Occurrences and behaviors of naphthenic acids in a petroleum refinery wastewater treatment plant

Sample preparation, analytical characterization, monitoring, risk assessment and treatment of naphthenic acids in industrial wastewater and surrounding water impacted by unconventional petroleum production

Industrial extraction of unconventional petroleum results in notable volumes of oil sands process water (OSPW), containing elevated concentrations of naphthenic acids (NAs). The presence of NAs represents an intricate amalgamation of dissolved organic constituents, thereby presenting a notable hurdle for the domain of environmental analytical chemistry. There is growing concern about monitoring the potential seepage of OSPW NAs into nearby groundwater and river water. This review summarizes recent studies on sample preparation, characterization, monitoring, risk assessment, and treatment of NAs in industrial wastewater and surrounding water. Sample preparation approaches, such as liquid-liquid extraction, solid phase microextraction, and solid phase extraction, are crucial in isolating chemical standards, performing molecular level analysis, assessing aquatic toxicity, monitoring, and treating OSPW. Instrument techniques for NAs analysis were reviewed to cover different injection modes, ionization sources, and mass analyzers. Recent studies of transfer and transformation of NAs provide insights to differentiate between anthropogenic and natural bitumen-derived sources of NAs. In addition, related risk assessment and treatment studies were also present for elucidation of environmental implication and reclamation strategies. The synthesis of the current state of scientific knowledge presented in this review targets government regulators, academic researchers, and industrial scientists with interests spanning analytical chemistry, toxicology, and wastewater management.

Revealing the Pore Size-Dependent Sorption Mechanism of Toluene and Cetane in Porous Carbon by Nuclear Magnetic Resonance

The adsorption of contaminants by porous carbon has been extensively studied by conventional isotherm and kinetic methods. However, the co-adsorption behavior and sorption sites of multiple contaminants in different-sized pores remain unclear. Herein, the nuclear magnetic resonance (NMR) approach is performed to investigate the adsorption mechanism of toluene and cetane in the confined space of carbon at the molecular level. The ring current effect induces the variation in the NMR chemical shifts of in-pore adsorbed toluene and cetane, realizing the identification of pore-dependent adsorption sites for contaminant removal. Cetane has a slower adsorption kinetic but a higher binding energy than toluene, which could squeeze toluene from micropores to larger pores with increasing adsorption quantity. This leads to a stronger competitive adsorption effect in small micropores than in mesopores. Accordingly, hierarchical porous carbons are determined to be the most effective adsorbents for the adsorption of coexisting contaminants. This study not only provides an effective NMR method to reveal the adsorption mechanism in the confined space of porous carbon at the molecular level but also offers new insights into the pore size-dependent adsorption of activated carbon for petroleum contaminant treatment.

Transformation of dissolved organic matter at a full-scale petrochemical wastewater treatment plant

Transformation of dissolved organic matter (DOM) in petrochemical wastewater (PCW) treatment has rarely been studied. In this work, low- and high-salinity PCW were collected from a treatment plant and the transformations of DOM at molecular level along the treatment processes of both PCW were comparatively investigated. By using Orbitrap MS, the polar DOM constituents were categorized into five molecular classes namely saturated compounds, aliphatics, highly unsaturated and phenolic compounds (Huph), polyphenols and condensed polycyclic aromatics (Cpla). Aliphatics (58.62%) with low molecular weight (150-250 Da) and O/C (0-0.2) were dominant in raw low-salinity PCW; while Huph (65.03%) with O/C at 0.2-0.8 were rich in raw high-salinity PCW. After full-scale treatment, differentiated DOM constituents in both raw PCWs were transformed into aliphatics and Huph with O/C at 0.3-0.5. Anoxic/Oxic treatment of low-salinity system (L-A/O) removed a high fraction of aliphatics (53.05%); while Huph with low O/C (0.1-0.3) (65.68%) in the effluent of L-A/O were further mineralized by ozonation of low-salinity system (L-ozonation). In comparison, anoxic/oxic treatment of high-salinity system (H-A/O) mainly removed unsaturated Huph (34.10%) and aliphatics (30.86%). This resulted in a decrease of dissolved organic carbon as indicated via Spearman correlation. Different from L-ozonation, ozonation of high-salinity system (H-ozonation) degraded aliphatics (26.09%) and Huph (41.85%) with a relatively high O/C (0.2-1.2). After L-A/O and L-ozonation treatments, remaining saturated compounds that were originated from raw low-salinity PCW, were removed by subsequent biological aerated filter. Comparatively, after H-A/O and H-ozonation treatments, residual Huph and aliphatics which were mainly bio-derivates and ozonated intermediates, were further removed by air flotation filter. Hence, DOM transformation of different PCWs along similar treatments varied significantly. This study provides in-depth insights on DOM transformation along a full-scale PCW treatment process.

