Degradation Of Naphthenic Acids Research Articles

Biodegradation in oil sands process-affected water: A comprehensive laboratory analysis of the in situ biodegradation of dissolved organic acids

Oil sands process-affected water (OSPW) is a by-product of the extraction of bitumen, and volumes of OSPW have accumulated across the Alberta oil sands region due to the governments zero-discharge policy. Some dissolved organics in OSPW, including toxic naphthenic acids (NAs), can be biodegraded in oxic conditions, thereby reducing the toxicity of OSPW. While there has been much focus on degradation of NAs, the biodegradation of other dissolved organic chemicals by endogenous organisms remains understudied. Here, using the HPLC–ultrahigh resolution Orbitrap mass spectrometry, we examined the microbial biodegradation of dissolved organic acids in OSPW. Non-targeted analysis enabled the estimation of biodegradation rates for unique heteroatomic chemical classes detected in negative ion mode. The microcosm experiments were conducted with and without nutrient supplementation, and the changes in the microbial community over time were investigated. Without added nutrients, internal standard–adjusted intensities of all organics, including NAs, were largely unchanged. The addition of nutrients increased the biodegradation rate of O2− and SO2− chemical classes. While anoxic biodegradation can occur in tailings ponds and end pit lakes, microbial community analyses confirmed that the presence of oxygen stimulated biodegradation of the OSPW samples studied. We detected several aerobic hydrocarbon-degrading microbes (e.g., Pseudomonas and Brevundimonas), and microbes capable of degrading sulfur-containing hydrocarbons (e.g., Microbacterium). Microbial community diversity decreased over time with nutrient addition. Overall, the results from this study indicate that toxic dissolved organics beyond NAs can be biodegraded by endogenous organisms in OSPW, but reaffirms that biological treatment strategies require careful consideration of how nutrients and dissolved oxygen may impact efficacy.

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.

Fate of dissolved organics and generated sulfate ions during biofiltration of oil sands process water pretreated with sulfate radical advanced oxidation process

Fate of dissolved organics and sulfate ions was studied in fixed bed biofilters (FBBs) treating pre-treated oil sands process water (OSPW) in the presence of industrially relevant substrates namely petroleum coke (PC) and sand. For pre-treatment, the solar-activated sulfate radical advanced oxidation process (SR-AOP) was performed using 2.5 and 5 mM peroxymonosulfate (PMS) as a precursor with solar irradiation of 119.5 W h m−2. Excellent degradation of naphthenic acids (NAs) was attained by SR-AOP, attaining 88 % and 97 % total NAs after 9 h of treatment at 2.5 and 5 mM of PMS, respectively. However, the treatment increased the toxicity due to byproducts and metabolites following the poor removal of dissolved organics, i.e., 13 % and 21.5 %, respectively. Electron paramagnetic resonance spectrometry (EPR) analysis exhibited that hydroxyl radical (⋅OH) and singlet oxygen (1O2) were the predominant active species produced during SR-AOP. The post-treatment biofiltration improved the mineralization of dissolved organics (45 %) and NAs (99 %) as well as removed the residual toxicity (>80 %). Taxonomy-based transcriptomics analyses (RNA) confirmed the enrichment of microbes involved in the degradation of hydrocarbons and carboxylic acids, methylotrophy, and potentially C(1)-sulfur compounds metabolism. Scanning electron microscopy with energy-dispersive X-ray spectroscopy indicated the potential of PC to support sulfur deposition, but at slower rates. This study indicates that the produced water can be efficiently reclaimed by using advanced oxidation and biofiltration approaches.

