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The ethylenediamine-N,N′-disuccinic acid (EDDS) was utilized to form Fe-EDDS complex to activate peroxymonosulfate (PMS) in the electrochemical (EC) co-catalytic system for effective oxidation of naphthenic acids (NAs) under neutral pH conditions. 1-adamantanecarboxylic acid (ACA) was used as a model compound to represent NAs, which are persistent pollutants that are abundantly present in oil and gas field wastewater. The ACA degradation rate was significantly enhanced in the EC/PMS/Fe(III)-EDDS system (96.6%) compared to that of the EC/PMS/Fe(III) system (65.4%). The addition of EDDS led to the formation of a stable complex of Fe-EDDS under neutral pH conditions, which effectively promoted the redox cycle of Fe(III)-EDDS/Fe(II)-EDDS to activate PMS to generate oxidative species for ACA degradation. The results of quenching and chemical probe experiments, as well as electron paramagnetic resonance (EPR) analysis, identified significant contributions of •OH, 1O2, and SO4•− in the removal of ACA. The ACA degradation pathways were revealed based on the results of high resolution mass spectrometry analysis and calculation of the Fukui index. The presence of anions, such as NO3−, Cl−, and HCO3−, as well as humic acids, induced nonsignificant influence on the ACA degradation, indicating the robustness of the current system for applications in authentic scenarios. Overall results indicated the EC/PMS/Fe(III)-EDDS system is a promising strategy for the practical treatment of NAs in oil and gas field wastewater. [ABSTRACT FROM AUTHOR]

In this study, molybdenum disulfide (MoS 2) has been investigated as a catalyst to boost the redox cycle of Fe(III)/Fe(II) to activate peroxymonosulfate (PMS) to effectively break down cyclohexanecarboxylic acid (CHA), which is a model naphthenic acid (NA) pollutant. The optimum conditions of pH 3, MoS 2 concentration of 0.4 g/L, Fe(III) concentration of 0.3 mmol/L, and PMS concentration of 2 mmol/L has been applied for complete degradation of 0.1 mmol/L CHA in 10 minutes reaction time. Based on results of electron paramagnetic resonance analysis, chemical probe and quenching experiment, it was found that all of •OH, SO 4 •−, 1O 2 , and Fe(IV) contributed to the MoS 2 /Fe(III)/PMS oxidation system. Eighteen CHA byproducts and three primary CHA degradation pathways were revealed according to the results of UHPLC-QTOF-MS analysis. By using XPS, SEM, and XRD to characterize the MoS 2 powders before and after the reaction, MoS 2 was found with high stability and the oxidation of Mo(IV) on the surface was negligible. The impacts of background anions on CHA degradation were found to be nonimportant, and commercial NAs mixture were verified to be efficiently degraded in current system. Overall results indicate the capacity and potential of MoS 2 /Fe(III)/PMS system to be utilized for future treatment of authentic oil and gas field wastewater. [Display omitted] • Both Mo(IV) and S2- of MoS 2 can activate PMS to generate ROS to degrade CHA. • The main reactive species are 1O 2 , •OH, SO 4 •−and Fe(IV) in the system. • Chain scission, hydrogen extraction and decarboxylation are main reaction pathways. • No Mo(V) oxidation was found on the surface of MoS 2 powder after the reaction. • The commercial NAs mixture was examined for efficient degradation. [ABSTRACT FROM AUTHOR]

