Biological Hydrogen Production: A Comprehensive Review for Converting Wastes into Wealth

Energy shortages have hindered global economic development. By utilizing waste as a substrate for microbial fermentation, hydrogen production can transform waste into a valuable resource, significantly reducing the cost of hydrogen production and addressing a significant hurdle in achieving large-scale production of microbial hydrogen. This approach has significant potential for future hydrogen-production applications. Two-stage indirect photohydrolysis has recently emerged as a promising and efficient method for hydrogen production using cyanobacteria and green algae. However, this method cannot be directly applied to organic wastewater for hydrogen production. In contrast, dark fermentation by bacteria, particularly ethanol-type fermentation, is highly efficient for producing hydrogen. Therefore, the combination of the indirect photohydrolysis of algae and dark fermentation by bacteria is expected to significantly enhance the hydrogen-production capacity of organic wastewater, laying the groundwork for future large-scale microbial hydrogen production. This study reviews the main types and technical principles of microbial hydrogen production from waste, available waste types, research progress in the microbial hydrogen-production process, strategies to improve the hydrogen-production rate, and challenges faced during industrialization. Future research directions for microbial-waste hydrogen production are also proposed. The aim of this study is to provide a valuable reference for large-scale biological hydrogen-production research.