A Nitrogen Model for Onsite Wastewater Systems

Proceedings of the 2011 Georgia Water Resources Conference, April 11, 12, and 13, 2011, Athens, Georgia.A constructed wetland two-dimensional model 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. It predicts the fate and transport of nitrogen (N) 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. Concentrations of ammonium, nitrite, nitrate (NO3), nitrogen gas (N2), dissolved oxygen (DO), and three forms of organic matter are predicted. The mod-el simulations showed that conditions are dynamic in an OWS as water levels in the trench respond to daily dosing, precipitation, and evapotranspiration. The simulations indicated that NO3 losses occurred during dryer periods when DO concentrations were high enough in the trench for ammonium conversion to NO3, and outside the trench the high DO concentrations slowed denitrification, especially in the dryer area to the side of the trench. Predictions of NO3 losses compared well with an experimental OWS at Griffin, GA.Sponsored by: Georgia Environmental Protection Division U.S. Geological Survey, Georgia Water Science Center U.S. Department of Agriculture, Natural Resources Conservation Service Georgia Institute of Technology, Georgia Water Resources Institute The University of Georgia, Water Resources FacultyThis book was published by Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, Georgia 30602-2152. The views and statements advanced in this publication are solely those of the authors and do not represent official views or policies of The University of Georgia, the U.S. Geological Survey, the Georgia Water Research Institute as authorized by the Water Research Institutes Authorization Act of 1990 (P.L. 101-307) or the other conference sponsors