Microalgae mass culture: the constraints of scaling-up

There is overwhelming evidence that microalgae would be the logical source of oils for biodiesel production, the best option for CO2 sequestration and numerous other applications. However, this apparent lucrative approach is still in its infancy. In order to impact on global energy needs, bioremediation and other potential applications, vast quantities of biomass must be produced at a reliable rate and as cost-effective as possible. When extrapolating volumetric rates from laboratory or small-scale outdoor cultures to large-scale outdoor areal production rates, it becomes apparent that many of the potential claims are either misleading or still only a dream. Open raceway ponds are at present the only feasible culture system for the production of millions of tons of biomass. To date, at best photosynthetic efficiencies of around 1.2% have been achieved, but with present understanding and know-how efficiencies of double that should be achievable, especially when vertical mixing is increased in raceway ponds.