Considering syntrophic acetate oxidation and ionic strength improves the performance of models for food waste anaerobic digestion

Current mechanistic anaerobic digestion (AD) models cannot accurately represent the underlying processes occurring during food waste (FW) AD. This work presents an update of the Anaerobic Digestion Model no. 1 (ADM1) to provide accurate estimations of free ammonia concentrations and related inhibition thresholds, and model syntrophic acetate oxidation as acetate-consuming pathway. A modified Davies equation predicted NH3 concentrations and pH more accurately, and better estimated associated inhibitory limits. Sensitivity analysis results showed the importance of accurate disintegration kinetics and volumetric mass transfer coefficients, as well as volatile fatty acids (VFAs) and hydrogen uptake rates. In contrast to the default ADM1, the modified ADM1 could represent methane production and VFA profiles simultaneously (particularly relevant for propionate uptake). The modified ADM1 was also able to predict the predominant acetate-consuming and methane-producing microbial clades. Modelling results using data from reactors dosed with granular activated carbon showed that this additive improves hydrogen uptakeGabriel Capson-Tojo is grateful to the Xunta de Galicia for his postdoctoral fellowship (ED481B-2018/017). Sergi Astals is thankful to the Spanish Ministry of Science, Innovation and Universities for his Ramon y Cajal fellowship (RYC-2017-22372). Ángel Robles is grateful for the support from the Spanish Ministry of Science and Innovation and the Partnership for Research and Innovation in the Mediterranean Area (Grant PCI2020-112218)S