Biodegradation and detoxification of naphthenic acids in oil sands process affected waters

High-efficiency effect-directed analysis (EDA) advancing toxicant identification in aquatic environments: Latest progress and application status

Facing the great threats to ecosystems and human health posed by the continuous release of chemicals into aquatic environments, effect-directed analysis (EDA) has emerged as a powerful tool for identifying causative toxicants. However, traditional EDA shows problems of low-coverage, labor-intensive and low-efficiency. Currently, a number of high-efficiency techniques have been integrated into EDA to improve toxicant identification. In this review, the latest progress and current limitations of high-efficiency EDA, comprising high-coverage effect evaluation, high-resolution fractionation, high-coverage chemical analysis, high-automation causative peak extraction and high-efficiency structure elucidation, are summarized. Specifically, high-resolution fractionation, high-automation data processing algorithms and in silico structure elucidation techniques have been well developed to enhance EDA. While high-coverage effect evaluation and chemical analysis should be further emphasized, especially omics tools and data-independent mass acquisition. For the application status in aquatic environments, high-efficiency EDA is widely applied in surface water and wastewater. Estrogenic, androgenic and aryl hydrocarbon receptor-mediated activities are the most concerning, with causative toxicants showing the typical structural features of steroids and benzenoids. A better understanding of the latest progress and application status of EDA would be beneficial to further advance in the field and greatly support aquatic environment monitoring.

Microbial degradation of naphthenic acids using constructed wetland treatment systems: metabolic and genomic insights for improved bioremediation of process-affected water

Naphthenic acids (NAs) are a complex mixture of organic compounds released during bitumen extraction from mined oil sands that are important contaminants of oil sands process-affected water (OSPW). NAs can be toxic to aquatic organisms and, therefore, are a main target compound for OSPW. The ability of microorganisms to degrade NAs can be exploited for bioremediation of OSPW using constructed wetland treatment systems (CWTS), which represent a possible low energy and low-cost option for scalable in situ NA removal. Recent advances in genomics and analytical chemistry have provided insights into a better understanding of the metabolic pathways and genes involved in NA degradation. Here, we discuss the ecology of microbial NA degradation with a focus on CWTS and summarize the current knowledge related to the metabolic pathways and genes used by microorganisms to degrade NAs. Evidence to date suggests that NAs are mostly degraded aerobically through ring cleavage via the beta-oxidation pathway, which can be combined with other steps such as aromatization, alpha-oxidation, omega-oxidation, or activation as coenzyme A (CoA) thioesters. Anaerobic NA degradation has also been reported via the production of benzoyl-CoA as an intermediate and/or through the involvement of methanogens or nitrate, sulfate, and iron reducers. Furthermore, we discuss how genomic, statistical, and modeling tools can assist in the development of improved bioremediation practices.

Aerobic degradation of anionic polyacrylamide in oil sands tailings: Impact factor, degradation effect, and mechanism

An investigation was carried out to study the degradation of anionic polyacrylamide (A-PAM) under different temperature and microorganism conditions as well as to assess its effects on water chemistry and toxicity in oil sands tailings. The maximum removal efficiency of A-PAM was 41.0 % in tailings water with augmented microorganisms at 20 °C. No acrylamide (AMD) monomer was released during the A-PAM degradation, while residual AMD, from the manufacturing process to make A-PAM, was completely removed within 4 weeks. Both temperature and microorganisms showed significant effects (p < 0.05) on the degradation of A-PAM and residual AMD. Gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR) analyses showed that biodegradation could be the active pathway for A-PAM degradation in oil sands tailings. These analyses also indicated that macromolecular A-PAM was degraded into lower molecular weight organic compounds. No remarkable changes of the total concentration of naphthenic acids (NAs) were observed in A-PAM treated tailings water. However, low concentrations of fatty acids (<2.5 mg/L), which fit the NAs formula, were detected in pure polymer solution, indicating that A-PAM degradation would not affect the total concentration of NAs in tailings water but affect their distribution. Our results also showed that total organic carbon (TOC) and chemical oxygen demand (COD) could be used as indicators of A-PAM degradation in tailings water due to their strong linear correlations (R² > 0.90). Only slight increases in zeta potential and pH were found during A-PAM degradation. Limited effect on acute toxicity and no genotoxicity were found in A-PAM treated tailings water. Furthermore, the results suggest that A-PAM undergoes hydrolysis of amide groups by amidase enzymes, releasing ammonia and smaller molecules like organic acids. This research provides valuable information regarding the stability and impacts of A-PAM and thus will be beneficial for the management of oil sands tailings in long period of time.

