Search

Abstract Naphthenic acids (NAs) are one of the constituents of concerns in oil sands process water (OSPW) because of their persistence and recalcitrance. Herein, we investigated the degradation of five model NA compounds by UV-activated persulfate (UV/persulfate) process under medium-pressure UV lamp irradiation at pH 8.0. UV/persulfate process showed higher degradation efficiency towards cyclohexanoic acid (CHA) compared to UV/H 2 O 2 process under the same experimental conditions. CHA (0.39 mM) was completely removed within 30 min when 2 mM persulfate was used as oxidant, while more than 60 min were needed for the UV/H 2 O 2 process. The removal of CHA decreased from 100% to 10% when 300 mM tert-butyl alcohol (TBA) was used as the scavenger, indicating that hydroxyl radical (OH) was responsible for the CHA degradation in the UV/persulfate process. Sulfate (SO 4 −) radicals reacted slowly with CHA in the UV/persulfate process with a second-order rate constant of k = 5.3 × 107 M−1s−1. Relative kinetics studies using binary mixtures of model NA compounds showed similar structure-reactivity to that under UV/H 2 O 2 process. NAs with long carbon chain, cyclic ring, and aromatic ring were more reactive in the UV/persulfate process. The presence of high concentration of chloride ions dramatically inhibited the reaction. The OH radicals in the UV/persulfate process were generated by capturing OH− in solutions, as evidenced by the decrease of the pH value from 8.0 to 2.8 before and after treatment, respectively, in a pure water matrix. Primary intermediate products (oxy-CHA, hydroxyl-CHA, and dihydroxyl-CHA) of UV/persulfate process were confirmed by UPLC-MS. Highlights • UV activated persulfate oxidation process was used for the degradation of model NAs. • SO 4 − radical reacted slowly with CHA in UV/persulfate process compared to BA. • OH generated from SO 4 − and OH− were the main radicals responsible for the CHA removal. • Relative kinetics of model NA compounds in UV/persulfate process were studied. • The presence of chlorine ions was adverse to CHA removal and related chlorinated by-products were formed. [ABSTRACT FROM AUTHOR]

This study investigated the application of materials peat-mineral mix (PT) and Pleistocene fluvial sands from different location (PF-1 and PF-2) obtained from surface mining of oil sands as sorbents of naphthenic acids (NAs) from oil sands process water (OSPW). To understand the sorption properties and mechanisms of NAs in the materials, sorption and desorption studies were performed using decanoic acid (DA) and 5-phenylvaleric acid (PVA). Additionally, the removal efficiency was evaluated using real OSPW to understand the effect of NA structure on sorption. Equilibrium of DA and PVA was reached at 2 days for PT, and 3 and 6 days for PF materials, respectively. Langmuir isotherm best fitted the equilibrium data. Maximum sorption capacities for DA and PVA were, respectively, 16.8 × 103 and 104 mg/kg for PT, 142.9 and 81.3 mg/kg for PF-1, and 600 and 476.2 mg/kg for PF-2. Hydrophobic interactions, hydrogen bonding, and π−π interaction were the main sorption mechanisms. Desorption of model compounds from post-sorption materials was not observed for 14 days. The removal of NAs from real OSPW ranged from 20 to 54%. PT is the most promising sorbent of NAs from OSPW because it partially removed NAs with a wide range of molecular weights and structures at very low dosage. Sorption of NAs was affected by the total organic carbon of the materials, emphasizing the hydrophobic interaction as an important sorption mechanism. The results suggest that some mobility of NAs is expected to take place if the reclamation materials come in contact with OSPW, which might occur in an oil sands reclamation landscape. [Display omitted] • Three materials were studied as sorbents of model NA compounds and NAs from OSPW. • Sorption mechanisms included hydrogen bonding, hydrophobic and π−π interactions. • No desorption of model NAs from materials was observed up to 14 days of contact time. • Removal of NAs with different molecular weights and structures ranged from 9.9 to 68.3%. • TOC was the main characteristic of materials that affected the sorption of NAs from OSPW. [ABSTRACT FROM AUTHOR]

