Z-scheme plasmonic Ag decorated Bi2WO6/NiO hybrids for enhanced photocatalytic treatment of naphthenic acids in real oil sands process water under simulated solar irradiation.

A novel photocatalyst, Bi2WO6/NiO/Ag, with hierarchical flower-like Z-scheme heterojunction, which exhibited excellent stability and photocatalytic activity over a wide light spectrum, was firstly synthesized and used in the remediation of real oil sands process water (OSPW) and achieved complete removal of aromatics, classical naphthenic acids (NAs), and heteroatomic NAs after 6 h of photocatalytic treatment. The acute toxicity of OSPW was completely eliminated after only 2 h of treatment. h+ and ∙OH were found to be the major oxidative species in the photocatalytic system. The enhanced photocatalytic efficiency is the result of the unique Z-scheme electron transfer among electron mediators Ag, NiO, and Bi2WO6, which was supported by the in-situ irradiated XPS. The study benefits the design of engineered passive treatment approach for OSPW remediation through solar light-driven catalyst.

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review.

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH2Cl- and ClO2-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.

Sorption and desorption of naphthenic acids on reclamation materials: Mechanisms and selectivity of naphthenic acids from oil sands process water.

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.

Review on carbon-based adsorbents from organic feedstocks for removal of organic contaminants from oil and gas industry process water: Production, adsorption performance and research gaps.

Large amounts of process water with considerable concentrations of recalcitrant organic contaminants, such as polycyclic aromatic hydrocarbon (PAHs), phenolic compounds (PCs), and benzene, toluene, ethylbenzene, and xylene (BTEX), are generated by several segments of oil and gas industries. These segments include refineries, hydraulic fracturing (HF), and produced waters from the extraction of shale gas (SGPW), coalbed methane (CBMPW) and oil sands (OSPW). In fact, the concentration of PCs and PAHs in process water from refinery can reach 855 and 742 mg L-1, respectively. SGPW can contain BTEX at concentrations as high as 778 mg L-1. Adsorption can effectively target those organic compounds for the remediation of the process water by applying carbon-based adsorbents generated from organic feedstocks. Such organic feedstocks usually come from organic waste materials that would otherwise be conventionally disposed of. The objective of this review paper is to cover the scientific progress in the studies of carbon-based adsorbents from organic feedstocks that were successfully applied for the removal of organic contaminants PAHs, PCs, and BTEX. The contributions of this review paper include the important aspects of (i) production and characterization of carbon-based adsorbents to enhance the efficiency of organic contaminant adsorption, (ii) adsorption properties and mechanisms associated with the engineered adsorbent and expected for certain pollutants, and (iii) research gaps in the field, which could be a guidance for future studies. In terms of production and characterization of materials, standalone pyrolysis or hybrid procedures (pyrolysis associated with chemical activation methods) are the most applied techniques, yielding high surface area and other surface properties that are crucial to the adsorption of organic contaminants. The adsorption of organic compounds on carbonaceous materials performed well at wide range of pH and temperatures and this is desirable considering the pH of process waters. The mechanisms are frequently pore filling, hydrogen bonding, π-π, hydrophobic and electrostatic interactions, and same precursor material can present more than one adsorption mechanism, which can be beneficial to target more than one organic contaminant. Research gaps include the evaluation of engineered adsorbents in terms of competitive adsorption, application of adsorbents in oil and gas industry process water, adsorbent regeneration and reuse studies, and pilot or full-scale applications.

Decomplexation of Cu(II)-EDTA by synergistic activation of persulfate with alkali and CuO: Kinetics and activation mechanism.

