微藻膜收获过程中藻源型有机物的膜污染机制及对策研究

Membrane microalgae harvesting is the key downstream process which not only harvests the microalgal biomass from diluted culture, but provides filtered culture which can be ready for recycling. During membrane harvesting process, fouling of the membrane by Algogenic Organic Matter (AOM) is the biggest challenge which reduces membrane flux dramatically. Composition and concentration of AOM vary with microalgal strain and its culture conditions. Moreover, the fouling is also closely related with the characteristics of membrane material and operational conditions. Till now the methodology for a comprehensively fractionate AOM, and evaluation the influence of AOM on the membrane fouling has not been established, and thus the mechanisms of membrane fouling by AOM during microalgal harvesting process has not been revealed yet. In this study, we proposed to characterize AOM by size fractionation followed by composition fractionation. The fouling characteristics of fractionated carbohydrate, protein, humic acid on membrane will be tested by a self-developed membrane module with a single hollow fiber, once a time. The fouling mechanisms of each fraction will be disclosed, based on the resistance in series model analysis, and membrane-foulant adhesion force measured by atomic force microscopy (AFM). The bi-directional flow operation with air assisted backwashing will be developed for the membrane fouling mitigation. This project will not only establish a methodology for membrane fouling study caused by AOM during membrane microalgal harvesting, but advance our understanding on the fouling mechanisms and mitigation, which in turn will accelerate the commercialization development of microalgal based biofuel.

膜技术是解决微藻生物能源规模化生产中微藻收获与培养液回用的关键技术。高密度微藻培养液中的藻源型有机物（Algogenic Organic Matter, AOM）成分及特性的多样性以及膜污染的复杂性，使藻源型有机物随藻种及其培养条件的变化规律以及膜收获过程中藻源型有机物的膜污染机制还不明晰。本研究以三种典型能源微藻为对象，通过分子量及成分逐级分离的方式，揭示不同藻种及培养条件下藻源型有机物中各成分的变化规律，然后通过单丝膜组件量化藻源型有机物中各成分的膜污染特性，结合膜阻力分析以及膜污染成分与膜表面的AFM力学特性，深入研究藻源型有机物的膜污染机制。本项目的实施将完善研究复杂膜污染的方法学体系，揭示膜收获过程中藻源型有机物膜污机制，为提高膜收获效率提供依据。

微藻膜收获是微藻生物能源规模化生产中核心技术，在微藻生物质持续获取、培养液循环使用中起到了关键作用。藻源型有机物造成的膜污染是制约微藻膜收获效率的重要因子。藻源型有机物成分及特性的多样性，其对膜污染的过程复杂，使得藻源型有机物的膜污染特性及污染机制尚不明晰。本研究建立了藻源型有机物的亲疏水性分离及表征方法、分子量大小逐级分离藻源型有机物的方法，并通过分组分过滤的方式揭示了藻源型有机物的污染机制。研究发现，对数期的藻源性有机物造成更大程度的膜污染，其原因是对数期藻源头型有机物含有较高的多糖类物质以及大分子有机物。AOM 中大分子量有机物、多糖类有机物是膜过滤过程中的主导污染物，其在膜表面的快速堆积，造成堵塞膜孔，进而导致膜通量急剧下降。以葡聚糖(DEX)、腐植酸(HA)和牛血清白蛋白(BSA)为模式污染物，建立了通过考察过滤过程中的通量下降和物理反冲洗后通量恢复来分析膜污染和去污性能的方法，利用扩展的EDLVO理论模型计算膜与污染物，污染物与污染物之间的相互作用能。此外，通过改进的胶体探针原子力显微镜（AFM）进一步测量膜与污染物和污染物与污染物之间的粘附力，揭示了不同污染物在膜表面的作用机制。最后通过膜材料筛选发现5 μm混合纤维素膜具有良好的防污性能，进一步通过气助反洗和双向流操作为主的控制手段发现双向流可提高过滤通量17.9%，有效缓解了藻源型有机物造成的膜污染。并据此开展了中试规模微藻膜收获，通过两阶段膜收获、提高错流速度等策略，对于收获53m3的尖状栅藻悬浮液，膜平均通量可达到53.6L/(m2h），浓缩系数为145，最终干重为136g/L，反洗后生物量回收率为93%。