Application of UV-irradiated Fe(III)-nitrilotriacetic acid (UV-Fe(III)NTA) and UV-NTA-Fenton systems to degrade model and natural occurring naphthenic acids

Innovative Fe(IV)-Triggered Chemiluminescence Assay for Rapid and Selective Detection of Total Phenolic Content

Total phenolic content reflecting the overall concentration of phenolics in water is a valuable indicator for evaluating water quality. However, current total phenolic content quantification technologies are unsatisfactory due to their complexity, time-consuming nature, limited reliability, and low selectivity. To overcome these problems, we utilized the high reactivity and selectivity of tetravalent iron (Fe(IV)) toward phenolics to develop a surrogate method for total phenolic content based on the quenching effect of phenolics on the chemiluminescence (CL) produced during the oxidation of naproxen (NAP) by Fe(IV) in the Fe(II)-activated periodate (Fe(II)/PI) process. Experimental results showed a strong linear relationship between the chemiluminescence quenching capacity (CLQC) values and total phenolic content in the Fe(II)/PI-NAP process. The high reactivity and superior selectivity of Fe(IV) toward phenolics enable rapid, highly sensitive, and robust anti-interference quantification of total phenolic content using the developed CL method. The limit of quantitation and limit of detection of the developed CL method for total phenolics determination were 1.34 and 0.40 μM, respectively, expressed as phenol equivalents. Finally, we validated the feasibility of using the CLQC value as a surrogate indicator for total phenolic content in various real water samples. This work introduces a novel method for quantifying total phenolic content by determining the CLQC value of water samples using the Fe(II)/PI-NAP process, offering a promising alternative for controlling the discharge of phenolics.

Fate of dissolved organics in oil sands process water during long-term storage: Mechanistic insights into toxicity removal and microbial processes

Refining oil sand process water (OSPW), a byproduct of bitumen extraction from oil sands in Canada, presents significant environmental challenges due to its complex makeup. This complexity is mainly due to the presence of naphthenic acids (NAs), which play a substantial role in contributing to the toxicity of OSPW. Although various treatment technologies have been explored, the long-term behaviour of OSPW dissolved organics under different storage conditions has not been studied extensively. This study is the first to delve deeply into the natural attenuation of OSPW under diverse controlled conditions, focusing on the effects of temperature, dissolved oxygen, and ozone pretreatment on water quality, NAs degradation, toxicity, and bioavailability. Our results revealed the critical role of temperature in OSPW characteristics, with long-term storage at 4 °C demonstrating minimal degradation of dissolved organics, providing the first empirical support for current OSPW storage practices. In contrast, at 20 °C, ozoned OSPW exhibited maximum reduction in the following parameters: total NAs, 72.6 %; chemical oxygen demand, 25.3 %; acute toxicity towards A. fischeri by 60.7 %; and bioavailability of organics by 35.2 %. This suggests that ozone pretreatment facilitates the biodegradation process by breaking down NAs into more readily metabolized compounds, which are further degraded by microbial activity over time. Furthermore, the study identified evolving microbial communities during OSPW storage, highlighting the presence of Bacillus and Fontimonas genera, which may play a role in organics degradation but require further investigation into their specific functions. These findings provide critical insights into the long-term dynamics of organics in OSPW and provide a foundation for optimizing management strategies.

A chemometric approach to the interaction of hydrogen peroxide and thermally activated persulfate in the removal of aromatic compounds

