Silver-Ion Solid Phase Extraction Separation of Classical, Aromatic, Oxidized, and Heteroatomic Naphthenic Acids from Oil Sands Process-Affected Water

The separation of classical, aromatic, oxidized, and heteroatomic (sulfur-containing) naphthenic acid (NA) species from unprocessed and ozone-treated oil sands process-affected water (OSPW) was performed using silver-ion (Ag-ion) solid phase extraction (SPE) without the requirement of pre-methylation for NAs. OSPW samples before SPE and SPE fractions were characterized using ultra performance liquid chromatography ion mobility time-of-flight mass spectrometry (UPLC-IM-TOFMS) to corroborate the separation of distinct NA species. The mass spectrum identification applied a mass tolerance of ±1.5 mDa due to the mass errors of NAs were measured within this range, allowing the identification of O₂S−NAs from O₂−NAs. Moreover, separated NA species facilitated the tandem mass spectrometry (MS/MS) characterization of NA compounds due to the removal of matrix and a simplified composition. MS/MS results showed that classical, aromatic, oxidized, and sulfur-containing NA compounds were eluted into individual SPE fractions. Overall results indicated that the separation of NA species using Ag-ion SPE is a valuable method for extracting individual NA species that are of great interest for environmental toxicology and wastewater treatment research, to conduct species-specific studies. Furthermore, the separated NA species on the milligram level could be widely used as the standard materials for environmental monitoring of NAs from various contamination sites

Evaluation of Membrane Fouling for In-Line Filtration of Oil Sands Process-Affected Water: The Effects of Pretreatment Conditions

Membrane filtration is an effective reclamation option for oil sands process-affected water (OSPW). However, fresh OSPWs contain suspended solids and inorganic constituents in suspended and dissolved forms that can severely foul membranes. Pretreatment of OSPW with coagulation–flocculation (CF) was investigated to determine the effects of different coagulant aids (anionic, cationic, and nonionic polymers) on membrane surface properties and fouling. Our results showed that CF pretreatment effectively enhanced nanofiltration (NF) and reverse osmosis (RO) membrane permeate flux and salt rejection ratio through reducing membrane fouling. It was shown that coagulants and coagulant aids applied to OSPW feedwater can affect membrane physicochemical properties (surface hydrophilicity, zeta potential, and morphology), membrane performance, and the fouling indexes. Membrane rejection of ionic species increased significantly with the inclusion of an anionic coagulant aid and slightly with a cationic coagulant aid. Among three coagulant aids tested, anionic coagulant aids led to the most enhanced membrane performance through increasing membrane surface negativity and decreasing the formation of a fouling layer. Conversely, although cationic coagulant aids were the most effective in reducing OSPW turbidity, the application of cationic coagulant aids promoted the adsorption of foulants on membrane surfaces

Ultra Performance Liquid Chromatography Ion Mobility Time-of-Flight Mass Spectrometry Characterization of Naphthenic Acids Species from Oil Sands Process-Affected Water

Ultraperformance liquid chromatography ion mobility time-of-flight mass spectrometry (UPLC-IM-TOFMS), integrating traveling wave ion mobility spectrometry (TWIMS) with negative electrospray ionization (ESI) mode, was used to achieve two-dimensional (2D) separation (drift vs retention times) of naphthenic acids (NAs). Unprocessed and ozonated commercial NAs were used for method development. Only O₂–NAs were found in unprocessed NAs with ozonation creating O₃–NAs and O₄–NAs. Unprocessed and ozonated oil sands process-affected waters (OSPW) were examined to validate the method for complex matrix NAs. Ozonation increased the <i>x</i> number for O_<i>x</i>–NAs (2 ≤ <i>x</i> ≤ 5) and also impacted the −<i>Z</i> number distribution. OSPW extracted using dichloromethane removed the potential for sample matrix impacts and was used for MS/MS NAs characterization. The O_<i>x</i>–NAs (2 ≤ <i>x</i> ≤ 6) were identified with O₂–NAs separated into three clusters indicating isobaric and isomeric species. MS/MS was used to verify compounds, while also indicating the presence of CH₃CH₂S– NAs groups. This result may be useful for future studies of sulfur-NAs fate, toxicity, and treatment. Overall, the value-added information provided by UPLC-IM-TOFMS makes it a promising analytical technique for analysis of NAs in complex OSPW samples. Moreover, this methodology can be used for other matrices to investigate relative molecular sizes and to separate complex species (e.g., fatty acids, lipids), making it beneficial for environmental and bioanalytical applications

Impact of an extracellular polymeric substance (EPS) precoating on the initial adhesion of <i>Burkholderia cepacia</i> and <i>Pseudomonas aeruginosa</i>