Combined solar activated sulfate radical-based advanced oxidation processes (SR-AOPs) and biofiltration for the remediation of dissolved organics in oil sands produced water

• Effective degradation of dissolved organics in produced water by solar activated SR-AOPs. • SO 4 •− , • OH and 1 O 2 reactive species were formed during solar activated SR-AOPs. • Better performance by solar activated peroxymonosulfate compared to persulfate. • Excellent mineralization of dissolved organic by post-treatment biofilm filtration. • Microbial profiling indicated presence of hydrocarbons and carboxylic acid degraders. This study reported for the first time the potential of sequential solar activated sulfate radical advanced oxidation processes (SR-AOPs) and fixed bed biofiltration for the enhanced remediation of dissolved organics in oil sands process water (OSPW). The effect of initial sulfate precursors namely persulfate (PS) and monopersulfate (PMS) was examined on the degradation of naphthenic acid (NA) surrogates and various classes of organics in real OSPW. Effluents from solar activated SR-AOPs treatment of OSPW at specific conditions were subjected to biofiltration for 45 days. Fast and complete degradation of 5-phenylvalveric acid (PVA) and up to 99% degradation of various organics in OSPW were achieved by the solar activated SR-AOPs. Radical scavenger and spin-trap electroparamagnetic spectrometry analysis showed that hydroxyl ( • OH) and sulfate (SO 4 •− ) radicals were the major reactive species generated and participated in the oxidation of organics in SR-AOPs treatment with either PS or PMS along with a small proportion of singlet oxygen. The biofiltration post-treatment showed significant mineralization of dissolved organics in treated OSPW, achieving over 60% and 40% reduction in DOC and COD, respectively, surpassing most of the reported studies for such combined approach. The bacterial metataxonomic analysis indicated significant enrichment of hydrocarbons and carboxylic acid degraders ( Sphingomonas and Sphingopyxis ) in the biofilters treating PMS pre-treated OSPW. However, for biofilters treating raw OSPW and PS, the bacterial community was dominated by hydrocarbon degraders and methanotrophs. The treated OSPW was found completely non-toxic for the OSPW treated with PMS-9 h and biofiltration. This demonstrates the potential of combined treatment for the effective remediation of the oil sand industry effluent.

Insights into ultrasound-promoted degradation of naphthenic acid compounds in oil sands process affected water. Part II: In silico quantum screening of hydroxyl radical initiated and propagated degradation of benzoic acid

In Part I, we outlined the importance of sustainable sonochemical treatment to intensify oil sands process affected water (OSPW) treatment empirically and hypothesized degradation pathways. Herein, we elucidate the formation of intermediate products with well-defined molecular level solutions. Proposed mechanisms describe hydroxylation, decarboxylation and bond scission which drive the degradation of intermediates towards mineralization. This comprehensive first study on in silico screening of sonochemical degradation investigates quantum methods using density functional theory to explain the postulated degradation mechanisms through a theoretical radical attack approach, based on condensed Fukui reactivity indicators. A nudged elasticity band (NEB) approach is applied to find a minimum energy path (MEP), allowing the determination of intermediate products and energy barriers associated with naphthenic acid degradation. This approach provides structures and energies of the breakdown compounds formed along the reaction pathway enabling the determination of molecular reaction kinetics.In continuation of Part 1, the focus of this study is to evaluate sonochemically-induced hydroxyl radical (OH•) reactions of benzoic acid using density functional theory. Hydroxylation and decarboxylation mechanisms of the model naphthenic acid compound and its intermediates were simulated to determine the prospective pathway to ideal mineralization. DFT was applied to calculate interaction energies, Mulliken charges, Hirshfeld population analysis, dipole moments, frontier orbitals, and polarizability. Electronic properties and frontier orbital trends were also compared to computational work by Riahi et al.[1] to confirm the transition states by Nudged Elastic Band Transition State theory (NEB-TS). In combination with Hirshfeld Population analysis, Fukui indices suggest a more linear degradation pathway narrowed down from earlier experimental work by Singla et al.[2]. The linear free energy relationship for the newly suggested computational benzoic acid degradation can be determined by lnkTST/W=-1.677ΔG-15.41 with a R2 of 0.9997 according to classic transition state theory and Wigner tunneling. This computational method can be used to explore possible degradation pathways of other NAs and bridges molecular-to-macroscale sonochemical degradation of NA’s through a manifestation of molecular solutions.

Differential protein expression during growth on model and commercial mixtures of naphthenic acids in Pseudomonas fluorescens Pf-5.

