# Chemical and mineralogical characteristics of tropical soils on the transport of Na+, K+, Ca2+, and Mg2+ from the application of treated wastewater

## TL;DR

This study examines how tropical soils affect the movement of ions from treated wastewater, highlighting sodium's high mobility and potential for contamination.

## Contribution

The study introduces artificial wastewater to predict ion transport behavior in tropical soils, focusing on simplified solutions for safer environmental applications.

## Key findings

- Oxisol and Entisol Quartzipsamment showed the longest delays in ion transport relative to the wetting front.
- Sodium (Na+) exhibited high mobility in tropical soils, posing a contamination risk.
- Artificial wastewater can predict TWW ion transport behavior, except for Ca2+ retardation.

## Abstract

With the search for water security, the reuse of water in irrigation becomes interesting and inevitable. Given the complexity of soil–solute interactions, the use of simplified artificial solutions represents an innovative approach, as it facilitates understanding these interactions while posing no risk to human health or the environment. However, the more complex and inferior the quality of the water, the greater the environmental contamination risk. The objective of this study was to investigate ion retention in three tropical soils (Oxisol, Inceptisol, and Entisol Quartzipsamment) by applying treated domestic wastewater (TWW) and artificial wastewater, both with the same concentrations of Na+, K+, Ca2+, and Mg2+ as the TWW. Physical, chemical, and mineralogical properties of the soil were determined. Multivariate analysis was performed to elucidate the relationships between the solutes’ transport parameters, the soils’ mineralogy and texture, and the variation in their chemical characteristics resulting from wastewater application. Oxisol and Entisol Quartzipsamment contributed to principal component 1. The second principal component had a negative contribution from Inceptisol. Oxisol and Entisol Quartzipsamment showed the longest delays of ion transport relative to the wetting front. Inceptisol had the lowest retardation factors and the lowest affinity for ions. For the TWW on Oxisol, Na+ was the first ion to reach a relative concentration equal to 1, at an average pore volume of 4.3; however, the last pore volume collected for Ca2+ was 12.3, with a relative concentration of 0.6, showing that sodium in TWW is a point of attention, as observed by the low affinity with soils.

The evaluated wastewater quality resembles diluted wastewater.The Na+ is a point of attention due to its high mobility in tropical soils.The wastewater increased the pH and availability of K+, Ca2+, and Mg2+ in tropical soils.The artificial wastewater can be used to predict the treated domestic wastewater ions transport behavior, except for the Ca2+ retardation factor.

The evaluated wastewater quality resembles diluted wastewater.

The Na+ is a point of attention due to its high mobility in tropical soils.

The wastewater increased the pH and availability of K+, Ca2+, and Mg2+ in tropical soils.

The artificial wastewater can be used to predict the treated domestic wastewater ions transport behavior, except for the Ca2+ retardation factor.

The use of wastewater for irrigation of crops is interesting, since it allows the recycling of nutrients for plant development. But, if the application of this wastewater to the soil is not performed correctly, the ions present in the wastewater can move through the soil, and cause contamination of surface water and groundwater. We evaluated the transport of some ions in tropical soils, relating it to their chemical and mineralogical characteristics, so we could understand which factors would be most important to ensure safe wastewater application to the soils. Even with wastewater with relatively good quality, the Na was a key point of attention regarding soil and water contamination. The application of sewage to the soil also led to enhanced availability of K+, Ca2+, and Mg2+, a fact of relevant interest from an agricultural perspective, as these nutrients are essential for good plant development and contribute to the soil being suitable for its development.