Abstract
The green colonial microalga Botryococcus braunii produces large amounts of hydrocarbons and has attracted attention as a potential source of biofuel. When this freshwater microalga is cultured in a brackish medium, the hydrocarbon recovery rate increases; furthermore, the colony size becomes large. In this study, the effects of such changes on the energy balance of harvesting and hydrocarbon recovery were studied via filtrate experiments on an inclined separator and extraction from a concentrated slurry. The inclined separator was effective for harvesting large-colony-forming algae. The water content on the wire screen of slit sizes larger than 150 µm was <80% and a separation rate of >85% could be achieved. The input energy of the harvesting using the brackish medium with this separator was ≈44% of that using the freshwater medium with vacuum filtration, while the input energy of the hydrocarbon recovery using the brackish medium was ≈88% of that using the freshwater medium with pre-heating before n-hexane extraction. Furthermore, the energy profit ratio of the process in the brackish medium was 2.92, which was ≈1.2 times higher than that in the freshwater medium. This study demonstrated that filtration techniques and hydrocarbon recovery from B. braunii with a low energy input through culture in a brackish medium are viable.
Highlights
Botryococcus braunii (B. braunii) is an autotrophic alga that can potentially be employed as a biofuel resource because this alga produces hydrocarbons during cell division and secretes them in an oleophilic extracellular biopolymer
The inclined separator was used for harvesting algae harvesting were analyzed via the extraction from concentrated slurries and filtration using an cultured in the brackish medium (BM)
The energy profit ratio (EPR) of the BM process was 2.92, which was ≈1.2 times higher than that of screen, which was used for filtration, did not require electrical energy and was effective for largethe freshwater medium (FM) process (2.38)
Summary
Botryococcus braunii (B. braunii) is an autotrophic alga that can potentially be employed as a biofuel resource because this alga produces hydrocarbons during cell division and secretes them in an oleophilic extracellular biopolymer. B. braunii produces and stores hydrocarbons up to 86% of its dry weight [1,2]. Hydrocarbons are produced in species of all alga pyhla, their contents are low and the lipids that most microalgae can store with a high content rate are triglycerides or fatty acids [2,3]. Race B has been widely studied for liquid biofuel production because it stores hydrocarbons at relatively high volumes and can be decomposed into suitable fuels for internal combustion engines via hydrocracking [5]. B. braunii produces hydrocarbons during cell division [6]
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