Naphthenic acids (NAs) are carboxylic acids with the formula (C n H 2n + Z O2) and are among the most toxic, persistent constituents of oil sands process‐affected waters (OSPW), produced during oil sands extraction. Currently, the proteins and mechanisms involved in NA biodegradation are unknown. Using LC‐MS/MS shotgun proteomics, we identified proteins overexpressed during the growth of Pseudomonas fluorescens Pf‐5 on a model NA (4′‐n‐butylphenyl)‐4‐butanoic acid (n‐BPBA) and commercial NA mixture (Acros). By day 11, >95% of n‐BPBA was degraded. With Acros, a 17% reduction in intensity occurred with 10–18 carbon compounds of the Z family −2 to −14 (major NA species in this mixture). A total of 554 proteins (n‐BPBA) and 631 proteins (Acros) were overexpressed during growth on NAs, including several transporters (e.g., ABC transporters), suggesting a cellular protective response from NA toxicity. Several proteins associated with fatty acid, lipid, and amino acid metabolism were also overexpressed, including acyl‐CoA dehydrogenase and acyl‐CoA thioesterase II, which catalyze part of the fatty acid beta‐oxidation pathway. Indeed, multiple enzymes involved in the fatty acid oxidation pathway were upregulated. Given the presumed structural similarity between alkyl‐carboxylic acid side chains and fatty acids, we postulate that P. fluorescens Pf‐5 was using existing fatty acid catabolic pathways (among others) during NA degradation.

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.

Bacterial diversity in petroleum coke based biofilters treating oil sands process water

Adopting nature-based solutions for the bioremediation of oil sands process water (OSPW) is of significant interest, which requires a thorough understanding of how bacterial communities behave within treatment systems operated under natural conditions. This study investigates the OSPW remediation potential of delayed petroleum-coke (PC), which is a byproduct of bitumen upgrading process and is readily available at oil refining sites, in fixed-bed biofilters particularly for the degradation of naphthenic acids (NAs) and aromatics. The biofilters were operated continuously and total and active bacterial communities were studied by DNA and RNA-based amplicon sequencing in a metataxonomic fashion to extrapolate the underlying degradation mechanisms. The results of total community structure indicated a high abundance of aerobic bacteria at all depths of the biofilter, e.g., Porphyrobacter, Legionella, Pseudomonas, Planctomyces. However, redox conditions within the biofilters were anoxic (−153 to −182 mV) that selected anaerobic bacteria to actively participate in the remediation of OSPW, i.e., Ruminicoccus, Eubacterium, Faecalibacterium, Dorea. After 15 days of operation, the removal of classical NAs was recorded up to 20% whereas oxidized NAs species were poorly removed, i.e., O3-NAs: 4.8%, O4-NAs: 1.2%, O5-NAs: 1.7%, and O6-NAs: 0.5%. Accordingly, monoaromatics, diaromatics, and triaromatics were removed up to 16%, 22%, and 15%, respectively. The physiology of the identified genera suggested that the degradation in the PC-based biofilters was most likely proceeded in a scheme similar to beta-oxidation during anaerobic digestion process. The presence of hydrogenotrophic methanogens namely Methanobrevibacter and Methanomassiliicoccus and quantification of mcrA gene (2.4 × 102 to 8.7 × 102 copies/mg of PC) revealed that methane production was likely occurring in a syntrophic mechanism during the OSPW remediation. A slight reduction in toxicity was also observed. This study suggests that PC-based biofilters may offer some advantages in the remediation of OSPW; however, the production of methane could be of future concerns if operated at field-scale.

