Effects of Light Quality and Light Quantity on the Growth Kinetics of a Louisiana Native Microalgal/Cyanobacterial Co-culture

Abstract

One of the most important factors controlling the growth of microalgae is light. Light quality and light quantity have a dramatic effect on the production of biomass, lipids and pigments of microalgae. In this research, a native Louisiana co-culture containing Chlorella vulgaris (microalgae) and Leptolyngbya sp (cyanobacteria) was studied to determine the effects of various wavelength distributions and irradiance levels on growth kinetics. Growth rates, biomass levels, lipid contents and chlorophyll-a production was examined in batch cultures to determine which color light was optimum for cultivation. At 80 µmol/m^2-sec the species shifted from microalgae dominant to cyanobacteria dominant. The impact of four different light colors (blue, green, red and white) on the growth at 400 µmol/m^2-sec revealed that red light produced the highest growth rate (0.41 1/d) and final biomass concentration (913 mg/L). Red light was chosen as the optimum wavelength at 400 µmol/m^2-sec. When red light was compared to white light at higher light intensities red light produced the highest growth rate (0.47 1/d). Red light had the highest photosynthetic efficiency (1.29 %), while white light had the highest chlorophyll-a production (1874 µg/L) and the highest biomass (1207 mg/L). Overall, red light was determined to be the optimum wavelength to grow this co-culture because of the higher growth rates and photosynthetic efficiency. This co-culture was also grown in a continuous flow hydraulically integrated serial turbidostat algal reactor (HISTAR) system. This study showed that different dilution rates can affect the final harvested biomass weight. Also, at high biomass concentrations, light penetration is reduced enough for cyanobacteria filaments to form, which will hinder the growth of the microalgae.