This study evaluates the combined use of H₂O₂ and thermally activated S₂O₈2⁻ (T-PDS) for the degradation of phenolic compounds (PhOH) in wastewater, aiming to limit or eliminate sludge production. Phenolic compounds are common in industrial effluents, and their effective removal is crucial for reducing environmental impact. The study employs Response Surface Methodology (RSM) and Principal Component Analysis (PCA) to optimise critical variables such as temperature, pH, and oxidant concentrations. Optimal conditions were determined to be a temperature of 70 °C, pH 5, and a H2O2/S2O82- molar ratio of 1:6. Under these conditions, the system achieved an 89% PhOH degradation efficiency, reducing the concentration from 10 to 1.2 mg L-1 after 120 min of treatment. The kinetic analysis revealed a rapid initial reduction in PhOH concentration by 38% (from 10 to 6.2 mg L-1) within the first 15 min, followed by a slower degradation phase. This suggests a complex reaction mechanism, likely influenced by oxidant consumption and intermediate formation. The model demonstrated high precision, with R2 values of 0.99 for PhOH and S2O82-and slightly lower for H₂O₂ (R2 = 0.98). A brief cost analysis estimated the treatment cost at €6.86 per cubic meter of wastewater, showing the economic viability of the process. Additionally, eliminating sludge formation reduces operational costs related to sludge management and disposal, making the H2O2/T-PDS system a promising solution for large-scale industrial applications in sustainable wastewater treatment.

Single Phototrophic Bacterium-Mediated Iron Cycling in Aquatic Environments

Redox cycling of iron plays a pivotal role in both nutrient acquisition by living organisms and the geochemical cycling of elements in aquatic environments. In nature, iron cycling is mediated by microbial Fe(II)-oxidizers and Fe(III)-reducers or through the interplay of biotic and abiotic iron transformation processes. Here, we unveil a specific iron cycling process driven by one single phototrophic species, Rhodobacter ferrooxidans SW2. It exhibits the capability to reduce Fe(III) during bacterial cultivation. A c-type cytochrome is identified with Fe(III)-reducing activity, implying the linkage of Fe(III) reduction with the electron transport system. R. ferrooxidans SW2 can mediate iron redox transformation, depending on the availability of light and/or organic substrates. Iron cycling driven by anoxygenic photoferrotrophs is proposed to exist worldwide in modern and ancient environments. Our work not only enriches the theoretical basis of iron cycling in nature but also implies multiple roles of anoxygenic photoferrotrophs in iron transformation processes.

Fe2+-NTA synergized UV254 photolytic defluorination of perfluorooctane sulfonate (PFOS): Enhancing through intramolecular electron density perturbation via electron acquisition

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant posing a risk in environmental persistence, bioaccumulation and biotoxicity. This study was to reach a comprehensive and deeper understanding of PFOS elimination in a UV254 photolytic treatment with the co-presence of Fe2+ and nitrilotriacetic acid trisodium salt (NTA). PFOS defluorination was noticeably enhanced in the UV/Fe2+-NTA treatment compared with UV/NTA, UV/Fe2+ and our previously studied UV/Fe3+ treatments. UV-vis, FTIR, and UPLC/MS-MS results indicated the formation of PFOS-Fe2+-NTA complex in PFOS, Fe2+ and NTA mixture. The transition energy gap of PFOS-Fe2+-NTA decreased below the excitation energy supplied by UV254 irradiation, corresponding with red shift appearing in UV-vis scanning spectrum. This favored intramolecular electron transfer from Fe2+-NTA to PFOS under UV254 irradiation to form electron-accepting PFOS. Molecular electrostatic potential and atom charge distribution analyses suggested electron density rearrangement and perturbation in the perfluorinated carbon chain of electron-accepting PFOS, leading to the decrease in bond dissociation energies. Intermediate products detection suggested the parallel defluorination pathways of PFOS desulfonation, middle carbon chain scission and direct C-F cleavage. NTA exhibited crucial functions in the UV/Fe2+-NTA treatment by holding Fe2+/Fe3+ in soluble form as a chelant and favoring water activation to generate hydrated electrons (eaq-) under UV irradiation as a photosensitizer. Fe2+ acting as the conduit for electron transfer and the bridge of PFOS anion and NTA was thought functioning best at 200 µM in this study. The degree of UV/Fe2+-NTA -synergized PFOS defluorination also depended on eaq- yield and UV254 photon flux. The structure dependence on the electron transfer process of PFOS and PFOA was explored incorporating molecular structure descriptors. Because of possessing greater potential to acquire electrons or less likeliness to donate its electrons than PFOA, PFOS exhibited faster defluorination kinetics in the published "reduction treatments" than "oxidation" ones. Whereas, PFOA defluorination kinetics were at similar level in both "reduction" and "oxidation" treatments.

