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微藻细胞的磁性絮凝与规模化采收
Alternative TitleMagnetic Flocculation and Large-scale Harvesting of Microalgal Cells
胡一茹
Subtype工程硕士
Thesis Advisor郭晨
2014-04
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
KeywordFe3o4纳米颗粒   fe3o4-pei纳米颗粒   磁性分离   微藻采收   磁分离器
Abstract微藻能源是理想的可再生能源,能够部分替代化石能源。微藻能源的开发利用受到微藻细胞小、浓度低导致的采收困难、采收成本高的限制。传统的微藻采收方法,如过滤、絮凝、离心等,存在着采收效率低、采收能耗大等问题,阻碍了微藻能源的发展。 本文针对微藻采收中现存问题,分别以海洋藻微拟球藻和淡水藻小球藻为代表,采用磁性絮凝技术采收能源微藻细胞,将磁分离技术操作简便、快速、高效的特点应用到微藻采收领域。研究了裸露Fe3O4纳米颗粒对海洋藻微拟球藻的采收,测定了生长过程、pH、颗粒用量、温度等对采收效果的影响,并将采收微拟球藻细胞后获得的培养液用于微拟球藻的再培养;通过测定小球藻细胞的表面形貌、官能团,合成了针对性的多氨基Fe3O4-PEI纳米颗粒,同样考察了生长过程、pH、颗粒用量、温度等对小球藻采收效果的影响以及培养液的回用,探索了微藻采收机理;采用磁分离器对小球藻进行采收,并对采收过程的多个影响参数进行优化,最终获得了一个微藻采收的工艺和装置。通过实验得出以下结论: (1)Fe3O4纳米颗粒采收微拟球藻受微藻生长阶段的影响,微拟球藻生长到第18天时达到最大生物量,Fe3O4纳米颗粒对微拟球藻的采收能力达到最大值;Fe3O4纳米颗粒用量为120 mg/L对微拟球藻的采收效率在2 min内能达到95%以上;酸性条件下的静电力相互作用以及中碱性条件下微藻细胞的聚集有利于微拟球藻的采收;Fe3O4纳米颗粒在15、25、35 oC对微拟球藻的最大吸附能力分别为15.85、16.16、16.28 g-微藻干重/g-颗粒,即较高温度条件有利于Fe3O4纳米颗粒对微拟球藻的采收;Fe3O4纳米颗粒对微拟球藻的采收符合朗格缪尔吸附模型,为单分子层吸附;Fe3O4纳米颗粒采收微拟球藻细胞后的培养液用于微拟球藻的再培养,连续回用5次,生长相同周期后获得的微拟球藻生物量没有下降。 (2)通过傅里叶红外检测发现小球藻细胞表面带有-COOH、-OH等官能团,这些官能团的离子化作用导致小球藻细胞带负电荷,透射电镜分析显示小球藻细胞大小为2 μm,原子力显微镜扫描表明小球藻细胞表面是凹凸起伏的沟壑形貌,起伏范围约为-60 nm-60 nm,在此基础上指导制备了正电荷富集的磁性纳米颗。 在Fe3O4纳米颗粒表面修饰氨基富集的PEI分子合成Fe3O4-PEI纳米颗粒,颗粒粒径大小为12 nm,磁饱和强度为69.77 emu/g,具有超顺磁性;Fe3O4-PEI纳米颗粒对小球藻的采收在用量为20 mg/L时,在2 min内的采收效率能达到97%;在小球藻生长到第14天时,Fe3O4-PEI纳米颗粒对小球藻的采收能力最大,达到32.61 g-微藻干重/g-颗粒;酸性条件下对Fe3O4-PEI纳米颗粒采收小球藻有利;Fe3O4-PEI纳米颗粒对小球藻的采收符合朗格缪尔吸附模型,为单分子层吸附;在15、25、35 oC对小球藻的最大吸附量分别为84.03、86.21、93.46g-微藻干重/g-颗粒,因此对小球藻的采收应该选择较高温度时进行;采收小球藻细胞后的培养液用于微藻的再培养,循环使用10次,获得的生物量并没有明显下降。采收机理为Fe3O4-PEI纳米颗粒所带正电荷与小球藻细胞表面负电荷之间的静电力吸附作用,PEI在Fe3O4纳米颗粒表面围成的空间网状结构富集大量的正电荷氨基对负电荷微藻的吸引力强,以及Fe3O4-PEI纳米颗粒具有的纳米效应。Fe3O4-PEI纳米颗粒对小球藻的采收具有用量少,用时短,效率高的优势。 (3)利用磁分离器采收小球藻,以Fe3O4纳米颗粒为磁絮凝剂,采用分批磁分离方式和连续磁分离方式对小球藻进行采收,结果表明:分批磁分离方式采收微藻最佳停留时间为40 s,最佳微藻浓度为0.75 g/L,连续10批次不刮除磁鼓上的絮凝体对微藻的采收效率不变,絮凝体厚度由1.5 mm增加到5 mm;连续磁分离方式采收微藻在最佳流速100 mL/min时对微藻的采收效率为95%,最适微藻浓度为0.75 g/L,磁分离器连续运行1 h对微藻的采收效率保持不变。采用磁分离器操作简单、节约能源,可以实现微藻的大规模采收,容易实现工业化。
Other AbstractMicroalgae have been recognized as one of the most prospective renewable energy that is substitute of the fossil fuels. However, obtaining biofuels from microalgal biomass is associated with drawbacks such as high cost and/or energy usage due to their small size and low concentration. Conventional harvesting technologies have been developed such as filtration, flocculation centrifugation. However, those methods still have some limitations of low harvesting efficiency and energy consumption, the harvesting of microalgae continues to be a challenge. The objective of this study is to develop a simple and efficient harvesting method with magnetic separation which is simple operation, fast separation, and high efficiency to harvesting marine algae Nannochloropsis maritima and freshwater algae Chlorella ellipsoidea. The marine algae N. maritima was harvesting by naked Fe3O4 nanoparticles, and the effect of microalgal culture stages, pH, nanoparticles dosage and temperature on the harvesting efficiency was studies. The culture medium obtained from magnetic separation was reused for algal cultivation. Amino functional Fe3O4–PEI nanocomposites were synthesized based on the surface characteristics of C. ellipsoidea, and several operation parameters including growth stage, pH, nanocomposite dosage and temperature that affected the harvesting efficiency were carried out as well as the reusability of the culture medium. The adsorption mechanism was evaluated. A magnetic separator was developed and used for efficient microalgae harvesting by magnetic nanoparticles. The effects of key parameters