Effects of asphaltenes on the photolytic and toxic behavior of bitumen and conventional oil products on saltwater

The effects of asphaltenes on the photolytic and toxic behavior of petroleum oil on seawater was investigated by exposing five original oils and their maltenes to solar irradiation for seven days. Polycyclic aromatic hydrocarbons (PAHs) experienced the fastest photo-oxidation, but negligible photolytic loss was observed for most normal alkanes and all the petroleum biomarkers from tri-cyclic to pentyl-cyclic terpanes in the test total oil and maltenes. The removal of most PAHs from some maltenes was greater than the corresponding total oils. Deasphalting process did not affect the characteristics of naphthenic acid fraction components (NAFCs) in all control samples. In all test oils, solar irradiation formed abundant NAFCs, in particular those only containing oxygen as the heteroatoms (O_o species). The formed O_o species were abundant in congeners having highly saturated congeners, and shifted to a lighter carbon number after exposed. Deasphalting process significantly enhanced the formation of O_o species (o from 2 to 4) for all test oils, in particular for the Cold Lake Blend and Bunker C. The toxicity of exposed maltenes was generally higher than the exposed total oil for most oils, suggesting the aqueous toxicity level was positively related to the formed NAFC intermediates.

Transformation of bitumen-derived naphthenic acid fraction compounds across surface waters of wetlands in the Athabasca Oil Sands region

Bitumen is extracted from oil sands in the Athabasca Oil Sands region (AOSR) of Alberta, Canada. Much of the bitumen-derived toxicity in mine waste is attributable to naphthenic acid fraction compounds (NAFCs). Mines in the AOSR are required to be returned to a natural state after closure; thus, cost-effective strategies are needed to reduce toxicity from NAFCs. Previous studies have demonstrated the capability of constructed wetlands to attenuate NAFCs. However, the capacity of wetlands in the natural environment to degrade and transform NAFCs to less toxic components is poorly understood. To better understand the spatial distribution and fate of NAFCs in natural wetlands, samples were collected across the surfaces of two mature opportunistic wetlands near active oil sands mines. The first wetland has a well-defined surface flow pathway and inflows affected by overburden containing lean bitumen ore. The second wetland, in contrast, is a stagnant water body with raw bitumen visible along its edges. For the wetland with a well defined flow path, NAFCs decreased in concentration down gradient, while oxidized NAFCs constituted a greater proportion of NAFCs with increase in flow path. Likewise there was a decrease in the molecular weights of NAFCs, similar to trends observed in constructed wetland treatment systems. In comparison, NAFCs were more uniformly distributed across the relatively stagnant wetland. Overall, these data provide new evidence that mature opportunistic wetlands in the AOSR can promote the degradation and oxidation of bitumen-derived naphthenic acids into less toxic compounds.

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 O_xS₁ 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.