<div><p>Extracellular polymeric substances (EPS) significantly influence bacterial adhesion to solid surfaces, but it is difficult to elucidate the role of EPS on bacterial adhesion due to their complexity and variability. In the present study, the effect of EPS on the initial adhesion of <i>B. cepaciaepacia</i> PC184 and <i>P. aeruginosa</i> PAO1 on glass slides with and without an EPS precoating was investigated under three ionic strength conditions. The surface roughness of EPS coated slides was evaluated by atomic force microscopy (AFM), and its effect on initial bacterial adhesion was found to be trivial. X-ray photoelectron spectroscopy (XPS) studies were performed to determine the elemental surface compositions of bacterial cells and substrata. The results showed that an EPS precoating hindered bacterial adhesion on solid surfaces, which was largely attributed to the presence of proteins in the EPS. This observation can be attributed to the increased steric repulsion at high ionic strength conditions. A steric model for polymer brushes that considers the combined influence of steric effects and DLVO interaction forces is shown to adequately describe bacterial adhesion behaviors.</p> </div

Comparison of Nitrilotriacetic Acid and [<i>S</i>,<i>S</i>]‑Ethylenediamine‑<i>N</i>,<i>N</i>′‑disuccinic Acid in UV–Fenton for the Treatment of Oil Sands Process-Affected Water at Natural pH

The application of UV–Fenton processes with two chelating agents, nitrilotriacetic acid (NTA) and [<i>S</i>,<i>S</i>]-ethylenediamine-<i>N</i>,<i>N</i>′-disuccinic acid ([<i>S</i>,<i>S</i>]-EDDS), for the treatment of oil sands process-affected water (OSPW) at natural pH was investigated. The half-wave potentials of Fe­(III/II)­NTA and Fe­(III/II)­EDDS and the UV photolysis of the complexes in Milli-Q water and OSPW were compared. Under optimum conditions, UV–NTA–Fenton exhibited higher efficiency than UV–EDDS–Fenton in the removal of acid extractable organic fraction (66.8% for the former and 50.0% for the latter) and aromatics (93.5% for the former and 74.2% for the latter). Naphthenic acids (NAs) removals in the UV–NTA–Fenton process (98.4%, 86.0%, and 81.0% for classical NAs, NAs + O (oxidized NAs with one additional oxygen atom), and NAs + 2O (oxidized NAs with two additional oxygen atoms), respectively) under the experimental conditions were much higher than those in the UV–H₂O₂ (88.9%, 48.7%, and 54.6%, correspondingly) and NTA–Fenton (69.6%, 35.3%, and 44.2%, correspondingly) processes. Both UV–NTA–Fenton and UV–EDDS–Fenton processes presented promoting effect on the acute toxicity of OSPW toward <i>Vibrio fischeri</i>. No significant change of the NTA toxicity occurred during the photolysis of Fe­(III)­NTA; however, the acute toxicity of EDDS increased as the photolysis of Fe­(III)­EDDS proceeded. NTA is a much better agent than EDDS for the application of UV–Fenton process in the treatment of OSPW

Investigation of Mono/Competitive Adsorption of Environmentally Relevant Ionized Weak Acids on Graphite: Impact of Molecular Properties and Thermodynamics

The thermodynamics of adsorption and competitive interactions of five weak acids on a graphite surface was assessed in alkaline solutions. Adsorption of the acids in mono- and multicompound solutions followed their Freundlich isotherms which suggest a diversity of graphite adsorption sites as confirmed by the presence of carboxylic and phenolic groups observed on graphite surfaces. Thermodynamic calculations assigned the formation of the negatively charged assisted hydrogen bond (−CAHB) between ionized solutes and adsorbent surface groups as the possible adsorption mechanism. However, the similar p<i>K</i>_a values of current acids resulted in comparable free energies for −CAHB formation (Δ<i>G</i>^–CAHB) being less than solvation free energies (Δ<i>G</i>_Solv). Thus, additional Δ<i>G</i> is supplemented by increased hydrophobicity due to proton exchange of ionized acids with water (ΔΔ<i>G</i>_{Hydrophobicity}). Adsorption capacities and competition coefficients indicated that ΔΔ<i>G</i>_{Hydrophobicity} values depend on the neutral and ionized acid <i>K</i>_ow. Competitive adsorption implies that multilayer adsorption may occur via hydrophobic bonding with the CH₃ ends of the self-assembled layer which affects the acid adsorption capacities in mixtures as compared to monocompound solutions. The determination of adsorption mechanisms will assist in understanding of the fate and bioavailability of emerging and classical weak acids released into natural waters

Oxidation of Oil Sands Process-Affected Water by Potassium Ferrate(VI)

