Journal of Energy Bioscience 2024, Vol.15, No.5, 301-313 http://bioscipublisher.com/index.php/jeb 304 hydrogen and is sensitive to oxygen, which can inhibit its activity. Nitrogenase, primarily involved in nitrogen fixation, can also produce hydrogen as a by-product. The activity of these enzymes is influenced by various factors, including the availability of cofactors such as ferredoxin and flavodoxin, which transfer electrons to the hydrogenase enzyme. Optimizing the expression and activity of these enzymes is critical for enhancing biohydrogen production (Nagarajan et al., 2017; Ding et al., 2020; Tiang et al., 2020; Sharma et al., 2021; Sim et al., 2021). 4 Optimization of Environmental Conditions for Biohydrogen Production 4.1 Light intensity and quality Light intensity, duration, and spectrum play crucial roles in the photosynthetic efficiency of algae, which directly impacts biohydrogen production. High light intensity can lead to photoinhibition, reducing the activity of hydrogenase enzymes and thus decreasing hydrogen production. For instance, Chlamydomonas reinhardtii and Chlorella sorokiniana showed optimal hydrogen production at lower light intensities, with a significant drop in efficiency at higher intensities due to photoinhibition (Hwang and Lee, 2021). Additionally, innovations in light management, such as spectral filtration and plasmonic waveguides, have been shown to enhance photosynthetic productivity by improving light quality and distribution, thereby reducing non-productive pathways like the production of reactive oxygen species (Nwoba et al., 2019). Research has demonstrated that optimizing light conditions can significantly enhance hydrogen production in algae. For example, reducing the optical cross-section of the light-harvesting antenna by selectively decreasing chlorophyll b levels has been shown to improve photosynthetic efficiency and biomass yield. This approach allows algae to dynamically adjust their light-harvesting antenna sizes in response to varying light intensities, thereby maintaining high photosynthetic rates and biomass productivity (Sayre, 2020). Such strategies are essential for maximizing hydrogen production under different environmental conditions. 4.2 Temperature and pH Temperature is a critical factor influencing the metabolic processes of algae, including those involved in biohydrogen production. Optimal temperature ranges are necessary to maintain enzyme activity and metabolic rates. Deviations from these optimal ranges can lead to reduced hydrogenase activity and lower hydrogen yields. Effective temperature control in photobioreactors can help maintain the metabolic balance required for sustained hydrogen production (Nwoba et al., 2019). The pH level of the culture medium significantly affects the biohydrogen production process. Algae require specific pH conditions to optimize enzyme activity and metabolic functions. Maintaining an optimal pH range is crucial for maximizing hydrogen yield, as extreme pH levels can inhibit hydrogenase activity and disrupt cellular processes. Research indicates that fine-tuning pH levels in conjunction with other environmental factors can lead to improved hydrogen production efficiency (Nwoba et al., 2019). 4.3 Nutrient availability Nutrient availability, particularly nitrogen and phosphorus, plays a vital role in the growth and metabolic activities of algae. Adequate levels of these nutrients are necessary for maintaining cellular functions and supporting biohydrogen production. However, an excess of nutrients can lead to suboptimal hydrogen yields due to the preferential use of resources for biomass growth rather than hydrogen production. Balancing nutrient levels is therefore essential for optimizing biohydrogen production (Nwoba et al., 2019). Nutrient starvation, particularly nitrogen deprivation, has been shown to induce biohydrogen production in algae. Under nutrient-limited conditions, algae shift their metabolic pathways to favor hydrogen production as a survival mechanism. This process involves the downregulation of photosynthetic activity and the activation of hydrogenase enzymes. Studies have demonstrated that controlled nutrient starvation can significantly enhance hydrogen yields, making it a viable strategy for optimizing biohydrogen production (Hwang and Lee, 2021).
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