Overview - The Engineered Water Cycle
Increasing global population has amplified anthropogenic loading of organic matter to the water cycle, and increased the rate of incidental water reuse, both of which are core concepts of my team's research. We focus on environmental organic and inorganic chemistry and process based water treatment. Descriptions of several funded projects are below, but, the current focus of the lab is on:
1) Direct/indirect Potable Reuse. As our supplies of pristine drinking water sources dwindle, we will have to rely on less conventional sources of water, such as wastewater. If the International Space Station does it, why can't we? The challenges we specifically wish to address include removal of organic and inorganic constituents such as pharmaceuticals, heavy metals, and pathogens.
2) Wildfire impacts to drinking water quality. We seek to understand how wildfire impacts downstream drinking water intakes and the effects to drinking water quality. Current work is focusing on recent Sierra fires near Auburn, CA, and South Lake Tahoe, CA.
3) Anthropogenic Chemicals in the Natural and Built Environment. My broad interest is in the sources, fate, and impacts of anthropogenic chemicals in/on the environment. Research focuses on developing new analytical tools to quantify humankind's influence, and engineering tools to mitigate impact. Other research involves understanding human use of chemicals by measuring their concentrations in wastewater.
1) Direct/indirect Potable Reuse. As our supplies of pristine drinking water sources dwindle, we will have to rely on less conventional sources of water, such as wastewater. If the International Space Station does it, why can't we? The challenges we specifically wish to address include removal of organic and inorganic constituents such as pharmaceuticals, heavy metals, and pathogens.
2) Wildfire impacts to drinking water quality. We seek to understand how wildfire impacts downstream drinking water intakes and the effects to drinking water quality. Current work is focusing on recent Sierra fires near Auburn, CA, and South Lake Tahoe, CA.
3) Anthropogenic Chemicals in the Natural and Built Environment. My broad interest is in the sources, fate, and impacts of anthropogenic chemicals in/on the environment. Research focuses on developing new analytical tools to quantify humankind's influence, and engineering tools to mitigate impact. Other research involves understanding human use of chemicals by measuring their concentrations in wastewater.
Active Research
Understanding Wildfire Risks to Drinking Water Source Waters: Pyrogenic Changes to Organic Matter, Disinfection By-product Formation, and Disaster Response (Funded by NSF)

Wildfires are growing in size, severity, and frequency due to drought, forest management, and climate change. Wildfire mobilizes organic matter through partial combustion and pyrolysis. This pyrogenic organic matter is substantially different in composition from naturally occurring organic matter and it is transported through overland flow to downstream drinking water treatment. Disinfection is a key component of drinking water treatment and inactivates microorganisms by oxidation. However, the oxidants used also react with the diverse organic structures present in natural organic matter and some of these reactions result in the production of carcinogenic disinfection by-products, which have regulatory limits in finished drinking water set by the U.S. Environmental Protection Agency. Published literature has reported both, that pyrogenic organic matter is less reactive than naturally occurring organic matter in forming disinfection by-products, and also that pyrogenic organic matter is more reactive in forming disinfection by-products. The specific changes to the organic matter and what causes this divergence after fire are not clear. The goal of this research is to understand how fire severity affects drinking water and how to provide safe drinking water to consumers after wildfire.
Thermal Regeneration of PFAS-laden Granular Activated Carbon Presents an Opportunity to Break the Forever PFAS Cycle (Funded by NSF in collaboration with the University of Maine)

Pollution of the natural environment with per- and poly-fluorinated alkyl substances (commonly known as PFAS) is an overwhelming ecological and human health crisis. PFAS are toxic at low exposure levels and are difficult to destroy. Because they are difficult to destroy, solutions to PFAS contamination focus on removal from water, soil, and air, rather than destruction. One technique to remove PFAS from both air and water is adsorption to activated carbon. Activated carbon has already been demonstrated at scale for removal of PFAS. Consequently, thousands of activated carbon filters have been installed across the nation. This trend is likely to continue. However, activated carbon filters retain, but do not destroy PFAS which are removed from water or air. The spent filters can then act as PFAS sources if not disposed of properly. The goal of this research is to examine if thermal regeneration of activated carbon is a viable strategy to destroy retained PFAS while renewing the exhausted filter. There is little knowledge of PFAS destruction mechanisms and products during carbon regeneration. A lack of understanding of PFAS transformation and destruction during thermal regeneration may lead to rerelease of captured PFAS. The knowledge gained in this project will serve the public because it will facilitate the end to PFAS circulation in the environment. PFAS are estimated to impact at least 200 million U.S. citizens. A complete approach to destroy PFAS while also regenerating GAC will result in broad societal impacts with minimal or no new infrastructure investment.
Understanding use of Opioids and High-Risk Substances to Reduce Youth Risk (Nevada Department of Health and Human Services)
In collaboration with the University of Nevada - Las Vegas, Southern Nevada Water Authority, and the College of Southern Nevada, we are establishing a statewide opioid use monitoring program targeting youth groups. Stating 2025, we will monitor opioid and high-risk substance use by measuring concentrations of metabolites in wastewater. An understanding of use will improve rapid response, use mitigation, and reduce opioid overdose risk.
Perfluorinated Substance Release to Air (funded by NSF and SERDP)