Detection of naphthenic acid uptake into root and shoot tissues indicates a direct role for plants in the remediation of oil sands process-affected water

Bitumen extraction from surface-mined oil sands deposits results in the accumulation of large volumes of oil sands process-affected water (OSPW). Naphthenic acids (NAs) are primary contributors to OSPW toxicity and have been a focal point for the development of OSPW remediation strategies. Phytoremediation is an approach that utilizes plants and their associated microbes to remediate contaminants from soil and groundwater. While previous evidence has indicated a role for phytoremediation in OSPW treatment through the transformation and degradation of NAs, there are no reports that demonstrate the direct uptake of NAs into plant tissue. Using NAs labelled with ¹⁴C radioisotopes (¹⁴C-NAs) paired with whole-plant autoradiography, we show that NAs representing aliphatic (linear), single-ring, and diamondoid compounds were effectively removed from hydroponic solution and OSPW-treated soil by sandbar willow (Salix interior) and slender wheatgrass (Elymus trachycaulus) and their associated microbiomes. The NA-derived ¹⁴C label accumulated in root and shoot tissues of both plant species and was concentrated in vascular tissue and rapidly growing sink tissues, indicating that ¹⁴C-NAs or their metabolic derivatives were incorporated into physiological processes within the plants. Slender wheatgrass seedlings grown under axenic (sterile) hydroponic and soil conditions also effectively removed all ¹⁴C-NAs, including a highly stable diamondoid NA, demonstrating that plants can directly take up simple and complex NAs without the assistance of microbes. Furthermore, root and shoot tissue fractionation into major biomolecule groups suggests that NA-derived carbon is allocated toward biomolecule synthesis rapidly after NA treatment. These findings provide evidence of plant-mediated uptake of NAs and support a direct role for plants and their associated microbes in the development of future large-scale OSPW phytoremediation strategies.

Co-biodegradation of naphthenic acids in anoxic denitrifying biofilm reactors

Anoxic co-biodegradation of linear and cyclic naphthenic acids (NAs) namely octanoic acid, trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), cis- and trans-4-methyl-1-cyclohexane-acetic acids (cis-4MCHAA and trans-4MCHAA) was investigated in denitrifying biofilm reactors. In all evaluated compositions, co-biodegradation of NAs was coupled to denitrification, with octanoic acid showing the fastest biodegradation rate (1180.4 mg L^-1 h^-1 at loading rate of 1180.4 mg L^-1 h^-1), followed by trans-4MCHCA (398.1 mg L^-1 h^-1 at loading rate of 435.8 mg L^-1 h^-1), trans-4MCHAA (25.7 mg L^-1 h^-1 at loading rate of 221.7 mg L^-1 h^-1), and cis-4MCHAA (5.3 mg L^-1 h^-1 at loading rate of 16.9 mg L^-1 h^-1). Biodegradation of octanoic acid and trans-4MCHCA were not influenced by the presence of recalcitrant NAs (cis- and trans-4MCHAA). Co-biodegradation of cis- and trans-4MCHAA with octanoic acid, trans-4MCHCA, or their combination enhanced the biodegradability of these recalcitrant NAs, with the positive impact being more pronounced for trans-4MCHCA. Finally anoxic co-biodegradation of NAs under denitrifying conditions proceeded at rates that were faster than the aerobic rates obtained in similar mixtures. Anoxic biodegradation, therefore, is an effective alternative for in situ treatment of oil sands process water in anoxic stabilization ponds amended with nitrate, or as an ex situ treatment approach in denitrifying bioreactors whereby the cost and technical challenges of aeration are eliminated.

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.

Bioaccumulation potential of naphthenic acids and other ionizable dissolved organics in oil sands process water (OSPW) - A review

