Lipid production in algae stressed with sodium bicarbonate and sodium chloride

Abstract

Microalgae may play an important role in the path to a more sustainable future by producing valuable hydrocarbons using inorganic carbon, sunlight, and non-food source competitive supplies of nitrogen and phosphorus. The prospect of growing microalgae for the production of a stable and dependable source of biofuel is plausible only if done at scale with intricate attention applied to the biochemistry, geochemistry, and environmental conditions of each system. Extreme environments with low proton activity and high salinity conditions may harbor microalgae suitable for large scale outdoor cultivation. Several algal isolates native to Soap Lake in Washington State were screened for biofuel potential and three isolates were selected for further studies. These three isolates were characterized to assess impacts on biofuel production studying high ionic strength in the form of sodium chloride (NaCl) in excess of 18g/L, and carbon supplemented treatments through the addition of inorganic carbon in the form of sodium bicarbonate (NaHCO 3). Further, the ability of NaHCO 3 and NaCl to trigger lipid production was determined. The study was centered on understanding differences between two factors that will likely have implications in large-scale algal raceway ponds: inorganic carbon limitation, speciation, or bioavailability, and evaporative conditions resulting in high concentrations of salt. In this study, cell concentration, cell dry weight, nitrate, pH, biofuel potential, extractable lipid potential, and DIC (dissolved inorganic carbon), were monitored over time. Isolate GK5La grown in standard medium had the highest concentration of cell dry weight at the end of the study. Cultures supplemented with sodium bicarbonate were determined to be the most efficient way to produce biofuel in the form of extractable lipids. Supplementation with sodium bicarbonate and spiking to a concentration of 18g/L sodium chloride showed to be the most productive way to make triacylglyceride (TAG). Fatty acid methyl ester (FAME) production on a concentration basis was greatest in the control treatment grown in standard medium.