Recent advances in the design and use of Pickering emulsions for wastewater treatment applications

Pickering emulsions have recently emerged as versatile systems capable of targeting many applications of wastewater treatment. The unique properties, which include high emulsion stability, easy preparation, low toxicity, and stimuli-responsiveness, pave the way for advances in common pollutant control processes. This review aims to provide a comprehensive overview on different aspects in the Pickering emulsion design focusing on the key structural relations and their implications in specific applications. The first section is dedicated to the critical parameters governing the Pickering emulsion type, droplet size and stability. Furthermore, a section describing methods for demulsification and particle recovery is included, in which various stimuli have been explored. Finally, the most potent applications of Pickering emulsions such as photocatalytic degradation, adsorption, extraction, and separation of common wastewater pollutants are presented and discussed with a great deal of attention towards the efficacy, current limitations, and future potential. Recognizing the rise of innovative Pickering emulsion solutions is expected to induce profound effects facilitating the technology transfer to industrial processes.

Petroleum-derived naphthenic acids disrupt hormone-dependent sexual behaviours in male Western clawed frogs

Naphthenic acids (NAs), the carboxylic acids found in petroleum, are of emerging concern as they contaminate coastlines after oil spills, leech into freshwater ecosystems of oil sands areas and have wide industrial applications. They are acutely toxic in fish and tadpoles and may be endocrine disruptors at sublethal levels. We characterized androgen-dependent courtship behaviours and their disruption by NAs in male Western clawed frogs, Silurana tropicalis. Courtship primarily consists of males producing low trills and achieving amplexus, a mating position where a male clasps a female. Adult males were exposed for 5 days to 20 mg/l NA and injected with human chorionic gonadotropin to induce calling. The duration of calling activity was significantly reduced by NA exposure. Other acoustic parameters such as dominant frequency, click rate and trill length were not affected. Vocalization and amplexus were both inhibited after NA exposure and restored after 2 weeks of recovery in clean water. To determine possible disruption at the level of the testes, the effects of NA exposure on gene expression of key players in steroidogenesis was determined. Exposure to NAs decreased srd5a on average by ~ 25%. The enzyme 5α-reductase, encoded by srd5a, converts testosterone to its more bioactive form 5α-dihydrotestosterone (DHT), so NAs may be affecting this steroidogenic step. However, the observed upregulation of lhr, star and cyp17a1 suggests that NA-exposed males may be attempting to counteract the reduced potential to produce DHT. Yet, these NA-exposed frogs have dramatically reduced calling duration, so the observed upregulation of star and cyp17a1 is decoupled from the vocalizations. Calling duration and the ability of males to amplex females is reversibly disrupted by NA exposure, implying that environmental reduction and removal of NAs may help improve habitability of contaminated ecosystems.

Naphthenic Acids: Formation, Role in Emulsion Stability, and Recent Advances in Mass Spectrometry-Based Analytical Methods

Naphthenic acids (NAs) are compounds naturally present in most petroleum sources comprised of complex mixtures with a highly variable composition depending on their origin. Their occurrence in crude oil can cause severe corrosion problems and catalysts deactivation, decreasing oil quality and consequently impacting its productivity and economic value. NAs structures also allow them to behave as surfactants, causing the formation and stabilization of emulsions. In face of the ongoing challenge of treatment of water-in-oil (W/O) or oil-in-water (O/W) emulsions in the oil and gas industry, it is important to understand how NAs act in emulsified systems and which acids are present in the interface. Considering that, this review describes the properties of NAs, their role in the formation and stability of oil emulsions, and the modern analytical methods used for the qualitative analysis of such acids.

