Study of the Behavior of Alkalinities Predicted by the AM2 Model

Anaerobic digestion (AD) is an efficient wastewater bioprocess, suitable for treating agroindustrial residues with high organic loads and characterized by both a low environmental impact and energy generation. This process is conformed by several chemical and biological reactions in an oxygen free atmosphere, that degrades high molecular weight organic compounds into carbon dioxide and methane mainly but also into traces of hydrogen and ammonia. This process is potentially unstable to volatile fatty acids (VFA), and the alkalinity. variations and is satisfactorily described by the non-linear AM2 model. In this contribution, the AM2 model is modified to include a more general expression for the pH, a cheap and continuous measurement, and also to add more detail in the interactions of the VFA, bicarbonates, and the alkalinity, key factors in the process stability. The stability of the AM2 modified model is explored through a rigorous bifurcation analysis that identifies unstable operation zones and viability of operation trajectories as a function of the dilution rate. Finally, an experimental validation is carried out to show the feasibility and accuracy of the proposed modifications.

Automated summary

Anaerobic digestion is an efficient wastewater bioprocess suitable for agroindustrial residues with high organic loads, characterized by low environmental impact and energy generation. The process is sensitive to VFA and alkalinity, and the modified AM2 model includes more general pH expression and detailed interactions to improve stability. Rigorous bifurcation analysis has been conducted to explore the stability and viability of the modified model.