Journal of Energy Bioscience 2024, Vol.15, No.3, 171-185 http://bioscipublisher.com/index.php/jeb 177 intensity, photoperiod, temperature, and nutrient supply. In some studies, photobioreactors have demonstrated superior performance in terms of biomass and lipid productivity (Peng et al., 2020b). 6.3 Harvesting, lipid extraction, and biodiesel conversion processes Efficient harvesting methods such as flocculation, centrifugation, and filtration are used to separate the microalgal biomass from the culture medium. Flocculation, using agents like cationic cellulose nanocrystals, can aggregate microalgal cells for easier separation (Verfaillie et al., 2020). Lipid extraction from Nannochloropsis biomass is typically performed using solvent extraction or supercritical CO2 extraction. Solvent extraction with hexane and ethanol is common but can be environmentally harmful. Supercritical CO2 extraction, although more costly, provides a cleaner and more efficient method for extracting high-quality lipids (Taher et al., 2020). The extracted lipids are converted into biodiesel through transesterification. Enzymatic transesterification, using immobilized lipases, has been shown to be effective and environmentally friendly, producing high yields of biodiesel with good fuel properties (He et al., 2020). 6.4 Economic analysis and sustainability assessment The economic feasibility of Nannochloropsis-based biodiesel production is influenced by factors such as biomass productivity, lipid content, and processing costs. A study assessing commercial-scale production in Egypt found a return on investment (ROI) of 22%, indicating potential profitability when high-value co-products are considered alongside biodiesel (Mohammady et al., 2020). Sustainability is another critical aspect. Using CO2 from industrial emissions for microalgae cultivation can mitigate greenhouse gas emissions. Integrating wastewater treatment with microalgae cultivation can also provide a sustainable nutrient source, reducing the overall environmental footprint (Mitra and Mishra, 2019). Additionally, the use of renewable energy sources for powering cultivation and processing systems can further enhance the sustainability of the production process (He et al., 2019). 7 Integration with Wastewater Treatment 7.1 Utilization of marine microalgae in nutrient-rich wastewater Marine microalgae have shown significant potential in the treatment of nutrient-rich wastewater due to their ability to assimilate nutrients such as nitrogen and phosphorus, which are essential for their growth. This process not only helps in wastewater treatment but also supports the production of valuable biomass. Studies have demonstrated that microalgae can effectively remove high concentrations of nutrients from various types of wastewater, including industrial, agricultural, and aquaculture effluents. For instance, a study by Gupta et al. (2019) highlighted the use of microalgae in treating nutrient-rich wastewater from agro-based industries, achieving substantial removal rates for nitrogen and phosphorus while simultaneously producing biomass that can be used for bioenergy. Microalgae such as Chlorella vulgaris and Nannochloropsis sp. have been particularly effective in nutrient uptake. These microalgae can thrive in wastewater environments, utilizing the available nutrients for growth and thereby reducing the pollutant load. The integration of microalgae cultivation with wastewater treatment processes, such as in a biofilm membrane photobioreactor (BF-MPBR), has been shown to enhance nutrient removal efficiency. Peng et al. (2020b) demonstrated that this system could achieve removal rates of up to 99.6% for dissolved inorganic nitrogen and 98.4% for dissolved inorganic phosphorus, highlighting the effectiveness of microalgae in wastewater bioremediation. 7.2 Dual benefits: wastewater treatment and biomass production The integration of microalgae cultivation with wastewater treatment offers dual benefits: efficient wastewater treatment and the production of valuable biomass. Microalgae-based systems can convert wastewater pollutants into biomass, which can be further processed into biofuels, fertilizers, and other high-value products. This approach not only addresses environmental pollution but also contributes to the circular bioeconomy by transforming waste into resources.
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