Catalytic degradation of naphthenic acid in aqueous solution: A review

Naphthenic acids are among the water, oil and soil contaminants mostly by accident. The review was carried out to examine the types and sources of Naphthenic acids. The toxic nature of naphthenic acids is mostly attributed to their surface characteristics due to the presence of a hydrophobia alkyl group and hydrophilic carboxylic group in their salts. Different method based on the use of different test organism like bacteria, aspen, fish, zooplankton and rat have been used by researchers to measure the level of toxicity of naphthenic acid in substances. Naphthenic acid caused corrosion in the oil sand refining process. Many analytical procedures have been use for the characterization and quantification of naphthenic acids was discussed. The chemical treatment methods have been explained and prove effective for degradation of naphthenic acid in water. The plants used in phytoremediation of contaminated water was examined and discussed. Photocatalysis method that uses UV 252 radiation has the most potential for reducing naphthenic acids and increasing their bio availability has been reported. Naphthenic acid is one of natural constituent of asphalt and crude oil and mainly obtained as the by-product of petroleum refining process with inconstant composition and ingredient. In conclusion, certain properties and characteristic of Naphthenic acid have been partially reviewed.

Naphthenic acid anaerobic biodegrading consortia enriched from pristine sediments underlying oil sands tailings ponds

Seepage from oil sands tailings ponds (OSTP), which contain toxic naphthenic acids (NAs), can infiltrate into groundwater. Clay sediment layer beneath is a critical barrier for reducing the infiltration of NAs into the sand sediment layer, where groundwater channels reside. Biodegradation has great potential as a strategy for NAs removal, but little is known about NAs biodegradability and potential functional microbes in these pristine sediments. This study investigated the potential for anaerobic biodegradation of NAs by microbial consortia enriched from clay and sand sediments underlying OSTP, amended with either acid extracted organics or Merichem NAs, under nitrate- and sulfate-reducing conditions. Degradation of NAs only be detected after DOC concentration reached to steady state after 163 days. Microbial community analysis shows that different electron acceptors, sediment types, and NAs sources associated with specific microbial taxa and can explain 14.8, 13.9 % and 5% of variation of microbial community structures, respectively. The DOC and methane were the most important geochemical properties for microbial community variations. This study approved the potential capability of indigenous microbial communities from the pristine sediments in NA degradation, demonstrating the barrier function of pristine clay sediments underlying OSTP in prohibiting organic contaminants from entering into groundwater.

Biofiltration of oil sands process water in fixed-bed biofilm reactors shapes microbial community structure for enhanced degradation of naphthenic acids

Naphthenic acids (NAs) are a complex mixture of carboxylic acids present in oil sands process water (OSPW). Their recalcitrant nature makes them difficult to be removed from the environment using conventional remediation strategies. This study hypothesized that, upon continuous operation, biofiltration of OSPW in fixed-bed biofilm reactors would allow the development of NA-degrading microbial community within the biofilter following successful removal. Both raw and ozonated OSPW were treated in the biofilters and changes in microbial community were tested via 16S/18S amplicon sequencing and metatranscriptomics. Through switch from suspended growth to attached growth, a shift in indigenous microbial community was seen following by an increase in alpha diversity. Concomitantly, improved degradation of NAs was monitored, i.e., 35.8% and 69.4% of NAs were removed from raw and ozonated OSPW, respectively. Metatranscriptomics analysis suggested the presence of genes involved in the degradation of organic acids and petroleum-related compounds. Specifically, functional abundance of aromatic compounds' metabolism improved from 0.05% to 0.76%; whereas abundance of benzoate transport and degradation pathway increased from 0.04% to 0.64%. These changes conclude that continuous operation of OSPW in the bioreactors was in favor of shaping the overall microbiome towards better NA degradation.

Biodegradation of naphthenic acids: identification of Rhodococcus opacus R7 genes as molecular markers for environmental monitoring and their application in slurry microcosms.

