Improving Potable Reuse Water Quality by Understanding N-nitrosodimethylamine Precursors and Bulk Organic Matter Present during Advanced Oxidation Processes
Loading...
Authors
Song, Mingrui
Issue Date
2022
Type
Dissertation
Language
Keywords
disinfection byproduct , DMA , free chlorine , hydrogen peroxide , monochloramine , NDMA
Alternative Title
Abstract
Planned potable reuse is becoming a common strategy to relieve water scarcity throughout the world. Full-advanced treatment (FAT) systems consist of ultrafiltration/microfiltration, reverse osmosis (RO), and ultraviolet/advanced oxidation processes (UV-AOP) and are utilized at potable reuse facilities to degrade or remove contaminants present in wastewater effluents. Oxidants including hydrogen peroxide (H2O2), free chlorine (HOCl), and monochloramine (NH2Cl) are added during UV-AOP to produce radicals which degrade contaminants. Oxidant performance regarding specific contaminant removal has been compared in prior research, but there is no consensus on the overall comparative performance of these oxidants because the contaminants selected for each study are usually different. To address this, I investigated oxidant performance by considering a broader fraction of contaminants including known compounds and unknown/unidentified compounds via nontarget analysis and bioassays. Based on greater destruction of organic compounds, reduced transformation products, and a lack of oxidative stress induction, H2O2 was the most suitable oxidant tested for ultraviolet advanced oxidation in water reuse.Disinfection byproducts form when precursor chemicals are oxidized by disinfectants to new hazardous products. N-nitrosodimethylamine (NDMA), a carcinogenic disinfection byproduct, has been regulated with 10 ng/L drinking water notification level. Controlling specific regulated contaminants such as N-nitrosodimethylamine (NDMA) is also crucial for regulatory compliance, improving potable reuse water quality, and public acceptance. Its precursors can persist through advanced treatment trains including RO and UV-AOP contributing to NDMA formation during conveyance, and these precursors are not yet identified, making them difficult to treat. Dimethylamine (DMA) is a model NDMA precursor, which is usually present in wastewater that serves as potable reuse influent. DMA has been used extensively by others in bench-scale experiments to understand NDMA formation pathways but it has also been thought that it is not an important NDMA precursor in treated wastewater and surface water due to its low yield combined with relatively low concentrations in drinking water and wastewater samples. However, its occurrence in water reuse facilities has not been investigated. Samples from one pilot plant and four full-scale water reclamation facilities were collected to study DMA occurrence in FAT facilities. The median DMA concentrations in product and finished waters were 0.4 μg/L across six sampling events. DMA accounted for 5%-43% of the total NDMA precursor pool of the UV-AOP product water at one facility, and up to 40 of ng/L of NDMA at another. Although DMA substantially contributed to NDMA formation in potable reuse facilities, the complete NDMA precursor pool that enters typical surface water treatment plants has not been identified. Further, it is commonly thought that most NDMA precursors present in drinking water intakes originate from wastewater-derived anthropogenic chemicals but no study has conclusively determined the contribution from anthropogenic vs. naturally occurring precursors due to the difficulty in finding an appropriate environmental system to conduct such an experiment. The only study which attempted to answer whether the dominant surface water NDMA precursors are anthropogenic or environmental in origin compared NDMA precursor concentrations in wastewater effluents, a eutrophic water, stormwater/agricultural runoff, and a pristine river source. Wastewater effluents tended to contain relatively high concentrations of NDMA precursors but it was not clear how much they contributed to NDMA formation after dilution into the river systems. Although region-specific relationships between NDMA precursors and sucralose (one anthropogenic pharmaceutical) have also been reported, suggesting NDMA precursor sources are anthropogenic, the relationship is highly watershed specific, and does not lend itself to applications outside of the watershed where the relationship was original derived. To determine if the dominant NDMA precursor sources are wastewater effluents (anthropogenic source), I investigated NDMA precursors in Truckee River, which has only one anthropogenic point source. The background of NDMA precursors in the Truckee River is relatively low, and an apparent increase was observed downstream of wastewater effluents, suggesting that anthropogenic sources dominate NDMA precursor loading in surface waters within a limited length from wastewater effluent in the Truckee River.