Abstract：
Microalgae show great promise for producing valuable molecules like biofuels, but their large-scale production faces challenges, with harvesting being particularly expensive due to their low concentration in water, necessitating extensive treatment. While methods such as centrifugation and filtration have been proposed, their efficiency and cost-effectiveness are limited. Flotation, involving air-bubbles lifting microalgae to the surface, offers a viable alternative, yet the repulsive interaction between bubbles and cells can hinder its effectiveness. Previous research from our group proposed using an amphiphilic chitosan derivative, polyoctyl chitosan (PO-chitosan), to functionalize bubbles used in dissolved air flotation (DAF). Molecular-scale studies performed using atomic force microscopy (AFM) revealed that PO-chitosan\'s efficiency correlates with cell surface properties, particularly hydrophobic ones, raising the question of whether this molecule can in fact be used more generally to harvest different microalgae. Evaluating this, we used a different strain of Chlorella vulgaris and first characterized its surface properties using AFM. Results showed that cells were hydrophilic but could still interact with PO-chitosan on bubble surfaces through a different mechanism based on specific interactions. Although force levels were low, flotation resulted in 84% separation, which could be explained by the presence of AOM (algal organic matter) that also interacts with functionalized bubbles, enhancing the overall separation. Finally, flocculation was also shown to be efficient and pH-independent, demonstrating the potential of PO-chitosan for harvesting microalgae with different cell surface properties and thus for further sustainable large-scale applications.
摘要：
微藻在生产生物燃料等有价值的分子方面显示出巨大的希望，但是他们的大规模生产面临挑战，由于它们在水中的浓度低，收获特别昂贵，需要广泛的治疗。虽然已经提出了诸如离心和过滤的方法,他们的效率和成本效益是有限的。浮选,包括气泡将微藻提升到表面，提供了一个可行的替代方案，然而，气泡和细胞之间的排斥相互作用会阻碍其有效性。我们小组先前的研究提出使用两亲性壳聚糖衍生物，聚辛基壳聚糖（PO-壳聚糖），对溶解空气浮选(DAF)中使用的气泡进行功能化。使用原子力显微镜（AFM）进行的分子尺度研究表明，PO-壳聚糖的效率与细胞表面性质相关，特别是疏水性的，这就提出了一个问题，即这种分子是否可以更广泛地用于收获不同的微藻。评估这一点，我们使用了不同的小球藻菌株，并首先使用AFM表征了其表面特性。结果表明，细胞是亲水性的，但仍可以通过基于特定相互作用的不同机制与气泡表面上的PO-壳聚糖相互作用。虽然力量水平很低，浮选导致84%的分离，这可以解释为AOM（藻类有机物）的存在也与功能化气泡相互作用，加强整体分离。最后,絮凝也被证明是有效的，不依赖pH，证明了PO-壳聚糖用于收获具有不同细胞表面特性的微藻的潜力，从而进一步可持续的大规模应用。