Distinct naphthenic acid (NA) species were isolated from oil sands process water (OSPW) into 20 fractions via silver-ion solid phase extraction, prior to treatment using potassium ferrate(VI). Untreated and treated fractions F1–F20 were characterized using ultra performance liquid chromatography traveling-wave ion mobility time-of-flight mass spectrometry to identify classical NAs (aliphatic O 2 –NAs mainly found in fractions F1–F4), aromatic NAs (aromatic O 2 –NAs in F6–F9), oxidized NAs (O 3 –, O 4 –, and O 5 –NAs in F14–F17), and sulfur-containing NAs (F16–F19). The Fe(VI) oxidation reactivity of individual NA species was studied with minimized confounding effects from the complicated OSPW matrix. Aliphatic and aromatic O 2 –NAs were found to have different reactivity towards Fe(VI) oxidation, with removals ranging from <50% up to 90% at 200 mg/L ferrate dose. The O 3 –NAs and O 4 –NAs from raw OSPW were recalcitrant species with slight degradation under Fe(VI) oxidation conditions. The Fe(VI) oxidation of O 2 –NAs generated new O 3 –NAs as byproducts or intermediate byproducts which finally resulted in more oxygen-rich O x –NAs as the final byproducts depending on the Fe(VI) doses. Besides the obtained knowledge on chemical reactivity, current methodology (i.e., treatment of Ag-ion fractions of OSPW versus raw OSPW) could be applied to evaluate other treatment approaches as well as toxicity of distinct NA species for environmental applications. Unlabelled Image • The Ag-ion SPE allowed a good separation of OSPW into 20 fractions. • Fe(VI) reactivity of isolated NA species was studied for the first time. • Fe(VI) oxidation removed O 2 –NAs favorably rather than other oxidized NAs. • Fe(VI) treatment could oxidize O 2 –NAs to generate O 4 –NAs directly. [ABSTRACT FROM AUTHOR]

With the ever-increasing amounts of oil sands process-affected water (OSPW) accumulating from Canada's oil sands operations, its eventual release must be considered. As OSPW has been found to be both acutely and chronically toxic to aquatic organisms, remediation processes must be developed to lower its toxicity. Ozone treatment is currently being studied as a tool to facilitate the removal of organic constituents associated with toxicity. Biomarkers (e.g. gene expression) are commonly used when studying the effects of environmental contaminants, however, they are not always indicative of adverse effects at the whole organism level. In this study, we assessed the effects of OSPW exposure on developing zebrafish by linking gene expression to relevant cellular and whole organism level endpoints. We also investigated whether or not ozone treatment decreased biomarkers and any associated toxicity observed from OSPW exposure. The concentrations of classical naphthenic acids in the raw and ozonated OSPW used in this study were 16.9 mg/L and 0.6 mg/L, respectively. Ozone treatment reduced the total amount of naphthenic acids (NAs) in the OSPW sample by 92%. We found that exposure to both raw and ozonated OSPW had no effect on the survival of zebrafish embryos. The expression levels of biotransformation genes CYP1A and CYP1B were induced by raw OSPW exposure, with CYP1B being more highly expressed than CYP1A. In contrast, ozonated OSPW exposure did not increase the expression of CYP1A and only slightly induced CYP1B. A decrease in cardiac development and function genes (NKX2.5 and APT2a2a) was not associates with large changes in heart rate, arrhythmia or heart size. We did not find any indications of craniofacial abnormalities or of increased occurrence of apoptotic cells. Overall, our study found that OSPW was not overtly toxic to zebrafish embryos. [ABSTRACT FROM AUTHOR]

This work reports the monitoring and assessment of naphthenic acids (NAs) in oil sands process-affected water (OSPW), Pleistocene channel aquifer groundwater (PLCA), and oil sands basal aquifer groundwater (OSBA) from an active oil sands development in Alberta, Canada, using ultra performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) analysis with internal standard (ISTD) and external standard (ESTD) calibration methods and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) for compositional analysis. PLCA was collected at 45–51 m depth and OSBA was collected at 67–144 m depth. Results of O x −NA concentrations follow an order as OSPW > OSBA > PLCA, indicating that occurrences of NAs in OSBA were likely related to natural bitumen deposits instead of OSPW. Liquid-liquid extraction (LLE) was applied to avoid the matrix effect for the ESTD method. Reduced LLE efficiency accounted for the divergence of the ISTD and ESTD calibrated results for oxidized NAs. Principle component analysis results of O 2 and O 4 species could be employed for differentiation of water types, while classical NAs with C13−15 and Z (-4)−(-6) and aromatic O 2 −NAs with C16−18 and Z (-14)−(-16) could be measured as marker compounds to characterize water sources and potential temporal variations of samples, respectively. FTICR-MS results revealed that compositions of NA species varied greatly among OSPW, PLCA, and OSBA, because of NA transfer and transformation processes. This work contributed to the understanding of the concentration and composition of NAs in various types of water, and provided a useful combination of analytical and statistical tools for monitoring studies, in support of future safe discharge of treated OSPW. [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]

