Journal of Energy Bioscience 2024, Vol.15, No.5, 301-313 http://bioscipublisher.com/index.php/jeb 306 5.2 Co-culturing and Symbiotic Systems Co-culturing algae with bacteria has been explored as a strategy to enhance biohydrogen production. Bacterial-algal systems can create a symbiotic environment where bacteria provide essential nutrients or remove inhibitory by-products, thereby improving the overall efficiency of hydrogen production. For instance, the use of purple non-sulphur bacteria (PNSB) in photo-fermentative systems has shown to enhance hydrogen yields through various biotechnological approaches, including medium optimization and genetic engineering (Tiang et al., 2020). Successful examples of co-culture systems include the dynamic membrane bioreactor (DMBR) used for continuous biohydrogen production from red algal biomass. This system achieved a high hydrogen production rate by leveraging the metabolic activities of both algae and bacteria, with Clostridium sp., Anaerostipes sp., and Caproiciproducens sp. playing significant roles in the process (Sim et al., 2021). Another example is the integration of dark- and photo-fermentation processes, which has been suggested to further enhance hydrogen production in co-culture systems (Tiang et al., 2020). 5.3 Reactor Design and Process Engineering Optimizing bioreactor designs is crucial for maximizing biohydrogen production from marine algae. Photobioreactors, in particular, have been the focus of many studies due to their ability to provide controlled light conditions and enhance photosynthetic efficiency. Innovations in photobioreactor design, such as improved light distribution and mixing, have been shown to significantly increase hydrogen production rates (Vargas et al., 2016; Anwar et al., 2019). Additionally, the use of advanced materials and coatings can further optimize light absorption and reduce energy losses (Tiang et al., 2020). Scaling up biohydrogen production systems from laboratory to commercial scale presents several challenges, including maintaining consistent light and nutrient distribution, managing oxygen levels, and ensuring economic feasibility. Solutions to these challenges include the development of robust bioreactor designs that can operate efficiently under varying environmental conditions and the optimization of process parameters to reduce costs. For instance, the economic assessment of biohydrogen production from macroalgae has highlighted the need for cost-effective pretreatment methods and detoxification techniques to enhance the hydrolytic process during dark fermentation (Ahmed et al., 2021; Kumar et al., 2021). Additionally, integrating biotechnological advancements with process engineering can help overcome scale-up challenges and achieve sustainable biohydrogen production (Mathews and Wang, 2009; Dubini and Ghirardi, 2014). 6 Challenges in Biohydrogen Production Using Marine Algae 6.1 Energy balance and economic feasibility One of the primary challenges in biohydrogen production using marine algae is achieving a favorable energy balance and economic feasibility. The production processes, including pretreatment and fermentation, often require significant energy inputs, which can offset the benefits of the biohydrogen produced. For instance, hydrothermal pretreatment of marine macroalgae like Saccharina latissima has shown that while biohydrogen yields can be increased, the overall process energy efficiency can drop significantly when considering the energy input for pretreatment, fermentation, and digestion (Lin et al., 2019). Additionally, the high costs associated with cultivation, harvesting, and extraction of algal biomass further complicate the economic viability of biohydrogen production (Anto et al., 2020). Strategies such as integrating advanced pretreatment methods and optimizing bioreactor conditions are essential to improve energy efficiency and reduce costs (Shankaran et al., 2022). 6.2 Environmental impacts and sustainability considerations Biohydrogen production from marine algae presents several environmental and sustainability challenges. While biohydrogen is a clean fuel, the processes involved in its production can have environmental impacts. For example, the pretreatment of algae can generate inhibitory substances that need to be managed to prevent environmental contamination (Kumar et al., 2021). Moreover, the sustainability of biohydrogen production is closely linked to the lifecycle assessment of the entire process, including the energy and resources required for algal cultivation and processing. The use of marine algae also raises concerns about the potential impacts on marine ecosystems,
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