Ionization selectivity of electrospray and atmospheric pressure photoionization FT-ICR MS for petroleum refinery wastewater dissolved organic matter

Dissolved organic matter (DOM) in petroleum refinery wastewater is an extremely complex mixture. A better understanding of chemical compositions of DOM at the molecular level is necessary for the design and optimization of wastewater treatment processes. In this study, two largely different DOM samples, one from a petroleum refinery wastewater and the other from the Suwannee river water, were characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with positive-/negative-ion electrospray ionization (ESI), and positive-ion atmospheric pressure photoionization (APPI). For wastewater DOM, a total of 6226 molecular formulae were assigned in the three ionization modes. However, only 1182 molecular formulae were common in all three mass spectra, indicating that the techniques were highly complementary in the types of molecules they ionize. Acid O_x (x = 1-9) and basic N₁O_x (x = 0-2) classes were dominant in the wastewater DOM detected in negative-ion and positive-ion ESI mode, respectively. And the wastewater DOM contains considerable amounts of polycyclic aromatic hydrocarbons that did not respond to ESI but can be ionized selectively by APPI. Compared with riverine DOM, the refinery wastewater DOM has a higher molecular complexity and is more enriched in hydrocarbon, and nitrogen- and sulfur-containing compounds. The results show that the major components of refinery wastewater DOM were distinctive from those of the natural organic matter. Though not quantitative, the results obtained by various ionization techniques were found to be complementary, and are helpful to our understanding of the selectivity of different ionization techniques as well as the molecular compositions of DOM.

Detoxification of oil refining effluents by oxidation of naphthenic acids using TAML catalysts

The environmental problem stemming from toxic and recalcitrant naphthenic acids (NAs) present in effluents from the oil industry is well characterized. However, despite the numerous technologies evaluated for their destruction, their up-scaling potential remains low due to high implementation and running costs. Catalysts can help cutting costs by achieving more efficient reactions with shorter operating times and lower reagent requirements. Therefore, we have performed a laboratory investigation to assess iron-TAML (tetra-amido macrocyclic ligand) activators to catalyze the oxidation of NAs by activating hydrogen peroxide - considered environmentally friendly because it releases only water as by-product - under ultra-dilute conditions. We tested Fe-TAML/H₂O₂ systems on (i) model NAs and (ii) a complex mixture of NAs in oil refining wastewater (RWW) obtained from a refining site in Colombia. Given the need for cost-effective solutions, this preliminary study explores sub-stoichiometric H₂O₂ concentrations for NA mineralization in batch mode and, remarkably, delivers substantial removal of the starting NAs. Additionally, a 72-h semi-batch process in which Fe-TAML activators and hydrogen peroxide were added every 8 h achieved 90-95% removal when applied to model NAs (50 mg L^-1) and a 4-fold reduction in toxicity towards Aliivibrio fischeri when applied to RWW. Chemical characterization of treated RWW showed that Fe-TAML/H₂O₂ treatment (i) reduced the concentration of the highly toxic O₂ NAs, (ii) decreased cyclized constituents in the mixture, and (iii) preferentially degraded higher molecular weight species that are typically resistant to biodegradation. The experimental findings, together with the recent development of new TAML catalysts that are far more effective than the TAML catalysts deployed herein, constitute a foundation for cost-effective treatment of NA-contaminated wastewater.