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.

Continuous flow operation of solar photo-Fenton fused with NaOCl as a novel tertiary treatment

A novel strategy based on solar photo-Fenton mediated by ferric nitrilotriacetate (Fe3+-NTA) combined with NaOCl in continuous flow mode for wastewater reclamation has been studied. Escherichia coli (E. coli) inactivation attained ≥ 5 log10-units, meeting the most restrictive EU 2020/741 target (10 CFU/100 mL), and 75% of organic microcontaminant total load was removed. As a remarkable finding, trihalomethanes (THMs) concentration was insignificant, complying by far with the Italian legislation limit. To attain these results, first the effect of liquid depth on E. coli inactivation and imidacloprid (IMD) removal from spiked municipal effluents was evaluated in continuous flow pilot-scale raceway pond reactors at 60-min hydraulic residence time with low reagent concentrations (0.10 mM Fe3+-NTA, 0.73 mM H2O2 and 0.13 mM NaOCl). Disinfection was due to the bactericidal effect of chlorine. In contrast, liquid depth notably influenced microcontaminant removal, highlighting that operation at 10-cm liquid depth allows achieving treatment capacities higher than at 5 cm (16.50 vs 28.20 mg IMD/m2∙day). Next, the monitoring of THMs was carried out to evaluate the generation and degradation of disinfection by-products, along with the removal of actual microcontaminants. These promising results draw attention to the treatment potential and open the way for its commercial application.

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.

Impacts of bioreactor operating parameters on removal efficiency, biodegradation rate, molecular distribution, and toxicity of commercial naphthenic acids

Effects of naphthenic acids (NAs) concentration (50-200 mg NA L^-1; 35-140 mg TOC L^-1) and loading rate (1.4-1249 mg NA L^-1 h^-1; 1-874 mg TOC L^-1 h^-1) on removal efficiency, removal rate, and molecular distribution of NAs, and effluent toxicity were evaluated for biodegradation of commercial NAs mixture in circulating packed bed bioreactors (CPBBs). Increase of NAs concentration and loading rate (shorter residence times) increased the removal rate, while removal efficiency initially declined and then stabilized. The maximum biodegradation rates for 50, 100, 150, and 200 mg NA L^-1 were 128.0, 321.7, 430.2, and 630.0 mg TOC L^-1 h^-1 at loading rates of 218.5, 455.6, 673.5 and 874.0 mg TOC L^-1 h^-1, respectively, with removal efficiencies of 58.6, 70.6, 63.9 and 72.1%. Analysis of influent and treated effluents with gas chromatography-mass spectrometry showed that molecular weight and cyclicity (C and Z numbers) affected the biodegradation, with low molecular weight acyclic NAs (C = 6-12) were the most amenable to biodegradation and those with intermediate and high molecular weights (C = 13-22) and moderate cyclicity (Z = - 4, - 6) were the most recalcitrant. In the biofilm, Proteobacteria and Actinobacteria were the most abundant phyla, and Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria were the dominant classes. Toxicity analyses with Artemia salina and Vibrio fischeri (Microtox) showed that high influent concentrations and loading rates (short residence times) led to higher NAs residual concentration and effluent toxicity. To design and operate large-scale CPBBs, intermediate loading rates and residence times that result in high removal efficiency, reasonable removal rates, and low toxicity are recommended.