Ultra-performance liquid chromatography ion mobility time-of-flight mass spectrometry (UPLC-IM-TOFMS) was utilized for the analysis of naphthenic acids (NAs) in fractions of pH-dependent sequential liquid-liquid extractions from oil sands process-affected water. Ion-mobility separation technique allowed the differentiation of O y S−NAs (2 ≤ y ≤ 4) from O x −NAs (2 ≤ x ≤ 5) via drift time versus retention time separations. The results indicated that the addition of S atom to the O 2 −NA molecule led to a lower increase in the dissociation constant (pK a ) compared to that caused by the addition of O atom. Because additional O is present as OH while the S atom is present as the C S C structure, the latter does not involve into the deprotonation process directly. The pK a value decreased along with increasing carbon number and |Z| number for O 2 −, O 3 −, O 4 −, and O 2 S−NA species, except for O 5 −, O 3 S−, and O 4 S−NA species, each of which are comprised of chemical structures with distinct functional groups. A calculation model was developed to estimate pK a values for individual and total NA species via nonlinear regression curve fitting, utilizing the relative abundances of detected NA species. pK a values were calculated as 3.9 for total NAs, 3.3 for O 2 −NAs, 4.4 for O 3 −NAs, 7.3 for O 4 −NAs, and 4.1 for O 2 S−NAs. Knowledge of NAs pK a is crucially important for the comprehensive understanding of their potential transformation route and toxicity as well as for the development of water remediation applications. Both the ion-mobility separation technique and the new calculation model could be widely applied for the investigation of other complicated pollutants present in water and wastewater. [ABSTRACT FROM AUTHOR]

Naphthenic acids (NAs) are a highly complex mixture of organic compounds naturally present in bitumen and identified as the primary toxic constituent of oil sands process-affected water (OSPW). This work investigated the degradation of cyclohexanoic acid (CHA), a model NA compound, and natural occurring NAs during the UV photolysis of Fe(III)-nitrilotriacetic acid (UV-Fe(III)NTA) and UV-NTA-Fenton processes. The results indicated that in the UV-Fe(III)NTA process at pH 8, the CHA removal increased with increasing NTA dose (0.18, 0.36 and 0.72 mM), while it was independent of the Fe(III) dose (0.09, 0.18 and 0.36 mM). Moreover, the three Fe concentrations had no influence on the photolysis of the Fe(III)NTA complex. The main responsible species for the CHA degradation was hydroxyl radical ( OH), and the role of dissolved O 2 in the OH generation was found to be negligible. Real OSPW was treated with the UV-Fe(III)NTA and UV-NTA-Fenton advanced oxidation processes (AOPs). The removals of classical NAs (O 2 -NAs), oxidized NAs with one additional oxygen atom (O 3 -NAs) and with two additional oxygen atoms (O 4 -NAs) were 44.5%, 21.3%, and 25.2% in the UV-Fe(III)NTA process, respectively, and 98.4%, 86.0%, and 81.0% in the UV-NTA-Fenton process, respectively. There was no influence of O 2 on the NA removal in these two processes. The results also confirmed the high reactivity of the O 2 -NA species with more carbons and increasing number of rings or double bond equivalents. This work opens a new window for the possible treatment of OSPW at natural pH using these AOPs. [ABSTRACT FROM AUTHOR]

Abstract: This study evaluated the reaction kinetics and degradation mechanism of the pesticides bromoxynil and trifluralin during conventional ozonation. The second-order rate constants for the direct molecular ozone and hydroxyl radical reactions with bromoxynil and trifluralin were determined using a rapid-scan stopped-flow spectrophotometry, competition kinetics, and an organic substrate monitoring method. High reactivity toward ozone and hydroxyl radicals was observed for bromoxynil and trifluralin. The second-order rate constants for the reaction with ozone were about 102 M−1 s−1. The values of the second-order rate constants for the reaction between hydroxyl radicals and bromoxynil and trifluralin in ultrapure water at 20°C were estimated to be around 8.4×109 and 7.5×109 M−1 s−1, respectively. The identification of oxidation by-products generated during ozonation was also addressed. It was found that hydroxylation and debromination were the primary pathways for the bromoxynil degradation, whereas hydroxylation and dealkylation were found to be the major mechanisms for trifluralin oxidation. [Copyright &y& Elsevier]

