Effects of Light Exposure and Nitrogen Source on the Production of Oil from Freshwater and Marine Water Microalgae

Abstract

The biomass yield and oil content of Chlorella saccharophila (freshwater) and Tetraselmis suecica (marine) microalgae were investigated using various nitrogen source (ammonium nitrate, ammonium phosphate, ammonium sulfate and combination of nutrients) at various light durations (9, 16 and 24 h). NaHCO₃ was used as the carbon source. The nitrogen concentration, temperature and pH were maintained at 70 mg/L, 22°C and 8.5, respectively. The results indicated that T. suecica produced higher cell yield compared to the C. saccharophila under all levels of parameters tested. Light exposure of 24 h produced the highest biomass yield. However, the difference in cell yields between light duration of 16 and 24 h was not significant. The combination of nutrients resulted in the highest growth for both species of microalgae. However, high growth did not necessarily result in high oil yield. The oil content was much higher for C. saccharophila than T. suecica. Varying light duration had no direct effect on oil yield. The nutrient type significantly influenced the production of oil. C. saccharophila produced the highest oil yield using ammonium phosphate while T. suecica achieved the highest oil yield using ammonium nitrate. The results indicated that high algal growth does not necessarily result in high oil yield. Both, the generation of new cells and storage of oil require energy. When the cells used energy for generation of new cells they store less oil. Thus, growing C. saccharophila using the combination of nutrients at 16 h light exposure would be the optimal growth conditions for producing oil for biodiesel production.