Abstract

Organic combustion and anaerobic digestion are two important types of redox reactions. The former uses molecular oxygen as oxidizing agent and organic carbon as reducing agent. The latter uses organic carbons as both oxidizing agent and reducing agent. Anaerobic digestion is represented by Buswell’s equation. It is composed of series of bioredox and biohydrolysis reactions. To count heat of anaerobic digestion, structural formula and heat of formation of organic matter are required. To overcome these restrictions, this research establishes a simple equation for determining heat of anaerobic digestion. Hess’s Law is used to convert organic combustion equations to Buswell’s equation. Then, the corresponding thermochemical equation for standard heat of anaerobic digestion is deduced. This research concludes that: (i) ideal standard heat of anaerobic digestion is equal to zero, (ii) heat of bioredox is dependent on Buswell’s electron, (iii) standard heat of biohydrolysis is equal to the negative value of standard heat of bioredox, and (iv) standard Gibbs free energy change is equal to the negative product of temperature times standard entropy change.

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