Bitumen recovery via mining in Alberta's Athabasca region generates large quantities of oil sands process water (OSPW). Aquatic toxicity of OSPW has been well-studied and the class of organic compounds referred to as naphthenic acids (NAs) are consistently implicated as the primary driver. Proposed lease closure options include treated produced waters in reclaimed landscapes such as pit lakes and wetlands. Consequently, it is crucial to understand the bioaccumulation potential of NAs and other OSPW dissolved organics in these environments. Early studies were focussed only on NAs due to analytical limitations, however, later studies investigated additional classes of dissolved organics in OSPW. Reported bioconcentration factors (BCFs) for NAs in fish and amphibians range from 0.24 to 53 L/kg wet-weight. Most quantitative assessments of NAs bioaccumulation potential evaluated commercial NAs mixtures as a surrogate for OSPW and used using single-ion monitoring for measuring NAs concentrations. The resulting BCF values are based on the NA isomers that conform to the formula, C₁₃H₂₂O₂. More recently, an advanced analytical technique capable of determining the profile of different isomer classes in OSPW showed that NAs and other OSPW ionizable dissolved organics (OSPW-IDO) have low partitioning to simulated biological storage lipids, suggesting low bioaccumulation potential. Using the same analytical technique to assess in vivo fish exposures, a subsequent study reported a range of BCFs for OSPW NAs between 0.7 and 53 L/kg wet-weight and heteroatomic isomer classes containing S or N heteroatoms had BCFs between 0.6 and 28 L/kg wet-weight. Reported BCFs for all isomer classes of the OSPW-IDO fraction were less than the Canadian standard for bioaccumulative designation (i.e., BCF ≥ 5000).

Method for routine "naphthenic acids fraction compounds" determination in oil sands process-affected water by liquid-liquid extraction in dichloromethane and Fourier-Transform Infrared Spectroscopy

Formerly classified as naphthenic acids, "naphthenic acids fraction compounds" (NAFC) have become the subject of increasing research, in particular in view of their ubiquitous presence in the Canadian oil sands of Northern Alberta and oil sands process-affected waters (OSPW). NAFC, defined herein as the polar acid-extractable organics fraction of OSPW extractable in dichloromethane, are released into OSPW during the aqueous extraction of oil sands. A method for determining total NAFC concentration based on acidification, liquid-liquid extraction, and Fourier-Transform Infrared Spectroscopy (FT-IR) was developed by Jivraj et al. in 1995. It has become widely used in the oil sands industry for routine monitoring of NAFC. Since then, multiple variations of the method are practiced by different laboratories using different calibration materials and different extraction solvents, differences which were found to affect the results by as much as 38 and 64 percent respectively. The goal of this study was to establish a robust method for routinely quantifying NAFC that does not require complex and expensive laboratory equipment such as mass spectrometers. Described improvements include a semi-automated rolling extraction and the use of a vacuum evaporator unit to reduce the method's environmental impact. The improved FT-IR method avoids emulsions, is precise, provides good agreement with gravimetric determinations of NAFC, increases sample throughput, is inexpensive compared to MS methods, and offers a typical reporting limit of 0.1 mg kg^-1. The residue recovered by this method with minimal losses can be further analyzed by MS techniques to characterize and identify individual NAFC components if desired.

Bioreactors for oil sands process-affected water (OSPW) treatment: A critical review

Canada has the world's largest oil sands reservoirs. Surface mining and subsequent caustic hot water extraction of bitumen lead to an enormous quantity of tailings (volumetric ratio bitumen:water=9:1). Due to the zero-discharge approach and the persistency of the complex matrix, oil producers are storing oil sands tailings in vast ponds in Northern Alberta. Oil sands tailings are comprised of sand, clay and process-affected water (OSPW). OSPW contains an extremely complex matrix of organic contaminants (e.g., naphthenic acids (NAs), residual bitumen, and polycyclic aromatic hydrocarbons (PAHs)), which has proven to be toxic to a variety of aquatic species. Biodegradation, among a variety of examined methods, is believed to be one of the most cost effective and practical to treat OSPW. A number of studies have been published on the removal of oil sands related contaminants using biodegradation-based practices. This review focuses on the treatment of OSPW using various bioreactors, comparing bioreactor configurations, operating conditions, performance evaluation and microbial community dynamics. Effort is made to identify the governing biotic and abiotic factors in engineered biological systems receiving OSPW. Generally, biofilms and elevated suspended biomass are beneficial to the resilience and degradation performance of a bioreactor. The review therefore suggests that a hybridization of biofilms and membrane technology (to ensure higher suspended microbial biomass) is a more promising option to remove OSPW organic constituents.

