Optimal biogas production in a model for anaerobic digestion

Abstract

We investigate a model for anaerobic digestion, a process used to produce biogas. The model, introduced in Weedermann et al. (J Biol Dyn 7:59-85, 2013), consists of differential equations describing the interactions of microbial populations involved in three main stages of anaerobic digestion: acidogenesis, acetogenesis, and methanogenesis. We show that this model predicts that an increased yield in biogas can be achieved in regions where operating parameters push the system into a bistable state. In some regions of bistability, biogas production occurs at only one of the steady states while in others both steady states result in biogas production with one state being more productive than the other. We demonstrate which operating parameters and state variables have the most significant impact on system performance. Surprisingly, the optimal biogas production does not always occur at a steady state where all classes of microorganisms coexist.

On the steady state optimization of the biogas production in a two-stage anaerobic digestion model

“…This is true in the case of the ADM1 [1], a model that consists of 29 dynamic state variables, which makes it very difficult to carry out qualitative analysis. Simpler models focusing on different subprocesses of ADM1 have been proposed, as in [4] (two stages considered: acidogenesis and methanogenesis), [15] (three stages considered: acidogenesis, acetogenesis, and methanogenesis), and [5] (four stages considered: hydrolysis, acidogenesis, acetogenesis, and methanogenesis). Mathematical analysis was carried out for these models in [11,12,13,3,15,5].…”

Global Analysis of a Simplified Model of Anaerobic Digestion and a New Result for the Chemostat

“…Only one of the two stable equilibria corresponds to the production of biogas meaning that it depends on the initial conditions whether the reactor will produce biogas in the long-term. The system does not allow bistability involving two or more biogas producing equilibria, previously shown to be possible for the ADM1 model [1] and for the models studied in [24,25] The dynamics predicted by a bifurcation analysis of the model is qualitatively similar for all three prototype functions. Ammonia inhibition is included in the ADM1 model, however, in ADM1 ammonia is not included as a dynamic variable.…”

“…In an effort to formally analyze the system, several groups [4,10,12,24] have studied various subsystems of ADM1. Recently, Weedermann et al [24,25] combined two previous models [10,12] to get a reasonably complete picture using only eight state variables. Due to the inclusion of two pathways to biogas production in [24] and because the model captures the ADM1's sensitivity to the accumulation of acetic acid, [24] illustrates some of the complexity of ADM1, which must exhibit the same or an even richer dynamics than the model in [24].…”

Analysis of productivity and stability of synthetic microbial communities

“…Previous studies have also investigated ecosystems with more than two species, such as a three-species system competing for two resources [15]. Further, several studies have analysed syntrophic consortia where producers and consumers critically interdepend on each other, particularly in the anaerobic digestion process [16,17].…”

“…The above studies have mostly focused on only the stability of microbial communities, but not their productivity. One exception is a modelling study on anaerobic digestion which recognized that a bistable state of the system could also be where an increased yield occurs [17]. In general, the productivity of a microbial community represents an important aspect of its function (e.g.…”