|Thesis Advisor||单保庆 ; 魏源送|
|Place of Conferral||北京|
|Keyword||密闭生保系统 尿液 Closed Life Supporting System 纳滤 Urine 盐回收 Nanofiltration(Nf) 膜污染 Salt Recycling Membrane Fouling|
|Other Abstract|| 环境控制与生命保障系统（简称“环控生保系统”）直接关系到航天员的生命安全，是载人航天不可缺少的保障条件。它通过对航天器密闭舱环境进行控制，为航天员提供水、氧、食物等必需物质和其它的生活保障。水的再生利用和闭路循环不仅是空间站和长期载人航天飞行任务的必然需求，而且是再生生保系统的最为关键组成之一。尿液中有机物、氨氮和矿物质元素的含量都较高，是实现密闭生保系统废水闭路循环的难点和关键所在。目前国内外尿液处理的研究集中在水、N、P养分的回收利用，缺乏对单价盐（如氯化钠）回收利用的报道。因此，本文采用纳滤膜技术对密闭生保系统尿液中的单价盐进行回收，在纳滤膜组件筛选、操作参数优化、膜污染形成机制及控制等方面开展系统研究，以期探索密闭生保系统尿液中单价盐回收利用的有效方法，为实现密闭生保系统中矿物质元素的长期循环利用提供科学依据。|
膜污染特征及其防治的研究结果表明，DL膜处理空间站模拟尿液的膜污染随处理批次增加逐渐加剧，处理前三批时膜污染增加程度缓慢，第四批后膜污染形成速度快速增加，处理七批尿液后，DL膜的纯水通量较清洁膜纯水通量下降了25.7%。DL膜污染的类型为有机污染、无机污染和生物污染共存，其中有机污染主要为可溶性微生物代谢物（SMP）和芳香类蛋白质Ⅱ类物质，无机污染包括Ca、Mg的结垢污染，生物污染主要为微杆菌Microbacterium和不动菌Acinetobacter，分别占比52.17%和32.61%，此外还含有少量的绿脓杆菌Pseudomonas、杆菌Bacillus、丛毛单胞菌Comamonas、肠杆菌Enterobacter和类芽孢杆菌Paenibacillus。采用先碱洗(0.1wt%NaOH+0.03wt%SDS，pH10.5)后酸洗(HCl，pH2.5)的清洗策略可达到较好的膜清洗效果。; Environmental control and life support system (ECLSS) is a critical subsystem of manned space flight. It is an indispensable safeguard for the life of astronaut in space. In ECLSS, the water, oxygen, food and other life-support were provided for astronaut by controlling the environment of manned space flight. Water closed loop recycling is not only the inevitable demand in the space station and long-term manned space flight mission, but also one of the most critical component in life support system. Due to high concentrations of organics, ammonia, and minerals in urine, thus, the treatment and reclamation of urine is the key and difficulty to circulate the wastewater in closed life supporting system. Though there were a lot of studies on recycling water, N and P from urine, there is a missing gap between recycling minerals and urine reclamation. Therefore, nanofiltration (NF) was used to treat urine and recycle monovalent ions in it in this study. And the purpose of this study was to develop an effective method to recycle mineral element in urine through selecting NF membrane module, optimizing NF membrane operational parameters, investigating NF membrane fouling and developing membrane fouling control strategy.
Six NF membranes of DK，DL，NF2，NF3，NF200，DF, which were produced by GE Osmonics, Sepro，DOW and OriginWater Corp, respectively, were selected to treat space station ersatz urine. Results showed that there were apparent different on membrane flux and solute rejection between different membranes. The TOC rejection rates of other five NF membranes were below 60% except DF membrane. Both the monovalent and multivalent ions could be rejected effectively by both DK and NF200 membranes, however, NF2 membrane had the bad performance of rejecting monovalent and multivalent ions. Thus these three NF membranes of DK, NF200 and NF 2 were not suitable for separating monovalent and multivalent ions in this study. As far as the DF membrane was concerned, though it had low rejections of K+ and Na+, the rejections of Cl- was high, which induced poor separation of anions. The ion separation rates of both DL and NF3 membranes were about the same. Though the ion separation rate of NF3 membrane is a little higher than DL membrane, the flux is relatively low. Therefore, the DL and NF3 membranes were chosen for further research.
The operational parameters including transmembrane pressure (TMP), feed flow, pH and concentration factor were investigated for comparing their effects on performance of DL and NF3 membranes. Results showed that both the Scation and Sanion of the DL membrane were lower than those of the NF3 membrane, which illustrated that the ion separation of DL is better than NF3. Moreover, the membrane flux of DL is almost double as NF3 membrane. Therefore, the DL membrane was selected as the suitable NF membrane in recycling mineral element in closed life supporting system. The optimal operational parameters of the DL membrane were at TMP of 7~9 bar, influent flow of 4 L/min, pH of 6.0 and concentration factor of 3.0~4.0, respectively. After storing, the urea in the DL membrane permeate could be decomposed into ammonia, which could decrease the effect of TOC in the NF permeate. Under TMP of 8bar, influent flow of 4L/min, pH of 6.0, concentration factor of 4.0 and through storing for 72 hours, the concentrations of Na+, K+, Cl-, NH4+-N, TOC, Ca2+, Mg2+ SO42- and PO43-in the DL membrane permeate were at 871.6, 596.0, 1654.3, 2454.7, 143.2, 1.0, 2.7, 38.3 and 4.4mg/L, respectively. These results of the DL membrane permeate proved that the monovalent and multivalent ions could be separated effectively in space station ersatz urine by NF membrane. In addition, the large amount of ammonia could be removed by the following step of evaporation.
Membrane fouling analysis results showed that, the fouling of the DL membrane became gradually severe according to the increase of treatment batches. At the first three batches, the increase of fouling rate was not quickly. From the forth batch, the fouling rate of the DL membrane was increased. The pure water flux decreased by 25.7% comparing with the virgin DL membrane when treating seven batches of space station ersatz urine. The DL membrane fouling contains organic fouling, inorganic fouling and bio-fouling. SMP and aromatic protein Ⅱwere the main composition of organic fouling, while Ca and Mg were the main composition of inorganic fouling. Bio-fouling mainly contained Microbacterium and Acinetobacter, which took up 52.17% and 32.61% of the microbes, respectively. In addition, there were also some Pseudomonas, Bacillus, Comamonas, Enterobacterand Paenibacillus in membrane bio-fouling. The foulants of the DL membrane could be removed by chemical cleaning, including a basic cleaning at pH 10.0-10.5 with 0.3 wt% sodium dodecyl sulfate (NaDS) (C12H25SO4Na), and followed an acid cleaning at pH 2.0-2.5 which was diluted by concentrated hydrochloric acid (HCl, 37%), under which it could get cleaning effect very well.
|王健行. 密闭生保系统中基于盐回收的纳滤膜技术及膜污染防治[D]. 北京. 中国科学院研究生院,2016.|
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