Nowadays, the increase of the unconventional oil deposit exploitation and the amount of oil sands process-affected waters (OSPW) in tailing ponds emerges the importance of developing bio-monitoring strategies for the restoration of these habitats. The major constituents of such deposits are naphthenic acids (NAs), emerging contaminant mixtures with toxic and recalcitrant properties. With the aim of developing bio-monitoring strategies based on culture-independent approach, we identified genes coding for enzymes involved in NA degradation from Rhodococcus opacus R7 genome, after the evaluation of its ability to mineralize model NAs. R. opacus R7 whole-genome analysis unveiled the presence of pobA and chcpca gene clusters putatively involved in NAs degradation. Gene expression analysis demonstrated the specific induction of R7 aliA1 gene, encoding for a long-chain-fatty-acid-CoA ligase, in the presence of cyclohexanecarboxylic acid (CHCA) and hexanoic acid (HA), selected as representative compounds for alicyclic and linear NAs, respectively. Therefore, aliA1 gene was selected as a molecular marker to monitor the biodegradative potential of slurry-phase sand microcosms in different conditions: spiked with CHCA, in the presence of R. opacus R7, the autochthonous microbial community, and combining these factors. Results revealed that the aliA1-targeting culture-independent approach could be a useful method for bio-monitoring of NA degradation in a model laboratory system.

Activity and stability of biochar in hydrogen peroxide based oxidation system for degradation of naphthenic acid

This study investigated the stability and catalytic activity of wheat straw biochar (WS), hardwood biochar (HW) and commercial activated carbon (AC) in hydrogen peroxide (H2O2) based oxidation system for degradation of model naphthenic acids compound, 1-methyl-1- cyclohexane carboxylic acid (MCCA). WS showed excellent catalytic activity for decomposition of H2O2 and MCCA degradation as demonstrated by high H2O2 decomposition rate (2.0*10−4 M−1s−1), amount of hydroxyl (OH) radicals generated (182 mg/L) and degradation efficiency of MCCA (100% at Co – 100 mg/L). 2-Methyl pentatonic acid was identified as reaction intermediate and 99% mineralization of MCCA was obtained within 4 h. The real wastewater conditions were simulated by addition of chloride (Cl−) and bicarbonate ions (HCO3−) and found that lower concentrations of Cl− and HCO3− have minimal influence on MCCA removal. Overall, biochar catalyzed H2O2 based oxidation process has great potential and can be applied for degradation of NAs in oil-sand processed water.

Effects of carboxymethyl cellulose grafting on stability and reactivity of zerovalent iron in water systems

The present study investigated the effects of degree of substitution (DS) and grafting method (pre-grafting or post-grafting) of carboxymethyl cellulose (CMC) on particle size, surface chemistry, colloidal and oxidative stability and reactivity of zerovalent iron (ZVI) particles. CMC with different DS were systematically synthesized by etherification of cellulose using monochloroacetic acid (MCA) in alcoholic medium. Structural Identity and purity of CMC was confirmed using NMR, FTIR and XRD analyses. It was found that DS of CMC can regulate the particle size, stability, dispersibility and reactivity of stabilized ZVI particles. CMC stabilized ZVI particles had smaller particle size, higher surface area and high dispersibility as compared to bare ZVI particles. Further, less aggregation was observed in higher DS CMC stabilized ZVI samples compared to lower DS CMC stabilized ZVI samples due to the better shielding ability for van der waals attractive forces. Also, the reactivity of stabilized ZVI particles was better than bare ZVI particles as the complete degradation of naphthenic acid was achieved in 180 min (>95% in 60 min). The colloidal stability and reactivity of stabilized ZVI particles remained intact even after 6 months of storage. Overall, CMC was found most efficient in colloidal stabilization of ZVI particles both in pre-grafting as well as post-grafting mode.

Electro-oxidation by graphite anode for naphthenic acids degradation, biodegradability enhancement and toxicity reduction

Electro-oxidation (EO) by using graphite anode and at relatively low current densities was successfully applied for the degradation of commercial naphthenic acids (NAs) mixture in water samples. At current densities of 0.5, 2.5, and 5 mA/cm2, acid extractable fraction (AEF) was removed by 42.2%, 57.0% and 67.9%, respectively, while classical NAs were degraded by 76.9%, 77.6% and 82.4%, respectively. EO reactivity towards NAs increased with increasing the carbon number (n) and was higher for cyclic NAs compared to the acyclic component. Oxidized NAs containing O3 and O4 were also degraded effectively during EO. The biodegradability of organics in the NA mixture was clearly improved by 1.7, 2.5 and 2.7 folds when the samples were pre-treated with EO at current densities of 0.5, 2.5, and 5 mA/cm2, respectively. The aromatic fraction in the commercial NA mixture consisted mainly of single-ring aromatics and was degraded effectively by EO. Biodegradation alone was able to reduce the toxicity of the commercial NA mixture towards Vibrio fischeri; however, the combination of EO with biodegradation resulted in a complete removal of the toxicity, showing a synergistic effect of combining these two processes. Coupling EO with aerobic biodegradation can result in an effective and energy-efficient treatment option for NA-bearing waters such as oil sands process water (OSPW) and refinery effluents.