Heavy metals usually coexist with a variety of chelating agents to form heavy metal complexes in industrial wastewater. The decomplexation of heavy metal complexes is the crucial step before the removal of heavy metals via alkaline precipitation process. An efficient synergistic activation of persulfate (PS) with alkali and CuO was used for the simultaneous decomplexation of Cu-ethylenediamine tetraacetic acid (Cu(II)-EDTA) (3.14 mM) and the Cu(II) precipitation. The experimental results demonstrated that nearly complete removal of Cu(II) could be achieved by synergistic activation of PS with alkali and CuO at pH 11 after 2 h of decomplexation reaction. However, sole PS could not effectively decomplex Cu(II)-EDTA (13.5%), while the alkaline activation of PS could accomplish 57.0% removal of Cu(II). Radical scavenger tests indicated that reactive oxygen species (ROS) including SO4•-, •OH and O2•- were responsible for the decomplexation of Cu(II)-EDTA in the synergistic activation of PS with alkali and CuO. As a heterogeneous activator, CuO possessed excellent reusability and long-lasting catalytic activity and the rate constant value (k) of Cu(II) removal showed an increase (from 0.0326 min-1 in the first cycle to 0.0491 min-1 in the 24th cycle) with 24 cycles experiments. Furthermore, the biotoxicity evaluation of treated solution revealed that the biotoxicity of Cu(II)-EDTA contaminated wastewater could be effectively mitigated by the synergistic activation of PS with alkali and CuO because of the efficient precipitation of Cu(II) and oxidative degradation of EDTA organic ligands, which was favorable for the subsequent biochemical treatment.

The treatment of electroplating wastewater using an integrated approach of interior microelectrolysis and Fenton combined with recycle ferrite.

Heavy metal ions in chelated forms have aroused great concerns because of their high solubility, poor biodegradation and extreme stability. In this research, an efficient strategy, interior microelectrolysis-Fenton-recycle ferrite (IM-Fenton-RF), was developed to treat simulated electroplating wastewater containing chelated copper at room temperature. The decomplexation of chelated copper was carried out by both interior microelectrolysis and Fenton reactions. IM process can not only partly degrade the complexes of chelated copper via the microelectrolysis reaction but also it produces Fe2+ ions for the Fenton reaction. After decomplexation, the IM-Fenton effluent directly flowed into the RF reactor for copper ions removal. Under optimum reaction conditions (reflux ratio = 0.37, Fe2+ concentration = 9.20 g/L at pH 10.18), 99.9% copper was removed by the IM-Fenton-RF system. The produced IM-Fenton-RF sludge is based on ferrite precipitate and has several advantages over metal hydroxides sludge. Ferrite sludge is stable owing to the stability of ferrite's crystal structure, while the toxicity characteristic leaching procedure (TCLP) test meets relevant standards. The sedimentation rate and volume of ferrite sludge were 3.86 times faster and 11.0 times lower than those of metal hydroxides sludge. Furthermore, the yielding sludge of ferrite can be recovered and utilized for the synthesis of Fe-C metallic species, the main compound of IM packing for interior microelectrolysis reaction. All these results show that a combination of IM-Fenton and RF is an effective approach to treat wastewater containing chelated copper, showing great potential for industrial applications.

Influences of integrated coagulation-ozonation pretreatment on the characteristics of dissolved organic pollutants (DOPs) of heavy oil electric desalting wastewaters.

The quality of heavy oil electric desalting wastewaters (HO-EDWs) affects the effectiveness of refinery wastewater treatment plants. In this study, an integrated coagulation-ozonation (ICO) process was used to pretreat HO-EDWs and the influences on the characteristics of dissolved organic pollutants (DOPs) were investigated. Coagulation using aluminum sulfate removed 39% of soluble chemical oxygen demand (SCOD), 21% of dissolved organic carbon (DOC), 57% of petroleum hydrocarbons and 38% of polar oils from Liaohe HO-EDWs and the biodegradability was greatly improved. Ozonation removed 33% of SCOD and 88% of polar oils from the coagulated HO-EDWs. Most species of aromatic compounds, phenols, aliphatic acids, anilines and naphthenic acids with high C numbers and ring numbers were degraded and the unsaturation degrees of DOPs significantly decreased under ozonation. As a result, the biodegradability was further improved and the acute toxicity towards Vibrio fischeri was substantially reduced. Some OxS1 species and organic nitrogen compounds in HO-EDWs were penetrated through ozonation and caused the residual biotoxicity. The results demonstrate the potential of ICO pretreatment for improving the quality of refractory HO-EDWs.

Influences of coagulation pretreatment on the characteristics of crude oil electric desalting wastewaters.

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 Ox 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.

The removal of Cu(II)-EDTA chelates using green rust adsorption combined with ferrite formation process.

