Destruction of Per- and Polyfluoroalkyl Substances in Reverse Osmosis Concentrate Using UV-Advanced Reduction Processes.

UV-advanced reduction processes (UV-ARP), characterized by the strongly reducing aqueous electron (e ), have been shown to degrade perfluoroalkyl and polyfluoroalkyl substances (PFAS). Due to the high cost of PFAS destruction technologies, concentrated waste streams derived from physical treatment processes, such as ion exchange or membrane concentrates, are promising targets for implementation of these technologies. However, there are limited studies on the application of UV-ARP for PFAS destruction in concentrated waste streams.

Critical review of fluorescence and absorbance measurements as surrogates for the molecular weight and aromaticity of dissolved organic matter.

Dissolved organic matter (DOM) is ubiquitous in aquatic environments and challenging to characterize due to its heterogeneity. Optical measurements (, absorbance and fluorescence spectroscopy) are popular characterization tools, because they are non-destructive, require small sample volumes, and are relatively inexpensive and more accessible compared to other techniques (, high resolution mass spectrometry). To make inferences about DOM chemistry, optical surrogates have been derived from absorbance and fluorescence spectra to describe differences in spectral shape (, E2:E3 ratio, spectral slope, fluorescence indices) or quantify carbon-normalized optical responses (, specific absorbance (SUVA) or specific fluorescence intensity (SFI)).

Inferring the Molecular Basis for Dissolved Organic Matter Photochemical and Optical Properties.

Despite the widespread use of photochemical and optical properties to characterize dissolved organic matter (DOM), a significant gap persists in our understanding of the relationship among these properties. This study infers the molecular basis for the optical and photochemical properties of DOM using a comprehensive framework and known structural moieties within DOM. Utilizing Suwannee River Fulvic Acid (SRFA) as a model DOM, carboxylated aromatics, phenols, and quinones were identified as dominant contributors to the absorbance spectra, and phenols, quinones, aldehydes, and ketones were identified as major contributors to radiative energy pathways.

Meta-Analysis of Optical Surrogates for the Characterization of Dissolved Organic Matter.

Optical surrogates, derived from absorbance and fluorescence spectra, are widely used to infer dissolved organic matter (DOM) composition (molecular weight, aromaticity) and genesis (autochthonous vs allochthonous). Despite the broad adoption of optical surrogates, several limitations exist, such as context- and sample-specific factors. These limitations create uncertainty about how compositional interpretations based on optical surrogates are generalized across contexts, specifically if there is duplicative or contradictory information in those interpretations.

Evaluating the pH-dependence of DOM absorbance, fluorescence, and photochemical production of singlet oxygen.

The protonation state of dissolved organic matter (DOM) impacts its structure and function in natural and engineered environmental systems, including DOM's ability to absorb light and form photochemically produced reactive intermediates (PPRI). However, the impacts of pH on DOM optical properties and PPRI formation have largely been evaluated separately, with less information being available on their interrelationship as a function of pH for the same set of samples. It is also unclear whether the impact of pH on optical spectra and associated optical surrogates for molecular size (, E2 : E3) of DOM isolates is representative of the behavior of whole water samples.

Reactivity of Dissolved Organic Matter with the Hydrated Electron: Implications for Treatment of Chemical Contaminants in Water with Advanced Reduction Processes.

Advanced reduction processes (ARP) have garnered increasing attention for the treatment of recalcitrant chemical contaminants, most notably per- and polyfluoroalkyl substances (PFAS). However, the impact of dissolved organic matter (DOM) on the availability of the hydrated electron (e), the key reactive species formed in ARP, is not completely understood. Using electron pulse radiolysis and transient absorption spectroscopy, we measured bimolecular reaction rates constant for e reaction with eight aquatic and terrestrial humic substance and natural organic matter isolates ( ), with the resulting values ranging from (0.

Evaluating the Microheterogeneous Distribution of Photochemically Generated Singlet Oxygen Using Furfuryl Amine.

Singlet oxygen (O) is an important reactive species in natural waters produced during photolysis of dissolved organic matter (DOM). Prior studies have demonstrated that O exhibits a microheterogeneous distribution, with [O] in the interior of DOM macromolecules ∼30 to 1000-fold greater than in bulk solution. The [O] profile for DOM-containing solutions has been determined mainly by the use of hydrophobic probes, which are not commercially available.

Fluorescence Quenching of Humic Substances and Natural Organic Matter by Nitroxide Free Radicals.

