Modelling anaerobic digestion of food waste: the importance of syntrophic acetate oxidation and correct free ammonia estimation

Abstract

International audienceThe aim of this study was to assess the importance of two major modifications of the IWA ADM1 on its ability to model food waste anaerobic digestion: (i) estimating free ammonia nitrogen using a modified Davies equation and (ii) including syntrophic acetate oxidation as main acetate-consuming pathway. The obtained results show that, in agreement with the literature, including the Davies equation for free ammonia estimation avoided overestimations of up to 30% when compared to the ideal equation (standard in the ADM1). Further including syntrophic acetate oxidation allowed to properly represent the dynamics of methane production and the volatile fatty acid profiles (e.g. propionate accumulation). This also allowed to predict more accurately the structure of the microbial communities (e.g. with hydrogenotrophs as dominant methanogens). Combined, these modifications allowed to obtain more precise values of the inhibition constants for different microbial clades. In addition, a threshold inhibition function was used, which allowed a more accurate inhibition representation. Finally, the kLa values were drastically reduced to account for the decreased mass transfer rates. The presented work shows that these modifications must be considered to achieve an accurate representation of food waste anaerobic digestion using mechanistic models. Although further calibration and validations must be performed, the results are promising when considering the high ammonia nitrogen and transient volatile fatty acid concentrations in the reactors and the performance of the unmodified ADM1