值增加的主要因素,若以废液形式排放到环境中则会带来严重的环境问题,同时也造成了极大的浪费。
    
    针对这一问题,我们对采集到的废水样分别采用调节溶液pH值使其达到等电点进行沉淀分离、通过中空纤维膜超过滤装置进行超过滤的研究。目的是通过提高蛋白质回收率,减少蛋白质的排放,降低污染负荷,同时取得一定的经济效益。
    其反应机理是:当有机高分子处于等电点时,其正负电荷相等,即净电荷为零,分子颗粒在溶液中不存在相同电荷的相互排斥作用。这时溶液最不稳定,极易相互碰撞凝聚而沉淀析出,此时其溶解度最小。
    超过滤是在压力驱动下,溶液中的小分子溶质及溶剂透过膜,而溶质大分子被截留的分离过程,其基本原理为筛分效应,超滤技术具有设备简单,操作方便,可在分子级水平上进行分离,无相变,节约能源。
    试验表明,通过调节等电点、中空纤维膜超过滤装置进行超过滤分离可以使淀粉糖废水和淀粉废水的COD去除率达到90%以上。
    另外,在任何膜分离技术应用中,都会碰到膜污染问题,膜污染被认为是超滤过程的主要障碍。膜污染是指处理物料中的微粒、胶体粒子或溶质大分于由于与膜存在物理化学相互作用或机械作用而引起的在膜面上的沉淀与积累或膜孔内吸附造成膜孔径变小或堵塞,使水通过膜的阻力增加,妨碍了膜面上的溶解与扩散,从而导致膜产生通透流量与分离特性的不可逆变化现象。广义的膜污染不仅包括由于不可逆的吸附、堵塞引起的污染(不可逆污染)而且包括由于可逆的浓差极化导致凝胶层的形成(可逆污染),二者共同造成运行过程中膜通量的衰竭。水力清洗着重去除可逆污染物
    
    
    (凝胶层)及部分不可逆污染物(膜面沉积物)。归结起来浓差极化作用、凝胶层的形成和微生物的滋生是使膜分离过程的运行阻力增加、通量降低的主要因素,并且浓差极化会加剧膜的污染。影响膜污染的因素很多,比如溶质大小、膜结构、膜的物理特性、膜溶质溶剂之间的相互作用(包括静电作用力、范德华力、溶剂化作用、空间立体作用)。
     为了解决这一问题,我们在实验过程中对影响渗透流量的各因素进行了研究。
     试验表明,渗透流量随着温度升高而增大,渗透流量也随着膜组件内流速增大而增加,随着pH值增大而增加,适宜的压力为0.2~0.3MPa。
     以上试验证明,膜分离技术在回收废水中的蛋白质,减轻废水后续处理的负荷,取得经济回报方面具有很大的发展前途。
    本文研究为膜分离技术在废水处理和蛋白质回收上实现工业化提供了有价值的参考。
Membrane Separation Technology is an independent subject, which belongs to high technology. The study of micro-filtration Membrane has been started from 20th century in overseas. Until 60 ages, following the cellulose acetate filtration film of primitive exploitation, a lot of new variety has been developed, such as polyester, agamid fiber, polyfluorte, traethylene and so on. Initial stage of 70’s, commercial of micro filtration Membrane achieved in America at first, which provide an ideal filter Membrane for precision filtration. In the field of precision Technology, classic analysis and separate method has been gradually replaced of Membrane Separation Technology, Which become importance means of increased production’s quality, improved study’s methods, shorten produce’s cycle and raised the efficiency. With the growing of precision filtration technology in industry and scientific research, Membrane Separation Technology will be getting faster development.
    At present the familiar Membrane Separation Technology : Micro filtration (MF)、Ultra filtration (UF)、Reverse Osmosis(PO)、Electro dialysis(ED)、Pervaparation(PV)、Liquid Membrane(LM)、etc.
    With the development of industry, a great deal of wastewater of living and industry entered into water. Those water sources, which people depend on, suffer into pollution. Membrane Separation Technology as a growth subject in the high technology, its potential application region was realized. At recent, Membrane Separation Technology has been wildly attention in the field of environmental protection application.
    JiLin province is an important foodstuff producing area. A lot of large foods processing factories were founded. A lot of protein wastewater comes into being during working. Protein is very important nutritious substance and a mainly factor of causing to COD’s increase. If the wastewater enter into environment will bring severe environmental problem and immense waste.
    Aim at this issue, we adjust pH, which comes up to isoelectric point to make deposit Separation, and adopt hollow fiber ultra filtration
    
    
    apparatus respectively. In order to increase recovery ratio of protein, reduce emission of protein, decrease pollution load, and In the meantime obtain great economic effect.
    Reaction mechanism: The Organic High Polymer in isoelectric point, which positive and negative charge is equal, net charge is zero, molecule pellet exclude reaction, Solution isn’t steady, very easy collide cooperation each other and that to deposit and separate out .By now solubility is the lowest.
    Ultra-filtration is driven by pressure. Mini-molecules in the solution pass through Membrane, but Macromolecules of the solute is hold back. Basic principle is sieving domino effect, its equipments are simple, operation convenience, separation in level of molecule, no change in potential economize energy sources.
    Experiment indicates: adjusting isoelectric point and ultra filtrating by ultra filtration apparatus of hollow fiber. Elimination ratio of COD of starch sugar and starch reach is above 90%.
    In addition, it will be meet the issue of membrane pollutes in the any of technical application. Membrane pollution considered to be a mainly obstacle in ultra filtration. Membrane polluted refers to dealing with the particle, colloid particle or solute heavy in the supplies. Owing to physical chemistry interaction or mechanical function with the membrane, which cause membrane aperture diminish or fill in to bank up, then making water penetrating obstruction of membrane increase, hindering dissolution and diffusion of the membrane, and causing irreversible change phenomenon of characteristic on membrane produce penetrating flow and separate.
    The broadly-defined polluted membrane is not merely including because irreversible absorption, pollution owing to jam and including because reversible strong difference which causing gel forming (reversible to pollute) of layer to polarize, The two forms cause membrane flux depleted during operation course together. Water washes aims to get rid of
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