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Modeling Nitrogen Dynamics in a Soil Column with Reclaimed Water: Okinawa, Japan Application

During a continuous irrigation of simulated reclaimed water on an unsaturated soil column, the characteristics of pore water at different depths, effluent, initial and final soil indicated tbe simultaneous occurrence of nitrification, denitrification and ammonium adsorption. Nitrification and adsorption significantly depleted ammonium (NH, ) of the influent at the upper soil layers. The nitrate – nitrogen (NO, – – N) concentration of the pore water and effluent increased to a maximum preceding the steady state. Total Nitrogen (T-N) did not exceed its value in the influent (23 mg/L), and NO, – N was always less than 20 mg/L. The cumulative loss of T – N due to off-gassing to the soil air was 30.0 %. The loss of total organic carbon of influent was 62.9 %. The coupled material balance equations for both NH, – N and NO,- – N on entire soil volume were solved analytically to simulate the distribution of NO, – N concentrations with time along the soil depth. First-order rate constants for nitrification (k,) and denitrification (k,) were varied within a wide range until the simulated NO, – – N concentrations fit properly with the measured values. The optimum k, and k, obtained using the measured effluent data were 0.09 d ‘ and 0.003 d ‘, respectively. These are the global averages that represent the percolating water downward.