Selection of algal species for feasibility testing
Of the estimated 10 million algal species on the earth, some 40 000 separate
species have been identified. Most strains are photoautotrophs, but some genera
(e.g. Chlamydomonas) also grow heterotrophically in the dark (Hu et al. 2008).
An algal strain suitable for energy applications should have a high growth rate
and a high capacity for biomass and lipid production, as well as a suitable fatty
acid composition. A good strain should also be easy to cultivate and harvest, and
lipids from the cells should be easily extractable. Three algal strains were chosen,
after pre-cultivation in organic medium and preliminary testing of lipid content. Two
strains (Chlorella pyrenoidosa UTEX 1230 and Euglena gracilis CCAP 1224/5Z)
originated from culture collections.
One specific target of algal strain selection was the selection of strains capable
of mixotrophic growth, since most of the waste waters of interest contain organic
carbon and there is evidence that mixotrophy may enhance lipid production (Wan
et al. 2011). This was the main reason for also using a strain of Selenastrum,
isolated by the University of Helsinki and originating from a typical Finnish lake
(Lake Iso-Ruuhijärvi) with a high concentration of coloured organic, humic compounds
and thus from conditions favouring mixotrophy. Algae from northern humic
lakes are also presumably well adapted to low light conditions and can grow at low
temperatures, which are characteristics useful in commercial applications.