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) 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]

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]

This paper reported the impact of UV/H 2 O 2 , UV/chlorine, and UV/persulfate advanced oxidation processes on the molecular transformations of dissolved organic matter (DOM), removal of naphthenic acids (NAs) and acute toxicity in oil sands process water (OSPW). The UV/persulfate process exhibited the highest removal (81.2% with 2 mM dose) towards classical NAs and highest reduction in acute toxicity to Vibrio fischeri among the three processes. The fraction of DOM such as CHOS class species decreased along with the increase of the oxidant doses in all processes. The increase in O/C ratio and lack of change in the H/C and double bond equivalence indicated that H-abstraction followed by the OH-addition was the main reaction pathway for all processes. This observation aligned with previous studies using model compounds and proved that OSPW DOM reacted similarly to model compounds. Sulfur containing organic matters were the most liable compounds in OSPW NOM, while UV/chlorine was the most effective process to oxidize nitrogen containing organic matters. Overall results revealed that the UV/persulfate process could be used as a promising technique for the removal of OSPW NA and reduction of acute toxicity towards Vibrio fischeri. In addition, this DOM characterization approach could be utilized to investigate the transformation of complicated OSPW DOM and to identify the byproducts generated during different water treatment processes. Unlabelled Image • UV/persulfate had the highest O 2 -NA removal. • UV/persulfate had the highest reduction in acute toxicity to Vibrio fischeri. • H-abstraction followed by OH-addition was the main reaction pathway for all processes. • Sulfur containing organic matters were the most liable compounds in OSPW NOM. • Chlorinated byproducts were formed in both UV/chlorine and UV/persulfate. [ABSTRACT FROM AUTHOR]