Fate of oxygenated intermediates in solar irradiated diluted bitumen mixed with saltwater

Two types of diluted bitumen (dilbit) and a light crude oil spiked onto the surface of saltwater were irradiated with natural solar light in Ottawa to assess the impact of sunlight to the fate of oxygenated intermediates. Oxygenated components, including carbonyl polycyclic aromatic hydrocarbons (PAHs) and acidic polar fractions (naphthenic acid fraction compounds, NAFCs), were identified after periods of solar exposure under both winter and summer conditions. Carbonyl PAHs and NAFCs were formed in both seasons; however, light crude and summer irradiation produced higher abundance of them than dilbits and winter exposure. The formed NAFCs were abundant with the congeners containing a heteroatom of oxygen only (O_o species), accompanied by the minor amounts of sulfur- and nitrogen-containing acids. The produced O_o species were predominant with the congeners with light molecular weight, high degree of saturation and heavy oxygen numbers. For both carbonyl PAHs and NAFCs, their abundance continually increased throughout the period of winter exposure. In the summer, some carbonyl PAHs and all O_o species increased during the early exposure period; then they decreased with continued exposure for most oils, illustrating their transitional nature. Oxygenated intermediates thus appear to have been created through the photo-oxidation of non-to medium-polar petroleum hydrocarbons or the intermediates of aldehydes or ketones (O₁). Oil properties, the duration of exposure, exposure season and the chemical structure of these intermediates are critical factors controlling their fate through photo-oxidation. The observed chemical changes highlight the effects of sunlight on the potential behavior, fate and impact of spilled oil, with the creation of new resin group compounds and the reduction of aromatics and saturates. These results also imply that the ecological effects of spilled oil, after ageing in sunlight, depend on the specific oil involved and the environmental conditions.

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.

Chemical Fate of Photodegraded Diluted Bitumen in Seawater

Diluted bitumen (dilbit), an oil sands product, may present new response challenges differing from conventional crude oil in terms of its potential environmental impacts. Simple naphthenic acids (NAs), a complex group of monocarboxylic acids, with a general formula CnH2n+zO2, may be present in the source bitumen or may be created by photolytic weathering. Knowing the composition and concentrations of NAs created during the photo-degradation process of dilbit will help understand the fate, behavior and toxicity of dilbit.

In the present study, two diluted bitumen products, Cold Lake Blend (CLB) and Access Western Blend (AWB), were mixed with saltwater and irradiated with natural solar light (Ottawa, Canada, 45.4°N) over winter and summer seasons, to assess the impact of sunlight on the chemical fate of the dilbit. For comparison, a light, sweet crude oil was exposed under similar conditions. The samples were analyzed by high performance liquid chromatography-high resolution mass spectrometry to examine the molecular transformation of diluted bitumen by solar irradiation. The abundances of NAs in all three test oils increased significantly after 90 days of solar irradiation, strongly suggesting that polar NAs were formed by photolysis. Further, greater increases in NAs in the light crude were found than in the two dilbits. Similarly, the lighter oil had higher photolytic removal rates of petroleum hydrocarbons than the two dilbits.

The concentrations of NAs in oils exposed during the summer were generally higher than those exposed in winter. During summer exposure, the abundance of total NAs increased up to the 30-day’s solar exposure, then fell again, indicating the transient nature of these compounds. However, net increases in polar NA compounds were observed for all the winter exposed samples. Greater increases were observed in the smaller NA compounds (average C-number decreased), also accompanied by an increase in saturation (average z-number decreased).

These chemical changes strongly indicate the effect of sunlight on the potential behaviour, fate and effects of spilled oil, with creation of new resin group compounds and reduction of aromatics and saturates. These changes may affect the viscosity of the oil and its ability to uptake water. These chemical compositions also imply significant changes to the ecological effects of the oil following a spill when aged in sunlight.