A Reactive Transport Nitrogen Model for Onsite Wastewater Systems.

A constructed wetlands two-dimensional model (CW2D) developed by Langergraber and Simunek (2005) was adapted to onsite wastewater systems (OWS). The model is an optional module in the HYDRUS (2D3D) variably saturated flow model. The model predicts the fate and transport of nitrogen species in the drainage trench and surrounding soil of an OWS. It is a multi-component reactive transport model that simulates 12 components and 9 processes. Three microbe populations are simulated: heterotrophic bacteria, Nitrosomonas, and Nitrobacter. Concentrations of ammonium, nitrite, nitrate, dinitrogen, dissolved oxygen, and three forms of organic matter are predicted. The model results are compared to the concentrations of total nitrogen, ammonium, nitrate, and chloride measured at an experimental site in Georgia, USA.