This process is known as biological hydrogen methanation, which uses CH₄, CO₂, and H₂ that are generated in the methane fermentation process of waste biomass and makes up the deficit of H₂ with H₂ generated from electrolysis of water or other processes.
　The cost of producing CH₄ using this process is estimated at 6.9 JPY/MJ (the fixed cost of 4.0 JPY/MJ plus the variable cost of 2.9 JPY/MJ).
　Although the current gas rate is about 3.5 JPY/MJ, it will be around 5.7 JPY/MJ because of the additional cost of DAC in a ZC society.
　The price of CH₄ produced through the methane fermentation-methanation reaction is estimated a little higher, at 6.9 JPY/MJ. Given the benefit of treating waste biomass, the methane fermentation-methanation reaction system is worthwhile.
　In this study, we have found that the cost of producing CH₄ depends less on the presence or absence of hydrogen fermentation and more on the price of hydrogen supplied externally as well as the quantity of hydrogen generated. Studies on fermenter components and system optimization will be needed.
　Our analysis using a fermentation model suggests that the methane fermentation process lends itself to rationalizing processes and making predictions about fermentation systems. We thus propose widespreading and utilizing the fermentation model.