The treatment of a naphthenic acid model compound, cyclohexanoic acid, with classical Fenton, UV-H 2 O 2 , UV-Fenton, nitrilotriacetic acid (NTA)-Fenton, UV-NTA-Fenton, and UV photolysis of Fe-NTA processes at pHs 3 and 8 was investigated. At 1.47 mM H 2 O 2 , 0.089 mM Fe, and 0.18 mM NTA, the UV-NTA-Fenton process at pH 3 exhibited the highest H 2 O 2 decomposition (100% in 25 min), CHA removal (100% in 12 min) with a rate constant of 0.27 ± 0.025 min −1 , and NTA degradation (100% in 6 min). Due to the formation of H 2 O 2 -Fe(III)NTA adduct, the total Fe concentration in the UV-NTA-Fenton system (0.063 mM at the end of the reaction) at pH 8 was much higher than that in the UV photolysis of Fe(III)NTA process (0.024 mM). The co-complexing effect of borate buffer helped to keep iron soluble; however, it imposed a negative influence on the CHA degradation in the UV-NTA-Fenton process (68% CHA removal in 60 min in the borate buffer compared to 92% in MilliQ water). The results demonstrated that the most efficient process for the CHA degradation under the experimental conditions was the UV-NTA-Fenton process at pH 3. [ABSTRACT FROM AUTHOR]

The fractionation of oil sands process-affected water (OSPW) via pH-dependent extractions was performed to quantitatively investigate naphthenic acids (NAs, C n H 2 n + Z O 2 ) and oxidized NAs (O x -NAs) species (C n H 2 n + Z O 3 and C n H 2 n + Z O 4 ) using ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOFMS). A mathematical model was also developed to estimate the dissociation constant p K a for NAs species, considering the liquid–liquid extraction process and the aqueous layer acid-base equilibrium. This model provides estimated dissociation constants for compounds in water samples based on fractionation extraction and relative quantification. Overall, the sum of O 2 -, O 3 -, and O 4 -NAs species accounted for 33.6% of total extracted organic matter. Accumulative extracted masses at different pHs revealed that every oxygen atom added to NAs increases the p K a (i.e., O 2 -NAs < O 3 -NAs < O 4 -NAs), indicating that the additional O atoms exist as –OH in O 3 - and O 4 -NAs. Molecule electron-withdrawing groups such as double bonds and aromatic groups, as indicated by higher carbon and − Z number, may be responsible for the lower p K a of O 2 -, O 3 -, and O 4 -NAs. The model obtained estimated p K a values of 3.5 for O 2 -NAs, 4.8 for O 3 -NAs, and 6.8 for O 4 -NAs via nonlinear regression curve fittings. These p K a values are valuable physicochemical parameters for environmental engineering applications targeting OSPW NAs treatment. [ABSTRACT FROM AUTHOR]

There are several established methods for the determination of naphthenic acids (NAs) in waters associated with oil sands mining operations. Due to their highly complex nature, measured concentration and composition of NAs vary depending on the method used. This study compared different common sample preparation techniques, analytical instrument methods, and analytical standards to measure NAs in groundwater and process water samples collected from an active oil sands operation. In general, the high- and ultrahigh-resolution methods, namely high performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) and Orbitrap mass spectrometry (Orbitrap-MS), were within an order of magnitude of the Fourier transform infrared spectroscopy (FTIR) methods. The gas chromatography mass spectrometry (GC-MS) methods consistently had the highest NA concentrations and greatest standard error. Total NAs concentration was not statistically different between sample preparation of solid phase extraction and liquid-liquid extraction. Calibration standards influenced quantitation results. This work provided a comprehensive understanding of the inherent differences in the various techniques available to measure NAs and hence the potential differences in measured amounts of NAs in samples. Results from this study will contribute to the analytical method standardization for NA analysis in oil sands related water samples. [ABSTRACT FROM AUTHOR]

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/H 2 O 2 , 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/H 2 O 2 , and ozone transformed the distribution profiles of O x , O x S y , and O x N y organic fractions (i.e., species containing oxygen, sulfur, and nitrogen, with x, y specifying the oxygen number and sulfur/nitrogen number, respectively), with O x S y 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 O x 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. [ABSTRACT FROM AUTHOR]