Floating Photocatalysts for Passive Solar Degradation of Naphthenic Acids in Oil Sands Process-Affected Water

Oil sands process-affected water (OSPW), generated from bitumen extraction in the Canadian oil sands, may require treatment to enable safe discharge to receiving watersheds, as dissolved naphthenic acids (NAs) and other acid extractable organics (AEO), identified as the primary toxic components of OSPW, are environmentally persistent and poorly biodegradable. However, conventional advanced oxidation processes (AOPs) are impractically expensive to treat the volumes of OSPW stockpiled in the Athabasca region. Here we prepared floating photocatalysts (FPCs) by immobilizing TiO2 on glass microbubbles, such that the composite particles float at the air-water interface for passive solar photocatalysis. The FPCs were demonstrated to outperform P25 TiO2 nanoparticles in degrading AEO in raw OSPW under natural sunlight and gentle mixing conditions. The FPCs were also found to be recyclable for multiple uses through simple flotation and skimming. This paper thus demonstrates the concept of a fully passive AOP that may be scalable to oil sands water treatment challenges, achieving efficient NA reduction solely through the energy provided by sunlight and natural mixing processes (wind and waves).

Electrochemical mineralization and detoxification of naphthenic acids on boron-doped diamond anodes.

Electrochemical oxidation (ELOX) with boron-doped diamond (BDD) anodes was successfully applied to degrade a model aqueous solution of a mixture of commercial naphthenic acids (NAs). The model mixture was prepared resembling the NA and salt composition of oil sands process-affected water (OSPW) as described in the literature. The initial concentration of NAs between 70 and 120mg/L did not influence the electrooxidation kinetics. However, increasing the applied current density from 20 to 100A/m2 and the initial chloride concentration from 15 to 70 and 150mg/L accelerated the rate of NA degradation. At higher chloride concentration, the formation of indirect oxidative species could contribute to the faster oxidation of NAs. Complete chemical oxygen demand removal at an initial NA concentration of 120mg/L, 70mg/L of chloride and applied 50A/m2 of current density was achieved, and 85% mineralization, defined as the decrease of the total organic carbon (TOC) content, was attained. Moreover, after 6h of treatment and independently on the experimental conditions, the formation of more toxic species, i.e. perchlorate and organochlorinated compounds, was not detected. Finally, the use of ELOX with BDD anodes produced a 7 to 11-fold reduction of toxicity (IC50 towards Vibrio fischeri) after 2h of treatment.

Understanding the similarities and differences between ozone and peroxone in the degradation of naphthenic acids: Comparative performance for potential treatment

Ozonation at high doses is a costly treatment for oil sands process-affected water (OSPW) naphthenic acids (NAs) degradation. To decrease costs and limit doses, different peroxone (hydrogen peroxide/ozone; H2O2:O3) processes using mild-ozone doses of 30 and 50 mg/L were investigated. The degradation efficiency of Ox-NAs (classical (O2-NAs) + oxidized NAs) improved from 58% at 30 mg/L ozone to 59%, 63% and 76% at peroxone (1:1), 50 mg/L ozone, and peroxone (1:2), respectively. Suppressing the hydroxyl radical (•OH) pathway by adding tert-butyl alcohol did significantly reduce the degradation in all treatments, while molecular ozone contribution was around 50% and 34% for O2-NAs and Ox-NAs, respectively. Structure reactivity toward degradation was observed with degradation increase for both O2-NAs and Ox-NAs with increase of both carbon (n) and hydrogen deficiency/or |-Z| numbers in all treatments. However, the combined effect of n and Z showed specific insights and differences between ozone and peroxone treatments. The degradation pathway for |-Z|≥10 isomers in ozone treatments through molecular ozone was significant compared to •OH. Though peroxone (1:2) highly reduced the fluorophore organics and toxicity to Vibrio fischeri, the best oxidant utilization in the degradation of O2-NAs (mg/L) per ozone dose (mg/L) was observed in the peroxone (1:1) (0.91) and 30 mg/L ozone treatments (0.92). At n = 9–11, peroxone (1:1) had similar or enhanced effect on the O2-NAs degradation compared to 50 mg/L ozone. Enhancing •OH pathway through peroxone versus ozone may be an effective OSPW treatment that will allow its safe release into receiving environments with marginal cost addition.

