Vavilin V.A. New step in anaerobic digestion modeling: estimating changes in isotopic composition as a way to reveal metabolic pathways

Report. — In: Proc. . of 13th World Congress on Anaerobic Digestion: Recovering (bio) Resources for the World. — Santiago de Compostela (Spain), 25th-28th June 2013.Introducing the fractions of heavy isotope in products, substrate and biomass into the traditional anaerobic digestion models it was possible to reveal metabolic pathways of substrate transformation by microbial communities. In this paper, as an example, evolution of 13C/C and  13C in methane and carbon dioxide during labelled and natural acetate methanization in the parallel batch experiments under the different initial ammonium concentrations, previously carried out by Grossin-Debattista (2011), was mathematically described based on stoichiometric chemical reactions, microbial dynamics and equations for the isotope 13Caccumulation in products as well as its redistribution between substrate and products. Isotope fractionation of 13C and 12C was taken into account to estimate evolution of 13 C. First time, the same approach was used to describe substrate methanization using labelled and natural substrate in the parallel batch experiments. The model of batch reactors showed that an input of acetoclastic and non-acetoclastic methanogenesis depended on a ratio between the initial concentrations of Methanosarcinaceae, Methanosaetaceae and acetate-oxidizers. At the high ammonium concentration the input of syntrophic acetate oxidation was developing in time and becoming dominant during incubation.
Keywords
Labelled and natural acetate methanization, ammonium, acetoclastic and non-acetoclastic methanogenesis, kinetic isotope effect