Numerical investigation of pH control on dark fermentation and hydrogen production in a microbioreactor

Abstract

The efficiency of dark fermentation, as one of the most promising bioconversion technologies to produce biohydrogen , largely depends on some important parameters, such as pH, due to the sensitivity of anaerobic bacteria and biological metabolism to pH values. Understanding mechanisms of controlling the bacteria growth and dark fermentation is critical for effective improvements in biohydrogen production in bioreactors. In this study, a pore-scale model has been developed within a coupled lattice Boltzmann method and cellular automata (LBM-CA) platform to account for effects of spatiotemporal pH variations on dark fermentation and hydrogen production. We applied the model to simulate the dark fermentation processes and hydrogen production in a porous microbioreactor to quantify (1) the effects of local acids concentrations and pH on biofilm growth, (2) the effect of dynamic local acids concentrations on pH and overall hydrogen production and extraction, and (3) the effects of acid additives on local and average pH values and hydrogen production. The results showed the importance of acid and pH in biohydrogen production and extraction rates. The production rate reduced more than 25% when inlet pH was reduced from 5 to 6. Acid injection was able to increase up to 40% more biohydrogen extraction. It was observed that the biofilm growth can decrease (up to 63.18%) in the domain when pH changes from 4 to 6. This demonstrates that the present dark fermentation model can be applied for design of high-throughout bioreactor for effective improvement of dark fermentation and hydrogen production.