Simultaneous bacterial inactivation and microcontaminant removal by solar photo-Fenton mediated by Fe3+-NTA in WWTP secondary effluents

Simultaneous microorganism inactivation and organic microcontaminant removal in municipal wastewater treatment plant (WWTP) secondary effluents by the solar photo-Fenton process mediated by Fe³⁺-NTA is studied in depth. To achieve this objective, different key aspects were addressed: (i) the effect of initial Fe³⁺-NTA concentration at 1:1 molar ratio (0.10-0.30 mM) and H₂O₂ concentration (1.47-5.88 mM), (ii) the effect of initial microorganism load (10³ and 10⁶ CFU/mL) and (iii) the impact of the disinfection target on treatment cost. The first stage of this work was carried out in simulated WWTP effluent spiked with 100 µg/L of imidacloprid (IMD) as model microcontaminant and inoculated with Escherichia coli (E. coli) K-12 as reference strain, in a pilot scale raceway pond reactor with 5-cm of liquid-depth. Secondly, the most cost-effective conditions were validated in actual WWTP effluent. The kinetic analysis revealed that increasing Fe³⁺-NTA concentration over 0.20 mM does not significantly reduce treatment time due to the limited effect caused on the volumetric rate photon absorption. Treatment cost is determined by the disinfection process, since IMD removal was always faster than E. coli inactivation. The most cost-effective strategy to achieve 10 CFU/100 mL of E. coli (Regulation EU 2020/741) was 0.20/4.41 mM Fe³⁺-NTA/H₂O₂, with a cost of 0.32 €/m³. A less restrictive disinfection target, 100 CFU/100 mL, allowed reducing reactant concentration and cost, 0.10/1.47 mM Fe³⁺-NTA/H₂O₂ and 0.15 €/m³, respectively. In both cases, no regrowth at 24 h and more than 90% of IMD removal were observed.

Enhanced activation of persulfate by Fe(III) and catechin without light: Reaction kinetics, parameters and mechanism

An environmental-friendly plant polyphenol, catechin (CAT), was applied in Fe(III) activated persulfate (PS) system for naproxen (NPX) degradation in this research. Reaction kinetics, parameters, NPX degradation products and reaction mechanism were investigated. Combining the results of quenching experiments as well as Electron Spin Resonance (ESR), it was observed that SO₄^•- was critical in NPX degradation, and the contribution of HO^• was minor in the Fe(III)/CAT/PS system. O₂^•- was generated during the reaction but did not contribute to NPX degradation. SO₄^•- and HO^• were produced from the PS activation by Fe(II), which was formed from the transient complexing and reduction process between Fe(III) and CAT. The effects of Fe(III), CAT, PS concentration and pH value on NPX degradation were evaluated. Moreover, the mineralization rate was 20.2%, and the toxicity of the treated solution were lower than the initial solution. Nine possible intermediates were determined when using LC-QTOF-MS to analyze, and three degradation pathways were put ward. The results proved that CAT could accelerate the redox cycle of Fe(III)/Fe(II), consequently to strengthen PS activation without light. It was a promising oxidation technology as it offered an energy-saving and hypo-toxic way for refractory organic pollutants treatment, and it was applicable at a comparatively wide pH range.

Simultaneous Disinfection and Organic Microcontaminant Removal by UVC-LED-Driven Advanced Oxidation Processes

This work presents the comparison of four advanced oxidation processes driven by UVC-LED radiation (278 nm—2 W/m2) for simultaneous bacteria inactivation (Escherichia coli—106 CFU/mL) and microcontaminant removal (imidacloprid—50 µg/L) in simulated wastewater secondary effluent. To this end, the activation of H2O2 and S2O82− as precursors of HO• and SO4•−, respectively, by UVC-LED and UVC-LED/Fe3+–NTA (ferric nitrilotriacetate at 0.1 mM) has been studied at different oxidant concentrations. For the purpose of comparison, conventional chlorination was used as the baseline along with bacterial regrowth 24 h after treatment. Disinfection was achieved within the first 30 min in all of the processes, mainly due to the bactericidal effect of UVC-LED radiation. UVC-LED/H2O2 did not substantially affect imidacloprid removal due to the low HO• generation by UVC irradiation at 278 nm, while more than 80% imidacloprid removal was achieved by the UVC-LED/S2O82−, UVC-LED/Fe3+–NTA/S2O82−, and UVC-LED/Fe3+–NTA/H2O2 processes. The most efficient concentration of both oxidants for the simultaneous disinfection and microcontaminant removal was 1.47 mM. Chlorination was the most effective treatment for bacterial inactivation without imidacloprid removal. These findings are relevant for scaling up UVC-LED photoreactors for tertiary wastewater treatment aimed at removing bacteria and microcontaminants.

