Variable stoichiometry with thermodynamic control in ADM1

Jorger Rodríguez, J. M. Lema, M. C.M. van Loosdrecht, R. Kleerebezem

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

50 Scopus citations


The effect of a variable stoichiometry of the carbohydrate fermentation process in the IWA Anaerobic Digestion Model No.1 (ADM1) is investigated. Most existing anaerobic digestion models including ADM1 consider a fixed-stoichiometry for their conversion processes. The ADM1 model was first transformed into an only mol based model to remove some errors derived from the mixed COD-mol based standard model and to allow for implementation of the variable stoichiometry. Consequently, the values of the butyrate and acetate catabolic yields of carbohydrate fermentation are made dependent on the hydrogen concentration and the reactor pH according to the predictions of a recently developed mixed culture fermentation model based on thermodynamic considerations. The simulation results obtained showed no significantly different responses in terms of effluent quality and system robustness between the standard and the variable stoichiometry ADM1 under overload conditions, and for both single- and two-step anaerobic digestion configurations. This behaviour is explained by the non-limiting acetogenic activity that compensated for the changes in the acidogenic products, typical behaviour for serial processes close to equilibrium. Based on the results obtained, thermodynamic rather than kinetic control for these conversions is suggested. Depending on the objectives to be met, lumping of carbohydrate fermenters and oxidative acetogens into a single biomass group with a variable stoichiometry is proposed for further consideration.

Original languageBritish English
Title of host publicationAnaerobic Digestion Model No 1 - Developments and Applications
EditorsD.J. Batstone, J. Keller
Number of pages10
StatePublished - 2006

Publication series

NameWater Science and Technology
ISSN (Print)0273-1223


  • ADM1
  • Carbohydrate fermentation products
  • Variable stoichiometry


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