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

Abstract

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 CO2. It is known that during photolysis, algae are capable of producing hydrogen (H2) gas instead of oxygen (O2) 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 H2 production, it is still unclear whether supplying additional external H+ ions can enhance H2 production.Here, we demonstrate a feasibility study on improving algal H2 production using a dual PBR system. This system enables the continuous transfer of H+ ions generated from photolysis to an algal H2 PBR through a proton exchange membrane (PEM), thereby enhancing photo-algal hydrogen production. The maximum H2 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 H2 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 S2-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.