Fluorescence spectroscopy is one of the most frequently used techniques for studying dissolved organic matter (DOM) in natural and engineered systems. However, the spatial distribution and fluorophores, including local and interacting states, within DOM's larger structure remains poorly understood. In this study, we used two nitroxide fluorescence quenchers to evaluate the chemical and spatial heterogeneity of DOM fluorophores.

Quantifying Hydrated Electron Transformation Kinetics in UV-Advanced Reduction Processes Using the Method.

Ultraviolet advanced reduction processes (UV-ARP) have garnered significant attention recently for the degradation of several hard to treat contaminants, including recalcitrant per- and polyfluoroalkyl substances (PFAS). The rate of contaminant degradation in UV-ARP is directly related to the available hydrated electron concentration ([e]). However, reports of [e] and other parameters typically used to characterize photochemical systems are not widely reported in the UV-ARP literature.

Critical Review of UV-Advanced Reduction Processes for the Treatment of Chemical Contaminants in Water.

UV-advanced reduction processes (UV-ARP) are an advanced water treatment technology characterized by the reductive transformation of chemical contaminants. Contaminant abatement in UV-ARP is most often accomplished through reaction with hydrated electrons (e ) produced from UV photolysis of chemical sensitizers (e.g.

Assessing the source of the photochemical formation of hydroxylating species from dissolved organic matter using model sensitizers.

Dissolved organic matter (DOM) is ubiquitous in natural waters and can facilitate the chemical transformation of many contaminants through the photochemical production of reactive intermediates, such as singlet oxygen (O), excited triplet state DOM (DOM*), and hydroxylating species (˙OH and other intermediates of similar reaction chemistry). The formation mechanism of most reactive intermediates is well understood, but this is not the case for the formation of hydroxylating species from DOM. To investigate this chemistry, DOM model sensitizers were irradiated with two different probe compounds (benzene and benzoic acid) at two irradiation wavelengths (254 and 320 nm).

Pilot-scale field demonstration of a hybrid nanofiltration and UV-sulfite treatment train for groundwater contaminated by per- and polyfluoroalkyl substances (PFASs).

Previous laboratory scale studies indicate nanofiltration (NF) and UV-sulfite photochemical treatments as promising technologies for the removal and destruction, respectively, of per- and polyfluoroalkyl substances (PFASs) from contaminated water. This study reports on a field demonstration of a pilot-scale hybrid NF and UV-sulfite treatment train for the remediation of 12 PFASs detected in groundwater impacted by aqueous film-forming foam (AFFF) at a U.S.

Relationships between the Physicochemical Properties of Dissolved Organic Matter and Its Reaction with Sodium Borohydride.

The reaction of dissolved organic matter (DOM) with sodium borohydride has been used to understand the geographic origin of DOM and investigate the photophysical model underlying DOM's optical properties. However, the physicochemical properties of DOM (e.g.

Computational Assessment of the Three-Dimensional Configuration of Dissolved Organic Matter Chromophores and Influence on Absorption Spectra.

The three-dimensional configuration of dissolved organic matter (DOM) is an important factor in determining the role of DOM in natural and engineered systems, yet there is still considerable uncertainty regarding the formation and potential stability of molecular aggregates within DOM. In this paper, we describe a computational assessment of the three-dimensional configuration of DOM. Specifically, we were interested in evaluating the hypothesis that DOM forms thermodynamically stable molecular aggregates that as a result were potentially shielded from water solvent molecules.

Emerging investigator series: critical review of photophysical models for the optical and photochemical properties of dissolved organic matter.

Optical measurements (absorbance and fluorescence) are widely used to track dissolved organic matter (DOM) quantity and quality in natural and engineered systems. Despite many decades of research on the optical properties of DOM, there is a lack of understanding with regards to the underlying photophysical model that is the basis for these optical properties. This review both summarizes advances to date on the photophysical properties of DOM and seeks to critically evaluate the photophysical models for DOM optical properties.

Use of optical properties for evaluating the presence of pyrogenic organic matter in thermally altered soil leachates.

The increased frequency and severity of wildfires in forested watersheds has the potential to significantly impact the quantity and quality of water extractable organic matter (WEOM) exported from these ecosystems. This study examined the optical properties of WEOM from laboratory heated soil in order to understand physicochemical changes occurring in the organic matter as a result of heating, as well as test the usefulness of optical parameters for assessing the presence of pyrogenic organic matter. WEOM absorbance and fluorescence spectral shape and intensity varied systematically as a function of soil heating temperature.

