Abstract
A mathematical model was developed to simulate nitrate mass transport and transformations in soil during continuous application of reclaimed water in a laboratory scale soil column. The coupled material balance equations for both ammonia nitrogen (NH3-N) and nitrate nitrogen (NO3- -N) within the total soil volume were solved to simulate the NO3—N concentrations with time along the soil depth. The model is one-dimensional and based on the Galerkin technique of the Finite Element Method. It incorporates convection-dispersion processes of NH3-N and NO3--N, nitrification, denitrification and adsorption of ammonium on to soil grains. The adsorption of ammonium was assumed to be represented by the linear form of the Freundlich isotherm. The accuracy and validity of the developed model was examined by comparing simulated data with the experimental data. Optimization of the first order rate constants for nitrification (k1) and denitrification (k2) was conducted by varying both k1 and k2 within a wide range until the simulated NO3--N concentrations fitted properly with the corresponding measured values. Optimum k1 and k2 were found to be 0.188 d-1 and 0.0248 d-1, respectively. A sensitivity analysis of the kinetics of nitrate dynamics showed that the concentration of belowground nitrate is largely affected by the flow velocity (v), D, k1 and k2.
Highlights
Reclaimed water is receiving more attention as a reliable source of water
A number of researches have been conducted to evaluate belowground nitrate dynamics using laboratory scale soil column experiments followed by mathematical model developments, (McLaren (1969a, 1969b, 1970, 1971), Cho (1971) and Misra et al (1974)
The physical and biochemical factors and interrelations that cause nitrogen dynamics were made concise to a few processes and the linear form of variations
Summary
Reclaimed water is receiving more attention as a reliable source of water. As a solution for irrigation water scarcity which is a severe problem in the world, reclaimed water can be used with proper engineering practices. Mobile nitrate nitrogen (NO3--N) can percolate through soil and contaminate the ground water. It causes the deterioration of Modeling plays a vital role in estimating the NO3--N concentration that may result in the ground water. Both analytical and numerical techniques are used to simulate the subsurface transport of chemicals. A number of researches have been conducted to evaluate belowground nitrate dynamics using laboratory scale soil column experiments followed by mathematical model developments, (McLaren (1969a, 1969b, 1970, 1971), Cho (1971) and Misra et al (1974). A development of a numerical model using the Galerkin Technique of Finite Element Method to predict the
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