The ultraviolet light-activated persulfate process (UV/Persulfate) has received much attention in recent years as a novel advanced oxidation method for the treatment of municipal and industrial wastewater. This work investigated the UV/Persulfate and UV/H 2 O 2 processes for the treatment of real oil sands process water (OSPW) at ambient pH condition using a medium pressure mercury lamp (emission between 200 and 530 nm). The degradation performances towards fluorophore organic compounds and naphthenic acids (NAs) in OSPW were evaluated using synchronous fluorescence spectrometry and ultra performance liquid chromatography time-of-flight mass spectrometry, respectively. Compared to the UV/H 2 O 2 process, the UV/Persulfate process exhibited higher efficiency to remove both NAs and fluorophore organic compounds. Under 40 min of UV exposure and incident irradiance of 3.50 mW cm−2, fluorophore organic compounds were greatly degraded by UV/Persulfate (2 mM) and two- and three-ring fused organics were completely removed. 59.4%, 83.8% and 92.2% of O 2 -NAs in OSPW were removed with persulfate dosages of 0.5, 2, and 4 mM, respectively. The removal efficiency decreased along with the number of oxygen atoms in NAs (83.8%, 49.3%, and 46.8% for O 2 -, O 3 -, and O 4 -NAs, respectively) with 2 mM of persulfate, because of the formation of oxidized NAs in the same process. The structure-reactivity of O 2 -NA compounds fitted pseudo-first order kinetics in UV/Persulfate process with the rate constants ranging from 0.0156 min−1 to 0.1511 min−1. NAs with higher carbon numbers and double bond equivalence were more reactive in the UV/Persulfate oxidation process. The acute toxicity of OSPW to Vibrio fischeri was significantly reduced after the UV/Persulfate and UV/H 2 O 2 treatments. Overall results demonstrated that the UV/Persulfate oxidation can be an effective alternative for future reclamation of OSPW. Unlabelled Image • UV/Persulfate was investigated for the treatment of real OSPW. • Higher removal efficiency towards NAs was obtained with UV/Persulfate compared to UV/H 2 O 2. • NAs with higher carbon and |Z| numbers showed high reactivity in UV/Persulfate. • UV/Persulfate and UV/H 2 O 2 reduced the acute toxicity of OSPW towards Vibrio fischeri. [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient degradation of NAs was achieved by EC/PMS/Fe(III) system. • The redox cycle of Fe(III)/Fe(II) was triggered on the cathode. • The chemical structures of NA molecules affect their reactivity. • •OH, SO 4 •− and 1O 2 are the main reactive species in EC/PMS/Fe(III) system. • CHA degradation pathways and byproducts were revealed. In this study, an electrochemical/peroxymonosulfate/Fe(III) (EC/PMS/Fe(III)) system was established for efficient degradation of four naphthenic acids (NAs) compounds including cyclohexanecarboxylic (CHA), heptanoic (HPA), benzoic (BA) and 2-methylhexanoic acids (2-MHA). The introduction of electric field enhances the redox cycle of Fe(III)/Fe(II) to activate PMS for degredation of NAs. Complete degradation of NAs compounds (5 mg/L) has been achieved within 30 min in the EC/PMS/Fe(III) system. The results of electron paramagnetic resonance (EPR) analysis, scavenging experiment, and chemical probe experiments indicated hydroxyl radical (•OH), sulfate radical (SO 4 •−) and singlet oxygen (1O 2) are primary reactive oxygen species (ROS) in the EC/PMS/Fe(III) system. NAs compounds with different structures exhibit inconsistent degradation efficiency in current system (k CHA > k BA > k HPA > k 2-MHA), depending on the selectivity of the different ROS and stability of respective intermediate organic radicals. Besides, multiple degradation pathways of CHA, mainly including hydroxylation and carbonylation, were proposed by combining the results of mass spectrometry analysis with the calculated Fukui index based on density functional theory (DFT) calculation. In addition, the EC/PMS/Fe(III) system exhibited robust performance with the addition of co-existing ions. This work provides a novel strategy for efficient degradation of NAs for future remediation of petroleum wastewater. [ABSTRACT FROM AUTHOR]

• The EC/PMS/Fe(III)-EDTA system was tested under a pH range of 3–9. • Fe(II)-EDTA complex maintains high reaction rates to degrade ACA at neutral pH. • •OH, 1O 2 , SO 4 •− and Fe(IV) are the dominant reactive species in the system. • The addition of EDTA established a new pathway for producing 1O 2 in the system. • ACA degradation pathways and byproducts were revealed based on mass spectra. In this work, ethylene diamine tetraacetic acid (EDTA) was applied as a chelating agent to stabilize Fe(III)/Fe(II) cycle to effectively activate peroxymonosulfate (PMS) in an electrochemical (EC) co-catalytic system for elimination of naphthenic acids (NAs) under neutral pH condition. 1-Adamantanecarboxylic acid (ACA) was applied as the model compound for NAs that are persistent contaminants in petroleum industrial wastewater. In the PMS/EC/Fe(III)-EDTA system, complete removal of ACA has been achieved in 20-min reaction under neutral pH condition. Degradation mechanisms were investigated via electron paramagnetic resonance (EPR) analysis, probe experiments and quenching experiments to reveal the reactive species •OH, SO 4 •− and 1O 2 for ACA removal, the production of which have been significantly facilitated by the introduction of EDTA complex. A new pathway has been found for the production of 1O 2 via several intermediates including hydrogen peroxide and superoxide radicals. Density functional theory (DFT) calculations and mass spectrometry analysis were applied to predict ACA degradation pathways and byproducts. Decarboxylation, hydroxyl substitution and carbonyl substitution byproducts of ACA were detected. The PMS/EC/Fe(III)-EDTA system suffered nonimportant influence at the presence of humic acid, H 2 PO 4 -, HCO 3 –, NO 3 – and Cl- for ACA removal. Overall results demonstrate the effectiveness and reliability of the PMS/EC/Fe(III)-EDTA system for efficient removal of NAs in petroleum wastewater in natural environment under neutral pH condition. [ABSTRACT FROM AUTHOR]

