Journal of Energy Bioscience 2024, Vol.15, No.5, 301-313 http://bioscipublisher.com/index.php/jeb 302 biomass is essential to break down complex carbohydrates into fermentable sugars, thereby improving the efficiency of subsequent fermentation processes (Lin et al., 2019; Kumar et al., 2021). Addressing technical and scientific obstacles, such as the formation of inhibitory substances during pretreatment and the recalcitrance of algal cell walls, is vital for advancing biohydrogen production technologies (Nagarajan et al., 2020; Kumar et al., 2021). This study aims to explore the efficiency and condition optimization of biohydrogen production using algae, providing a comprehensive review of the advanced technologies and methods currently employed in algae-based biohydrogen production. Various metabolic pathways, pretreatment methods, and operational parameters influencing biohydrogen yield are discussed. The study also highlights the challenges that need to be addressed and the future research directions required to enhance the commercial feasibility of algae-based biohydrogen, with the hope of contributing to the development of a sustainable and efficient biohydrogen production system. 2 Marine Algae as a Feedstock for Biohydrogen Production 2.1 Characteristics of marine algae (biomass composition, growth rates, etc.) Marine algae, including both microalgae and macroalgae, are characterized by their high photosynthetic efficiency and ability to accumulate significant quantities of biomass. The biochemical composition of marine algae typically includes carbohydrates, lipids, and proteins, which are essential for biohydrogen production. For instance, microalgae have a high lipid content, which is advantageous for biofuel production (Williams and Laurens, 2010; Adeniyi et al., 2018). Additionally, marine macroalgae such as Ulva sp. can accumulate high amounts of starch and cellulose, making them suitable for bioethanol and biohydrogen production (Qarri and Israel, 2020). The growth rates of marine algae can vary significantly depending on environmental conditions. For example, Ulva sp. has shown specific growth rates (SGRs) ranging from 1.4% to 19.3% per day, depending on the season and cultivation conditions (Qarri and Israel, 2020). This high growth rate, coupled with the ability to grow in various water types, including seawater and wastewater, makes marine algae a versatile and sustainable feedstock for biohydrogen production (Wang and Yin, 2018) (Figure 1). 2.2 Advantages of marine algae over terrestrial biomass Marine algae offer several advantages over terrestrial biomass for biohydrogen production: Higher Growth Rates: Marine algae generally have higher growth rates compared to terrestrial plants, which allows for more rapid biomass accumulation (Wang and Yin, 2018; Qarri and Israel, 2020). Non-Arable Land Use: Marine algae do not require arable land for cultivation, thereby avoiding competition with food crops and reducing the pressure on terrestrial ecosystems (Wang and Yin, 2018). CO2 Fixation: Marine algae have superior CO2 fixation capabilities, which can help mitigate greenhouse gas emissions and contribute to environmental sustainability (Adeniyi et al., 2018; Wang and Yin, 2018). Figure 1 Potential pathways from microalgae to biofuels (Adopted from Wang and Yin, 2018)
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