Analyzing the effects of clay content on ammonium migration in soil using single- and dual-porosity models

The rapid growth of agricultural and industrial sectors has led to inappropriate disposal of pesticides and effluents thereby causing massive ammonium contamination of soil and groundwater resources. Contaminant transport is governed by the adsorption mechanism, which varies as the contaminant migrates through different types of soils. It is important to determine the model that best defines the adsorption mechanism of ammonium ions and the factors influencing it to predict and mitigate their contamination. This work focuses on studying the effects of clay content present in the soil on the adsorption and eventually on the retardation of ammonium ions transport through soil media using single- and dual-porosity models. The movement of ammonium ions was analyzed for three soil types with different clay proportions, by column and batch experiments. The experimental results were verified by simulating ammonium migration by numerical modeling using HYDRUS-2D software. It was observed that the ammonium ions adsorption increases with the increase in the clay content of the soil. Therefore, greater content of clay in the soil enhances the attenuation of ammonium migration in the soil media. Further, the dual-porosity model was found to be a significant factor in analyzing ammonium migration where the presence of an immobile phase in the system contributes to the transport and sorption mechanism of ammonium ions into the porous medium.

Keywords: Clay content, Ammonium ions, Single-porosity, Dual-porosity, Adsorption.