基于造纸白水特性的超滤膜污染及控制研究

发布时间：2018-08-02 09:05

【摘要】：超滤技术作为一种高效、安全的物理分离方式在造纸白水封闭循环系统有机污染物的去除领域具有广阔的应用前景。然而白水复杂的水体环境及其中各类有机物所引起的超滤膜污染降低了白水中有机组分的去除效率,制约了膜技术在造纸白水处理领域的进一步推广。因此,深入研究造纸白水中有机物特性及白水环境对膜污染的影响,针对造纸工艺特点选择合理的预处理方式对于超滤技术处理造纸白水过程中产生的膜污染程度的缓解具有十分重要的作用。本论文以造纸白水中溶解性、胶体性有机物为研究对象,考察了白水中有机物特性以及白水环境对超滤膜污染的影响,同时采用阴离子垃圾固着剂去除白水中引起膜通量下降的主要有机污染物,以此缓解膜系统运行负荷,减轻膜污染。溶解性有机物是造纸白水中的主要有机成分之一。论文采用大孔树脂吸附及超滤膜分子量分级法对白水中溶解性有机物的亲疏水特性及分子量分布进行了表征,并研究了溶解性有机物特性对超滤膜污染的影响。结果表明,溶解性有机物以亲水性组分含量最高,占溶解性有机物总量的67.83%,而疏水性组分含量相对较少。溶解性有机物中亲水性组分、疏水性组分分子量分布与试验原水相似,均以分子量小于5KDa的小分子有机物为主。在溶解性有机物进行超滤过程中,亲水性有机物是造成膜通量下降的主要组分。这一类有机物能够在超滤初期便迅速到达膜表面,其中小分子量的亲水性组分引起膜孔堵塞,大分子的亲水性组分易造成浓差极化污染,从而引起严重的膜通量下降;疏水性有机物与聚醚砜超滤膜表面存在疏水作用,吸附在膜表面形成滤饼污染,膜通量下降较为缓慢。此外,研究通过扫描电镜及Hermia线性方程拟合分析了溶解性有机物分子量分布对超滤膜污染的影响机理。结果表明,大分子有机物更多地被机械截留于膜表面形成滤饼层污染,而堵塞污染则是小分子有机物引起膜通量下降的主要机理。白水环境是影响超滤膜污染的重要因素。本论文采用聚丙烯酸钠、硬脂酸钠作为造纸白水中溶解性及胶体性有机物的模拟物,分别研究了不同白水环境对有机物造成膜污染的影响。研究结果表明,较低的p H值能够减弱溶解性有机物与超滤膜表面的静电斥力,加速有机物在膜表面的吸附沉积,造成严重的膜通量下降。离子强度的增加同样会屏蔽有机物与膜表面的静电斥力,同时Na+的存在还能够通过压缩双电层的作用使得有机物更易接近膜表面,造成膜污染加剧。多价金属离子的存在不仅通过“主体架桥作用”造成白水中有机物分子之间相互连接形成复杂的空间网络状大分子,同时还能够在有机物与超滤膜之间形成“表面架桥作用”,增加有机物在超滤膜表面的吸附沉积,进而造成严重的膜通量下降。相同浓度条件下,Fe~(3+)比Ca~(2+)对膜通量下降的危害更大。白水环境对胶体性有机物引起的膜通量下降与溶解性有机物具有一定的相似性。酸性条件以及较高的离子强度能够加重胶体性有机物对膜污染的影响。多价金属离子的存在造成了胶体性组分粒径的增加,加重有机物在膜表面的吸附沉积,造成严重的滤饼层污染。由于白水中溶解性与胶体性有机物的存在对超滤系统具有明显的污染作用。论文针对造纸工艺特点及白水中有机物负电性较强的特点,采用高阳电荷密度的聚乙烯亚胺捕集白水中的有机污染物,同时利用聚乙烯亚胺与纸浆纤维之间的静电作用、氢键作用,最终将白水中有机污染物固着于纸浆纤维,带出白水系统,减轻超滤膜系统负荷。结果表明,随着聚乙烯亚胺用量的增加,白水中有机物发生聚集,并固着于纸浆纤维,经过动态滤水仪过滤之后,滤液中有机物引起的阳离子需求量明显降低,滤液浊度下降。当聚乙烯亚胺用量达到1%(相对于绝干纤维质量)时,滤液阳离子需求量、浊度分别下降了56.42%,63.16%,说明聚乙烯亚胺能够较好的捕集白水中的阴离子有机物并固着于纸浆纤维,明显改善进入超滤系统的白水水质。从聚乙烯亚胺(PEI)预处理前后的白水模拟溶液进行超滤的膜通量测定及膜表面扫描电镜可以看出,白水PEI预处理可以通过减少到达膜系统的有机物浓度,改变膜表面滤饼层结构提高膜通量,缓解膜污染程度。本论文完成了造纸白水中溶解性有机物亲疏水性和分子量分布特性的表征,研究了白水中主要有机物特性及白水环境包括p H值、Na+浓度、多价金属离子的存在对超滤膜污染的影响,同时提出了适合于造纸白水超滤处理的预处理方案,为白水封闭循环中的超滤膜系统稳定运行提供技术支持。
[Abstract]:Ultrafiltration technology has a wide application prospect in the field of organic pollutants removal in papermaking white water closed circulation system as a high efficient and safe physical separation method. However, the complex water environment of white water and the ultrafiltration membrane pollution caused by various kinds of organic compounds reduce the removal efficiency of organic components in white water, and restrict the membrane technology. It is further popularized in the field of papermaking white water treatment. Therefore, the characteristics of organic matter in papermaking white water and the effect of white water environment on the membrane fouling are deeply studied. The selection of reasonable pretreatment methods for the characteristics of papermaking process is very important for the mitigation of the degree of membrane pollution produced during the process of white water in papermaking. The characteristics of organic matter in white water and the effect of white water environment on the pollution of ultrafiltration membrane were investigated in white water and the effect of white water environment on the pollution of ultrafiltration membrane was investigated. At the same time, the main organic pollutants that caused the decrease of membrane flux caused by the anion solid solid agent were used to relieve the operating load of the membrane system and reduce the membrane pollution. The organic compounds are one of the main organic components in the white water of paper making. The macroporous resin adsorption and ultrafiltration molecular weight classification are used to characterize the hydrophobicity and molecular weight distribution of dissolved organic compounds in white water, and the effects of the properties of dissolved organic matter on the ultrafiltration contamination are studied. The results show that dissolved organic matter is used as a result. The hydrophilic component content is the highest, accounting for 67.83% of the total dissolved organic matter, but the hydrophobic component content is relatively small. The hydrophilic component in the dissolved organic matter, the molecular weight distribution of the hydrophobic component is similar to the test raw water, all with the small molecular weight less than 5KDa, and the hydrophilic property in the ultrafiltration process of dissolved organic matter. The main components of the membrane flux decrease. This kind of organic matter can quickly reach the membrane surface at the early stage of ultrafiltration, in which the hydrophilic components of small molecular weight cause the plugging of the membrane pores, and the hydrophilic components of the macromolecules are easily caused by the concentration polarization pollution, thus causing a serious decline in the membrane flux, and the hydrophobic organic matter and the Polyethersulfone ultrafiltration membrane table. There is a hydrophobic effect on the surface, which is adsorbed on the surface of the membrane to form a filter cake pollution, and the membrane flux decreases slowly. In addition, the influence