Naphthenic acids (NAs) from oil sand process-affected water (OSPW) were liquid–liquid extracted using six organic solvents (n-pentane, n-hexane, cyclohexane, dichloromethane, ethyl ether, and ethyl acetate) at three pHs (2.0, 8.5, and 12.0). The NAs exist in ionic (ions) and non-ionic (molecules) forms in the water phase depending on their dissociation constants and the solution pH. Results showed the extractability of NA molecules depends on the solvent polarity and the extractability of NA ions on the water solubility in solvent. The organic solvent type and solution pH were found to not only impact the extracted amounts of each NA species, but also the NAs distribution in terms of molecule carbon number and hydrogen deficiency. Overall, it is concluded that ethyl ether can be used as an alternative to dichloromethane (DCM) given their similar extraction efficiencies and extracted NA profiles. This is important since DCM is known to have metabolic toxicity and transitioning to the safer ethyl ether would eliminate laboratory DCM exposures and risk to human health. Despite the higher extraction efficiency of NAs at pH 2.0, extraction at pH 12.0 could be useful for targeted extraction of low-concentration nonpolar organic compounds in OSPW. This knowledge may assist in the determination of the specific NAs species that are known to have chronic, sub-chronic and acute toxicity to various organisms, and the potential targeting of treatment to these NAs species. [ABSTRACT FROM AUTHOR]

Highly polluted crude oil electric desalting wastewaters (EDWs) severely affect the efficiency of refinery wastewater treatment plants (WWTPs). Coagulation is an efficient pretreatment to reduce the impacts of EDWs. In the present study, the influences of coagulation pretreatment on the characteristics of EDWs of three typical Chinese crude oils, Liaohe heavy oil (LHO), Karamay heavy oil (KHO) and Daqing light oil (DLO), were investigated. The stability of three raw EDWs was broken and the contents of organic pollutants were significantly reduced by aluminum sulfate coagulation. More soluble COD and polar oils were removed from LHO-EDW (1241 and 98 mg L−1) and KHO-EDW (779 and 57 mg L−1) compared to DLO-EDW (417 and 11 mg L−1). Coagulation significantly changed the compositions of the organic pollutants of two heavy oil EDWs; however, slightly influenced DLO-EDW, particularly the polar organic pollutants. Most types of aromatic compounds, aliphatic acids and O x polar compounds were removed from two heavy oil EDWs, but mainly alkanes were removed from DLO-EDW. As such, the differences in the types of dominant polar compounds became insignificant among treated heavy oil and light oil EDWs. Coagulation notably decreased the acute biotoxicity and improved the biodegradability of all treated EDWs. The residual organic nitrogen compounds in treated KHO-EDW contributed to a higher residual biotoxicity compared to treated LHO-EDW. The results demonstrate that coagulation can effectively improve the qualities of heavy oil EDWs by lowering the contents of organic pollutants and removing recalcitrant compounds, thus guaranteeing the efficiency of refinery WWTPs. Image 1 • Coagulation is effective in breaking the stability and reducing pollutants contents. • Coagulation decreased the acute biotoxicity and improved the biodegradability of all EDWs. • Mainly polar compounds were removed from two heavy oil EDWs. • Mainly alkanes were removed from DLO-EDW. [ABSTRACT FROM AUTHOR]

Owing to the complexity of naphthenic acids (NAs) in oil sands process water (OSPW), previous ozone-treatment studies mainly investigated the removal of classical NAs (aliphatic O 2 -NAs) and the understanding of ozonation reactivity of other NA species has been limited. This work utilized a silver-ion solid phase extraction (SPE) approach to separate individual NA species into 20 fractions before subsequent ozone treatment. The ozonation reactivity of aromatic and oxidized NA species in isolated fractions was studied for the first time. Untreated and ozone-treated SPE fractions were characterized using ultra performance liquid chromatography ion mobility time-of-flight mass spectrometry. The removals of aliphatic O 2 -NAs (Fraction 3), aromatic O 2 -NAs (Fraction 8), O 3 -NAs (Fraction 11), and O 4 -NAs (Fraction 17) with an applied ozone dosage of 16.8 mg L -1 were 97.2%, 94.7%, 59.4% and 44.7%, respectively. The results showed that aromatic and oxidized NAs with larger carbon number were favorably removed during ozonation treatment. Comparison of the ozone utilization efficiency for different NA species indicated that the degradation of oxidized NAs consumed more ozone in molar ratio than the degradation of classical and aromatic NAs. The reactivity of oxidized NAs was lower than that of classical NAs because the former consumed more ozone in molar ratio during reactions. Knowing the reactivity of different NA species is crucial for the design of ozonation systems targeting species with high toxicity. Moreover, the utilization of silver-ion SPE pre-separation approach has been demonstrated for future studies investigating the degradation mechanism of distinct NA species under other treatment conditions., (Copyright © 2018 Elsevier Ltd. All rights reserved.)