In this study, the Fe(III)/WS 2 /peroxymonosulfate (PMS) system was found to remove up to 97% of cyclohexanecarboxylic acid (CHA) within 10 min. CHA is a model compound for naphthenic acids (NAs), which are prevalent in petroleum industrial wastewater. The addition of WS 2 effectively activated the Fe(III)/PMS system, significantly enhancing its ability to produce reactive oxidative species (ROS) for the oxidation of CHA. Further experimental results and characterization analyses demonstrated that the metallic element W(IV) in WS 2 could provide electrons for the direct reduction of Fe(III) to Fe(II), thus rapidly activating PMS and initiating a chain redox process to produce ROS (SO 4 •−, •OH, and 1O 2). Repeated tests and practical exploratory experiments indicated that WS 2 exhibited excellent catalytic performance, reusability and anti-interference capacity, achieving efficient degradation of commercial NAs mixtures. Therefore, applying WS 2 to catalyze the Fe(III)/PMS system can overcome speed limitations and facilitate simple, economical engineering applications. [Display omitted] • Fe(III)/WS 2 /PMS system can achieve 97% removel rate of CHA within 10 min. • •OH, SO 4 •−, and 1O 2 are main ROS in the Fe(III)/WS 2 /PMS system. • W(IV) contained in WS 2 can promoting Fe(III)/Fe(II) cycle by providing electrons. • Fe(III)/WS 2 /PMS system can achieve efficient degradation of commercial NAs. • Fe(III)/WS 2 /PMS system exhibits excellent reusability and anti-interference. [ABSTRACT FROM AUTHOR]

Naphthenic acid fraction compounds (NAFCs), defined herein as the polar organic compounds extracted from the acidified oil sands process water (OSPW) samples using dichloromethane, are becoming the research hotspot due to their presence in large amount in OSPW and along with other potentially NA-contaminated water streams from the mining site. Fourier transform infrared spectroscopy (FTIR) method is commonly used to quantify NAFCs and assumes that the total NA concentration is measured as the sum of the responses for all carboxylic acid functional groups. In this study, the NAFCs in various OSPW and groundwater (GW) samples from an active oil sands mining site were analyzed using FTIR. All water samples were pretreated using either solid-phase extraction (SPE) or liquid-liquid extraction (LLE) methods before analysis. The results showed that SPE produced higher recoveries of NAFCs than LLE for most water samples under current experimental conditions. For the quantification of NAFCs, commercial Fluka NA mixture and a pre-calibrated OSPW extract were employed as the calibration standards. The NAFCs calibrated with Fluka NA mixture and OSPW extract had clear linear relationships. The concentrations of NAFCs obtained using OSPW extract standard curve were 2.5 times the NAFC concentrations obtained using the Fluka NA mixture standard curve. Additionally, good linear correlations were observed between the total NAs and O 2 -O 6 NA species determined by ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry (UPLC-TOFMS) and the NAFCs measured by FTIR. According to these correlations, the NA compositions in NAFCs were developed, and the relative abundances of O 2 -O 6 NA species in NAFCs were similar for SPE and LLE pretreated samples. The findings of this study demonstrated that FTIR could be used as a promising tool to monitor total NA species and to estimate the NA profile in different environmental water samples. Unlabelled Image • We compared FTIR and UPLC-TOFMS with different extraction methods (LLE and SPE). • SPE produced higher recoveries of NAFCs than LLE for most water samples. • Higher NAFC concentrations were produced with OSPW extract than those with Fluka. • Good linear correlations were observed between UPLC-TOFMS and FTIR. • FTIR provided fast and accurate estimation of the NA species composition. [ABSTRACT FROM AUTHOR]

