Stress-Induced Production of Lipids in Oleaginous Microalgae for Biofuel Optimization

The purpose of this experiment was to determine the effects of nitrogen and phosphorus wastewater nutrients on the lipid productivity, dissolved oxygen content, and biomass yield of microalgal strains Chlorella sp. and Nannochloropsis sp. Recently, it was determined algal biofuels can be possibly cultured in a wastewater medium due to its high levels of elemental nutrients nitrogen and phosphorus, possibly reducing economic costs. Further efforts are needed in strain selection of microalgae to be cultured in nutrient-rich wastewater or inexpensive fertilizer. Common algal strains Nannochloropsis sp. and Chlorella sp. were studied to determine any possible effects. Both algal strains were exposed to standard nutrient contents, which acted as a control, and relatively high levels of nitrogen and phosphorus to simulate amounts present in wastewater. It was hypothesized that if Chlorella sp. is exposed to levels of nitrogen and phosphorous, then it will have the highest growth after its respective growing period, amount of lipids present, and amount of dissolved O₂. This is based on previous experiments where Chlorella sp. had the both the highest biomass and lipid productivities under optimal experimental conditions. The results revealed that nitrogen and phosphorus had a positive effect on the turbidity and dissolved oxygen while decreasing the lipid productivities by an average of 36.5%. Specifically, Nannochloropsis sp., had overall higher values for all dependent variables. A t-test/ANOVA performed on the data revealed that the data were significant at almost all levels of independent variable. The results not did support the research hypothesis based on the data collected. It is believed that under nutrient limiting conditions the cells deposited fatty acids in a triacylglycerol pathway. Future research should focus on optimizing lipid production under these stressed conditions using genetic engineering or different algal strains/parameters such as salinity stress.