Abstract

Buswell’s equation for biohydrogen is a stoichiometric model for representing dark fermentation. With this equation, the biodegradability performance and energy change of organic matter can be well understood. In this research, thermodynamics is used to assess energy properties and temperature sensitivity of organic matter in dark fermentation. The unified thermodynamic framework is applied to quantify standard enthalpy change, standard entropy change, standard Gibbs free energy change of dark fermentation, and to establish the relationship between the energy change of organic matter and the spontaneity of dark fermentation. This research concludes: (1) dark fermentation is an endothermic reaction, (2) dark fermentation is an entropy-dominated reaction, (3) only limited numbers of organic matter such as carbohydrates, formic acid, and chloroform are spontaneous in dark fermentation at standard state, (4) temperature increase transforms non-spontaneous organic matter into spontaneous organic matter for biohydrogen formation, and (5) positive Gibbs free energy change and high spontaneous temperature of organic matter are the thermodynamic constraints for low biohydrogen yield in dark fermentation.

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