Effects of light quality supplied by light emitting diodes (LEDs) on microalgal production

Dissertação de mestrado, Aquacultura, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2014

Light-emitting diodes (LEDs) will become one of the world´s most important light sources and their integration in microalgal production systems (photobioreactors) needs to be considered. Microalgae need a balanced mix of wavelengths for normal growth, responding to light differently according to the pigments acquired or lost during their evolutionary history. In the present study, Nannochloropsis oculata and Tetraselmis chuii were exposed to different light qualities, and their effects on growth, biochemical components (carbohydrate, protein, total lipid and fatty acids) and morphologic traits (cell shape, size, growth phase, absorption spectrum, N-P-C elemental composition in biomass) were investigated. An additional experiment employed different LEDs in order to obtain di- and multichromatic tailored light to increase biomass production. Both N. oculata and T. chuii showed a higher maximal volumetric ash free dry weight content in the culture when exposed to blue (465 nm) and red (660 nm) light, respectively. However, balanced light quality, provided via fluorescent light (FL) and dichromatic blue and red light treatment, was found to be beneficial for biomass growth rates of both algae. Significant changes in the biochemical composition were observed among treatments. Furthermore, algae treated with monochromatic blue light (λe = 405 and 465 nm) often displayed higher nutrient uptake and different morphological traits as compared to algae exposed to red light (λe = 630 and 660 nm). It is suggested that differential response to light quality is partially influenced by observed changes in nutrient consumption and biomass productivity. In terms of biomass per input energy, the most efficient light sources were those with photon output peaks at 660 nm (e.g. LED 660 and FL for plant growth). Research and the application of LED technology to microalgal production is often hindered by inadequate light quantity measurements as well as by inadequate LED manufacture and engineering, leading to the use of inefficient LED modules, which, in turn, may affect microalgal growth and biochemistry.