Bioscience Evidence 2024, Vol.14, No.2, 81-92 http://bioscipublisher.com/index.php/be 87 For instance, co-culturing Clostridium thermocellum, a cellulose-degrading bacterium, with hydrogen-producing bacteria such as Thermotoga maritima has been shown to improve hydrogen yield from lignocellulosic biomass (Figure 2) (Ben Gaida et al., 2022). The cellulose is first broken down into simpler sugars by C. thermocellum, which are then utilized by T. maritima to produce hydrogen. This cooperative interaction not only enhances the efficiency of substrate utilization but also stabilizes the production process under varying environmental conditions. Figure 2H2 Production (HP, empty symbol) and H2 production rate (HPR, full symbol) by Thermotoga maritima (Adopted from Ben Gaida et al., 2022) Microbial consortia can also be engineered to optimize the metabolic environment for hydrogen production. By selecting and cultivating strains that complement each other’s metabolic activities, researchers can create highly efficient consortia that outcompete single-species cultures in terms of hydrogen yield and stability. 5.4 Environmental and process conditions optimization Optimizing environmental and process conditions is critical for maximizing the efficiency of biohydrogen production. Factors such as pH, temperature, substrate concentration, and hydraulic retention time (HRT) can significantly influence the metabolic activity of hydrogen-producing bacteria. Maintaining an optimal pH, typically in the range of 5.5 to 6.0, is crucial for ensuring the activity of hydrogenases and preventing the accumulation of inhibitory by-products. Similarly, controlling the temperature within the optimal range for the specific bacterial species being used can enhance metabolic rates and hydrogen yield (Zhu et al., 2021). Substrate concentration and the type of feedstock also play a pivotal role in hydrogen production. Using pretreated or hydrolyzed substrates can improve the availability of fermentable sugars, leading to higher hydrogen yields. Additionally, optimizing HRT in bioreactors ensures that the microbial community has sufficient time to degrade the substrate and produce hydrogen, while also preventing washout of the bacteria (Tang et al., 2021). Advanced bioprocessing techniques, such as fed-batch and continuous-flow systems, can also be employed to optimize hydrogen production. These systems allow for the controlled addition of substrates and the removal of inhibitory by-products, thereby maintaining optimal conditions for sustained hydrogen production (Saidi et al., 2018). The optimization of metabolic pathways, the application of directed evolution, the development of co-culture systems, and the fine-tuning of environmental and process conditions are all crucial strategies for enhancing
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