Mass, Energy, and Electron-based Metrics in Anaerobic Digestion

Anaerobic digestion is a sustainable process, which generates biomethane using organic matters as feedstocks, and can be represented by Buswell's equation. When the chemical formula of organic matter is identified, the mean oxidation number of organic carbons, theoretical amount of biomethane, theoretical biomethane potential, and theoretical number of transferred electrons can be determined. Currently, the biodegradability performance of organic matters in anaerobic digestion is measured by two metrics- the biodegradability index and the energy conversion efficiency. However, the concept of electron conversion efficiency has not been rigorously studied. This article serves two purposes- to develop a new electron-based metric, and to investigate the relationships between this metric and the two preexisting biodegradability performance metrics. Having calculated these said metrics through a series of procedures using mass percentages of elements and experimental biomethane potential as key parameters, this research concludes that the microscopic electron conversion efficiency and the macroscopic mass-based biodegradability index are numerically identical, and the electron conversion efficiency and energy conversion efficiency display a strong linear correlation.