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

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 (R-2) 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 R-2 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 R-2 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 (mu(max)) 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. (C) 2017 Elsevier B.V. All rights reserved.