Bromide Transport through Soil Columns in the Presence of Pumice

Abstract

Solute transport parameters, similar to soil physical and chemical properties, can be affected by the presence of organic and mineral soil conditioners. In this study, the effect of different levels (0, 3, and 6 weight percent) of the inexpensive and easily accessible pumice conditioner on the parameters of bromide transport in sandy loam soil columns (diameter and height of 10 cm) was investigated. The transport parameters were estimated based on the breakthrough curves (BTCs) by the inverse modelling of the convection-dispersion equation (CDE) and the mobile-immobile model (MIM) using the CXTFIT software. The BTCs showed that bromide transport in the sandy loam soil columns, regardless of the presence of pumice, was mainly equilibrium, and the CDE was more efficient than the MIM, which is based on non-Fickian and non-equilibrium transport. The peak of the BTCs (maximum relative concentration) was lower in the treatments containing pumice and belonged to more pore volume than the controlled treatment did. This indicates a lack of preferential flow and thus, a reduction in the amount of bromide consumed in the treatments containing pumice. The increase of pumice content did not have a significant effect on the parameters of mobile water fraction (β) and mass transfer coefficient (ω) in the MIM, confirming the equilibrium transport of bromide. A 3% increase in the pumice content in the soil caused an increase and a decrease of 47% in dispersivity (λ) and Peclet number (Pe), respectively. In general, it can be concluded that the use of pumice in field conditions can prevent water loss and nutrients and reduce groundwater contamination by reducing the preferential paths.