Journal of Energy Bioscience 2024, Vol.15, No.1, 32-47 http://bioscipublisher.com/index.php/jeb 37 4 Energy Conversion Processes 4.1 Photosynthesis and biomass production Energy conversion processes are essential for transforming agricultural products into usable forms of energy. These processes leverage natural and technological mechanisms to convert biomass into biofuels and other energy carriers. Photosynthesis is the fundamental biological process by which green plants, algae, and certain bacteria convert light energy into chemical energy (Nimir and Zhou, 2018). During photosynthesis, these organisms absorb carbon dioxide (CO2) from the atmosphere and water (H2O) from the soil, using sunlight to produce glucose (C6H12O6) and oxygen (O2). This process forms the basis for biomass production, as the glucose produced during photosynthesis is used to build plant tissues and generate energy for growth and development. The biomass accumulated through photosynthesis serves as the primary raw material for biofuel production. Crops such as corn, sugarcane, and soybeans, as well as non-food plants like switchgrass and algae, are cultivated specifically for their high biomass yield and energy content (Brandes et al., 2018; Peng et al., 2019). Research has found that intercropping switchgrass in corn/soybean fields is economically viable under certain conditions, particularly in regions with significant crop yield variability. This has important implications for designing policies aimed at enhancing the sustainability of agricultural production (Brandes et al., 2018). Algae and bacteria perform photosynthesis under sunlight, storing chemical energy and serving as feedstocks for biofuels. Algae can grow in saltwater and produce various biofuels, including biodiesel, methane, ethanol, and hydrogen. Developing efficient production processes is crucial for the successful utilization of these systems (Kumar, 2019). Research indicates that algae, due to their high photosynthetic efficiency and oil content, are considered a significant future source of biofuels. Although the cost of microalgal fuels is high, genetic and metabolic engineering can enhance production efficiency (Peng et al., 2019). 4.2 Biochemical conversion methods Biochemical conversion methods utilize biological processes to transform biomass into biofuels. The most common biochemical conversion methods include fermentation and anaerobic digestion. The fermentation process involves converting sugars and starches in biomass into ethanol and other alcohols through microorganisms such as yeast. For example, corn and sugarcane can be fermented to produce ethanol. The ethanol produced through fermentation is often used as a fuel additive in gasoline to increase octane levels and reduce emissions (He et al., 2018). In addition to ethanol, fermentation can also produce other types of alcohols, such as butanol, which has a higher energy density and better blending properties than ethanol. The anaerobic digestion process involves the decomposition of organic matter by anaerobic bacteria under oxygen-free conditions, producing biogas that is primarily composed of methane (CH4) and carbon dioxide (CO2) (Goh et al., 2023). Typical feedstocks for anaerobic digestion include agricultural residues, manure, and food waste. The biogas produced can be used for heating, electricity generation, and as vehicle fuel. Besides energy production, the byproducts of anaerobic digestion—digestate and solid residues—can be used as efficient organic fertilizers to improve soil quality and structure. The advantages of biochemical conversion methods lie in their ability to utilize a wide range of biomass feedstocks and their relatively low energy requirements compared to thermochemical methods. Moreover, biochemical conversion processes typically operate at lower temperatures and pressures, resulting in lower equipment and operating costs (Osman et al., 2021). Since these methods rely on the metabolic activities of microorganisms, researchers can use genetic engineering to modify microorganisms, enhancing their metabolic efficiency and adaptability to different feedstocks, thereby further increasing the yield and quality of biofuels. In recent years, the use of microalgae has emerged as a new area of research in biochemical conversion. Microalgae possess high photosynthetic efficiency and rapid growth characteristics, and their cells are rich in lipids and carbohydrates that can be converted into biofuels through fermentation and other biochemical methods. Cultivating microalgae does not require fertile land and freshwater resources, making it a biomass feedstock with minimal environmental impact and significant potential (Meng et al., 2019; Colomer-Vidal et al., 2021).
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