Abstract
For developing a multipurpose Botryococcus braunii utilization system, in which water purification and biofuel production will be achieved simultaneously, the growth behavior of B. braunii under a simulated open-air condition was clarified, where Microcystis aeruginosa was assumed to coexist. Microcystis aeruginosa is one of the typical algae in eutrophic water. The monoculture experiments revealed that the growth rate of a B. braunii strain was lower than that of a microcystin-producing M. aeruginosa strain under various phosphate concentrations. Meanwhile, the phosphate uptake rate of B. braunii was higher than that of M. aeruginosa. In the batch monoculture experiments, the promising hydrocarbon production of B. braunii was observed within a wide range of initial phosphate concentrations (11 to 216 mg-PO43-/L). In the two-algal species mixed culture experiments, the growth characteristics were different with the coexisting species. When a non-microcystin-producing M. aeruginosa strain was cultured with B. braunii, the domination of M. aeruginosa within the experimental period was observed especially in the cases where the initial biomasses of M. aeruginosa were high compared to those of B. braunii. On the other hand, when microcystin-producing M. aeruginosa was cultured with B. braunii, the abundant microcystin production was observed without domination of M. aeruginosa. These results suggested the importance of the effective utilization of the high phosphate uptake ability of B. braunii, and the control of the initial biomass ratio of algae for the realization of B. braunii system under the open-air condition.