Solar photocatalytic degradation of naphthenic acids in oil sands process-affected water.

Bitumen mining in the Canadian oil sands creates large volumes of oil sands process-affected water (OSPW), the toxicity of which is due in part to naphthenic acids (NAs) and other acid extractable organics (AEO). The objective of this work was to evaluate the potential of solar photocatalysis over TiO2 to remove AEO from OSPW. One day of photocatalytic treatment under natural sunlight (25 MJ/m(2) over ∼14 h daylight) eradicated AEO from raw OSPW, and acute toxicity of the OSPW toward Vibrio fischeri was eliminated. Nearly complete mineralization of organic carbon was achieved within 1-7 day equivalents of sunlight exposure, and degradation was shown to proceed through a superoxide-mediated oxidation pathway. High resolution mass spectrometry (HRMS) analysis of oxidized intermediate compounds indicated preferential degradation of the heavier and more cyclic NAs (higher number of double bond equivalents), which are the most environmentally persistent fractions. The photocatalyst was shown to be recyclable for multiple uses, and thus solar photocatalysis may be a promising "green" advanced oxidation process (AOP) for OSPW treatment.

Culturing oil sands microbes as mixed species communities enhances ex situ model naphthenic acid degradation.

Oil sands surface mining for bitumen results in the formation of oil sands process water (OSPW), containing acutely toxic naphthenic acids (NAs). Potential exists for OSPW toxicity to be mitigated by aerobic degradation of the NAs by microorganisms indigenous to the oil sands tailings ponds, the success of which is dependent on the methods used to exploit the metabolisms of the environmental microbial community. Having hypothesized that the xenobiotic tolerant biofilm mode-of-life may represent a feasible way to harness environmental microbes for ex situ treatment of OSPW NAs, we aerobically grew OSPW microbes as single and mixed species biofilm and planktonic cultures under various conditions for the purpose of assaying their ability to tolerate and degrade NAs. The NAs evaluated were a diverse mixture of eight commercially available model compounds. Confocal microscopy confirmed the ability of mixed and single species OSPW cultures to grow as biofilms in the presence of the NAs evaluated. qPCR enumeration demonstrated that the addition of supplemental nutrients at concentrations of 1 g L-1 resulted in a more numerous population than 0.001 g L-1 supplementation by approximately 1 order of magnitude. GC-FID analysis revealed that mixed species cultures (regardless of the mode of growth) are the most effective at degrading the NAs tested. All constituent NAs evaluated were degraded below detectable limits with the exception of 1-adamantane carboxylic acid (ACA); subsequent experimentation with ACA as the sole NA also failed to exhibit degradation of this compound. Single species cultures degraded select few NA compounds. The degradation trends highlighted many structure-persistence relationships among the eight NAs tested, demonstrating the effect of side chain configuration and alkyl branching on compound recalcitrance. Of all the isolates, the Rhodococcus spp. degraded the greatest number of NA compounds, although still less than the mixed species cultures. Overall, these observations lend support to the notion that harnessing a community of microorganisms as opposed to targeted isolates can enhance NA degradation ex situ. Moreover, the variable success caused by NA structure related persistence emphasized the difficulties associated with employing bioremediation to treat complex, undefined mixtures of toxicants such as OSPW NAs.