Abstract
In this work, a fundamental study was carried out on the role of surfactants in bubble-algae interaction to improve the understanding of how surfactants influence the flotation performance. Flotation tests for harvesting Chlorella vulgaris were first conducted using two surfactants, hexadecyltrimethyl ammonium bromide (C16TAB) and tea saponin. The effect of surfactants on harvesting efficiency was found to depend on their type and concentration. The present results also indicated that C16TAB exhibited higher harvesting efficiency than tea saponin. The adsorption experiments of surfactants onto C. vulgaris and the characterization measurements of algae surface were then carried out to reveal underlying interaction mechanisms between surfactants and algae in air flotation process. The results confirmed the adsorption process of surfactants onto C. vulgaris was feasible, spontaneous and endothermic. Subsequently, two mechanism models were proposed to qualitatively establish the interaction relationship among algae, surfactants and bubbles in the flotation. According to two models, C16TAB could neutralize the algal potential, while tea saponin converted algal surface from hydrophilic into hydrophobic. Overall, two surfactants used here could facilitate attachment of C. vulgaris onto bubbles, making the algae easier to be harvested, thereby increasing the flotation recovery.
Highlights
Algae are regarded as a promising resource because it is renewable and environmentally friendly; algae-based bioproducts such as biodiesel and health products are becoming more and more concern nowadays
The addition of C16TAB exhibited higher harvesting efficiency than tea saponin. This is similar to the result from Agnes et al.[28], in which C16TAB was more effective in harvesting Scenedesmus obliquus, in 40, 60 and 80 mg/L
To deeply understand the role of surfactants in bubble-algae attachment interaction, two mechanism models were established to reveal the relationship among the algae, surfactants and flotation performance based on the results of adsorption of C16TAB and tea saponin onto C. vulgaris
Summary
Algae are regarded as a promising resource because it is renewable and environmentally friendly; algae-based bioproducts such as biodiesel and health products are becoming more and more concern nowadays. Bubble-algae interaction can be divided into three processes: collision, attachment and detachment[10]. As the algae and bubble come closer, the influence of intermolecular and interfacial forces is decisive for attachment and detachment processes. Among these three processes, addition of surfactants has been reported to improve the flotation performance by mainly influencing the attachment step. Different kinds of surfactants have different adsorbed ratios onto the algae, and adsorption process is supposed to play key role in attachment process. In this way, surfactants could contribute to the harvesting performance. Few works have been conducted into the adsorption between surfactants and algae in flotation process
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