Research on per- and polyfluoroalkyl substances (PFASs) released from aqueous film-forming foams (AFFFs) has primarily focused on soil and groundwater contamination, or atmospheric transport. However, gas phase PFAS release from AFFF and from thermal treatment of PFAS-contaminated media has not been well examined. Our team uses infrared spectroscopy and mass spectrometry to understand products of incomplete destruction of PFAS produced during thermal treatment of PFAS-contaminated media and the feasibility of contaminated pavement recycling. We are also working to develop new methods for measuring organofluorine which will help to close the fluorine mass balance during remediation.
Destruction of PFAS using UV light (funded by Nevada Center for Water Resiliency)
We have previously investigated the destruction of PFAS using 254 nm light coupled with sulfite (publication here), which produces aqueous electrons that defluorinate PFAS. More recently, we have been investigating 222 nm light coupled with sulfite. 222 nm light directly destroys PFAS and, in combination with sulfite, is likely to be more effective than 254 nm light. UV 222 lamps have only recently been commercialized.
|
|
Prior Research (but I am still interested in!)
Identification and Removal of N-nitrosodimethylamine Precursors from Drinking and Wastewater (Funded by NSF. Prior funding from WRF)

We attempted to remove NDMA precursors from wastewater using powdered and granular activated carbon (PAC and GAC) without knowing their exact chemical structure, using NDMA formation potential (FP) as a surrogate for precursor removal. In addition, we attempted to sorb some NDMA yielding pharmaceuticals to PAC. We found that NDMA FP removal was always better than dissolved organic carbon and UV254, indicating potential for NDMA precursors to act as "trace" organic compounds. Other research by us has shown that one of these trace organic compounds is methadone which is excrete in the urine and feces of individuals, but is later a potent NDMA precursor in wastewater and surface waters.
Impacts from Emerging Contaminants in Reclaimed Water used for Urban and Per-Urban Agriculture (Funded by USDA)

Wastewater from domestic and industrial sources is a resource for urban and peri-urban irrigated agriculture because it can provide both water and nutrients which are critical inputs to food production. But wastewater contains anthropogenic chemicals including pharmaceuticals and endocrine disrupters, which may pose a risk to grazing animals or humans. Research has been conducted in greenhouses and at bench-scale to assess these risks, but little research has been conducted at the field-scale with reclaimed wastewater used as the irrigation water. Our goal was to identify chemical contaminants in reclaimed water used for urban and peri-urban irrigated agriculture (forage crop and animal production); determine pathways (namely, water, soils, and sediments) of contaminant entrainment into agricultural products; determine associated health risks; and develop strategies for mitigation of those risks over the agricultural production chain, particularly focusing on reclaimed water production and point-of-use
Figure - Boxplot of lowest observable adverse effect concentrations for crops exposed to various individual xenobiotics from 25 publications using either hydroponics or watered soil as the exposure medium. Only publications with growth endpoints studying food crops or selected forage crops (e.g., alfalfa) exposed to municipal wastewater relevant xenobiotics are included. Individual xenobiotics are typically present in treated wastewater at <1e^-5 g/L in treated water.
Figure - Boxplot of lowest observable adverse effect concentrations for crops exposed to various individual xenobiotics from 25 publications using either hydroponics or watered soil as the exposure medium. Only publications with growth endpoints studying food crops or selected forage crops (e.g., alfalfa) exposed to municipal wastewater relevant xenobiotics are included. Individual xenobiotics are typically present in treated wastewater at <1e^-5 g/L in treated water.
Comparison of Environmental Stress Induced by Organic Chemical and Physical Sunscreens (Funded by EPA)

Sunscreens contain either an organic chemical UV filter (oxybenzone and others) or a physical sun barrier, typically nano-scale TiO2 or ZnO because these nanomaterials are nearly transparent to visible light when applied properly. Several organic chemical filters have been shown to cause photo-sensitization of the skin when exposed to light (likely through a reactive oxygen species [ROS] pathway) and are known to cross the epidermis into the blood, where they are eventually hepatically cleared. On the other hand, both TiO2 and ZnO are photo-active, which produce DNA damaging ROS when exposed to UV light such as that from the sun. Proprietary formulations of nano-containing sunscreens aim to either cease reactive oxygen species from being formed by coating the TiO2 or ZnO in aluminum or silica polymer, or quench the ROS as it is produced, presumably before it damages DNA. However, environmental release and transformation of these particles can cause them to be separated from their aluminium shell or ROS quencher, and produce environmental ROS that likely causes stress to aquatic ecosystems.
To-date, research assessing the impact of physical barrier (nano) sunscreens on ecosystems has been conducted using nanomaterials purchased from manufacturers with no guarantee of environmental relevance (use in actual sunscreens). Therefore, I have developed a method to extract nanomaterials from sunscreens. As of December, 2015, I am working to characterize these particles at Arizona State University using TEM with energy disspersive X-ray (EDX), single particle inductively coupled plasma mass spectrometry (spICP-MS), and laser induced breakdown spectroscopy (LIBS). In the near future I will work with collaborators at Oregon State University to compare the zebrafish toxicity and developmental stress caused by 10 nano sunscreen extracts to 5 FDA approved and 5 EU approved active organic sunscreen chemicals.
To-date, research assessing the impact of physical barrier (nano) sunscreens on ecosystems has been conducted using nanomaterials purchased from manufacturers with no guarantee of environmental relevance (use in actual sunscreens). Therefore, I have developed a method to extract nanomaterials from sunscreens. As of December, 2015, I am working to characterize these particles at Arizona State University using TEM with energy disspersive X-ray (EDX), single particle inductively coupled plasma mass spectrometry (spICP-MS), and laser induced breakdown spectroscopy (LIBS). In the near future I will work with collaborators at Oregon State University to compare the zebrafish toxicity and developmental stress caused by 10 nano sunscreen extracts to 5 FDA approved and 5 EU approved active organic sunscreen chemicals.