A novel double-layered photobioreactor for simultaneous Haematococcus pluvialis cell growth and astaxanthin accumulation

This study proposes a novel double-region photobioreactor to simplify the commercial two-stage process of astaxanthin production by the cultivation of Haematococcus pluvialis. The feasibility of the double-region photobioreactor has been investigated and found to achieve high biomass yield in the inner core region and simultaneous astaxanthin accumulation in the outer jacket region. Among many environmental factors, light condition and nitrate level were manipulated for selective cell growth and astaxanthin production. In the outer jacket region, efficient astaxanthin production was accomplished by excessive irradiation (770 ± 20 μE m−2 s−1) and nitrate starvation, resulting in a dramatic increase of astaxanthin productivity (357 mg l−1). Meanwhile, attenuated light energy (40 ± 3 μE m−2 s−1) and sufficient nitrates were supplied to the vegetative cells in the inner core region, which continued to grow to a high cell concentration of 4.0 × 105 cells ml−1. The sequential batch run was performed by utilizing the high-density vegetative cells as inoculum for the next batch run. The cultivation results exhibited similar trends as the previous run, reaching high cell density (4.3 × 105 cells ml−1) in the inner core region and high astaxanthin content (5.79% on a dry weight basis) in the outer jacket region. The present study indicates that the double-region photobioreactor and its method of operation possess a good potential for commercial production of astaxanthin by H. pluvialis.