Efficient removal of bisphenol A with activation of peroxydisulfate via electrochemically assisted Fe(III)-nitrilotriacetic acid system under neutral condition

In this work, an innovative electrochemically assisted Fe(III)-nitrilotriacetic acid system for the activation of peroxydisulfate (electro/Fe(III)-NTA/PDS) was proposed for the removal of bisphenol A (BPA) at neutral pH with commercial graphite electrodes. The efficient BPA decay was mainly originated from the continuous activation of PDS by Fe(II) reduced from Fe(III)-NTA complexes at the cathode. Scavenger experiments and electron paramagnetic resonance (EPR) measurements confirmed that the removal of BPA occurred through graphite adsorption, direct electron transfer (DET) and radical oxidation. Sulfate and hydroxyl radicals were primarily responsible for the oxidation of BPA while graphite adsorption and DET played a minor role in BPA removal. The influence of Fe(III) concentration, PDS dosage, input current, NTA to Fe(III) molar ratio as well as coexisting inorganic anions (Cl^-, NO₃^-, H₂PO₄^- and HCO₃^-) on BPA elimination was explored. The BPA removal efficiency reached 93.5 % after 60 min reaction in the electro/Fe(III)-NTA/PDS system under the conditions of initial pH 7.0, 0.30 mM Fe(III), 0.15 mM NTA, 5 mM PDS and 5 mA constant current. Overall, this research provided a novel perspective and potential for remediation of organic wastewater using NTA in combination with electrochemistry in the homogeneous Fe(III)/persulfate system.

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

Degradation kinetics, by-products identification and pathways of a model naphthenic acid, cyclohexanecarboxylic acid (CHA), by the UV/Chlorine process were investigated in this study. Mathematical modeling indicated that the initial CHA decay rate increased rapidly with the chlorine dose when the chlorine dose was lower than 45 mg/L and decreased with further chlorine dose increases. Increasing the chlorine dose from 400 to 800 mg/L resulted in a steady increase in the total removal of CHA after 60 min of UV photolysis. By dividing the 700 mg/L chlorine dose into five separated doses (140 mg/L each) added at 10 min intervals, the total CHA removal increased from 72% to 91%. This implies that the ideal condition of the UV/Chlorine process in degrading CHA is to add chlorine continuously at a constant rate to compensate any chlorine consumption to reduce the radical scavenging effect. It was found that the CHA decay was mainly attributed to the hydroxyl radical (OH) attack and the reactive chlorine species (RCS) contribution was relatively small. Various by-products, including the mono-chlorinated and di-chlorinated by-products, were identified and the reaction pathway for CHA degradation during UV/Chlorine treatment was proposed.

Low-current electro-oxidation enhanced the biodegradation of the recalcitrant naphthenic acids in oil sands process water

Combining electro-oxidation (EO) with biodegradation for real oil sands process water (OSPW) treatment was evaluated in terms of naphthenic acid (NA) biodegradation enhancement. Ion mobility spectrometry (IMS) qualitative analysis showed that EO by graphite was able to degrade the different NA clusters in OSPW including: classical, oxidized and heteroatomic NAs. Applying EO even at current density as low as 0.2 mA/cm² was still able to reduce classical NAs and acid extractable fraction (AEF) by 19% and 7%, respectively. EO pretreatment preferentially broke long carbon chains and highly cyclic carboxylic fractions of NAs in OSPW to improve the biodegradation of NAs. Aerobic biodegradation for 40 days reduced NAs by up to 30.9% when the samples were pre-treated with EO. Applying EO at current densities below 2 mA/cm² maintained current efficiency as high as 48% and resulted in improvement in the biodegradation rate of remaining NAs by up to 2.7 folds. It was further revealed that applying EO before biodegradation could reduce the biodegradation half-life of classical NAs by up to 4.4 folds. 16S amplicon sequencing analysis showed that the samples subjected to biodegradation had increased abundances of Sphingomonadales and Rhodocyclales with increasing applied current density for EO pre-treatments.