Classical adsorbents such as activated carbon are inefficient to remove Cu(II)-EDTA in solution. Moreover, the heavy metals in the generated sludge can easily be dissolved back into solution. In this research, a novel strategy developed by coupling green rust adsorption and ferrite formation technology was proposed for Cu(II)-EDTA chelate removal. At the adsorption stage, green rust sulfate (GRME(SO42-)) showed a high adsorption efficiency of chelated copper, with a capacity of 126.41 mg g-1, compared to other classical adsorbents. During the ferrite formation stage, GRME(SO42-)-based precipitate with high moisture content and slow settling rate could be transformed into ferrite-based precipitate with low moisture content and rapid settling rate. The volume and moisture content of ferrite were 2.20 and 1.45 times lower than those of GRME(SO42-) and the sedimentation velocity of ferrite was also 1.23 times higher than that of GRME(SO42-), which strongly demonstrated the necessity of the ferrite formation process. Toxicity characteristic leaching procedure (TCLP) test results showed that the metallic copper of GRME(SO42-) sludge could be more easily dissolved back into solution than that of ferrite precipitate under weak-acid conditions, indicating the stability of ferrite. In addition, after the ferrite process, the generated sludge exhibited soft magnetism and could be quickly separated within few seconds using an external magnetic field. All these results showed that the combined green rust adsorption with ferrite formation method was an efficient, recyclable and eco-friendly method for the treatment of wastewater containing Cu(II)-EDTA.

Molecular transformation of dissolved organic matter in process water from oil and gas operation during UV/H2O2, UV/chlorine, and UV/persulfate processes.

This paper reported the impact of UV/H2O2, 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.

Fourier transform infrared spectroscopy as a surrogate tool for the quantification of naphthenic acids in oil sands process water and groundwater.

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 O2-O6 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 O2-O6 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.

Comprehensive chemical analysis and characterization of heavy oil electric desalting wastewaters in petroleum refineries.

Large quantities of highly polluted point-source wastewaters (EDWs) are generated from electric desalting process of heavy oils (HOs), resulting in severe impacts on the efficiency of wastewater treatment plants in petroleum refineries. In the present study, a comprehensive chemical analysis and characterization of EDWs of two typical Chinese heavy oils, Liaohe heavy oil (LHO) and Karamy heavy oil (KHO), were investigated using Daqing light oil (DLO) as a control. The HO-EDWs (LHO-EDW and KHO-EDW) show high pollutants contents with complicated compositions, more polar dissolved organic pollutants (DOPs), strong emulsion stability and high acute biotoxicity towards Vibrio fischeri, compared to DLO-EDW. LHO-EDW and KHO-EDW have nearly equal pollutants contents but different compositions and distributions, where more types of DOPs exist in KHO-EDW. Large amounts of biologically recalcitrant aromatic compounds, as well as heteroatomic compounds such as CHO, CHOS and CHON species, extensively distribute in HO-EDWs. The organic nitrogen compounds (e.g., anilines and N2-3Ox, N1OxS1) in KHO-EDW most probably contribute to and thus leading to elevated levels of acute biotoxicity. Additionally, highly dispersed colloidal, micron-sized particles and polar compounds promote the emulsification and stabilization of HO-EDWs. These results can guide the development of pretreatment technologies for HO-EDWs, thus improving the treatment and management of heavy oil refineries' wastewater streams.

Comparison of UV/Persulfate and UV/H2O2 for the removal of naphthenic acids and acute toxicity towards Vibrio fischeri from petroleum production process water.

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/H2O2 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/H2O2 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 O2-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 O2-, O3-, and O4-NAs, respectively) with 2 mM of persulfate, because of the formation of oxidized NAs in the same process. The structure-reactivity of O2-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/H2O2 treatments. Overall results demonstrated that the UV/Persulfate oxidation can be an effective alternative for future reclamation of OSPW.

Ferrate oxidation of distinct naphthenic acids species isolated from process water of unconventional petroleum production.

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 O2-NAs mainly found in fractions F1-F4), aromatic NAs (aromatic O2-NAs in F6-F9), oxidized NAs (O3-, O4-, and O5-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 O2-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 O3-NAs and O4-NAs from raw OSPW were recalcitrant species with slight degradation under Fe(VI) oxidation conditions. The Fe(VI) oxidation of O2-NAs generated new O3-NAs as byproducts or intermediate byproducts which finally resulted in more oxygen-rich Ox-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.

