『Abstract
The concentration of NO3--N in
some of the geothermal water samples collected from Kaifeng City,
Henan Province, China has exceeded the World Health Organization's
guideline value for drinking water (10 mg/L). The NH4+-N
concentration cannot also meet the demand for quality standard
for groundwater (0.2 mg/L) in China. There is a need to predict
the mobility of these two ions in a geothermal reservoir. Column
experiments were performed at temperatures from 15℃ to 60℃ and
the computer code CXTFIT was used to fit the experimental data
and to determine the transport parameters and ammonium adsorption
parameters. Effects of both the flow rate and temperature on nitrate
transport parameters were evaluated. The convection-dispersion
equation (CDF) was used to describe the nitrate transport process
at temperature from 15℃ to 60℃, where the tracer transport was
dominated by advection under experimental conditions. The solute
hydrodynamic dispersion and dispersivity in the simulated sandy
column were enhanced with the increase of temperature. The asymmetrical
shape and tailing of the ammonium breakthrough curve showed the
ammonium was subject to nonequilibrium transport. The amounts
of adsorbed ammonium increased significantly, while the first-order
kinetic rate decreased along with the drop of temperature.
Keywords: Nitrate; Ammonium; Breakthrough curve; Loose-pore geothermal
reservoir; Fine sand』
1. Introduction
2. Materials and methods
2.1. Column material
2.2. Ammonium and nitrate solution preparation and analysis
2.3. Column displacement experiments
2.4. Transport model
2.4.1. Local equilibrium assumption (LEA)
2.4.2. Nonequilibrium assumption
2.4.2.1. Two-region nonequilibrium transport
2.4.2.2. Two-site nonequilibrium transport
2.4.2.3. Dimensionless transport equations
2.5. Parameter estimation
3. Results and discussion
3.1. Tracer experiments
3.1.1. Analysis of nitrate breakthrough curves
3.1.2. Effect of temperature on the nitrate transport
3.2. Ammonium breakthrough curves
3.2.1. Comparison of nitrate and ammonium breakthrough curves
3.2.2. Effect of temperature on the ammonium transport
4. Conclusion
Acknowledgments
References