Application of microbial electrochemical technologies for the treatment of petrochemical wastewater with concomitant valuable recovery: A review

Petrochemical industry is one of the major and rapidly growing industry that generates a variety of toxic and recalcitrant organic pollutants as by-products, which are not only harmful to the aquatic animals but also affects human health. The majority of the components of petrochemical wastewater (PW) are carcinogenic, genotoxic and phytotoxic in nature; hence, this complex wastewater generated from different petrochemical processes should be efficiently treated prior to its disposal in natural water bodies. The established technologies like advanced oxidation, membrane bioreactor, electrocoagulation and activated sludge process employed for the treatment of PW are highly energy intensive and incurs high capital and operation cost. Moreover, these technologies are not effective in completely eliminating petroleum hydrocarbons present in PW. Thus, to reduce the energy requirement and also to transform the chemical energy trapped in these organic matters present in this wastewater into bioelectricity and other value-added products, microbial electrochemical technologies (METs) can be efficaciously used, which would also compensate the treatment cost by transforming these pollutants into bioenergy and valuables. In this regard, this review elucidates the feasibility and application of different METs as an appropriate alternative for the treatment of PW. Furthermore, the numerous bottlenecks towards the real-life application and commercialization of pioneering METs have also been articulated.

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 O_x polar compounds were removed from two heavy oil EDWs, but mainly alkanes were removed from DLO-EDW. As such, the differences in the types of dominant polar compounds became insignificant among treated heavy oil and light oil EDWs. Coagulation notably decreased the acute biotoxicity and improved the biodegradability of all treated EDWs. The residual organic nitrogen compounds in treated KHO-EDW contributed to a higher residual biotoxicity compared to treated LHO-EDW. The results demonstrate that coagulation can effectively improve the qualities of heavy oil EDWs by lowering the contents of organic pollutants and removing recalcitrant compounds, thus guaranteeing the efficiency of refinery WWTPs.

Naphthenic acids are key contributors to toxicity of heavy oil refining effluents

Oil refining produces vast quantities of wastewater with harmful contaminants that can be released back into the environment with a possible risk of toxicity to aquatic wildlife and human populations. Hence the importance of adequate wastewater treatment to achieve safe effluents that protect both ecological and human health. However, some refining effluents are linked to serious pollution problems even after treatment, partly because little progress has been made in determining the causative agents of the observed biological effects, resulting in non-targeted treatment. Here, we followed an effect-directed analysis (EDA) approach using Aliivibrio fischeri as biosensor to show that naphthenic acids (NAs) are important components of refining wastewater resulting from the processing of heavy crude oil. Furthermore, we demonstrate that besides mixture effects, NAs have a significant contribution to the toxicity exerted by these effluents. Profiling of the NA mixture was conducted using high resolution liquid chromatography-Orbitrap, which evidenced that O₂ NAs corresponded to 90% of the NAs detected. Our findings contrast with previous reports where classic NAs have been found between 15% and 72% and could explain the significant biological effects observed in A. fischeri. This study broadens the body of evidence pointing at mixture effects and low-concentration pollutants as the cause of toxicity from RWW, in addition to NAs resulting from the processing of heavy crude oil. Our results can serve as a starting point for setting better effluent discharge standards relevant to oil refining wastewater resulting from heavy crude oil and help improve wastewater treatment plants to reduce effluent toxicity.

Derivatization for Nontargeted Screening of Acids in Oilfield Refinery Wastewater: Identification and Behaviors of Recalcitrant Chlorinated Naphthenic Acids

