Current Research Areas
Seawater Photochemistry
Concerns over the toxicity of sunscreens to corals has led to bans on certain ingredients without a clear understanding of the toxicity mechanism. Our previous work demonstrating that the photoexcited states of dissolved organic matter formed after absorption of UV light can formed reactive halogen species (RHS) by oxidation of seawater chloride and bromide. We are currently evaluating how corals and sea anemones metabolize common sunscreen components, converting them from sunscreens to potent phototoxins that generate RHS, damaging these animals when exposed to sunlight. Understanding the mechanism of toxicity facilitates the development of sunscreen components that are truly safe for reefs.
Food Disinfection
Rising concerns over foodborne pathogens have placed a renewed focus on the application of chemical disinfectants (e.g., chlorine and ozone) during washing of produce and meat in food packaging facilities. However, these disinfectants can react with the food to produce potentially unhealthy byproducts of disinfection. Compared to drinking water disinfection, the concentrations of disinfectants (20-100 mg/L vs. 3 mg/L chlorine) and organic precursor materials (solid produce vs. ~1 mg/L dissolved organic matter) can be promote much higher levels of disinfection byproducts (DBPs). Our research is characterizing the products of disinfectant reactions with the biopolymers (e.g., proteins and lipids) within food during washing. By characterizing these products, we can optimize disinfectant exposures to minimize the production of DBPs while achieving pathogen reduction goals.
Electrochemical Reduction Processes for Water Treatment
Electrochemical treatment systems are gaining attention due to their potential to generate reagents on-site, thereby minimizing the need to purchase and transport chemical reagents. However, most research has focused on electrochemical oxidation systems, which can generate halogenated byproducts via oxidation of chloride and bromide at the anode. Our research is evaluating electrochemical reduction systems to avoid this formation, focusing on the use of inexpensive electrode materials. Current projects are evaluating the use of stainless steel cathodes to degrade chloramine disinfectants in wastewater prior to surface water discharge and the use of activated carbon-based cathodes to degrade halogenated organic contaminants sorbed to their surface.
Potable Reuse of Municipal Wastewater
Utilities across the arid southwestern US are increasingly implementing the purification of municipal wastewater as a local, reliable water supply for this drought-prone region. In addition to pathogens, the ability of the advanced treatment trains to remove chemical contaminants (pharmaceuticals, pesticides, disinfection byproducts) is a key concern. Our research evaluates the ability of novel advanced treatment trains to remove chemical contaminants and reduce the chemical-associated toxicity from municipal wastewater. Current projects include the pilot-scale evaluation of a an anaerobic biological secondary treatment system that ferments dissolved organics to methane that can be harvested for energy generation. This is the first energy-positive wastewater treatment plant of which we are aware. Our project is linking this anaerobic wastewater effluent to a potable reuse treatment train so that the system can produce both energy and potable water. Another current project is demonstrating that the high level of treatment employed in potable reuse facilities (with or without reverse osmosis treatment) can produce a water quality that exceeds that of surface water-derived conventional drinking waters as indicated by the cytotoxicity associated with chemical contaminants.
Advanced Oxidation Processes (AOPs)
Designed to generate radicals, AOPs form a key component of the advanced treatment trains used to degrade chemical contaminants for potable reuse systems. Our work develops a fundamental understanding of the reactions occurring within AOPs, ultimately leading to the development of models that can predict process performance. Previous work focused on the UV/chlorine and UV/chloramine AOPs that are being explored for use in potable reuse systems. A current project is quantifying the gains in energy efficiency associated with switching from lamps that emit 254 nm UV light to 222 nm light to initiate radical production within AOPs in potable reuse facilities.