Simulation of hydrodynamics and nitrogen transformation processes in HSF constructed wetlands and porous media using the advection–dispersion-reaction equation with linear sink-source terms

The simulation of flow and nitrogen removal processes in horizontal subsurface flow (HSF) constructed wetland (CW) facilities is investigated by using the advection–dispersion-reaction modeling approach, with linear sink-source terms. Two forms of the model above are considered: a chain-reaction description of nitrogen kinetics, which involve three Partial Differential Equations (PDEs), and the classical one-equation model. The performance of these approaches is validated by comparing the simulation results to existing experimental data taken from five pilot-scale CW facilities containing different vegetation and porous material types. Our analysis suggests that the approach cited above is most valid for the “pure porous media” case (unplanted bed), but also provides a good description of the nitrogen removal in facilities equipped with vegetation, which is appropriate for practical applications. Characteristic values of the decay-rate coefficients are estimated, which incorporate the influence of vegetation and temperature and are useful in the design of constructed wetlands or the simulation of nitrogen fate in geological formations.