Improving anaerobic digestion mass balance calculations through stoichiometry and usual substrate characterization

In recent years, anaerobic digestion (AD) of organic waste has raised as a winning strategy to produce energy and organic fertilizer. To optimize such a technology, mass balance is needed to model or simply monitor the process. This paper describes a theoretical framework allowing process indicators to be derived from estimates of organic waste elemental composition. Using a database of 128 typical feedstocks, semi-empirical equations are provided to estimate this elemental composition in case of a missing analysis. Then, a revised stoichiometric reaction of anaerobic digestion is proposed considering biomass yield and nitrogen. Biomass yield induces a more accurate estimation of the ammonia production and the volatile solids (VS) loss. The stoichiometric reaction allows the prediction of biogaz quality and mass loss and a correction factor for VS removal is proposed. The use of real case studies highlights the need to consider this correction (correction factor range: 1.01-1.2), especially for dry AD.