Supplementation of Kelp Waste Extract with Different Nitrogen Sources as a Promising Technique to Enhance Growth and Lipid Accumulation in Chlorella sorokiniana

Microalgae have been investigated for the production of different biofuels, and the feedstock is gaining interest in the present day due to their fast growth potential added to relatively high lipid, carbohydrate, and nutrient contents. The purpose of this study is to perform research to grow commercial microalgae and to produce a significant amount of lipid content from microalgae harvested as a viable alternative to renewable energy. The commercial microalga chosen is Chlorella sorokinian. Nitrogen is an essential element for microalgal growth, lipid synthesis, and several physiological processes. Microalgae can utilize several nitrogen sources, including nitrate and ammonium. The growth and lipid content of microalgae cultures and their biochemical structures are influenced by the type of nitrogen utilized, which is contingent upon the specific species of algae and the quantities and sources of nitrogen. This study aims to increase the growth and lipid accumulation of the microalga Chlorella sorokiniana by varying the nitrogen sources NaNO₃, KNO₃, and NH₄ Cl concentration in the culture medium. Results indicate that the highest cell density of 28.83 × 10⁷ cell mL^-1 and the maximum 4.1 g L^-1 dry biomass were obtained under the treatment of sodium nitrate. Among nitrogen sources, the better pigment contents chl a 17.2 mg L^-1 and chl. b contents were recorded in the case of sodium nitrate, followed by potassium nitrate and ammonium chloride. However, carbohydrate production was found to be a maximum of 390.1 μg mL^-1 in ammonium chloride culture. The lipid content was measured using the Bligh and Dyer method and observed the highest 19% in sodium nitrate culture compared to other nitrogen sources. Overall, it can be concluded that sodium nitrate culture produced promising results regarding biomass production and different biochemical attributes.