This work investigated the activation of peroxymonosulfate by electrochemical (EC) system assisted with Fe(III)-nitrilotriacetic acid (NTA) complex for degradation of persistent naphthenic acids (NAs) under neutral initial pH conditions. As NAs are a complicated mixture, 1-adamantanecarboxylic acid (ACA) was selected as the model NA compound for degradation experiment. The addition of NTA is to chelate with Fe(III), gaining stability under neutral pH condition to facilitate the circulation of Fe(II)/Fe(III) by the electrochemical process to activate PMS. The EC/Fe(III)-NTA/PMS system was explored with applicable pH range of 3–9 and an optimized molar ratio 1: 2 for Fe: NTA. Results of quenching and chemical probe experiment together with results of electron paramagnetic resonance (EPR) analysis revealed the main reactive species of the system, including •OH, SO 4 •−, 1O 2 and possibly Fe(IV). With the addition of NTA, the yields of •OH, SO 4 •−, 1O 2 were enhanced. Results of mass spectrometry analysis and DFT calculations indicated the formation of 9 degradation byproducts of ACA via three primary degradation pathways such as hydroxyl substitution, carbonyl substitution, and decarboxylation. Furthermore, the EC/Fe(III)-NTA/PMS system could achieve excellent removal efficiency of ACA with different anions such as Cl-, HCO 3 -, NO 3 - and H 2 PO 4 - in the background. The practical applicability of the system was also verified with the high removal of commercial NAs mixture standard. Overall results have indicated the EC/Fe(III)-NTA/PMS system could be utilized for efficient reclamation of authentic oil and gas industrial wastewater under natural pH conditions. [Display omitted] • The EC/Fe(III)-NTA/PMS system was explored with applicable pH range 3–9. • The redox cycle of Fe(III)-NTA/Fe(II)-NTA was boosted to activate PMS. • Fe(II)-NTA complex maintains high reaction rates to activate PMS at neutral pH. • •OH, SO 4 •−, 1O 2 and Fe(IV) are the main reactive species in the system. • ACA degradation pathways and byproducts were revealed based on mass spectra. [ABSTRACT FROM AUTHOR]

Oil sands process water (OSPW) contains complex components of inorganics and organics. This is the first study that separated OSPW inorganic and organic fractions and examined their relative acute toxicity when compared with the original whole OSPW using an in-vitro cell-based bio-indicator system. The separation of OSPW inorganic and organic fractions would be conducive to the understanding of the toxic contribution of organic and inorganic fractions as well as the identification and treatment of organic fractions. In this research, we demonstrated that the highest organic fraction extraction was obtained using HLB solid phase extraction with 95.4 ± 0.7% of dissolved organic carbon (DOC) and 90.0 ± 5.3% of naphthenic acid (NA) recovered from OSPW, which were higher than those obtained using the traditional dichloromethane liquid-liquid extraction (48.8 ± 0.2% of DOC and 81.0 ± 2.6% of NA recovery) or other SPE cartridges tested. We also reported the first isolation method for OSPW inorganic fraction by removing 96.1 ± 0.2% of DOC in OSPW using granular activated carbon. The difference of other parameters such as pH, alkalinity, conductivity, and concentration of detected ions between OSPW and isolated inorganic fraction was negligible. The acute toxicity of whole OSPW, separated OSPW inorganic fraction and organic fraction, and the reconstituted fractions were assessed using in-vitro bioassays with RAW 264.7 mouse macrophage cell lines. OSPW organic fraction demonstrated significant cytotoxicity at 14 mg/L O 2 -NA and affected the cellular metabolic activity at 10 mg/L of O 2 -NAs. No significant cytotoxicity or effect on cellular metabolic activity was observed for whole OSPW, OSPW inorganic fraction and the reconstituted fractions. Overall, this study provides the procedure for the isolation of the major components of OSPW (i.e., organics and inorganics), which allows the assessment of their relative toxicological effects using a standard in-vitro bioassay and would allow more accurate characterization and treatment study for each fraction in OSPW. Unlabelled Image • HLB cartridge effectively recovered DOC and NAs from oil sands process water (OSPW). • HLB cartridge was able to extract O 2 – to O 5 –NAs. • GAC effectively removed the organics in OSPW and isolated the OSPW inorganics. • Isolated OSPW organics showed enhanced cytotoxicity compared to whole OSPW. [ABSTRACT FROM AUTHOR]