Assessment and characterization of dissolved organic nitrogen removal in simulated soil aquifer treatment systems
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Authors
Gharoon, Niloufar
Issue Date
2023
Type
Dissertation
Language
Keywords
Fluorescence spectroscopy , Managed Aquifer Recharge , Organic Nitrogen , PARAFAC , Soil Aquifer Treatment , Soil Columns
Alternative Title
Abstract
Treated wastewater (reclaimed water) is becoming more critical as an alternative water source due to population growth and extreme precipitation patterns. The more we rely on water reuse schemes, the more we have to expand our knowledge about the efficiency of treatment processes. As part of the water reuse programs, soil aquifer treatment systems are widely applied to enhance groundwater resources and the quality of treated wastewater by providing environmental barriers, including soil and water. There have been decades of applied research on different types of soil/aquifer-based treatment systems focusing on their operation and maintenance as well as their capability to remove contaminants. However, considering the fact that the list of contaminants of concern are continually developing and these systems are highly site-specific, there is always a need to understand better the fate of compounds that can act as a contaminant themselves in specific doses or become pre-cursors of other contaminants.Therefore, this research focused on dissolved organic nitrogen (DON) that has yet to be adequately investigated. Effluent DON could be problematic in the receiving waters as a nitrogen source causing eutrophication. It can also act as a precursor for nitrogenous disinfection by-products. In this study, we used unsaturated soil columns to simulate the vadose zone treatment systems in the lab. We simulated field characteristics by using the soil from the vadose of effluent rapid infiltration basins and reclaimed water from a full scale water reclamation rather than artificial wastewater. We observed steady DON removal in the columns for more than a year and a half, as well as the improvement of water quality through the removal of other organic compounds. Since N-Nitroso-dimethylamine (NDMA), one of the nitrogenous disinfection by-products, concentrations were pretty low in our feed reclaimed water, and we did not reach conclusive results about the columns’ capability of further removal of NDMA. However, our results showed that the columns could remove NDMA precursors by removing the reclaimed water organic matter.
In addition, we characterized the organic matter in the reclaimed water applied to the columns using fluorescence spectroscopy EEM spectra. EEM spectra analysis has been widely used for organic matter characterization in drinking or surface water. Here, we focused on its capability to monitor the performance of soil aquifer treatment systems. We were able to detect humic-like, fulvic-like, and tyrosine-like compounds in the influent and effluent of the columns using the fluorescence regional technique. We followed their change through the columns and found that most of the DON removal was attributed to humic-like compounds, even though the removal was observed in different defined regions. We fitted a PARAFAC model with four components to our data that was able to be compared with other models across different aquatic systems. The main component of the model (C1) was attributed to the aromatic molecules of terrestrial origin and associated with humic-like compounds. Another detected component (C3) corresponded with microbial humic-like and terrestrially delivered and was reported at drinking water treatment plants. The results confirmed the capability of EEM spectra as a monitoring tool for the organic material and that its potential should be further investigated in the lab and field-scale soil aquifer treatment systems under different hydrogeological conditions, operation and maintenance techniques, and source water quality.