Degradation pathway of the naphthalene azo dye intermediate 1-diazo-2- naphthol-4-sulfonic acid using Fenton's reagent

Simultaneous removal of tetracycline hydrochloride and hexavalent chromium by heterogeneous Fenton in a photocatalytic fuel cell system

In this work, a novel double-chamber system (PFC-Fenton), combined photocatalytic fuel cell (PFC) with Fenton, was constructed for tetracycline hydrochloride (TCH) and hexavalent chromium (Cr(VI)) removal and electricity production. Therein, Zn5(OH)6(CO3)2/Fe2O3/BiVO4/fluorine-doped SnO2 (ZIO/BiVO4/FTO) and carboxylated carbon nanotubes/polypyrrole/graphite felt (CCNTs/Ppy/GF) were served as photoanode and cathode, respectively. Under light irradiation, the removal efficiencies of TCH and Cr(VI) with the addition of H2O2 (2 mL) could reach 93.1% and 80.4%, respectively. Moreover, the first-order kinetic constants (7.37 × 10-3 min-1 of TCH and 3.94 × 10-3 min-1 of Cr(VI)) were 5.26 and 5.57 times as much as the absence of H2O2. Simultaneously, the maximum power density could be obtained 0.022 mW/cm2 at a current density of 0.353 mA/cm2. Therein, the main contribution of TCH degradation was ·OH and holes in anode chamber. The synergistic effect of photoelectrons, generated ·O2-, and H2O2 played a crucial role in the reduction of Cr(VI) in cathode chamber. The high-performance liquid chromatography-mass spectrometry indicated that TCH could be partially mineralized into CO2 and H2O. X-ray photoelectron spectroscope and X-ray absorption near-edge structure spectra showed that Cr(VI) could be reduced to Cr(III). After 5 times of cycling, the removal efficiencies of TCH and Cr(VI) were still greater than 70%, indicating the remarkable stability of the PFC-Fenton system. Overall, this system could remove TCH/Cr(VI) and generate power simultaneously without iron sludge formation, demonstrating a promising method to further develop PFC-Fenton technology.

Recycle graphite from spent lithium-ion batteries for H2O2 electrosynthesis

On-site H2O2 synthesis via the two-electron route oxygen reduction reaction for environmental remediation is attractive. This work offers a novel strategy for both spent graphite recovery and H2O2 electrosynthesis catalyst preparation. The graphite is directly recycled from spent lithium-ion batteries to an H2O2 electrosynthesis catalyst. From the view of sustainable development and environmental protection, the H2O2 electrosynthesis catalyst prepared using spent graphite is eco-friendly and cost-efficient. The surface functional groups of the recycled graphite are finely tuned by the HNO3 medium to induce -COOH and C-O-C groups. The activated graphite exhibits high H2O2 activity and selectivity, compared to the raw spent graphite. The activated graphite can achieve an H2O2 Faradic efficiency of about 80%. The activated graphite has a good prospect for T-acid wastewater treatment as the H2O2 generation catalyst. Almost 92% of chemical oxygen demand can be removed.

Removal of p-arsanilic acid and phenylarsonic acid from water by Fenton coagulation process: influence of substituted amino group

Phenylarsonic acid compounds, which were widely used in poultry and swine production, are often introduced to agricultural soils with animal wastes. Fenton coagulation process is thought as an efficient method to remove them. However, the substituted amino group could apparently influence the removal efficiency in Fenton coagulation process. Herein, we investigated the optimal conditions to treat typical organoarsenic contaminants (p-arsanilic acid (p-ASA) and phenylarsonic acid (PAA)) in aqueous solution based on Fenton coagulation process for oxidizing them and capturing the released inorganic arsenic, and elucidated the influence mechanism of substituted amino group on removal. Results showed that the pH value and the dosage of H₂O₂ and Fe²⁺ significantly influenced the performance of the oxidation and coagulation processes. The optimal conditions for removing 20 mg L^-1-As in this research were 40mg L^-1 Fe²⁺ and 60mg L^-1 H₂O₂ (the mass ratio of Fe²⁺/H₂O₂ = 1.5), initial solution pH of 3.0, and final solution pH of 5.0 adjusting after 30-min Fenton oxidation reaction. Meanwhile, the substituted amino group made p-ASA much more easily be attacked by ·OH than PAA and supply one more binding sites for forming complexes with Fe³⁺ hydrolysates, resulting in 36% higher oxidation rate and 7% better coagulation performance at the optimal conditions.