Assessment of ozonation reactivity of aromatic and oxidized naphthenic acids species separated using a silver-ion solid phase extraction method.

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 O2-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 O2-NAs (Fraction 3), aromatic O2-NAs (Fraction 8), O3-NAs (Fraction 11), and O4-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.

Degradation of naphthenic acid model compounds in aqueous solution by UV activated persulfate: Influencing factors, kinetics and reaction mechanisms.

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/H2O2 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/H2O2 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 (SO4-) 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/H2O2 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.

Monitoring of classical, oxidized, and heteroatomic naphthenic acids species in oil sands process water and groundwater from the active oil sands operation area.

The classical, oxidized, and heteroatomic naphthenic acids (NAs) species were monitored in the oil sands process water (OSPW) and groundwater from the active oil sands operation area, using solid phase extraction sample preparation and high resolution mass spectrometry analysis. Groundwater samples include Pleistocene channel aquifer groundwater (PLCA) and oil sands basal aquifer groundwater (OSBA) from different depth of underground. The concentrations of Ox-NAs decreased from OSPW to PLCA, and then increased from PLCA to OSBA, which is deeper than PLCA. The NAs in PLCA mainly comprised of Ox-NAs and N-NAs and the percentage of S-NAs was negligible. Results revealed relative abundances of individual NA species in total NAs varies among different water layers and the potential environmental impacts are expected to be variable. Principal component analysis results of O2-NAs or O4-NAs could be used for differentiation of water types. O2-NAs with n = 12-16 and |Z| = 4-6, and O4-NAs with n = 14-20 and |Z| = 6-8, were identified as marker compounds that could serve as surrogates of the larger complex NA mixture for source differentiation. This work utilized a combination of sample preparation, instrumental analysis, and statistical analysis methods to obtain knowledge of the occurrence, composition, and transfer of NAs in the groundwater of the Alberta oil sands operation area.

Characterization and determination of naphthenic acids species in oil sands process-affected water and groundwater from oil sands development area of Alberta, Canada.

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 Ox-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 O2 and O4 species could be employed for differentiation of water types, while classical NAs with C13-15 and Z (-4)-(-6) and aromatic O2-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.

Comparison of methods for determination of total oil sands-derived naphthenic acids in water samples.

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.

Fate and abundance of classical and heteroatomic naphthenic acid species after advanced oxidation processes: Insights and indicators of transformation and degradation.

The toxicological effects from all components in oil sands process-affected water (OSPW) are not known. Alternatively, monitoring the variations and abundance of different classes and compounds after treatments might be a useful approach in OSPW remediation. In this study, the variations in the compositions of classical and heteroatomic naphthenic acids (NAs) after treatment using advanced oxidation processes (AOPs), mainly ozone and peroxone, and two different mass spectrometry methods; ultra-performance liquid chromatography time-of-flight (UPLC-TOFMS) and Fourier transform ion cyclotron resonance (FTICR-MS), were examined. Two markers (O2S:O3S:O4S and O2:O4 ratios) were used to reveal changes and similarities of the treated water characteristics with those in natural waters. Both ratios decreased after all treatments, from 2.7:4.8:2.1 and 3.59 in raw OSPW to 0:1.4:0.5 and 0.7, respectively, in peroxone (1:2), becoming close to the reported ratios in natural waters. Toxicity toward Vibrio fischeri showed residual toxic effects after AOPs, suggesting that part of OSPW toxicity may be caused by specific compounds of NAs (i.e., similar reduction (50%) was achieved in both toxicity and abundance in O2 species with carbon 15-26) and/or generated by-products (e.g., O3S classes at double bond equivalent (DBE) = 4 and C9H12O2 at DBE = 4). Although by-products were generated, the best biodegradability enhancement and chemical oxygen demand reduction were achieved in peroxone (1:2) compared to ozone, suggesting the possibility of using combined OSPW remediation approaches (i.e., peroxone coupled with biological process). The recommended indicators can assist in evaluating the treatments' performance and in examining the best removal levels to accomplish significant toxicity reduction.