Exploring Electron Conversion Efficiency for Biohydrogen in Dark Fermentation

Buswell’s equation for biohydrogen can represent dark fermentation in accordance with the elemental composition of any organic matter. When the empirical formula or structural formula of an organic matter is identified, the theoretical amount of biohydrogen, theoretical biohydrogen potential, theoretical biohydrogen yield, and theoretical number of transferred electrons can be determined. Currently the metrics that measure the biodegradability performance of organic matters in dark fermentation are biodegradability index and energy conversion efficiency. However, the concept of electron conversion efficiency has not been well investigated. The aims of this article are to develop the electron conversion efficiency for biohydrogen to be a metric and explore the relationships between the biodegradability index and the energy conversion efficiency. The article shows that among the three metrics, electron conversion efficiency and biodegradability index are numerically identical, and that there is a strong positive correlation between electron conversion efficiency and energy conversion efficiency. In addition, the established electron conversion efficiency functions as a cross-reference for dark fermentation, dark fermentation coupled photochemical system, and electrochemical system under anaerobic conditions.