Microbial fuel cell coupled Fenton oxidation for the cathodic degradation of emerging contaminants from wastewater: Applications and challenges

Urbanization and industrialization have resulted in the escalation of the occurrence of emerging contaminants (EC) in the wastewater and ultimately to the receiving water bodies due to their bio-refractory nature. The presence of ECs in the water bodies adversely affects all three domains of life, viz. bacteria, archaea and eukaryotes, and eventually the ecosystem. Fenton oxidation is one of the most suitable method that is capable of degrading a variety of ECs by employing a strong oxidizing agent in the form of •OH. The coupling of Fenton oxidation with microbial fuel cell (MFC) offers benefits, such as low-cost, minimal requirement of external energy, and in-situ generation of oxidizing agents. The resulting system, termed as bio-electro-Fenton MFC (BEF-MFC), is capable of degrading the ECs in the cathodic chamber, while harvesting bioelectricity and simultaneously removing oxidizable organic matter from wastewater in the anodic chamber. This review discusses the applications of BEF-MFC for the treatment of dyes, pharmaceuticals, pesticides, and real complex wastewaters. Additionally, the effect of operating conditions on the performance of BEF-MFC are elaborated and emphasis is also given on possible future direction of research that can be adopted in BEF-MFC in the purview of up-scaling.

Degradation and chlorination mechanism of fumaric acid based on SO4•-: an experimental and theoretical study

It is well known that chloride ions could affect the oxidation kinetics and mechanism of contaminant based on SO₄^•- in the wastewater. Here, the degradation of an organic acid, fumaric acid (FA), was investigated in the presence of chloride (0-300 mM) by the Fe(II)/peroxymonosulfate (Fe(II)/PMS) system. A negative impact of chloride was observed on the rates of FA degradation. The degree of inhibitory effect was higher in Fe(II)/PMS addition order. Some chlorinated byproducts were identified during the FA oxidation process in the presence of Cl^- by the ultraperformance liquid chromatography and quadrupole-time of flight mass spectrometer (UPLC-QTOF-MS). With the increasing content of Cl^-, an accumulation of adsorbable organic halogen (AOX), an increase in acute toxicity, and an inhibition of mineralization were observed. According to the results of kinetic modeling, the production and transformation of oxidative species were dependent on Cl^- dosage and reaction time. SO₄^•- was supposed to be the main radical for FA degradation with Cl^- concentration below 5 mM, whereas Cl₂^•- was primarily responsible for the depletion of FA at [Cl^-] > 5 mM. A possible degradation pathway of FA was discussed. This study reveals the potential environmental risk of organic acid and is necessary to explore useful strategies for ameliorating the treatment of chloride-rich wastewater.

Mycoremediation of azo dyes using Cyberlindnera fabianii yeast strain: Application of designs of experiments for decolorization optimization

This study investigated the dye decolorization capacity of three yeast strains. Cyberlindnera fabianii was shortlisted for its high decolorization capacity and was further tested on various azo dyes. Based on the color of the biomass, and the UV-Vis analysis, Acid Red 14 was selected as a model dye, to examine the enzymatic biodegradation. The results showed significant increase in the intracellular and extracellular activities of laccase, tyrosinase, manganese peroxidase, and azoreductase. Phytotoxicity assessment indicated that the AR14 biodegradation by-products were not phytotoxic compared to the original dye molecules. Regarding the decolorization optimization, the screening of factors using the Plackett-Burman design showed that pH, dye concentration, and shaking speed had significant effects. These factors and their combined effect were evaluated using response surface methodology with the Box-Behnken model. The pH was the most significant factor, followed by dye concentration. The analysis of the contour plot and the 3D response surface diagram showed that the decolorization was inversely proportional to the increase in the initial dye concentration, but proportional to the initial pH and shaking speed. At optimal conditions (pH = 5.154, AR14 = 50 mg/L), C. fabianii could decolorize more than 97% of AR14 within 12 hr. PRACTITIONER POINTS: Cyberlindnera fabianii is a successful candidate for dye mycoremediation. Oxidase and reductase are the key enzymes involved in the biodegradation of azo dyes. By-products of Acid red 14 biodegradation are not phytoxic compared to the original dye. Design of experience tools enables to determine optimum conditions for efficient decolorization.

