Degradation of cyclohexanecarboxylic acid as a model naphthenic acid by the UV/chlorine process: Kinetics and by-products identification

Fluorescence visualization of CO2-responsive phase transfer materials targeting at the heterogeneous interfacial reactions in advanced oxidation of naphthenic acid in wastewater

Treatment of naphthenic acids (NAs) in wastewater is necessary due to its high toxicity and difficult degradation. In the heterogeneous Fenton-like advanced oxidation of organic pollutant system, the insufficient accessibility of oxidizing agent and NAs greatly hamper the reaction efficiency. CO2-responsive phase transfer materials derived from polyethylene glycol (PEG)-based deep eutectic solvents were specific targeted at the immiscible-binary phase system. The NAs oxidative degradation process was optimized including the kinds of catalyst (Molecular weight of PEG, constitute of DESs, and dosage.), temperature, flow rate of CO2, et al. With the help of fluorescence properties of catalyst, the hydrophilic-hydrophobic interaction was visual-monitored and further studied. The amphipathic property of PEG-200/Sodium persulfate/Polyether amine 230 (PEA230) greatly reduced the aqueous/organic phase transfer barrier between sodium persulfate and NAs (up to 84 %), thus accreting oxidation rate. The surface tension decreased from 35.364 mN/m to 28.595 mN/m. To control the reaction rate, the CO2 respond structure of amido played an important role. In addition, the interfacial transfer intermediates and oxidation pathways were also explored by nuclear magnetic resonance, flourier transform infrared spectroscopy, surface tension, and radical inhibition experiments. The mechanism of advanced oxidation of NAs catalyzed by CO2-responsive phase transfer catalyst was proposed, which would made up for the deficiency of the system theory of heterogeneous chemical oxidation of organic pollutants.

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.

Efficient removal of naphthenic acids from real petroleum wastewater by natural pyrite activated persulfate system

The petroleum wastewater (PWW) contains a diverse range of recalcitrant organic contaminants. Of particular concern is the removal of naphthenic acids (NAs) due to the high toxicity and persistence. Persulfate (PS) based oxidation processes have shown promising in treating refractory wastewater, while the high costs of prepared catalysts limited their widespread implementation. This study aims to develop a cost-effective natural pyrite activated PS system for PWW treatment. The removal of NAs by pyrite/PS system was initially investigated. More than 90% of cyclohexanoic acid (CHA), a model NA, was removed in pyrite/PS system (2.0 g/L pyrite, 4.0 mM PS) at initial pH of 3-11. Scavenging experiments revealed that Fe(II) on pyrite surface was the reactive site for PS activation to generate reactive species, including sulfate radical (SO4·-), Fe(IV) and hydroxyl radical (·OH) for CHA degradation. Reactions of Fe(III) with S helped restore Fe(II) and enhance PS activation, resulting in the sustained catalytic activity of pyrites over five cycles. Cl-, SO42- and NO3- below 10 mM had minimal impact on CHA degradation in pyrite/PS system. However, over 1 mM of HCO3- inhibited 80% of CHA removal due to the buffer effect to maintain the high solution pH. Removing HCO3- from real PWW restored the removal of CHA and of total organic carbon (TOC) to over 90% and 71.3% in pyrite/PS system, respectively. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results indicated that O2‒6 species including NAs were primarily eliminated through mineralization and oxygen addition. Besides, O3-5S, NO3-5S and N3O2‒4 species were the most susceptible to oxidation in PWW, resulting in the increase of the oxidation level (i.e., O/Cwa) from 0.41 to 0.56 after treatment. This study provides valuable insights into the treatment of NAs in real PWW, and potential application of natural minerals in the treatment of industrial wastewater.

Utilization of Fe-Ethylenediamine-N,N'-Disuccinic Acid Complex for Electrochemical Co-Catalytic Activation of Peroxymonosulfate under Neutral Initial pH Conditions

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

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.

Efficient removal of recalcitrant naphthenic acids with electro-cocatalytic activation of peroxymonosulfate by Fe(III)-nitrilotriacetic acid complex under neutral initial pH condition

This work investigated the activation of peroxymonosulfate by electrochemical (EC) system assisted with Fe(III)-nitrilotriacetic acid (NTA) complex for degradation of persistent naphthenic acids (NAs) under neutral initial pH conditions. As NAs are a complicated mixture, 1-adamantanecarboxylic acid (ACA) was selected as the model NA compound for degradation experiment. The addition of NTA is to chelate with Fe(III), gaining stability under neutral pH condition to facilitate the circulation of Fe(II)/Fe(III) by the electrochemical process to activate PMS. The EC/Fe(III)-NTA/PMS system was explored with applicable pH range of 3-9 and an optimized molar ratio 1: 2 for Fe: NTA. Results of quenching and chemical probe experiment together with results of electron paramagnetic resonance (EPR) analysis revealed the main reactive species of the system, including ^•OH, SO₄^•-, ¹O₂ and possibly Fe(IV). With the addition of NTA, the yields of ^•OH, SO₄^•-, ¹O₂ were enhanced. Results of mass spectrometry analysis and DFT calculations indicated the formation of 9 degradation byproducts of ACA via three primary degradation pathways such as hydroxyl substitution, carbonyl substitution, and decarboxylation. Furthermore, the EC/Fe(III)-NTA/PMS system could achieve excellent removal efficiency of ACA with different anions such as Cl^-, HCO₃^-, NO₃^- and H₂PO₄^- in the background. The practical applicability of the system was also verified with the high removal of commercial NAs mixture standard. Overall results have indicated the EC/Fe(III)-NTA/PMS system could be utilized for efficient reclamation of authentic oil and gas industrial wastewater under natural pH conditions.

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.