Effect of initial biomass density on growth and astaxanthin production of Haematococcus pluvialis in an outdoor photobioreactor

Initial biomass density (IBD) is an important factor that affects the viability and productivity of microalgae particularly when sunlight is used for photosynthesis. In this paper, the effect of IBD on photosynthesis, growth, and astaxanthin production of the green microalga Haematococcus pluvialis during the astaxanthin induction stage was studied in a glass column photobioreactor during different seasons. Of seven IBDs, i. e., 0.1, 0.5, 0.8, 1.5, 2.7, 3.5, and 5.0 g L^-1 tested, 0.8 g L^-1 IBD was optimal and resulted in the highest astaxanthin productivity of 17.1 mg L^-1 day^-1. Severe photoinhibition of photosynthesis occurred at low IBD (e. g., 0.1 g L^-1) cultures, especially in the winter, and severe light limitation to individual cells in high IBD cultures (>2.7 g L^-1) were responsible for reduced astaxanthin production. This was the first report quantitatively assessing IBD as the key limiting factor for astaxanthin production in H. pluvialis outdoor cultivation.