A Critical Review of Continuous Biohydrogen Production

Biohydrogen is a feasible and environmentally sustainable fuel for the world's growing energy demand. As an alternative renewable energy source, hydrogen contains ۲.۷۵ times more energy per gram than any other known source. Biohydrogen is produced from various microorganisms and renewable materials through anaerobic dark fermentation and phototrophic bacteria, operating in batch, semi-continuous, and continuous modes. Anaerobic dark fermentation has a higher production rate and yield compared to photo-fermentation. In this review, the dark fermentation of hydrogen is discussed concerning key influential parameters and environmental factors such as temperature, pH, hydraulic retention time, mass transfer coefficient, and recycle ratio. A low initial pH affects metabolic pathways, prolongs the lag phase, and enhances Fe-hydrogenase activity. Mesophilic, thermophilic and ultrathermophilic strains could tolerate maximum operating temperature of ۴۰, ۶۵ or ۱۰۸°C, respectively. A varity of fermenters are continuously used for biohydrogen production, with a few discussed here. Tower-type fermenters are more feasible than CSTRs as they provide a higher hydraulic retention time for continuous biohydrogen production. Fluidized beds are used for both short- and long-term hydraulic retention time operations. Hydraulic retention time (HRT) typically depends on the bioreactor type, geometry, and feed composition, particularly the carbon source. When wastewater is used, HRT generally ranges from ۸ to ۱۴ hours. However, the process requires more detailed data to fully understand and overcome thermodynamic limitations. These limitations could be addressed through genetic modification or metabolic pathway alterations to enhance biohydrogen yield, making large-scale and commercial production more feasible.

کلیدواژه ها:

Biohydrogen ، Fermenters ، Continuous operation ، Dark fermentation