Design, modelling and simulation of a thermosiphon photobioreactor for photofermentative hydrogen production

Currently, most photobioreactors have been designed for cyanobacteria and green algae with comparatively few designed for photofermentative hydrogen production by purple non-sulphur bacteria. Photofermentation experiments are time-consuming and expensive, driving the development of alternative methods for the design of photobioreactors. In this study, computational fluid dynamics (CFD) was used (ANSYS® software package, 2019 R) to design two new thermosiphon photobioreactor (TPBR) configurations for the application of photofermentative hydrogen production by Rhodopseudomonas palustris. The TPBR designs (tubular loop and flat-plate) were simulated and evaluated based on temperature profiles, fluid flow and radiation distribution. Under constant illumination, both reactor designs displayed simulated temperatures suitable for R. palustris as well as achieved fluid velocities exceeding the settling velocity of R. palustris cells; however, both these designs also displayed significant light attenuation. The CFD simulation results were verified by experimental measurements of temperature (< 2.5% error) and fluid velocity (47% error) in a prototype TPBR. Collectively, both the proposed TPBR designs were found to be suitable for photofermentative hydrogen production by R. palustris, with the tubular loop design slightly outperforming the flat-plate in terms of fluid velocity. Furthermore, the proposed CFD method was found to be suitable for the design of photobioreactors, with simulated results closely mimicking their experimentally measured counterparts.