The fate of fluorescent dissolved organic matter molecules in recharged secondary treated wastewater within soil aquifer treatment (SAT) basin

Soil Aquifer Treatment (SAT) is a widely adopted managed aquifer recharge technique that employs natural soil filtration processes to improve the quality of secondary treated wastewater. As treated wastewater percolates through the unsaturated zone, complex interactions occur between dissolved organic matter (DOM) and the soil matrix, leading to the transformation or retention of organic contaminants. Understanding the fate of DOM within SAT systems is essential for optimizing water quality outcomes and ensuring the sustainability of water reuse practices.

Fluorescent dissolved organic matter (fDOM) has emerged as an effective tracer for characterizing DOM dynamics in water systems. By utilizing excitation-emission matrices (EEMs) in conjunction with parallel factor analysis (PARAFAC), fDOM allows for the identification of distinct molecular fractions, their origins (such as microbial or terrestrial), and their reactivity within SAT environments. However, the mechanisms that govern the retention and transformation of specific fDOM fractions during soil passage remain inadequately understood.

In this study, we employed advanced fluorescence spectroscopy to monitor the behaviour of fDOM molecules in a full-scale SAT basin recharging treated wastewater. By integrating EEM-PARAFAC analysis with in-situ water sampling along the vertical profile of the soil, we uncovered complex and varied transformations in DOM as treated wastewater permeated through the soil. Shifts in fluorescence signals indicated a dynamic interplay of processes affecting DOM fractions, including changes in composition and reactivity throughout the infiltration pathway. These patterns illuminate the evolving interactions between organic matter and the soil environment, influenced by biotic and abiotic factors.

This research underscores the potential of fluorescence-based monitoring tools to provide high-resolution, molecular-level insights into DOM dynamics in SAT systems. Such advancements can enhance the design and operation of SAT basins for improved water quality management and resource sustainability.