Oxygen reduction reaction electrocatalysis inducing Fenton-like processes with enhanced electrocatalytic performance based on mesoporous ZnO/CuO cathodes: Treatment of organic wastewater and catalytic principle

To treat typical organic wastewater efficiently, a novel Fenton-like processes based on ZnO/CuO composite cathode induced by oxygen reduction reaction (ORR) electrocatalysis with enhanced electrocatalytic performance was established successfully. Electrochemical testing investigation indicated that the ZnO/CuO cathode possessed conspicuous redox peak and better conductivity than uncompounded electrodes. Additionally, the removal efficiency of methylene blue and its chemical oxygen demand (COD) reached 96.4% and 70.8% after 120 min, respectively. Next, the feasibility of the material in practical application was also discussed. Subsequently, electrocatalytic principle based on valence state changes of metal elements on the electrode surface were also studied by x-ray photoelectron spectroscopy (XPS). Redox reactions between the active species H₂O₂ and the species Cu⁺ promoting Fenton-like processes were deduced. Namely, the conversion of Cu(I) and Cu(II) on the electrode surface was accompanied by OH generation. The combination of ZnO and CuO improved the surface morphology, increasing the active site of ORR and the yield of H₂O₂, thus greatly enhanced the Fenton-like activity. Finally, the main intermediates were identified by Gas chromatography-mass spectrometer (GC-MS), and possible pathways for dye degradation were proposed. In short, the research of ZnO/CuO cathode provided great significance for heterogeneous Fenton-like degradation and also showed its application potential in water treatment and remediation.

Fe3+-NTA as iron source for solar photo-Fenton at neutral pH in raceway pond reactors

This work presents, for the first time, a kinetic study of the solar photo-Fenton process at neutral pH mediated by the Fe³⁺-NTA complex (molar ratio 1: 1) applied to remove contaminants of emerging concern (CECs). To this end, wastewater treatment plant (WWTP) secondary effluents were treated in a raceway pond reactor (RPR) at pilot plant scale with 0.1 mM Fe³⁺-NTA and 0.88 mM H₂O₂ under average solar UVA irradiance of 35 W/m². Sulfamethoxazole and imidacloprid, at 50 μg/L of initial concentration each, were selected as model CECs. Up to 40% of the sum of both model CECs was removed from simulated WWTP effluent by the Fe³⁺-NTA Fenton-like process, and >80% was removed by solar photo-Fenton. The effect of liquid depth in the reactor was evaluated, showing an increase of the treatment capacity from 12 mg CEC/m²·h to 18 mg CEC/m²·h when liquid depth increased from 5 to 15 cm. Afterwards, these results were validated with real WWTP effluents and compared with the results obtained with the Fe³⁺-EDDS complex under the same operating conditions. The same CEC removal rates were obtained with Fe³⁺-NTA and Fe³⁺-EDDS at 5 cm of liquid depth (kinetic constants of 0.110 min^-1 and 0.046 min^-1 for sulfamethoxazole and imidacloprid, respectively). Conversely, at 15 cm of liquid depth, the degradation rates were lower with Fe³⁺-NTA (kinetic constants of 0.034 min^-1 for sulfamethoxazole and 0.017 min^-1 for imidacloprid), whereas with Fe³⁺-EDDS the values were 0.076 min^-1 and 0.047 min^-1 for sulfamethoxazole and imidacloprid, respectively. Regarding process cost estimation, the use of NTA as iron chelate for solar photo-Fenton at neutral pH at pilot plant scale resulted very cost-effective (0.13-0.14 €/m³) in comparison with the use of EDDS (0.46-0.48 €/m³) at the two liquid depths tested.