Kinetic and thermodynamic studies of the degradation of methylene blue by photo-Fenton reaction

Syrian natural magnetite has been utilized for the removal of methylene blue from aqueous solutions by photo-Fenton reaction. Experiments were carried out to evaluate the kinetic and thermodynamic parameters.

Pseudo-first order, pseudo-second-order models were used to analyze the kinetic data obtained at different initial MB concentrations and temperatures.

The photo-Fenton degradation process of MB is better described by the pseudo-first-order model. The activation energy Ea = 16.89 and 18.02 kJ/mol for MB degradation at concentrations 40 and 80 mg/l respectively, and that suggesting the degradation reaction proceeded with a low energy barrier, the values obtained (ΔG∗, ΔS∗, and ΔH∗) indicate that the process is endothermic and spontaneous.

Reactivity-directed analysis - a novel approach for the identification of toxic organic electrophiles in drinking water

Drinking water consumption results in exposure to complex mixtures of organic chemicals, including natural and anthropogenic chemicals and compounds formed during drinking water treatment such as disinfection by-products. The complexity of drinking water contaminant mixtures has hindered efforts to assess associated health impacts. Existing approaches focus primarily on individual chemicals and/or the evaluation of mixtures, without providing information about the chemicals causing the toxic effect. Thus, there is a need for the development of novel strategies to evaluate chemical mixtures and provide insights into the species responsible for the observed toxic effects. This critical review introduces the application of a novel approach called Reactivity-Directed Analysis (RDA) to assess and identify organic electrophiles, the largest group of known environmental toxicants. In contrast to existing in vivo and in vitro approaches, RDA utilizes in chemico methodologies that investigate the reaction of organic electrophiles with nucleophilic biomolecules, including proteins and DNA. This review summarizes the existing knowledge about the presence of electrophiles in drinking water, with a particular focus on their formation in oxidative treatment systems with ozone, advanced oxidation processes, and UV light, as well as disinfectants such as chlorine, chloramines and chlorine dioxide. This summary is followed by an overview of existing RDA approaches and their application for the assessment of aqueous environmental matrices, with an emphasis on drinking water. RDA can be applied beyond drinking water, however, to evaluate source waters and wastewater for human and environmental health risks. Finally, future research demands for the detection and identification of electrophiles in drinking water via RDA are outlined.

Persulfate assisted hydrothermal processing of spirulina for enhanced deoxidation carbonization

The influence of persulfate assisted hydrothermal carbonization (HTC) (160 °C-220 °C) of spirulina and hydrochar properties was assessed. The elementary composition and proximate analysis of hydrochar were investigated on the carbonization degree and basic fuel properties, and the surface functional groups and morphological characteristics of hydrochar were analyzed as well as thermal stability. Results suggested that persulfate assisted process enhanced the carbonization degree of hydrochar by oxygen reduction (1.53%-2.74%) and increase of C ratio, and HHVs increased 0.81-1.39 MJ/kg at temperature above 180 °C. The -OH and CO on hydrochar surface were significantly reduced, and C-(C, H) and C-(O, N) were weakened by persulfate addition and more C-H peaks was formed. Additionally, the persulfate addition enhanced the thermal stability of hydrochar by lowing the maximum mass loss rate. The result suggested that HTC can be conducted with persulfate at lower temperature for hydrochar biofuel production.

