Enhancing lipid production in attached culture of a thermotolerant microalga Desmodesmus sp. F51 using light-related strategies

In attached culture, concentrated cells are grown on the substratum, which makes the light adsorption mechanism quite different from those of suspended cultures. An energy conservation biofilm reactor based on capillary-effect was firstly introduced for attached culture of the thermotolerant microalga Desmodesmus sp. F51. The effects of light-related strategies (including light intensity, photoperiod and light-switching strategies) on lipid production were investigated. It was found that the light requirements for biomass or lipid accumulation varied greatly at different growth stages, probably due to increasing biofilm thickness. By switching the light intensity from 700 to 1134 μmol m⁻² s⁻¹ at day 3 in Strategy I, a maximum biofilm/lipid production of 241.67/53.62 g m⁻² was achieved at day 8. A similar operation was conducted in Strategy II except a further switch to light intensity of 938 μmol m⁻² s⁻¹ at day 5, a maximum biofilm/lipid production of 223.58/66.65 g m⁻² was achieved at day 8. This performance is better than most of the previously reported values. Light-switching operation was proved to be an effective strategy to supply the appropriate light for each growth stage of the immobilized cells, and was beneficial for biofilm/lipid production.