Algae and Organic Matter Laboratory (AOM Lab), School of Chemical Engineering, The University of New South Wales, Sydney, Australia; Centre for Advanced Macromolecular Design (CAMD), School of Chemical Engineering, The University of New South Wales, Sydney, Australia.
Centre for Advanced Macromolecular Design (CAMD), School of Chemical Engineering, The University of New South Wales, Sydney, Australia.
Water Res. 2021 Feb 15;190:116747. doi: 10.1016/j.watres.2020.116747. Epub 2020 Dec 14.
Coagulation-flocculation followed by sedimentation or dissolved air flotation (DAF) are processes routinely used for separating microalgae from water; however, during algae separation then can exhibit inconsistent separation, high coagulant demand, and high operating cost. To circumvent these problems, previous studies reported the development of a novel DAF process in which bubbles were modified instead of particles. While this process was shown to be sustainable and inexpensive, the problem of inconsistent algal separation across species remained. Recent research has suggested that this could be due to the varying concentration and character of algal-derived proteins and carbohydrates within the extracellular organic matter (EOM) and their associated interactions. This hypothesis is tested in the current study using the novel modified-bubble DAF process, which has been highly susceptible to EOM protein and carbohydrate concentrations and character. Biomolecular additives (commercially available proteins and carbohydrates, and algal-extracted proteins) of widely differing molecular weight (MW) and charge were dosed in varying proportions into samples containing either Chlorella vulgaris CS-42/7, Microcystis aeruginosa CS-564/01, or Microcystis aeruginosa CS-555/1 after removing the intrinsic EOM. These cell-rich suspensions were then subject to flotation using cationic bubbles modified with poly(diallyldimethylammonium chloride) (PDADMAC). When additives were dosed independently, separation increased from <5% to up to 62%. The maximum separation was obtained when the dose was double the respective biopolymer concentration measured in the intrinsic EOM for the equivalent species, and, in the case of protein additives, when MW and charge were >50 kDa, and >0.5 meq·g, respectively, irrespective of the species tested. When evaluating steric- and charge-based protein-carbohydrate interactions on cell separation by simultaneously dosing high MW and high charge protein- and carbohydrate-additives, enhanced separation of up to 79% was achieved. It is suggested that enhanced cell separation is achieved due to proteins and carbohydrates bridging with cells and forming protein-carbohydrate-cell suprastructures in the presence of a flocculant, e.g. PDADMAC, and this only occurs when the intrinsic EOM comprises proteins and carbohydrates that have high MW (>25 kDa) and charge (>0.2 meq·g), and interactions with each other and with the cell surface.
混凝-絮凝后再进行沉淀或溶气浮选（DAF）是常用于从水中分离微藻的常规工艺；然而，在藻分离过程中，可能会出现分离效果不一致、对混凝剂需求高以及运行成本高的问题。为了解决这些问题，先前的研究报道了一种新型 DAF 工艺的开发，其中气泡被改性而不是颗粒。虽然该工艺被证明是可持续且经济实惠的，但不同物种的藻分离问题仍然存在。最近的研究表明，这可能是由于细胞外有机物（EOM）中藻类衍生的蛋白质和碳水化合物的浓度和性质以及它们之间的相互作用不同。本研究使用新型改性气泡 DAF 工艺来检验这一假设，该工艺对 EOM 蛋白质和碳水化合物的浓度和性质非常敏感。将广泛的分子量（MW）和电荷差异的生物分子添加剂（市售的蛋白质和碳水化合物以及藻类提取的蛋白质）以不同的比例添加到含有去除了固有 EOM 的普通小球藻 CS-42/7、铜绿微囊藻 CS-564/01 或铜绿微囊藻 CS-555/1 的样品中。然后，用用聚二烯丙基二甲基氯化铵（PDADMAC）改性的阳离子气泡对这些富含细胞的悬浮液进行浮选。当单独添加添加剂时，分离率从<5%提高到 62%。当添加剂量是固有 EOM 中相应物种的生物聚合物浓度的两倍时，可获得最大的分离率，对于蛋白质添加剂，当 MW 和电荷分别大于 50 kDa 和 0.5 meq·g 时，无论测试的物种如何，均可获得最大的分离率。当同时添加高 MW 和高电荷的蛋白质和碳水化合物添加剂以评估基于空间位阻和电荷的蛋白质-碳水化合物相互作用对细胞分离的影响时，可实现高达 79%的增强分离效果。据推测，由于蛋白质和碳水化合物与细胞桥接并在絮凝剂（例如 PDADMAC）存在下形成蛋白质-碳水化合物-细胞超结构，从而实现了增强的细胞分离，仅当固有 EOM 包含具有高 MW（>25 kDa）和电荷（>0.2 meq·g）的蛋白质和碳水化合物，并且它们之间以及与细胞表面之间存在相互作用时才会发生这种情况。
