Autotrophic growth and carotenoid production of Haematococcus pluvialis in a 30 liter air-lift photobioreactor

Growth and ketocarotenoid (astaxanthin) production by the fresh-water green unicellular alga Haematococcus pluvialis has been evaluated in a 30 l air-lift photobioreactor. Due to the different culture requirements of the alga during the various stages of its development a two-stage batch production process (effectively before and after addition of NaCl to the culture) was employed for (i) biomass and (ii) astaxanthin by this alga. During the first stage, conditions within the reactor (light intensity, levels of nitrogen and phosphate) were maintained so as to achieve high rates of algal growth. When the algae in the reactor reached the stationary phase of growth and levels of nitrogen and phosphate in the medium had become severely depleted NaCl was added to stimulate the synthesis of ketocarotenoids (> 95% astaxanthin, mainly in the form of mono- and especially di-esters), partly overcoming the need to increase irradiance levels. H. pluvialis exhibited relatively high rates of growth in the air-lift and accumulated up to 2.7% astaxanthin (of the dry cell weight of the alga). This was, however, lower than could be achieved under laboratory-scale conditions (>5.5%). The use of a batch-production process in a air-lift reactor for the synthesis of algal carotenoids is discussed.