Effects of Ozone on the Photochemical and Photophysical Properties of Dissolved Organic Matter.

This study focused on the effects of ozonation on the photochemical and photophysical properties of dissolved organic matter (DOM). Upon ozonation, a decrease in DOM absorbance was observed in parallel with an increase in singlet oxygen (O) and fluorescence quantum yields (Φ and Φ). The increase in Φ was attributed to the formation of quinone-like moieties during ozonation of the phenolic moieties of DOM, while the increase in Φ can be explained by a significant decrease in the internal conversion rate of the first excited singlet state of the DOM (DOM*).

Temperature Dependence of Dissolved Organic Matter Fluorescence.

The temperature dependence of organic matter fluorescence apparent quantum yields (Φ) was measured for a diverse set of organic matter isolates (i.e., marine aquatic, microbial aquatic, terrestrial aquatic, and soil) in aqueous solution and for whole water samples to determine apparent activation energies ( E) for radiationless decay processes of the excited singlet state.

Ozone and chlorine reactions with dissolved organic matter - Assessment of oxidant-reactive moieties by optical measurements and the electron donating capacities.

Oxidation processes are impacted by the type, concentration and reactivity of the dissolved organic matter (DOM). In this study, the reactions between various types of DOM (Suwannee River fulvic acid (SRFA), Nordic Reservoir NOM (NNOM) and Pony Lake fulvic acid (PLFA)) and two oxidants (ozone and chlorine) were studied in the pH range 2-9 by using a combination of optical measurements and electron donating capacities. The relationships between residual electron donating capacity (EDC) and residual absorbance showed a strong pH dependence for the ozone-DOM reactions with phenolic functional groups being the main reacting moieties.

Low levels of iron enhance UV/HO efficiency at neutral pH.

While the presence of iron is generally not seen as favorable for UV-based treatment systems due to lamp fouling and decreased UV transmittance, we show that low levels of iron can lead to improvements in the abatement of chemicals in the UV-hydrogen peroxide advanced oxidation process. The oxidation potential of an iron-assisted UV/HO (UV + HO + iron) process was evaluated at neutral pH using iron levels below USEPA secondary drinking water standards (<0.3 mg/L).

The Case Against Charge Transfer Interactions in Dissolved Organic Matter Photophysics.

The optical properties of dissolved organic matter influence chemical and biological processes in all aquatic ecosystems. Dissolved organic matter optical properties have been attributed to a charge-transfer model in which donor-acceptor complexes play a primary role. This model was evaluated by measuring the absorbance and fluorescence response of organic matter isolates to changes in solvent temperature, viscosity, and polarity, which affect the position and intensity of spectra for known donor-acceptor complexes of organic molecules.

Temperature dependence of hydroxyl radical reactions with chloramine species in aqueous solution.

The absolute temperature-dependent kinetics for the reaction between hydroxyl radicals and the chloramine water disinfectant species monochloramine (NHCl), as well as dichloramine (NHCl) and trichloramine (NCl), have been determined using electron pulse radiolysis and transient absorption spectroscopy. These radical reaction rate constants were fast, with values of 6.06 × 10, 2.

Photochemical generation of reactive intermediates from urban-waste bio-organic substances under UV and solar irradiation.

Singlet oxygen (O), hydroxyl radicals (OH), and excited triplet states of organic matter (OM) play a key role in the degradation of pollutants in aquatic environments. The formation rates and quantum yields (Φ) of these reactive intermediates (RI) through photosensitized reactions of dissolved organic matter (DOM) have been reported in the literature for decades. Urban biowaste-derived substances (UW-BOS), a form of organic matter derived from vegetative and urban waste, have recently been shown to be efficient sensitizers in the photo-degradation of different contaminants.

Predicting Reactive Intermediate Quantum Yields from Dissolved Organic Matter Photolysis Using Optical Properties and Antioxidant Capacity.

The antioxidant capacity and formation of photochemically produced reactive intermediates (RI) was studied for water samples collected from the Florida Everglades with different spatial (marsh versus estuarine) and temporal (wet versus dry season) characteristics. Measured RI included triplet excited states of dissolved organic matter (DOM*), singlet oxygen (O), and the hydroxyl radical (OH). Single and multiple linear regression modeling were performed using a broad range of extrinsic (to predict RI formation rates, R) and intrinsic (to predict RI quantum yields, Φ) parameters.