On the increasing competitiveness of UV/Cl to UV/H2O2 advanced oxidation as the organic carbon concentration increases.

UV/Cl and UV/H2O2 are advanced oxidation processes (AOPs) used for drinking water treatment and water reuse. This work explored the hypothesis that UV/Cl becomes more competitive to UV/H2O2 at neutral-to-high pH as the concentration of total organic carbon (TOC) increases. Lab experiments and kinetic modelling were used to compare initial pseudo first-order contaminant decay rate coefficients between the AOPs at various pH and TOC conditions. The relative effect of increasing TOC concentrations on UV/Cl vs. UV/H2O2 depended on the pH, contaminant, and organic matter reactivity towards radicals. For example, while the reaction rate coefficients during both AOPs generally decreased with increasing TOC, the UV/Cl reaction rate coefficients for the solely •OH-reactive sucralose decreased 41-138% less than the UV/H2O2 coefficients as the TOC concentration was increased from 0 to 5 mg-C L-1. However, UV/Cl was more affected than UV/H2O2 when targeting caffeine (a contaminant reactive to chlorine radicals). The data were used to define TOC-pH conditions for which either AOP would be more energy-efficient, under a set of standard conditions. The results suggest that UV/Cl may be competitive to UV/H2O2 under a wider range of treatment scenarios than has been conventionally thought based on tests in pure water.

Impact of groundwater quality and associated byproduct formation during UV/hydrogen peroxide treatment of 1,4-dioxane.

In this study, a semi-batch, bench-scale UV/hydrogen peroxide (UV/H2O2) advanced oxidation process system was used to investigate how typical groundwater quality parameters (pH, alkalinity, natural organic matter (NOM), nitrate, and iron) influence the treatment of 1,4-dioxane. Deionized (DI) water spiked with 1,4-dioxane (100 µg L-1), treated using H2O2 (10 mg L-1) in a commercially available UV system (40 W low-pressure lamp) showed an UV fluence-based first-order rate constant (k') and electrical energy-per-order (EEO) of 4.32✕10-3 cm2-mJ-1 and 0.15 kWh-m-3-order-1, respectively. The most abundant byproduct generated in spiked-DI water was oxalic acid (up to 55 µg L-1), followed by formic and acetic acids. The k' showed no significant difference at pH ranging from 5 to 7 and at low alkalinity concentrations (<20 mg-CaCO3 L-1), typical of sandy aquifers. The k' declined by up to 85% with increasing NOM concentration. Elevated production (up to ∼400% increase) of aldehydes and organic acids was observed in NOM-spiked water, implying that NOM is a significant byproduct precursor during UV/H2O2 treatment. High NO3- concentration (10 mg-N L-1) in source water reduced the k' by 25%, while no significant impact was observed at lower concentrations (<2 mg-N L-1). Addition of Fe(II) at 0.5 mg-L-1 resulted in an instantaneous Fenton-reaction-assisted removal of ∼10% 1,4-dioxane in the presence of H2O2, but did not enhance the performance of UV/H2O2 treatment over time. In contrast, both Fe(II) and Fe(III) addition lowered the k' by 15-27%. The decline of k' observed in these experiments was attributed to reduced UVT (Fe), .OH radical scavenging (pH), or both (NO3-, NOM). Treatment of groundwater samples collected from three 1,4-dioxane-contaminated wells located in Long Island, NY, showed k' values of 13-40% lower than what was observed for DI water due to radical scavenging from a combination of high NO3- and NOM in the samples. A multiple linear-regression model, developed using water quality data as model input, showed good agreement with field observations (paired t-test: p > 0.05) in predicting k' for the removal of 1,4-dioxane from groundwater. This study provides the first systematic evaluation of the impacts of groundwater quality on UV/H2O2 process to remove environmentally relevant levels of 1,4-dioxane and reports standardized performance-related parameters to aid in the design and evaluation of full-scale systems.

Photochemical treatment of tyrosol, a model phenolic compound present in olive mill wastewater, by hydroxyl and sulfate radical-based advanced oxidation processes (AOPs).