This paper investigates the oxidation of oil sands process-affected water (OSPW) by potassium ferrate­(VI). Due to the selectivity of ferrate­(VI) oxidation, two-ring and three-ring fluorescing aromatics were preferentially removed at doses <100 mg/L Fe­(VI), and one-ring aromatics were removed only at doses ≥100 mg/L Fe­(VI). Ferrate­(VI) oxidation achieved 64.0% and 78.4% removal of naphthenic acids (NAs) at the dose of 200 mg/L and 400 mg/L Fe­(VI) respectively, and NAs with high carbon number and ring number were removed preferentially. ¹H nuclear magnetic resonance (¹H NMR) spectra indicated that the oxidation of fluorescing aromatics resulted in the opening of some aromatic rings. Electron paramagnetic resonance (EPR) analysis detected signals of organic radical intermediates, indicating that one-electron transfer is one of the probable mechanisms in the oxidation of NAs. The inhibition effect of OSPW on <i>Vibrio fischeri</i> and the toxicity effect on goldfish primary kidney macrophages (PKMs) were both reduced after ferrate­(VI) oxidation. The fluorescing aromatics in OSPW were proposed to be an important contributor to this acute toxicity. Degradation of model compounds with ferrate­(VI) was also investigated and the results confirmed our findings in OSPW study

Application of a Solar UV/Chlorine Advanced Oxidation Process to Oil Sands Process-Affected Water Remediation

The solar UV/chlorine process has emerged as a novel advanced oxidation process for industrial and municipal wastewaters. Currently, its practical application to oil sands process-affected water (OSPW) remediation has been studied to treat fresh OSPW retained in large tailings ponds, which can cause significant adverse environmental impacts on ground and surface waters in Northern Alberta, Canada. Degradation of naphthenic acids (NAs) and fluorophore organic compounds in OSPW was investigated. In a laboratory-scale UV/chlorine treatment, the NAs degradation was clearly structure-dependent and hydroxyl radical-based. In terms of the NAs degradation rate, the raw OSPW (pH ∼ 8.3) rates were higher than those at an alkaline condition (pH = 10). Under actual sunlight, direct solar photolysis partially degraded fluorophore organic compounds, as indicated by the qualitative synchronous fluorescence spectra (SFS) of the OSPW, but did not impact NAs degradation. The solar/chlorine process effectively removed NAs (75–84% removal) and fluorophore organic compounds in OSPW in the presence of 200 or 300 mg L^–1 OCl^–. The acute toxicity of OSPW toward Vibrio fischeri was reduced after the solar/chlorine treatment. However, the OSPW toxicity toward goldfish primary kidney macrophages after solar/chlorine treatment showed no obvious toxicity reduction versus that of untreated OSPW, which warrants further study for process optimization

Impact of Peroxydisulfate in the Presence of Zero Valent Iron on the Oxidation of Cyclohexanoic Acid and Naphthenic Acids from Oil Sands Process-Affected Water

Large volumes of oil sands process-affected water (OSPW) are produced during the extraction of bitumen from oil sands in Alberta, Canada. The degradation of a model naphthenic acid, cyclohexanoic acid (CHA), and real naphthenic acids (NAs) from OSPW were investigated in the presence of peroxydisulfate (S₂O₈^2–) and zerovalent iron (ZVI). For the model compound CHA (50 mg/L), in the presence of ZVI and 500 mg/L S₂O₈^2–, the concentration decreased by 45% after 6 days of treatment at 20 °C, whereas at 40, 60, and 80 °C the concentration decreased by 20, 45 and 90%, respectively, after 2 h of treatment. The formation of chloro-CHA was observed during ZVI/S₂O₈^2– treatment of CHA in the presence of chloride. For OSPW NAs, in the presence of ZVI alone, a 50% removal of NAs was observed after 6 days of exposure at 20 °C. The addition of 100 mg/L S₂O₈^2– to the solution increased the removal of OSPW NAs from 50 to 90%. In absence of ZVI, a complete NAs removal from OSPW was observed in presence of 2000 mg/L S₂O₈^2– at 80 °C. The addition of ZVI increased the efficiency of NAs oxidation by S₂O₈^2– near room temperature. Thus, ZVI/S₂O₈^2– process was found to be a viable option for accelerating the degradation of NAs present in OSPW

Probing the Adsorption of Weak Acids on Graphite Using Amplitude Modulation–Frequency Modulation Atomic Force Microscopy

Recent thermodynamics calculations and adsorption isotherms showed that the adsorption of a self-assembled layer (SAL) of ionized weak acids to carbon was attributed to the negatively charged hydrogen bonding (−CAHB), yet the direct visualization and characterization of this adsorption behavior have not been reported. Here, an amplitude modulation–frequency modulation atomic force microscopy (AM–FM AFM) technique was applied to discriminate the adsorption of decanoic acids (DA) on highly ordered pyrolytic graphite (HOPG). Thermodynamics calculations revealed that the adsorption of SAL was driven by the formation of −CAHB with negatively charged functional groups of HOPG. Multilayer adsorption could occur over the adsorbed ionized SAL, leading to the development of aggregates. AM–FM AFM imaging showed that the adsorption of the DA molecules forming aggregates occurred only for the HOPG-functionalized steps, while DA molecules were found to adsorb over the entire functionalized HOPG surface after water-plasma treatment, as evident from the frequency shifts identified in AFM images