Selection of microalgae with potential for cultivation in surfactant-stabilized foam

Abstract

Recently, microalgal cultivation in liquid foams has been developed. Compared to the traditional systems, this concept is expected to offer advantages such as increased mass transfer and reduced biomass harvesting costs and water consumption. However, there is limited information, thus far, on the microalgal performance in foam-bed photobioreactors. Therefore, this study was aimed at comparing the foaming properties of six algal strains to identify the criteria that could be broadly employed for assessing the microalgal potential for cultivation in a foam-bed photobioreactor. The microalgal strains investigated were selected based on their different nature and potential uses. All the microalgal strains could not naturally produce stable foam, thus necessitating the use of a surfactant. To investigate the differences in the foaming properties of the selected microalgae, the natural surfactant, bovine serum albumin, was employed. Factors such as culture age, algal hydrophobicity, and biomass concentration differently influenced the key foaming properties (foamability, microalgal partitioning, and foam stability) depending on the microalgal strain. In conclusion, the assessment of the foaming properties of microalgal strains together with their inherent growth characteristics revealed large differences in the potentiality of microalgae to be cultivated in a foam-bed photobioreactor. In particular, among the microalgal strains tested, the commercial strains Chlorella sorokiniana, Nannochloropsis gaditana, and Scenedesmus obliquus showed the highest potentiality for cultivation in foam. Overall, the following criteria could be broadly applied to select suitable microalgae for cultivation in a foam-bed photobioreactor: high or moderate foamability of the microalga-surfactant suspension, and microalgal partitioning, stability of the foam formed, and robustness and fast growth of the strains.