The nontargeted scanning chemical profiling approach has shown great potential to identify unknown pollutants or novel biological markers; however, the structure identification of unknown compounds is a challenge. In this study, a carboxyl-specific derivatization reagent, N-(4-aminomethylphenyl) pyridinium (AMPP), was coupled with QTOF-MS^E-MS scanning to establish a high-throughput nontargeted scanning method for acid compounds. The scanning method can isolate the precursor by data-independent acquisition and can select all of the acid compounds based on the characteristic fragment generated from the derivatization reagent. The method was applied to scan naphthenic acid fraction compounds in petroleum refinery wastewater and identify 70-126 NAs, 30-68 oxy-NAs, 54-60 NAs containing nitrogen, and 66-75 NAs containing both nitrogen and oxygen. Chlorinated NAs (Cl-NAs) including monochlorinated NAs (Cl-NAs), monochlorinated hydroxylated NAs (Cl-OH-NAs), and dichlorinated dihydroxylated NAs (Cl₂-(OH)₂-NAs) were first identified with the aid of chlorine isotopic patterns. The Cl-NAs might be naturally presented in crude oil together with NAs. Occurrences and mass balances of Cl-NAs were further assessed in the wastewater treatment plant in north China. The total concentrations of ∑Cl-NAs were estimated to be 12 ± 7.8-18 ± 17 μg/L and 8.5 ± 2.0-68 ± 35 μg/g in the wastewater and solid samples, respectively. The removal efficiencies of Cl-NAs (-29.9 to 34.3%) were much lower than those of NAs, suggesting the high recalcitrance of chlorinated compounds during the treatment processes. The estimated mass loss fractions due to degradation for Cl-NAs were 26.5-53.4% of initial loadings, and relatively high fractions (32.1-56.8%) were observed in the effluent directly discharged to the environment. Advanced treatment techniques are needed to effectively reduce the persistent Cl-NAs in the wastewater.

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.

Naphthenic acids removal from high TDS produced water by persulfate mediated iron oxide functionalized catalytic membrane, and by nanofiltration

Oil industries generate large amounts of produced water containing organic contaminants, such as naphthenic acids (NA) and very high concentrations of inorganic salts. Recovery of potable water from produced water can be highly energy intensive is some cases due to its high salt concentration, and safe discharge is more suitable. Here, we explored catalytic properties of iron oxide (FexOy nanoparticles) functionalized membranes in oxidizing NA from water containing high concentrations of total dissolved solids (TDS) using persulfate as an oxidizing agent. Catalytic decomposition of persulfate by FexOy functionalized membranes followed pseudo-first order kinetics with an apparent activation energy of 18 Kcal/mol. FexOy functionalized membranes were capable of lowering the NA concentrations to less than discharge limits of 10 ppm at 40 °C. Oxidation state of iron during reaction was quantified. Membrane performance was investigated for extended period of time. A coupled process of advanced oxidation catalyzed by membrane and nanofiltration was also evaluated. Commercially available nanofiltration membranes were found capable of retaining NA from water containing high concentrations of dissolved salts. Commercial NF membranes, Dow NF270 (Dow), and NF8 (Nanostone) had NA rejection of 79% and 82%, respectively. Retentate for the nanofiltration was further treated with advanced oxidation catalyzed by FexOy functionalized membrane for removal of NA.

Continuous Bulk FeCuC Aerogel with Ultradispersed Metal Nanoparticles: An Efficient 3D Heterogeneous Electro-Fenton Cathode over a Wide Range of pH 3-9

Novel iron-copper-carbon (FeCuC) aerogel was fabricated through a one-step process from metal-resin precursors and then activated with CO2 and N2 in environmentally friendly way. The activated FeCuC aerogel was applied in a heterogeneous electro-Fenton (EF) process and exhibited higher mineralization efficiency than homogeneous EF technology. High total organic carbon (TOC) removal of organic pollutants with activated FeCuC aerogel was achieved at a wide range of pH values (3-9). The chemical oxygen demand (COD) of real dyeing wastewater was below China's discharge standard after 30 min of treatment, and the specific energy consumption was low (9.2 kW·h·kg(-1)COD(-1)), corresponding to a power consumption of only ∼0.34 kW·h per ton of wastewater. The enhanced mineralization efficiency of FeCuC aerogel was mostly attributable to ultradispersed metallic Fe-Cu nanoparticles embedded in 3D carbon matrix and the CO2-N2 treatment. The CO2 activation enhanced the accessibility of the aerogel's pores, and the secondary N2 activation enlarged the porosity and regenerated the ultradispersed zerovalent iron (Fe(0)) with reductive carbon. Cu(0) acted as a reduction promoter for interfacial electron transfer. Moreover, activated FeCuC aerogel presented low iron leaching (<0.1 ppm) in acidic solution and can be molded into different sizes with high flexibility. Thus, this material could be used as a low-cost cathode and efficient heterogeneous EF technology for actual wastewater treatment.