Experiment and numerical simulation of nitrogen transport in soils irrigated with treated sewage

A Nitrogen-2D model to analyse the nitrogen dynamics during treated wastewater application to FILTER (Filtration and Irrigated cropping for Land Treatment and Effluent Reuse) systems was developed. The model simulates both water movement and solute transformations in two-dimensional saturated-unsaturated soil. The transformations of nitrogen in both organic and inorganic matters are considered. The transport equation includes the adsorption, nitrification, denitrification, volatilisation, and root uptake of the nitrogen with the general equilibrium equations. The effects of temperature, water content, N/C ratio, and pH on the nitrogen transformation are considered in the model. The model is calibrated using field data from FILTER plots of 4 ha during 170 days' effluent application and is validated using data from sewage irrigation in four lysimeters for 86 days in China. The model accurately predicts the changes in the groundwater table depths, as well as the concentration of nitrate-nitrogen and ammonium-nitrogen in the subsurface drainage water outflows from the plots. The model was used to predict groundwater flow and nitrogen transport of the lysimeters using the same water flow and nitrogen transformation parameters, and the good agreement of the simulation value and experimental data shows the reliability of the model for the analysis of water and nitrogen transport. Copyright (C) 2008 John Wiley & Sons, Ltd.