In this study, a mathematical model based on nonlinear differential equations was developed to describe nitrate (NO3−) removal in a woodchip denitrification bioreactor treating tile drainage water. The model captures temperature-dependent denitrification kinetics and transport processes under variable operating conditions. The model was validated using pilot-scale experimental data collected at different inflow water temperatures. The results indicated a strong temperature dependence of nitrate removal efficiency, with higher performance at elevated temperatures due to increased microbial activity and reaction rates. After validation, numerical simulations using a finite difference scheme were performed to evaluate bioreactor performance under varying hydraulic and geometric conditions. The analysis focused on the effect of bioreactor length, assuming constant width and depth (1.0 m each). Results showed that increasing reactor length enhances NO3− removal by extending hydraulic retention time, although the effect becomes nonlinear due to substrate limitation along the flow path. Simulations further demonstrated that a target NO3− removal efficiency of approximately 40% can be achieved through different combinations of temperature, bioreactor length, and hydraulic loading, indicating a compensatory relationship between kinetic and design parameters. Overall, this study provides a predictive framework for optimizing bioreactor design and operation, offering practical guidance for improving nitrate removal in agricultural drainage systems.
Dabulytė-Bagdonavičienė et al. (Mon,) studied this question.