Journal of Energy Bioscience 2024, Vol.15, No.5, 301-313 http://bioscipublisher.com/index.php/jeb 308 demonstrated promising results with gas production rates of 96.30 mol/m³-d and 224.68 mol/m³-d for dark- and photo-fermentation, respectively (Lu et al., 2020). Another study focused on the hydrothermal pretreatment of the brown seaweed Saccharina latissima, which significantly improved the solubilization and subsequent production of biohydrogen and biomethane, achieving a maximum energy conversion efficiency of 72.8% (Lin et al., 2019). These pilot projects highlight the potential for scaling up biohydrogen production, although they also underscore the need for further optimization and cost reduction. 7.3 Barriers to scaling up production and reducing costs Several barriers hinder the scaling up of biohydrogen production from marine algae. One of the primary challenges is the high cost associated with the cultivation, harvesting, and extraction processes of algal biomass (Anto et al., 2020). Additionally, the low hydrogen yield from current biological processes remains a significant bottleneck (Goswami et al., 2020; Sharma et al., 2021). Technical and scientific obstacles, such as the need for efficient pretreatment methods to enhance hydrolysis and the control of inhibitory substances formed during pretreatment, also pose challenges (Lin et al., 2019; Kumar et al., 2021). Furthermore, the complexity of integrating upstream and downstream processes to achieve economic viability and the need for advanced strategies to improve biohydrogen production efficiency are critical areas that require attention (Jiménez-Llanos et al., 2020; Sharma et al., 2021). Addressing these barriers through technological innovations and process optimizations is essential for the successful commercialization and industrial-scale production of biohydrogen from marine algae. 8 Environmental Sustainability of Marine Algal Biohydrogen Production 8.1 Ecological impacts of large-scale algae cultivation Large-scale cultivation of marine algae for biohydrogen production can have significant ecological impacts. The cultivation process can enhance biomass production and nutrient recycling, especially when using polycultures, which have been shown to improve energy return on investment (EROI) and reduce greenhouse gas emissions (GHGs) compared to monocultures (Carruthers et al., 2019). However, the environmental sustainability of these systems is highly dependent on the specific cultivation methods and geographic locations. For instance, open raceway ponds (ORP) and tubular photobioreactors have different environmental impacts, with ORPs being more feasible under favorable climatic conditions (Pérez-López et al., 2017). Additionally, the use of marginal lands and industrial flue gases for CO2 can further mitigate the ecological footprint of algae cultivation (Zaimes and Khanna, 2013). 8.2 Life cycle analysis (LCA) of biohydrogen from marine algae Life cycle analysis (LCA) is a crucial tool for evaluating the environmental sustainability of biohydrogen production from marine algae. Various studies have highlighted the importance of LCA in identifying the most sustainable pathways for algal biofuel production. For example, a comparative LCA of different algal species and cultivation methods showed that certain bicultures could significantly improve sustainability metrics (Carruthers et al., 2019). Another study demonstrated that using advanced cultivation and processing methods could reduce the environmental impacts of macroalgae-based biofuels (Aitken et al., 2014). Furthermore, the LCA of microalgae production for aquaculture purposes revealed that upscaling could improve resource efficiency and reduce the carbon footprint (Taelman et al., 2013). These findings underscore the importance of optimizing cultivation and processing methods to enhance the environmental sustainability of marine algal biohydrogen production. 8.3 Strategies for minimizing environmental footprint Several strategies can be employed to minimize the environmental footprint of marine algal biohydrogen production. One effective approach is the use of advanced metabolic engineering to enhance the productivity and efficiency of algal strains. For instance, genetically engineered cyanobacteria with higher photon conversion efficiency can significantly reduce the environmental impacts of biofuel production (Villacreses-Freire et al., 2021). Additionally, optimizing the cultivation and harvesting processes, such as using flat panel enclosed
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