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题名: 正渗透-膜蒸馏(FO-MD)集成膜脱盐过程温度效应分析
作者: 李洁
学位类别: 硕士
答辩日期: 2014
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 栾兆坤 ; 王军
关键词: 正渗透 ; forward osmosis ; 膜蒸馏 ; membrane distillation ; FO-MD集成工艺 ; FO-MD integrated process ; 温度效应 ; temperature effect ; 脱盐 ; desalination
其他题名: Effect of temperature on forward osmosis-membrane distillation (FO-MD) integrated system for desalination
中文摘要:       本研究针对低能耗、环境友好型正渗透(FO)膜分离技术中高盐汲取剂安全、高效、低成本循环回收的关键难题,在前期膜蒸馏(MD)研究基础上,构建FO-MD集成膜分离工艺。系统考察FO-MD集成膜过程的温度效应,重点探讨温度对FO过程的影响机理。在此基础上,以实际污水作为处理对象考察FO-MD工艺处理效果,探讨其同时实现污水浓缩与海水脱盐的可行性。取得创新性研究成果如下: 1. 系统考察了FO-MD集成膜工艺操作参数,分析了工艺运行基本规律。PRO模式(膜活性层朝向汲取液)较FO模式(膜活性层朝向原料液)的初始通量高,但随时间衰减明显;料液流动方式对FO通量性能影响不明显;增大膜面流速,能缓解外浓差极化和膜污染的影响,提高膜通量;增大汲取液浓度,能够提高FO驱动力,通量明显增加;FO系统温度越高,水通量越大,且FO膜两侧料液温差越大,水通量越高,汲取液温度影响比原料液显著。优化工艺操作条件如下:FO运行模式,对流操作方式,膜面流速0.28m/s,汲取液浓度35g/L,原料液和汲取液侧温度分别为20℃和53℃;MD热侧温度53℃,冷测温度20℃,热侧流速0.50m/s,冷侧流速0.15m/s,并流方式。在此条件下,集成工艺水传输量趋于平衡,汲取液浓度基本保持恒定。 2. 分析探讨了温度对FO过程的影响机理。温度影响汲取液与FO膜的性质,即随温度升高,汲取液渗透压、溶质扩散系数、质量传递系数增加,溶液粘度下降;纯水渗透系数、溶质渗透系数均随料液温度上升而增加;从而促进稀释作用导致通量衰减;并增大反向扩散趋势,但未影响膜的选择性能;稀释性的内浓差极化效应对FO影响较大,且温度升高效应降低;而浓缩性的外浓差极化效应对FO影响较小,温度对其无明显影响;温度越高,膜表面污染越严重,但高温条件对污染膜的清洗无不利作用,采用物理清洗的方式即可明显改善膜污染状况。 3. 研究考察了实际生活污水的FO-MD集成脱盐效果。结果表明,集成工艺对生活污水中大部分污染物去除效率优于FO工艺单元,达90%以上。色氨酸类芳香族蛋白质基本被去除,仍含有低浓度的酪氨酸类芳香族蛋白质类有机物和溶解性微生物代谢产物,其中大分子量有机物全部截留,仅有少量小分子有机物透过膜。膜表面主要污染物为多糖类和蛋白质类有机物,无机污染物以硅酸盐为主,污染物结构松散,能够有效地被物理清洗去除。由于FO膜截留了原料液中的大部分污染物,MD膜污染情况较轻,工艺运行120h产水量稳定并获得较好的产水水质。
英文摘要:       In view of the technical advantages of forward osmosis (FO), such as less energy input, lower fouling tendency, and higher water recovery over conventional membrane technology, the FO related research was carried out. In order to realize highly efficient recovery and recycling of draw solution during FO process with low cost, a forward osmosis–membrane distillation (FO–MD) integrated membrane system were constructed in this study. On the basis of the study of FO and MD processes, the temperature effect on the performance of FO-MD integrated process was investigated. Besides, the mechanism of the temperature-induced effect on FO was discussed. The treatment efficiency of sewage by FO-MD system was studied to explore its feasibility for simultaneous desalination and wastewater treatment. The main conclusions are as follows: 1. The operation parameters of FO-MD process were investigated. Results showed that water flux decline was more significant in PRO mode with higher initial flux compared to FO mode. And little influence of liquid flow pattern on FO flux performance was observed. Higher water flux was achieved at higher flow rate and higher draw solution (DS) concentration separately. This was due to the increased driving force across the membrane. Higher transmembrane temperature difference between the feed and draw solutions contributes to enhanced water. Water flux was significantly increased with less heat consumption by elevating only the DS temperature rather than feed solution (FS). The operating conditions for following FO experiments were as follows: FO mode, counter-current flow, flow rate of 0.28m/s, DS concentration of 35g/L, FS and DS temperature of 20℃ and 53℃; MD feed and downstream temperature of 53℃ and 20℃, flow rate of 0.50m/s and 0.15m/s, co-current flow. 2. The mechanism of the temperature-induced effect on FO was discussed. The osmotic pressure of DS, diffusion coefficient of draw solutes, mass transfer coefficient, and the water and solute permeability coefficient of the membrane increased at higher temperature, while the viscosity decreased with the increase in temperature, resulting in the dynamic dilution effect and the tendency of reverse diffusion. The selectivity of FO membrane did not affected by temperature increase. Higher temperature caused mitigation of diluted internal concentration polarization (ICP) effect. ICP effect had much more significant influence on FO process than concentrated external concentration polarization (ECP) effect. Besides, higher temperature caused adverse effects on membrane scaling. However, the fouling on membrane surface is reversible, which can be removed by physical cleaning. 3. The treatment of sewage by FO-MD process was investigated. The results show that the removal efficiency of anions, TOC, NH3-N, TN and TP was more than 90%, which is better than FO process alone. Tryptophan proteins have been removed, while low concentrations of tyrosine proteins and soluble microbial products remained in product water. High molecular weight contaminants were completely removed with only a few low molecular weight contaminants permeate through the membrane. The main foulants on the membrane surface was organic matters like polysaccharides and proteins, and the main inorganic pollutant was silicate. Fouling layer can be effectively removed by physical cleaning due to its loose structure. Besides, as an effective pretreatment barrier of most contaminants, FO contributes to the light MD membrane fouling.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/35203
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
李洁. 正渗透-膜蒸馏(FO-MD)集成膜脱盐过程温度效应分析[D]. 北京. 中国科学院研究生院. 2014.
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