Abstract:Microalgae are an alternative and sustainable source of lipids that can be used as a feedstock for biodiesel production. Nitrate is a good nitrogen source for many microalgae and affects biomass and lipid yields of microalgae. In this study, the effect of nitrate on cell growth and lipid production and composition in Monoraphidium contortum, Tetraselmis suecica, and Chlorella minutissima was investigated. Nitrate affected the production of biomass and the production and composition of lipids of the three microalgae tested. Increasing the nitrate concentration in the culture medium resulted in increased biomass production and higher biomass productivity. Furthermore, increasing the nitrate concentration resulted in a reduction in lipid content and productivity in M. contortum; however, the opposite effect was observed in T. suecica and C. minutissima cultures. diesel infrastructure for storage and distribution. Biodiesel offers several advantages over petroleumbased diesel. For example, biodiesel is a renewable and biodegradable energy resource, it produces fewer toxic emissions (carbon monoxide, aromatic compounds, hydrocarbons, particulate matter, sulfur oxides, nitrogen oxides, and metals), it is less volatile and safer to transport, store and handle, and it increases efficiency, reduces wear, and extends engine life [2,3].Currently, biodiesel is produced from vegetable oils (edible or inedible), waste oils, and animal fats. However, this practice has raised serious concerns in the international community regarding the production, price, and availability of food. Other concerns include the deforestation of large areas of land that could be used to grow oleaginous vegetables, the huge amounts of water needed for irrigation, and the inability of these biodiesel sources to meet current and future fuel demands [4,5]. A sustainable biodiesel industry needs alternative raw materials that can be obtained easily from alternative renewable and biodegradable sources, allowing continuous operation and avoiding the limitations described [6].Currently, there is a consensus that microalgae are an alternative and sustainable source of lipids that can be used as a feedstock for biodiesel production. Microalgae are suitable for this purpose because they are photosynthetic microorganisms with a simple cellular structure and are easy to culture. Furthermore, microalgae grow in a variety of environments, their growth rate is 20 to 30 times faster than other sources of biofuels, they exhibit high photosynthetic efficiency, contribute greatly to the sequestration of atmospheric CO 2 , thereby mitigating climate change, can be harvested 365 days a year, can be grown in areas unsuitable for agriculture, livestock, industry, or tourism, require smaller volumes of water than oleaginous plants and can use water unsuitable for human consumption, their intracellular lipid content is high and the productivity of lipids per unit area is considerably higher than that of oleaginous plants [7][8][9][10].Several studies have shown that...