氮调控下自絮凝微藻的絮凝特性及其絮凝机理研究

Self-flocculating microalgae is a type of microalgae, which can aggregate together or form large particles by themselves. The aggregate can be then deposited at the bottom of the reactor at the end of the culture without extra harvesting, which effectively reduces the recovery cost. The nitrogen is important to microalgal growth, lipid metabolism and pollutants removal. Nevertheless, the flocculating characteristic of self-flocculating microalgae under nitrogen regulation is not clear, and the regulation mechanism behind self-flocculation is also unclear. These drawbacks limit a large-scale application of the flocculating technology to a certain extent. Consequently, the flocculating characteristic of self-flocculating microalgae under different nitrogen sources and concentrations will be analyzed and the variation regularity of flocculating characteristic will be grasped. Then the control strategy on flocculation of self-flocculating microalgae via nitrogen regulation will be formulated. Besides, considering the importance of extracellular polymeric substances (EPS) in the process of self-flocculation, surface characteristics (hydrophobicity and surface potential), functional groups, protein content, amino acid composition and protein secondary structure of self-flocculating microalgae under nitrogen regulation are analyzed. The change of surface characteristics and their relationships with functional groups and proteins of EPS are characterized to establish the relationship among nitrogen, EPS and flocculation. Finally, the self-flocculating mechanism mediated by EPS under the nitrogen regulation will be revealed. The project can provide some theoretical bases and technical supports for the future development and application of self-flocculating microalgae.

自絮凝微藻是一类细胞能够自发聚集的微藻的总称，其在培养结束时沉积在反应器底部而无需额外采收，有效降低了采收成本。氮是调控微藻生长代谢的重要因子。然而，氮对自絮凝微藻絮凝特性的影响及其作用机制尚不清楚，极大地限制了自絮凝微藻的应用。本项目拟重点分析氮源种类及其浓度对自絮凝微藻絮凝特性的影响，掌握氮调控下自絮凝微藻絮凝特性的变化规律，制定氮调控自絮凝微藻絮凝的控制策略。此外，鉴于胞外聚合物(extracellular polymeric substances, EPS)对微藻絮凝的重要性，对不同氮源及其浓度下自絮凝微藻的表面特征(疏水性和表面电势)、EPS的官能团、蛋白含量和二级结构以及氨基酸组成进行表征，分析表面特性的变化规律及其与EPS官能团和蛋白的关系，建立起氮、EPS与絮凝间的联系，揭示氮调控下EPS介导自絮凝微藻絮凝的机理。本研究可望为自絮凝微藻的应用提供一定的理论基础和技术支持。

自絮凝微藻是一类细胞能够自发聚集的微藻的总称，其在培养结束时沉积在反应器底部而无需额外采收手段的辅助。因此，通过微藻的絮凝特性完成藻水分离有效降低了采收成本。氮是调控微藻生长代谢的重要因子。然而，氮对自絮凝微藻絮凝特性的影响及其作用机制尚不清楚，极大地限制了自絮凝微藻的应用。本项目从采集自山西省的土壤和苔藓中分离纯化获得3株具有自絮凝性状的藻株Chlorococcum sphacosum GD、Scenedesmus rubescens SX和Neocystis mucosa SX。将这三株藻株于BG11培养基中培养至稳定期，静置3小时后的絮凝效率达到80%以上。以这3株藻株为研究对象，我们发现污水中氮源和氮浓度的变化会影响藻株的絮凝效率。硝态氮污水中藻株的絮凝效率要优于铵态氮和有机氮污水中藻株的絮凝效率，高浓度氨氮污水中藻株的絮凝效率要优于低浓度氨氮污水中藻株的絮凝效率。进一步分析发现，微藻培养过程中氮的变化主要影响了污水pH以及钙镁离子的形态，同时影响了胞外多糖含量而非组成，导致胞外聚合物(extracellular polymeric substances, EPS)中羧基和羰基等可作为结合位点的官能团数量发生变化，最终影响了钙镁离子诱导下絮体沉淀的形成。本研究为实现藻水分离提供了新思路，为高效低成本微藻采收技术的开发与应用提供一定的理论基础和技术支持。