The photochemical degradation and mineralization of tyrosol (TSL), a model phenolic compound present in olive mill wastewater, were studied by UV-254 nm irradiated peroxymonosulfate (PMS), hydrogen peroxide (H2O2) and persulfate (PS). Effects of initial TSL concentration, UV fluence, pH, phosphate buffer and presence of inorganic anions (i.e., Cl-, SO42- and NO3-) were also investigated. Sulfate and hydroxyl radicals were demonstrated to be responsible for TSL degradation and mineralization. Regardless of the treatment conditions, pseudo-first-order kinetics could be obtained, with the efficiencies following UV/PS > UV/H2O2 > UV/PMS. The better removal of TSL by UV/PS correlated with the quantum yield and concentration of sulfate radical in the system. Albeit acidic condition slightly enhanced the performance of the AOPs, complete oxidation of TSL was achieved at pH 6.8 by both UV/PS and UV/H2O2. Though, inorganic anions or different concentrations of phosphate buffer did not affect TSL degradation kinetics, presence of inorganic ions decreased significantly the TOC removal for both UV/PMS and UV/H2O2 processes. Meanwhile, UV/PS process was the least influenced by inorganic ions and showed the highest TOC removal of ∼35%. Overall, UV/PS process was the most effective for TSL degradation and mineralization in the presence or absence of common water constituents.

Positive and negative electrospray ionization analyses of the organic fractions in raw and oxidized oil sands process-affected water.

This work investigated the oxidative transformation of the organic species in oil sands process-affected water (OSPW) using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) in both negative and positive electrospray ionization (ESI) modes. This is the first time to apply FTICR-MS to investigate species transformation in OSPW treatments by ferrate (VI), UV/H2O2, and molecular ozone, and also this is the first preliminary study to use positive ESI to investigate organic species in addition to naphthenic acids (NAs) in these treatment processes. The oxidation processes with potassium ferrate (VI), UV/H2O2, and ozone transformed the distribution profiles of Ox, OxSy, and OxNy organic fractions (i.e., species containing oxygen, sulfur, and nitrogen, with x, y specifying the oxygen number and sulfur/nitrogen number, respectively), with OxSy distribution profiles showing the most sensitive responses to the oxidation extent and can be used as a signature fraction to evaluate the oxidation effectiveness. Negative mode UPLC-TOF-MS confirmed the transformation pattern of Ox species observed with FTICR-MS, but positive mode UPLC-TOF-MS results showed severe discrepancies with FTICR-MS results and should be subjected for future further investigation, regarding the relatively low mass resolution of UPLC-TOF-MS. The investigation of the transformation patterns of different organic species using two ionization modes was a preliminary study to enhance the understanding of the efficiency, selectivity, and mechanism of different oxidation processes in OSPW remediation for both NAs and non-NA species.

Comparison of UV/hydrogen peroxide, potassium ferrate(VI), and ozone in oxidizing the organic fraction of oil sands process-affected water (OSPW).

The efficiency of three different oxidation processes, UV/H2O2 oxidation, ferrate(VI) oxidation, and ozonation with and without hydroxyl radical (OH) scavenger tert-butyl alcohol (TBA) on the removal of organic compounds from oil sands process-affected water (OSPW) was investigated and compared. The removal of aromatics and naphthenic acids (NAs) was explored by synchronous fluorescence spectra (SFS), ion mobility spectra (IMS), proton and carbon nuclear magnetic resonance ((1)H and (13)C NMR), and ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry (UPLC TOF-MS). UV/H2O2 oxidation occurred through radical reaction and photolysis, transforming one-ring, two-ring, and three-ring fluorescing aromatics simultaneously and achieving 42.4% of classical NAs removal at 2.0 mM H2O2 and 950 mJ/cm(2) UV dose provided with medium pressure mercury lamp. Ferrate(VI) oxidation exhibited high selectivity, preferentially removing two-ring and three-ring fluorescing aromatics, sulfur-containing NAs (NAs + S), and NAs with high carbon and high hydrogen deficiency. At 2.0 mM Fe(VI), 46.7% of classical NAs was removed. Ozonation achieved almost complete removal of fluorescing aromatics, NAs + S, and classical NAs (NAs with two oxygen atoms) at the dose of 2.0 mM O3. Both molecular ozone reaction and OH reaction were important pathways in transforming the organics in OSPW as supported by ozonation performance with and without TBA. (1)H NMR analyses further confirmed the removal of aromatics and NAs both qualitatively and quantitatively. All the three oxidation processes reduced the acute toxicity towards Vibrio fischeri and on goldfish primary kidney macrophages (PKMs), with ozonation being the most efficient.