mechanism of the molecular weight distribution of dissolved organic matter to the ultrafiltration membrane fouling is analyzed by scanning electron microscopy and Hermia linear equation. The results show that the macromolecules are more mechanically trapped on the surface of the membrane to form the filter. The main mechanism of the decrease of membrane flux caused by small molecule organic matter is the pollution of cake layer. The white water environment is an important factor affecting the ultrafiltration membrane fouling. This paper uses sodium polyacrylate and sodium stearate as the analogue of soluble and colloidal organic compounds in white water of paper making, and studies the effects of different white water environment on the organic matter. The results show that the lower P H value can weaken the electrostatic repulsion of dissolved organic matter and ultrafiltration surface, accelerate the adsorption and deposition of organic matter on the surface of the membrane, and cause a serious decrease of membrane flux. The increase of ionic strength will also shield the electrostatic repulsion of organic and membrane surfaces, while the existence of Na+ can also pass through The effect of the compression of the double layer makes the organic matter more accessible to the surface of the membrane, resulting in the aggravation of the membrane fouling. The existence of the polyvalent metal ions not only causes the interconnections among the organic molecules in white water to form complex space network macromolecules, but also can form a "surface frame" between the organic matter and the ultrafiltration membrane by the "main bridge action". "Bridge action" increases the adsorption and deposition of organic matter on the surface of the ultrafiltration membrane, resulting in a serious decrease in membrane flux. Under the same concentration, Fe~ (3+) is more harmful to the decrease of membrane flux than Ca~ (2+). The decrease of membrane flux caused by colloidal organic matter in white water environment is similar to that of dissolved organic matter. Acid conditions and higher levels are also higher. The ionic strength can aggravate the effect of colloidal organics on membrane fouling. The presence of polyvalent metal ions increases the particle size of colloidal components, aggravates the adsorption and deposition of organic compounds on the surface of the membrane, and causes serious contamination of the filter cake layer. The presence of dissolved and colloidal organic compounds in white water has obvious pollution to the ultrafiltration system. In view of the characteristics of papermaking process and the strong negative power of organic matter in white water, this paper uses polyethyleneimine with high positive charge density to capture organic pollutants in white water. At the same time, using the electrostatic interaction between polyethyleneimine and pulp fiber and hydrogen bond, the organic pollutants in white water are finally fixed to the pulp fiber and are taken out. The white water system reduces the load of the ultrafiltration system. The results show that with the increase of the polyethylenimide, the organic matter in the white water is aggregated and fixed on the pulp fiber. After the filtration of the dynamic filter, the demand for the organic matter in the filtrate is obviously reduced and the turbidity of the filtrate drops. When the amount of polyethyleneimine is 1% (relative) In the dry fiber quality, the demand of the filtrate cation, the turbidity decreased by 56.42%, 63.16% respectively, indicating that polyethyleneimine can better capture anionic organic compounds in white water and be fixed on the pulp fiber, obviously improving the white water quality into the ultrafiltration system. The white water simulated solution before and after the pretreatment of polyethyleneimine (PEI) is over. The filtration membrane flux measurement and membrane surface scanning electron microscopy (SEM) show that white water PEI pretreatment can reduce the concentration of organic matter to the membrane system and change the membrane surface filter cake layer structure to improve the membrane flux and alleviate the membrane fouling. The study has completed the characterization of the hydrophobic and molecular weight distribution characteristics of the dissolved organic matter in white water. The main characteristics of organic matter in white water and white water environment include the effect of P H, Na+ concentration and polyvalent metal ions on the ultrafiltration membrane pollution. At the same time, a pre treatment scheme suitable for ultrafiltration of white water in papermaking is proposed to provide technical support for the stable operation of the ultrafiltration system in the white water closed cycle.
【学位授予单位】：南京林业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X793;TQ051.893

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