Coccolithophorid algae, halophilic diatoms and the economics of large scale culture of microalgae

Currently produced microalgae for commercial purposes, such as nutrient supplements, fine chemicals or for the feeding of aquaculture species, have production costs ranging from about $5 to $1000/kg. An analysis of contributors to the cost shows that capital costs make up the most significant part, generally followed by labor costs. The analysis also shows that the costs of production are strongly scale-dependent, with the lowest cost producers being the large Dunaliella salina plants in Australia. Recently, the potential of growing microalgae for carbon dioxide bioremediation (as CO2 sinks) and/or as a source of biodiesel has become a great interest. The algae best suited for these applications are the coccolithoporid algae (Haptophyta), because they fix C into both organic carbon and into CaCO3, and other haptophytes and diatoms, because of their high lipid content. Our experiments with the coccolithoporid, Pleurochrysis carterae, have shown that this alga can be grown reliably all year round in outdoor raceway ponds with productivities exceeding 30g dry wt/sqm/d under Perth, Western Australia, climatic conditions. The authors have achieved similar results with several halophilic diatom species. Clearly, any production plant for these purposes would have to be significantly larger than any existing algae production plant. However, in order to be commercially viable as a lipid source for biodiesel production and to be competitive with other plant oils, the production cost of the biomass must be in the range of $0.50 to $0.80/kg i.e., about on tenth of the currently cheapest production costs. If this is to be achieved, there has to be either a marked improvement in productivity (a tenfold improvement, however, is extremely unlikely) without a concomitant increase in capital and labor costs, or some significant improvement in the design and construction costs of the culture and harvesting systems, together with reduced running costs. Because of the high capital investment required, any production plant must be able to operate 365 days a year. This paper discusses the challenge to researchers in trying to develop microalgae for this purposes, and attempts to prevent some key directions for research.