ABSTRACT
The two fundamental microalgae biomass production technologies aiming to supply the global demand for renewable biofuels are known as ‘open’ ponds and ‘closed’ bioreactor/fermentor systems (Borowitzka 1999, Ugwu et al. 2008, Vasudevan and Briggs 2008, McHenry 2010). Whilst many microalgae species must be cultured in highly controlled conditions, species that exhibit a selective advantage in particular environments are able to be cultured in open-air systems such as ponds (Borowitzka 1999). The majority of microalgae biofuel companies are designing commercial production systems based on open cultivation of particular species/cultivars due to the advantages of relatively lower capital and production costs of open systems compared to the currently available closed systems, and a historically proven record of production (Borowitzka 1999, Spolaore et al. 2006). At present, the most common open system designs include the use of natural water bodies, constructed ponds of a variety of shapes, depths, and sizes, and also tanks (Ugwu et al. 2008). Each system exhibits unique advantages and disadvantages. For example, while commonly used raceway ponds improve yields and reliability relative to simple shallow ponds, they can be an expensive design to construct and operate (Borowitzka 1992, Kunjapur and Eldridge 2010).
