Regular articleSimulation of simultaneous anammox and denitrification for kinetic and physiological characterization of microbial community in a granular biofilm system

•A biofilm model based on ASM1 was proposed for denitrification and anammox.•A novel stoichiometric matrix was initiated for anammox process.•An idea of differentiating between major anammox species in the model was used.•Sensitivity and identifiability analysis of model parameters were elaborated.•For Ca. Brocadia and Ca. Scalindua. μmax were estimated at 0.0025 and 0.0048 h−1.

A mathematical model is proposed and validated for biological nitrogen removal in a granular biofilm reactor to describe independent batch processes under anoxic conditions. The activated sludge model consists of anammox and heterotrophic bacteria using a novel stoichiometric matrix. Identifiability of sensitive biokinetic parameters of the model was assessed with regards to observed concentrations of ammonium-, nitrite-, and nitrate-nitrogen. The Chi-squared function was used for the error estimation and the R-squared index (R2) was used for the regression analysis. The results imply that the model can elucidate the interactions of nitrogen converting bacteria in a biofilm system for various feeding characteristics. The calibration results showed satisfactory R2 equal to 0.95, 0.97 and 0.67 for NH4-N, NO2-N and NO3-N respectively. For validation, model simulations were performed under three varying scenarios and R2 was more than 0.9 so that all forecasted values lied within the 95% confidence interval. In addition, the estimated physiologic characterization of two dominant anammox species was discussed upon calibration and validation of the model. The maximum specific bacterial growth rates (μmax) for Candidatus Brocadia anammoxidans and Ca. Scalindua sp. were estimated at 0.0025 h−1 and 0.0048 h−1 respectively. Decay rate of Ca. Brocadia anammoxidans was estimated at 0.0003 h−1 which is 15% higher than decay rate of species belonging to Ca. Scalindua.

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