of the harvesting process were optimized to provide a promising method for efficient microalgae harvesting in practice. The main results are as follows: (1) The harvesting of N. maritima by naked Fe3O4 nanoparticles was effected by culture, the algal biomass reached the maximum of 1.02 g/L at day 18 and the recovery capacity of the magnetic nanoparticles for the algal cells also reached the maximum of 10.05 g DCW/ g particles at day 18. The harvesting efficiency reached more than 95% when the nanoparticles dosage was 120 mg/L within 2 min. Electrostatic attraction at acidic pH and cell aggregation under neutral and alkaline conditions was beneficial for harvesting the algal cells. The maximum adsorption of nanoparticles for algae was 15.85、16.16、16.28 g-DCW/g-particles at 15、25、35oC, respectively. It indicated that higher temperature resulting in better harvesting. The adsorption fitted the Langmuir model indicated that adsorption was monolayer coverage. The medium was reused for 5 cycles and got similar biomass production of the fresh medium. (2) The study of C. ellipsoidea by ATR-FTIR showed that the surface contained –COOH and –OH groups and its ionization effect resulting in the negatively charged. The TEM showed the algal cells was of 2 μm. The AFM revealed the algal cell surface appeared rough with sphere-like mound structures varying from -60 nm-60 nm. Designing and synthesizing of functional magnetic nanoparticles with positive charge was based on the characteristics of the microalgal cells. Fe3O4-PEI nanocomposites was synthesized by coating the PEI which contained a high concentration of NH2 groups onto the Fe3O4 nanoparticles surface. The nanocomposites were 12 nm in diameter and 69.77 emu/g of saturation magnetization. A harvesting efficiency of 97% was achieved when the dosage was 20 mg/L in 2 min. The recovery capacity of the Fe3O4–PEI nanocomposites reached a maximum value of 32.61 g-DCW/g-nanocomposites at day 14. Low pH value favored the harvesting process. The Langmuir model had a better fit with the adsorption process indicated that the adsorption was monolayer. The maximum adsorption was 84.03, 86.21, 93.46 g-DCW/g-nanocomposites at 15、25、35oC, respectively. The culture medium was successfully reused for microalgal cultivation over 10 cycles. The adsorption mechanism was showed to be the electrostatic attraction and nanoscale interactions between the nanocomposites and the microalgal cells, and the branched PEI molecules on the Fe3O4 nanoparticles formed a network structure which resulted in a very strong attractive interaction. The harvesting of microalgae by Fe3O4 –PEI nanocomposites was low dosage, short time and high efficiency. (3) A magnetic separator was applied to harvesting microalgae by Fe3O4 nanoparticles in batch and continuous operations. The results showed that the batch operation was 40 s with optimal microalgal concentration of 0.75 g/L, and the harvesting efficiency kept constant over 10 times of batch operation without collecting the aggregates and the thickness was from1.5 mm to 5 mm. In the continuous operation, the harvesting efficiency kept more than 95% when the flow rate was 100 mL/min, the optimal microalgal concentration was 0.75 g/L, and the harvesting efficiency kept constant for running 1 h. The magnetic separator provided a promising simple operation and energy save approach for further scale-up of efficient microalgae harvesting in industry.
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15580
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
胡一茹. 微藻细胞的磁性絮凝与规模化采收[D]. 中国科学院研究生院,2014.
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