(4mn) Predicting Photodegradation of Contaminants of Emerging Concern in Aquatic Systems Using Optical Parameters

Understanding the photodegradation of contaminants of emerging concern (CECs) in aquatic systems is crucial due to incomplete removal of CECs by wastewater treatment plants, leading to their release into water bodies and potential ecological or human health impacts. Upon releasing into aquatic system, CECs can undergo direct and indirect photodegradation by sunlight. Direct photodegradation happens when some of CECs absorb light, breaking down into less harmful compounds. Indirect photodegradation of CECs in aquatic systems occurs through the involvement of various photosensitizers, with dissolved organic matter (DOM) being the most significant precursor. DOM can absorb sunlight and undergo photochemical reactions, generating reactive intermediates such as singlet oxygen, hydroxyl radicals, and excited triplet states. These reactive intermediates can then react with CECs molecules, initiating degradation processes even in the absence of direct interaction between CECs and sunlight. Analyzing DOM is crucial for understanding the formation of reactive intermediates and, consequently, the photodegradation mechanisms of CECs. Nonetheless, these methods for characterization can often be expensive and intricate. Utilizing UV-Vis and fluorescence spectroscopy to measure optical parameters offers valuable insights into the composition of DOM and the generation of reactive species. These optical parameters can help quantify the abundance and reactivity of DOM in water bodies, facilitating the prediction of its role in CECs photodegradation. By correlating optical parameters with reactive intermediate production, predictive models can estimate CECs degradation kinetics, thus informing mitigation strategies. Therefore, this research focused on utilizing optical parameters to predict CECs photodegradation for environmental risk assessment and mitigation.

To achieve this objective, various DOM samples were collected, encompassing a diverse range of sources including samples from the Swannee River, Upper Mississippi River, and effluent organic matter from five different treatment plants in Michigan. These samples were carefully characterized using UV-Vis and fluorescence spectroscopy to assess their composition and structure. This comprehensive characterization provided insights into the variability of DOM across different water bodies and treatment processes, laying the groundwork for understanding its interactions with CECs during photodegradation processes. Next, photodegradation experiments were meticulously conducted on two significant CECs, p-cresol, and propranolol, within all of DOM samples. Through a series of controlled laboratory experiments, we simulated sunlight irradiation conditions to evaluate the degradation kinetics of these CECs in the presence of varying DOM compositions. High-Performance Liquid Chromatography with UV detection (HPLC UV) was employed as an analytical tool to quantify the concentrations of the target CECs before and after photodegradation, allowing for the assessment of degradation rates and pathways. Additionally, scavenging experiments were undertaken to elucidate the role of reactive intermediates in the photodegradation process. By introducing scavengers with known reactivities towards specific reactive species, we aimed to identify key intermediates involved in the degradation pathways of p-cresol and propranolol. This mechanistic understanding is crucial for predicting the fate of CECs in natural aquatic environments and designing strategies to mitigate their environmental impact effectively. Finally, Pearson correlation analysis was subsequently performed to establish robust relationships between the optical parameters of DOM samples and the kinetic parameters of CECs photodegradation. This statistical analysis provided valuable insights into the connections between the structural and optical properties of DOM and its ability to facilitate or inhibit the photodegradation of CECs. Leveraging these correlations, a predictive method was developed using Python programming to predict the degradation kinetics of individual CECs based on specific optical parameters of the DOM matrix. The prediction method based on these relationships demonstrated remarkable accuracy across various initial concentrations and DOM samples, validating its reliability.

This research highlights the potential of optical parameters as cost-effective indicators for predicting CECs concentrations in DOM-containing aquatic environments, offering valuable insights for environmental monitoring and management, with implications for policy decisions in environmental protection. It also contributes significantly to advancing our understanding of CECs fate and transport in aquatic systems, particularly focusing on their photodegradation behavior. By harnessing the predictive power of optical parameters, this study offers a practical approach for assessing the environmental fate of CECs and guiding the development of strategies for water and wastewater treatment and management.

Research Interests:

• Fate and transport of contaminants of emerging concern (CECs) in aquatic systems
• Photodegradation of CECs in water bodies
• Usage of membrane in water and wastewater treatment
• Photocatalytic membrane for CECs removal
• Water and wastewater treatment
• Prediction modeling of CECs in aquatic systems
• Studying fate and transport of per- and polyfluoroalkyl substances (PFAS) by light in water
• Prediction of PFAS behavior in aquatic systems
• Water and wastewater management
• Life cycle assessment

Research experience and skills in graduate research and internship roles:

Sampling:

• Implemented systematic sampling techniques at diverse treatment facilities and river locations as required for experimental purposes.
• Conducted sampling of leachate from solid waste sites to facilitate thesis research.

Setup and design:

• Engineered a novel laboratory-scale setup tailored specifically for electrocoagulation treatment of landfill leachate.
• Designed and constructed innovative photocatalytic membrane configurations aimed at efficient contaminant removal from water sources, contributing to sustainable water treatment approaches.
• Organized the development of state-of-the-art anti-fouling membranes optimized for effective water and wastewater treatment applications.

Publication:

• Designed visually compelling educational posters on environmental topics for international conferences.
• Authored papers published in peer-reviewed journals
• Led and served as the primary author for a literature review paper project on CECs' photodegradation.
• Provided significant contributions as co-author to chapter books.

Laboratory:

• Applied fluorescence and UV-Vis spectroscopy techniques for the analysis of environmental samples.
• Utilized High-performance Liquid Chromatography (HPLC) methods for precise analysis and quantification of CECs.
• Introduced and meticulously examined new measurement parameters to enhance the efficiency and optimization of the electrocoagulation process for landfill leachate treatment.
• Conducted various analyses, including Chemical Oxygen Demand (COD), turbidity, and color measurements.

Programming:

• Developed a novel prediction model using Python to forecast CECs' photodegradation in water.