Ultraviolet (UV) disinfection can be wavelength optimized to damage specific biomolecular targets, including DNA and proteins, in various waterborne pathogens. A multi-wavelength approach can increase disinfection while decreasing microorganism regrowth due to photorepair and decreasing electrical requirements. These advancements can increase UV implementation in developing contexts where taste and odor concerns impede chemical disinfection. Disinfection and regrowth were measured using culture assays, and biomolecular damage was measured using enzyme-linked immunosorbent assays for damaged DNA and photorepair protein after exposure to UV sources emitting various peak wavelengths (222, 254, 255, 265, and 285 nm). E. coli disinfection by 222 and 254 nm was similar, but 222 nm better damaged photorepair proteins and inhibited regrowth. Potential multi-wavelength synergies of disinfection and repair inhibition are being investigated in ongoing collimated beam and flow-through experiments. Additionally, the potential of UV LEDs for off-grid pressurized water disinfection was compared in flow-through tests using hydropower, hydropower-charged batteries, and wall-plug energy sources. Flow-through disinfection test results showed prototype hydropowered UV LEDs achieved ~0.5 log inactivation of MS2 at flow rates between 4-5 liters per minute. The existing off-the-shelf turbines were low-efficiency and unable to supply the required power for UV LEDs. Additional flow-through disinfection testing will be performed following redesign of the hydropowered UV LED system. This research addresses two limitations of UV disinfection, microbial repair and electrical requirements, by tailoring wavelengths and designing novel reactors which can help advance the safe and effective application of UV disinfection in decentralized, small, off-grid, and even remote water systems.

Although unregulated, nitrogenous disinfection byproducts (N-DBPs) have higher associated cytotoxic and genotoxic effects when compared to carbonaceous DBPs. This study investigates the effect of wavelength and power for effective N-DBP photolysis, reducing overall drinking water toxicity. Dibromoacetonitrile (DBAN), a photosensitive, toxic, unregulated N-DBP was selected for analysis. UV C LEDs with characteristic wavelengths of 265, 275, and 280 nm and output power ranging from 1.74 - 16.8 W were used for aqueous DBAN degradation. This presentation discusses the calculated kinetic rate constant for each wavelength and output power. The rate of photodegradation follows pseudo-first order kinetics, and the observed quantum yield decreases with increasing wavelength. However, the electrical energy consumption per order was the lowest at 80.43 kWh per m³ order for the 265 nm high power UV C LED with a degradation efficiency of 96.32%. Additionally, this study investigates the effects of using different solvents on DBAN photolysis during the preparation of the water matrix. Higher dehalogenation was observed with acetone as a solvent than with MTBE. The results of this study provide key insights for selecting wavelengths to target DBAN photolysis and to optimize UV C-based point of use treatment design for drinking water systems.

Aniline and related structures are common in anthropogenic chemicals such as pharmaceuticals, personal care products, and pesticides, and can form as transformation products of nitrogenous heterocyclic compounds (e.g., the indole side chain in tryptophan. In this study, we first evaluated the haloacetonitrile (HAN) formation potential of a series of 18 aniline compounds with different substitutions. HANs were targeted because they are a group of high-priority disinfection byproducts (DBPs) due to their frequent occurrence and high toxicity. Out of the 9 anilines that have been tested so far, two thirds formed more brominated HANs than tryptophan, a known high-yield HAN precursor from previous studies: 2-ethylaniline exhibited the greatest dibromoacetonitrile yield, at 3.5% (Br:N = 10, 24 h, 10 mM phosphate pH 7). Furthermore, the relative yields among aniline compounds differed greatly between chlorination and bromination, suggesting different formation mechanisms. The anilines’ formation potential of the regulated trihalomethanes correlated with their HAN formation potential. However, no correlation between HAN yields and the electron donating/withdrawing ability of the substituted groups (Hammett constant) has been observed. Work is ongoing to expand the tests to include 9 more aniline compounds. Second, to explore the HAN formation mechanisms (involving ring opening) and other small-molecule DBPs from anilines, work is underway utilizing liquid chromatography–orbitrap high resolution mass spectrometry (LC-HRMS). We are developing an LC method that covers the full polarity range of potential transformation products including the (likely) highly polar ring opening products. Data processing will be performed using a new open-source python package, Mass-suite.

Because of its large, tunable surface and tendency to aggregate dynamically in water, graphene makes an excellent adsorbent for water treatment applications. The adsorption of organic contaminants can further be improved by tailoring oxygen-containing functional groups on its edges. However, the fundamental understanding of edge-tailored graphene oxide (GO) is still underexplored. Thus, the overarching aim of this study is to synthesize edge-tailored GO without deteriorating the basal plane properties to improve its organic contaminant adsorption capacity and energy-efficient regeneration. In this regard, GO was synthesized from graphene using a wide range of HNO₃ concentrations from 3 to 52 v/v%. Pristine graphene and GO samples were characterized by scanning emission microscopy (SEM), elemental analysis, particle size analysis, and aggregation properties. Even though the oxygen content of all GOs was observed the same, a significant difference in other properties was evident. After exfoliation with HNO₃, the fluffiness of pristine graphene was completely altered, and more compact sheets were formed with sharp, wrinkled, and folded edges. GOs have conspicuously smaller particle sizes and uniform particle distributions compared to pristine graphene. Further, this material will be evaluated for the adsorption of organic contaminants, i.e., phenanthrene, and will also be regenerated with microwave (MW) heating. It is envisioned that this study will fulfill the knowledge gap for the synthesis, characterization, and application of edge-functionalized graphene for the adsorption of organic pollutants. In addition to that, MW heating regeneration will lead to an energy-efficient sustainable solution reducing overburden on landfills.

Halogenated organic compounds such as disinfection byproducts (DBPs) and perfluoroalkyl substances (PFAS) are recalcitrant pollutants that present significant ecological and human health concerns. Catalytic dehalogenation, through electrocatalysis specifically, has emerged as an appealing remediation strategy; electrochemical operations can be run at ambient conditions and are compatible with the renewable energy transition. Thus, this work begins to investigate palladium single-atom catalysts (Pd SACs) for the electrocatalytic reduction of C-X bonds in halogenated phenols. Different than bulk metals, single atoms maximize atomic efficiency and minimize catalyst cost. Palladium, known for its ability to selectively reduce C-X bonds, has been successfully synthesized in a single-atom morphology using an underpotential electrodeposition framework. Pd SACs were deposited on a carbon paper electrode by applying an electrochemical potential above the standard redox potential required for the formation of palladium metal-metal bonds (+0.591 V vs. SHE). To verify single-atom formation, electrodes were analyzed using materials characterizations techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Electrodes also underwent electrochemical characterization including current density and cyclic voltammetry (CV) analysis. Following underpotential deposition, Pd SAC/carbon paper electrodes were transferred to an electrochemical dehalogenation cell for the reduction of C-X bonds in halogenated phenols. A significant decrease in 4-chlorophenol and 4-bromophenol concentration was observed after applying a reductive potential as compared to the decrease observed with carbon paper controls. This work deepens the fundamental understanding of electrocatalytic dehalogenation and develops a low-cost, scalable system for the sustainable treatment of industrial wastewaters.