Bioreactors and biophoton-driven biohydrogen production strategies

Hydrogen energy systems: Technologies, trends, and future prospects

This review critically examines hydrogen energy systems, highlighting their capacity to transform the global energy framework and mitigate climate change. Hydrogen showcases a high energy density of 120 MJ/kg, providing a robust alternative to fossil fuels. Adoption at scale could decrease global CO2 emissions by up to 830 million tonnes annually. Despite its potential, the expansion of hydrogen technology is curtailed by the inefficiency of current electrolysis methods and high production costs. Presently, electrolysis efficiencies range between 60 % and 80 %, with hydrogen production costs around $5 per kilogram. Strategic advancements are necessary to reduce these costs below $2 per kilogram and push efficiencies above 80 %. Additionally, hydrogen storage poses its own challenges, requiring conditions of up to 700 bar or temperatures below -253 °C. These storage conditions necessitate the development of advanced materials and infrastructure improvements. The findings of this study emphasize the need for comprehensive strategic planning and interdisciplinary efforts to maximize hydrogen's role as a sustainable energy source. Enhancing the economic viability and market integration of hydrogen will depend critically on overcoming these technological and infrastructural challenges, supported by robust regulatory frameworks. This comprehensive approach will ensure that hydrogen energy can significantly contribute to a sustainable and low-carbon future.

Improving Biohydrogen Production by Dark Fermentation of Milk Processing Wastewater by Physicochemical and Enzymatic Pretreatments

Biohydrogen is considered an alternative energy reserve. Dark fermentation is one of the important green hydrogen production techniques that utilizes organic waste as raw material. It is a promising bioconversion, easy, not expensive, and cost-effective process. Milk processing wastewater (MPWW) is an organic effluent generated in large volumes on a daily basis and disposed directly into the environment. In this research, the study of biochemical hydrogen potential (BHP) test of MPWW was evaluated and used as substrate (S). A waste sludge was used as an inoculum (I) and source of bacteria. Both substrate and inoculum were analyzed and the study was based mainly on the ratio of volatile solids (VS) of inoculum and substrate subsequently, which was noted as I/S. Different substrate pretreatments were performed: ultrasonic, thermal, chemical, and enzymatic hydrolysis. The I/S ratio impact was investigated and evaluated the hydrogen production improvement. Modified Gompertz and modified Logistic kinetic models were employed for the kinetic modeling of cumulative hydrogen production values. Results show that I/S ratio of 1/4 gVS/gVS resulted from the best hydrogen production of 59.96 mL during 30 days of MPWW fermentation without pretreatment. It was also shown that all the adopted pretreatments enhanced hydrogen production, whereas ultrasonic pretreatment for 5 min increased the production by only 14.84%. Heat pretreatment was more efficient, where the hydrogen production increased from 60 to 162 mL (170% of improvement) using heat shock at 90 °C for 30 min. The impact of chemical pretreatment was different from a reagent to another. Pretreatment using calcium hydroxide resulted in the biggest hydrogen production of 165.3 mL (175.5%) compared to the other chemical pretreatments. However, the best hydrogen production was given by the biological pretreatment using enzymatic hydrolysis (Lactase) resulting in 254 mL of hydrogen production, which is equivalent to 323.62% of production improvement. Modified Gompertz and Logistic kinetic models fitted well with experimental data. Thus, the enzymatic hydrolysis of MPWW proved to be a promising technique for biohydrogen production enhancement.

Epitomizing biohydrogen production from microbes: Critical challenges vs opportunities

Hydrogen is a clean and green biofuel choice for the future because it is carbon-free, non-toxic, and has high energy conversion efficiency. In exploiting hydrogen as the main energy, guidelines for implementing the hydrogen economy and roadmaps for the developments of hydrogen technology have been released by several countries. Besides, this review also unveils various hydrogen storage methods and applications of hydrogen in transportation industry. Biohydrogen productions from microbes, namely, fermentative bacteria, photosynthetic bacteria, cyanobacteria, and green microalgae, via biological metabolisms have received significant interests off late due to its sustainability and environmentally friendly potentials. Accordingly, the review is as well outlining the biohydrogen production processes by various microbes. Furthermore, several factors such as light intensity, pH, temperature and addition of supplementary nutrients to enhance the microbial biohydrogen production are highlighted at their respective optimum conditions. Despite the advantages, the amounts of biohydrogen being produced by microbes are still insufficient to be a competitive energy source in the market. In addition, several major obstacles have also directly hampered the commercialization effors of biohydrogen. Thus, this review uncovers the constraints of biohydrogen production from microbes such as microalgae and offers solutions associated with recent strategies to overcome the setbacks via genetic engineering, pretreatments of biomass, and introduction of nanoparticles as well as oxygen scavengers. The opportunities of exploiting microalgae as a suastainable source of biohydrogen production and the plausibility to produce biohydrogen from biowastes are accentuated. Lastly, this review addresses the future perspectives of biological methods to ensure the sustainability and economy viability of biohydrogen production.