Journal of Energy Bioscience 2024, Vol.15, No.3, 171-185 http://bioscipublisher.com/index.php/jeb 173 3 Cultivation Conditions and Optimization 3.1 Nutrient requirements and management Nutrient management is critical for the optimal growth of marine microalgae used in biodiesel production. Nitrogen (N) and phosphorus (P) are particularly important macronutrients. The appropriate balance of these nutrients can significantly influence algal biomass productivity and lipid content. Studies have shown that effluents from anaerobic digestion, which are rich in nitrogen and phosphorus, can be effectively used to cultivate marine microalgae like Nannochloropsis sp., achieving up to 50% lipid content under nitrogen stress conditions (Mayers et al., 2017). Phosphorus is another crucial nutrient, and its availability can affect nitrogen assimilation and overall growth. Efficient phosphorus management can enhance biomass production and lipid accumulation. The recycling of nutrients from various waste sources, such as municipal wastewater or biogas slurry, has also been explored to provide a sustainable nutrient supply for microalgae cultivation (Yaakob et al., 2021). Silica is essential for the growth of diatoms, a type of microalgae with silica-based cell walls. Its availability can influence the growth and development of these species, which are also considered for biodiesel production due to their high lipid content (Zhuang et al., 2018). 3.2 Light intensity, photoperiod, and wavelength effects on growth Light is a fundamental factor influencing the growth and lipid accumulation in microalgae. The intensity, photoperiod, and wavelength of light all play crucial roles in optimizing photosynthetic efficiency. Higher light intensities generally enhance growth rates, but excessive light can lead to photoinhibition. Therefore, optimizing light intensity is essential for maximizing biomass yield without causing damage to the cells (Molina-Miras et al., 2022). The photoperiod, or the duration of light exposure, also impacts microalgae growth. A balanced light-dark cycle can enhance growth and lipid production. For instance, a 16:8 light-dark cycle has been shown to be effective for many microalgal species, promoting efficient photosynthesis during the light phase and allowing for cellular maintenance and repair during the dark phase (Atmanli, 2020). Different wavelengths of light can also affect the growth and biochemical composition of microalgae. Blue and red light are particularly effective for photosynthesis, as they are absorbed by chlorophylls and other pigments, driving the growth and lipid accumulation in microalgae (Mayers et al., 2017). 3.3 Temperature and salinity optimization for maximal lipid accumulation Temperature and salinity are environmental factors that significantly influence the growth and lipid production of marine microalgae. Optimal temperature ranges for most microalgae species are between 20 ℃ and 30 ℃. Within this range, microalgae exhibit maximal growth and lipid accumulation. Deviations from the optimal temperature can lead to reduced growth rates and lipid content (Zhou et al., 2018). Salinity also plays a crucial role in the cultivation of marine microalgae. Species adapted to high salinity environments can utilize seawater, reducing the need for freshwater resources. Proper salinity levels must be maintained to prevent osmotic stress, which can adversely affect cell physiology and lipid production (Kim et al., 2017). 3.4 Carbon dioxide utilization and optimization techniques Carbon dioxide (CO2) is a critical component of microalgae cultivation, as it is a carbon source for photosynthesis. Optimizing CO2 concentration can enhance biomass production and lipid accumulation. High CO2 levels, up to 5%-10%, can significantly increase growth rates and lipid content in microalgae (Ge and Champagne, 2017). Several techniques have been developed to optimize CO2 utilization in microalgal cultures. These include the use of gas spargers to ensure efficient CO2 distribution in photobioreactors and the integration of CO2 capture systems
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