A Strategy to Enhance Photo-Algal Hydrogen Production Using External H⁺ Ions in a Dual Photobioreactor

The use of microalgae for direct biohydrogen energy generation exhibits significant promise as an alternative to traditional bio-energy production due to zero-emission of CO 2 . It is known that during photolysis, algae are capable of producing hydrogen (H 2 ) gas instead of oxygen (O 2 ) under enriched acetate conditions by algal fermentative metabolisms [1]. The utilization of acetate as a practical oxygen regulator in photosystem II (PSII), but the algal hydrogen production was relatively low due to the insufficient H + ions available in the photobioreactor (PBR) [2]. Therefore, given that hydrogen ions from acetate contribute to H 2 production, it is still unclear whether supplying additional external H + ions can enhance H 2 production. Here, we demonstrate a feasibility study on improving algal H 2 production using a dual PBR system. This system enables the continuous transfer of H + ions generated from photolysis to an algal H 2 PBR through a proton exchange membrane (PEM), thereby enhancing photo-algal hydrogen production. The maximum H 2 production of 108 µmol L -1 was obtained for Chlamydomonas reinhardtii in a single PBR for 15 days at a light intensity of 100 µmol m -2 s -1 [3]. However, by leveraging the external H + ions supply, the dual PBR system increased photo-algal hydrogen production from 108 up to 760 µmol L -1 for the same period, which is 7 times greater compared to single chamber operation. This indicates that supplying external H + ions in the operation of the dual PBR is one of the important parameters for improving biohydrogen production. Our findings contribute to the ongoing development of high-performance algal H 2 production, offering valuable insights into optimizing the amount of H + ions for enhanced hydrogen production. [1] Clemens KL, Force DA, Britt RD. Acetate binding at the photosystem II oxygen evolving complex: an S 2 -state multiline signal ESEEM study. J Am Chem Soc. 2002;124(36):10921-33. [2] Hwang J-H, Church J, Lim J, Lee WH. Photosynthetic biohydrogen production in a wastewater environment and its potential as renewable energy. Energy. 2018;149:222-9. [3] Hwang J-H, Lee WH. Continuous photosynthetic biohydrogen production from acetate-rich wastewater: Influence of light intensity. Int J Hydrogen Energy. 2021;46(42):21812-21.