In Situ Tracking Photodegradation of Trace Graphene Oxide by the Online Coupling of Photoinduced Chemical Vapor Generation with a Point Discharge Optical Emission Spectrometer

The photostability of graphene oxide (GO) strongly affects the performance of its products in optics and photonics. However, the photostability of GO, especially at trace levels, remains largely unexplored mainly because of the lack of available techniques. Herein, we developed a novel online system consisting of a highly efficient photoinduced chemical vapor generation reactor and an in situ measurement technique using a miniaturized and sensitive point discharge optical emission spectrometer. On the basis of the results of inorganic carbon species, abundant oxygen-containing functional groups on GO nanosheets made the degradation much easier than graphene. Under the optimized conditions (e.g., initial pH of 2.8 and binary photocatalysts dose of 200 mM H₂O₂, 1.0 mM Fe³⁺ ions, and 50 mg/L TiO₂ NPs), the limit of detection for GO was 87.5 μg/L C with a linear range of 0.5-10 mg/L C. Specifically, the accuracy and reliability of the developed system was verified by quantifying self-prepared GO as well as aggregated GO in natural organic matter-rich water samples. Finally, the sunlight-induced photodegradation of GO under simulated environmental conditions was successfully tracked. The developed system is a promising platform for in-time quality control of GO-based products as well as predicting the occurrence, transformation, and fate of GO at environmentally relevant concentrations in the natural aquatic environment.

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

The ultraviolet light-activated persulfate process (UV/Persulfate) has received much attention in recent years as a novel advanced oxidation method for the treatment of municipal and industrial wastewater. This work investigated the UV/Persulfate and UV/H₂O₂ processes for the treatment of real oil sands process water (OSPW) at ambient pH condition using a medium pressure mercury lamp (emission between 200 and 530 nm). The degradation performances towards fluorophore organic compounds and naphthenic acids (NAs) in OSPW were evaluated using synchronous fluorescence spectrometry and ultra performance liquid chromatography time-of-flight mass spectrometry, respectively. Compared to the UV/H₂O₂ process, the UV/Persulfate process exhibited higher efficiency to remove both NAs and fluorophore organic compounds. Under 40 min of UV exposure and incident irradiance of 3.50 mW cm^-2, fluorophore organic compounds were greatly degraded by UV/Persulfate (2 mM) and two- and three-ring fused organics were completely removed. 59.4%, 83.8% and 92.2% of O₂-NAs in OSPW were removed with persulfate dosages of 0.5, 2, and 4 mM, respectively. The removal efficiency decreased along with the number of oxygen atoms in NAs (83.8%, 49.3%, and 46.8% for O₂-, O₃-, and O₄-NAs, respectively) with 2 mM of persulfate, because of the formation of oxidized NAs in the same process. The structure-reactivity of O₂-NA compounds fitted pseudo-first order kinetics in UV/Persulfate process with the rate constants ranging from 0.0156 min^-1 to 0.1511 min^-1. NAs with higher carbon numbers and double bond equivalence were more reactive in the UV/Persulfate oxidation process. The acute toxicity of OSPW to Vibrio fischeri was significantly reduced after the UV/Persulfate and UV/H₂O₂ treatments. Overall results demonstrated that the UV/Persulfate oxidation can be an effective alternative for future reclamation of OSPW.

Efficient degradation of pharmaceutical micropollutants in water and wastewater by FeIII-NTA-catalyzed neutral photo-Fenton process

