NSF-BSF: UV Advanced Oxidation of Industrial Groundwater Contaminants: The Key Role of Nitrate as *OH Sensitizer and Scavenger

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Groundwater is one of the Nation’s most important sources of freshwater. However, many groundwater aquifers are threatened by contamination from industrial and agricultural chemicals. Due to increased water scarcity, municipalities may need to utilize contaminated water sources that require water purification before use. Unfortunately, many of the most common water treatment techniques are expensive, energy intensive, and may not completely remove the contaminants. This can lead the abandonment of contaminated wells and the loss of valuable water unless we can develop more effective and sustainable treatment processes. To address this challenge, this study will utilize and evaluate ultraviolet (UV) light – based oxidation as a treatment solution for contaminated groundwater. While we know this technology can degrade organic contaminants, there are gaps in our knowledge that need to be addressed for sustainable and effective treatment. Most importantly, the complex nature of groundwater that contains salts and other compounds that impact UV oxidation treatment in unknown ways. This study provides a comprehensive investigation of these chemical interactions through an international collaboration with researchers from the United States and Israel that can lead to efficient groundwater treatment. The findings will be broadly distributed and transferred to water professionals and other relevant stakeholders to help build new groundwater treatment facilities, improve groundwater quality, and increase freshwater supply. Chemicals such as 1,4-dioxane and chlorinated hydrocarbons are frequently used as industrial solvents. Release of these compounds to the environment has resulted in them being detected in groundwater at many locations in the USA. Treatment approaches for the removal of these contaminants typically include air stripping and/or adsorption on activated carbon. However, these techniques merely transfer contaminants to another phase, and the residuals still need to be treated. Furthermore, the low sorption potential and low volatility of contaminants such as 1,4-dioxane render them unable to be removed by these technologies. In these cases, advanced oxidation processes (AOPs) such as the use of UV/H2O2 are considered to be attractive treatment alternatives. A key factor affecting UV-based AOP treatment of groundwater is the presence of nitrate (NO3-). NO3- is frequently detected in groundwater aquifers globally, mainly as a result of agricultural activity. Nitrate absorbs UV light, and in the process produces OH radicals (•OH) and nitrite (NO2-). While the production of •OH is desirable as the radicals are responsible for the oxidation of the contaminant, NO2- is a strong radical scavenger and results in reduction in oxidation potential. The collaborative research in this proposal focuses on UV- NO3- photochemistry to elucidate the impact of NO3- on the generation of •OH and halogenated organic contaminant oxidation efficiency during UV-based AOP treatment. This will be achieved by an international collaboration that leverages the complementary expertise of researchers in the United States and Israel to identify the contribution of nitrate and carbonate induced radicals to pollutant oxidation to elucidate the underlying reaction mechanisms. Successful completion of this research will lead to treatment optimization and the development of more sustainable approaches for groundwater contamination and remediation. These results will be broadly applicable to other fields such as water treatment and wastewater treatment. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.