The various modes of cultivation of Chaetoceros calcitrans in airlift photobioreactors (ALPBRs) were examined. The batch system illustrated that the airlift configuration was superior to the bubble column as the airlift supported the circulation of the cell within the system, leading to a better light utilization. The cultivations in both semi-continuous and continuous systems resulted in a high cell productivity, although the steady state cell concentrations in both systems were lower than that obtained from the batch system. The behavior of the large-scale airlift system was not significantly different from the conventional bubble column where the diatom could only be produced at low cell density. Despite this, among all of the systems investigated in this work, the large-scale system gave the highest productivity. The main limiting factor for the large-scale airlift culture was the availability of light. Based on economical analysis, the continuous cultivation in the 2.8 L ALPBR with a medium feed rate of 3 mL min(-1) was most attractive where the operation cost could be maintained at a minimum of approx. 7.95 X 10(-4) THB L-1 h(-1). However, this continuous small-scale system still suffered from relatively low cell productivity (8.10 X 10(4) cells s(-1)). (c) 2006 Elsevier Ltd. All rights reserved.