Geometrical parameters effects on biohydrogen production through photolysis in a two-stage bioreactor

Biohydrogen production is important as a sustainable alternative to fossil fuels, while potentially utilizing waste materials as feedstock. In this study, a coupled platform based on the lattice Boltzmann method and cellular automata approach was utilized to examine the effects of bioreactor geometries on fluid flow, species transport, biofilm formation, and biohydrogen extraction during indirect photolysis. Four rectangular obstacle heights (0.75h, 1.0h, 1.25h, and 1.5h, h equals a quarter of the bioreactor's channel height) and four obstacle shapes (rectangular, half-circular, left-sided triangular, and right-sided triangular) were analyzed. Results indicate that the 1.0h rectangular obstacle had the highest biohydrogen production, achieving the highest hydrogen extraction rate and biofilm growth. Variations in obstacle height significantly affected flow dynamics and shear stress, with the 1.5h model showing a 29% higher biofilm concentration, but a 54% lower hydrogen extraction rate compared to the 1.0h model. Obstacle shape also influenced performance, with the rectangular obstacle surpassing circular and triangular shapes in hydrogen extraction and biofilm growth. The findings highlight the critical role of bioreactor design in enhancing biohydrogen production, a promising carbon-free, high-energy-density fuel produced by microorganisms like cyanobacteria. This work provides insights into enhancing biophotolysis-based bioreactors for sustainable hydrogen production.