Presentation Information
[P04-497]Foundational Study for Carbon Nitride-Assisted Light-Driven Biological CO2 Methanation
○Indra Jaya Budiarso1, Masaki Umetsu1, Koji Yokoyama1, Yuta Nakayasu1, Masanobu Kamitakahara1 (1. Tohoku University (Japan))
Keywords:
Methanogenesis,Carbon nitride,Photocatalyst,Biocatalyst
Natural hydrogenotrophic methanogenesis is an effective way for converting carbon dioxide (CO2) to methane (CH4), but it relies on externally supplied hydrogen (H2), which introduces inefficiencies in production, transport, and gas-liquid mass transfer. Light-driven biological CO2 methanation offers an alternative route by using a photocatalyst to supply reducing equivalents (i.e. electrons) for methanogens under light irradiation, therefore bypassing the need for molecular hydrogen. Potassium poly(heptazine imide) (KPHI) is a promising candidate as photocatalyst due to its charge storage ability, visible-light activity, and potentially non-toxic to methanogens. In this study, we examined the key prerequisites for KPHI-assisted light-driven methanogenesis using Methanosarcina barkeri (M. barkeri).
To this end, KPHI was synthesized via a molten salt (KCl-LiCl) method with varying polymeric carbon nitride-to-salt ratios. A ratio of 1:20 gave a KPHI yield of 50% and produced KPHI with an excellent charge storage ability. After irradiating a KPHI dispersion in 10% v/v methanol solution under fluorescent light irradiation for 12 h, the characteristic blue state of charged KPHI persisted until exposure to air, indicating stable electron storage in the absence of oxygen. In addition, methane production in a KPHI-containing medium was comparable to that of KPHI-free medium, suggesting that KPHI did not show apparent toxicity toward M. barkeri under the tested conditions.
In parallel, the effect of light irradiation on methanogenic activity was evaluated under different substrate conditions. Using an H2/CO2medium, light irradiation decreased methane production by 13% compared with unirradiated cultures. In contrast, under methanol-containing medium, light irradiation did not reduce total methane production but only slowed methanogenic activity during the early cultivation stage. These results indicate that the effect of light irradiation on methanogens is substrate-dependent and should be carefully considered in system design.
These findings establish a practical basis for designing KPHI-assisted light-driven biological CO2 methanation in the future. Performance evaluation of light-driven biological CO2 methanation using KPHI photocatalyst is still being studied.
To this end, KPHI was synthesized via a molten salt (KCl-LiCl) method with varying polymeric carbon nitride-to-salt ratios. A ratio of 1:20 gave a KPHI yield of 50% and produced KPHI with an excellent charge storage ability. After irradiating a KPHI dispersion in 10% v/v methanol solution under fluorescent light irradiation for 12 h, the characteristic blue state of charged KPHI persisted until exposure to air, indicating stable electron storage in the absence of oxygen. In addition, methane production in a KPHI-containing medium was comparable to that of KPHI-free medium, suggesting that KPHI did not show apparent toxicity toward M. barkeri under the tested conditions.
In parallel, the effect of light irradiation on methanogenic activity was evaluated under different substrate conditions. Using an H2/CO2medium, light irradiation decreased methane production by 13% compared with unirradiated cultures. In contrast, under methanol-containing medium, light irradiation did not reduce total methane production but only slowed methanogenic activity during the early cultivation stage. These results indicate that the effect of light irradiation on methanogens is substrate-dependent and should be carefully considered in system design.
These findings establish a practical basis for designing KPHI-assisted light-driven biological CO2 methanation in the future. Performance evaluation of light-driven biological CO2 methanation using KPHI photocatalyst is still being studied.
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