Journal of Energy Bioscience 2024, Vol.15, No.2, 96-107 http://bioscipublisher.com/index.php/jeb 100 reducing contamination risks (Liu et al., 2013). Lastly, the use of thin-layer photobioreactors in outdoor settings has demonstrated high photosynthetic efficiency and biomass yields, even under suboptimal climatic conditions, making it a viable option for large-scale bioethanol production (Doucha and Lívanský, 2009). Figure 2 Outdoor cultivation system of large-scale tubular photobioreactors: a cultivation location, b S. obliquus CNW-N, and c plastic tubular PBR (60 L) (Adopted from Ho et al., 2017) Image caption: An indigenous microalga, Scenedesmus obliquus CNW-N, with a high cell growth rate and satisfactory carbohydrate content, as demonstrated in our previous research, was selected to develop an outdoor microalgal-based bioethanol production system in southern Taiwan (22°99′74.29″N, 120°22′22.30″E). The influences of different water temperatures and qualities on the cell growth and CO2 fixation rate were first investigated on the laboratory-scale to evaluate the environmental tolerance of S. obliquus CNW-N (Adopted from Ho et al., 2017) 5 Harvesting and Pretreatment of Microalgal Biomass 5.1 Harvesting techniques: flocculation, centrifugation, filtration Harvesting microalgal biomass is a critical step in the production of bioethanol, as it significantly impacts the overall efficiency and cost-effectiveness of the process. Various techniques are employed to harvest microalgae, including flocculation, centrifugation, and filtration. Flocculation is widely regarded as a cost-effective and efficient method for harvesting microalgae. It involves the aggregation of microalgal cells into larger flocs, which can then be easily separated from the culture medium. Chemical flocculants, such as chitosan, have been shown to achieve high clarification efficiency, reducing the volume to be processed by subsequent dewatering steps (Xu et al., 2013). Bioflocculation, which uses natural compounds or microorganisms to induce floc formation, is also a promising approach due to its environmental friendliness and potential for large-scale application (Wan et al., 2015; Ummalyma et al., 2017; Nguyen et al., 2019).
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