Chemical Engineering Journal 105 (2005) 91–98 Optimal growth conditions and the cultivation of Chaetoceros calcitrans in airlift photobioreactor Sontaya Krichnavaruk a , Worapannee Loataweesup a , Sorawit Powtongsook b , Prasert Pavasant a,∗ a Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand b Marine Biotechnology Research Unit, Chulalongkorn University, National Center of Genetic Engineering and Biotechnology, Bangkok, Thailand Received 17 July 2004; received in revised form 18 October 2004; accepted 23 October 2004 Abstract The optimal conditions for the growth of a diatom Chaetoceros calcitrans were investigated in a 2.5 L glass bubble column. The light intensity for the highest growth rate was shown to be at around 400 mol photons m -2 s -1 . A modified standard F/2 medium with a two- fold of silica and phosphorus concentrations was illustrated to result in a better growth of this diatom. Vitamin B 12 in the range from 1 to 3 gL -1 did not significantly affect the growth. A maximum cell density obtained from this small glass bubble column was approximately 5.8 × 10 6 cells mL -1 with a maximum specific growth rate of 3.80 × 10 -2 h -1 . The cultivation of C.calcitrans in the 17 L airlift photobioreactor (ALPBR) was illustrated to be superior to that in the bubble column with the same size. The operation with superficial gas velocity of 3 cm s -1 was found to give a maximum specific growth rate of 7.41 × 10 -2 h -1 with a maximum cell concentration of 8.88 × 10 6 cells mL -1 in a batch culture. A semi-continuous culture could be achieved where the harvest was performed at every 12h. In this case, the maximum specific growth rate (μ) achievable was 9.65 × 10 -2 h -1 and the cell concentration during the harvest period was 4.08 × 10 6 cells mL -1 . © 2004 Elsevier B.V. All rights reserved. Keywords: Single cell algae; Light intensity; F/2 medium; Nutrient; Flow pattern; Growth rate; Semi-continuous culture; Bubble column; Airlift bioreactor 1. Introduction Diatom is a basic component of marine hatchery opera- tions because it serves as one alternative natural resource for poly unsaturated fatty acids [1]. The diatom C.calcitrans is considered one of the most popular strains used as a feed for shrimp larvae. C.calcitrans is a diatom with chlorophyll con- tent and it is usually cultivated in a similar fashion to single cell algae where, apart from other common nutrients, light plays a significant role in controlling its growth rate. Very few investigations on the optimal condition for the growth of C.calcitrans are available. The only report indicated that the highest yield for this diatom was obtained at an initial silica concentration of 400 gL -1 (as sodium metasilicate) [2]. However, this operation was subject to a cool environ- ∗ Corresponding author. Tel.: +66 2 2186870; fax: +66 2 2186877. E-mail address: prasert.p@chula.ac.th (P. Pavasant). ment and the optimal growth was significantly different from that in warmer locations like tropical countries such as Thai- land where there is a high demand of C.calcitrans for marine hatcheries, particularly shrimp larvae. The development of bioreactor for mass cultivation of single cell algae or diatom always enables the adjustment of the light intensity, which leads to a successful production of high cell density culture. Examples of the novel designed photobioreactors include a tubular reactor [3,4] and the flat plate bioreactor [5]. How- ever, these existing closed systems suffer serious drawbacks from poor mixing and gas–liquid mass transfer. Airlift bioreactors (ALBR) have recently become an at- tractive alternative for cell cultivation [6]. This might be due to several main advantages such as good mixing, well-defined fluid flow pattern, relatively high gas–liquid mass transfer rate, and low capitals and operating costs. The mixing in the ALBR could be obtained without causing too much shear force in the liquid phase, which could inhibit the growth 1385-8947/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2004.10.002