Ferric-nitrilotriacetate complex (Fe^III-NTA) has been adopted to catalyze the photo-Fenton degradation of emerging pharmaceutical micropollutants in water and wastewater at neutral pH. The generation of hydroxyl radicals (HO) in UVA/Fe^III-NTA/H₂O₂ was identified by using electron spin resonance (ESR) trapping technique. The effects of critical parameters (e.g., NTA:Fe^III molar ratio, Fe^III-NTA and H₂O₂ dosages) on the steady-state HO concentrations were studied in terms of the degradation of carbamazepine (CBZ, as a model compound) in Milli-Q water. In addition, the degradation of pharmaceuticals mixtures (including CBZ, crotamiton (CRMT) and ibuprofen (IBP)) in wastewater effluents from a biological aerated filter (BAF) by UVA/Fe^III-NTA/H₂O₂ was studied in continuous-flow mode. The results showed that the efficacies of Fe^III-NTA in catalyzing photo-Fenton degradation of pharmaceuticals in wastewater effluents were comparable to those obtained by Fe^III-ethylenediamine-N,N'-disuccinic acid (Fe^III-EDDS), and far exceeded other Fe^III-L complex (e.g., citric acid, malonic acid, oxalic acid and tartaric acid). More than 92% degradation efficiencies of CBZ, CRMT and IBP were obtained in continuous-flow mode under the given conditions of 0.178 mM Fe^III-NTA (1:1), 4.54 mM H₂O₂, UVA intensity 4.05 mW cm^-2, hydraulic retention time (HRT) 2 h, influent pH 7.6 (±0.2) and temperature 20 °C. The results presented herein suggest that Fe^III-NTA-catalyzed neutral photo-Fenton reaction can be an alternative tertiary process for the treatment of pharmaceutical micropollutants in secondary wastewater effluents.

Construction of an in-situ Fenton-like system based on a g-C3N4 composite photocatalyst

In this study, g-C₃N₄/PDI/Fe (gCPF) composite material was prepared by incorporating Fe ion on the composite catalyst of g-C₃N₄/PDI (gCP). X-ray photoelectron spectroscopy (XPS) showed that the Fe was successfully incorporated on the pristine g-C₃N₄/PDI. UV-vis diffuse reflectance spectrometry (UV-vis DRS) and Photoluminescence spectral (PL) analysis confirmed the enhancement of the visible absorption band following a decline in the photoelectron/hole recombination rate with gCPF. A preparatory experiment was performed on photocatalytic degradation of p-nitrophenol (PNP) to examine the activity of gCPF. Results obtained in the radical quenching and the electron paramagnetic resonance (EPR) spectroscopic studies indicated that an in-situ Fenton-like system has been successfully established and the main reactive oxygen species (ROS) changed from O₂- to both O₂- and OH in the gCPF system. However, a competition toward conduction band electrons between Fe³⁺ and O₂ caused an inhibitory effect on PNP degradation. To overcome the effect, nitrilotriacetic acid (NTA) was introduced as a reducing agent for Fe³⁺. Upon adding NTA, the efficiency of PNP degradation greatly enhanced from 33 to 80%. The effect of initial pH, dosage of NTA and content of dissolved O₂ on PNP degradation was also studied. The photocatalytic stability was confirmed by recycling experiments.

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

Naphthenic acids (NAs) are one of the constituents of concerns in oil sands process water (OSPW) because of their persistence and recalcitrance. Herein, we investigated the degradation of five model NA compounds by UV-activated persulfate (UV/persulfate) process under medium-pressure UV lamp irradiation at pH 8.0. UV/persulfate process showed higher degradation efficiency towards cyclohexanoic acid (CHA) compared to UV/H₂O₂ process under the same experimental conditions. CHA (0.39 mM) was completely removed within 30 min when 2 mM persulfate was used as oxidant, while more than 60 min were needed for the UV/H₂O₂ process. The removal of CHA decreased from 100% to 10% when 300 mM tert-butyl alcohol (TBA) was used as the scavenger, indicating that hydroxyl radical (OH) was responsible for the CHA degradation in the UV/persulfate process. Sulfate (SO₄^-) radicals reacted slowly with CHA in the UV/persulfate process with a second-order rate constant of k = 5.3 × 10⁷ M^-1s^-1. Relative kinetics studies using binary mixtures of model NA compounds showed similar structure-reactivity to that under UV/H₂O₂ process. NAs with long carbon chain, cyclic ring, and aromatic ring were more reactive in the UV/persulfate process. The presence of high concentration of chloride ions dramatically inhibited the reaction. The OH radicals in the UV/persulfate process were generated by capturing OH^- in solutions, as evidenced by the decrease of the pH value from 8.0 to 2.8 before and after treatment, respectively, in a pure water matrix. Primary intermediate products (oxy-CHA, hydroxyl-CHA, and dihydroxyl-CHA) of UV/persulfate process were confirmed by UPLC-MS.