Using Electrolytic Manganese Residue to prepare novel nanocomposite catalysts for efficient degradation of Azo Dyes in Fenton-like processes

In this study, Electrolytic Manganese Residue (EMR) was treated by EDTA-2Na/NaOH, ultrasonic etching, and hydrothermal reaction to obtain a novel nanocomposite catalyst (called N-EMR), which then was used, together with H₂O₂, to treat synthetic textile wastewater containing Reactive Red X-3B, Methyl Orange, Methylene blue and Acid Orange 7. Results indicated that the N-EMR had a nano-sheet structure in sizes of 100-200 nm; new iron and manganese oxides with high activity were produced. The mixture of a small amount of N-EMR (40 mg/L) and H₂O₂ (0.4 × 10^-3 M) could removal about 99% of azo dyes (at 100 mg/L in 100 mL) within 6-15 min, much faster than many advanced oxidation processes (AOPs) reported in the literature. The elucidation of the associated mechanism for azo dyes degradation indicates that azo dyes were attacked by superoxide radicals, hydroxyl radicals, and electron holes generated within system. N-EMR was found to be reusable and showed limited inhibition by co-existing anions and cations. Moreover, high removal efficiency of azo dyes could happen in the system with a wide range of pH (1-8.5) and temperatures (25-45 °C), indicating that the process developed in this study may have broad application potential in treatment of azo dyes contaminated wastewater.

Microbial degradation, spectral analysis and toxicological assessment of malachite green by Streptomyces chrestomyceticus S20

Malachite green (MG), a triphenylmethane dye is extensively used for coloring silk, aquaculture and textile industries, it has also has been reported toxic to life forms. This study aimed to investigate the biodegradation potential of MG by actinobacteria. The potent actinobacterial strain S20 used in this study was isolated from forest soil (Sabarimala, Kerala, India) and identified as Streptomyces chrestomyceticus based on phenotype and molecular features. Strain S20 degraded MG up to 59.65 ± 0.68% was studied in MSM medium and MG (300 mg l^-1) and degradation was increased (90-99%) by additions of 1% glucose and yeast extract into the medium at pH 7. The treated metabolites from MG by S20 characterized by FT-IR and GC-MS. The results showed MG has been degraded into nontoxic compounds evaluated by (1) phytotoxic assay on Vigna radiata, (2) microbial toxicity on Staphylococcus aureus, Bacillus subtilis, Micrococcus luteus, Streptococcus sp. and Escherichia coli, (3) cytotoxicity assay in a human cell line (MCF 7). The toxicity studies demonstrated that the byproducts from MG degradation by S. chrestomyceticus S20 were no toxic to plants and microbes and less toxic to human cells as compared to the parent MG. Perhaps this is the first work reported on biodegradation of MG by S. chrestomyceticus which could be a potential candidate for the removal of MG from various environments.

Remedial Technologies for Aniline and Aniline Derivatives Elimination from Wastewater

BACKGROUND

Aniline and its derivatives are widely used as intermediate chemicals in the pharmaceutical and dye industries and are present in their wastewaters. These chemicals are of concern due to their potential detrimental effects on public health and aquatic species in the environment.

OBJECTIVES

Various available remedial technologies presented in the literature were investigated to determine the most suitable technology for the elimination of aniline and aniline derivatives from waste streams.

METHODS

The related literature was collected electronically from ScienceDirect, Google Scholar, the International Agency for Research on Cancer (IARC), ResearchGate and Wiley Online Library for systematic review. The search terms included 'aniline', 'aniline degradation', 'advanced oxidation processes (AOPs)', 'aniline derivatives' and 'Fenton's reagent'.

DISCUSSION

Aniline and its derivatives are a serious issue in the effluents of dye and pharmaceutical industries, but a number of efficient treatment methods using biological, physical and AOPs have been presented in the literature.

CONCLUSIONS

Comparison of the available technologies showed that AOPs were the most cost effective and efficient technologies for eliminating aniline and its derivatives from wastewater.

COMPETING INTERESTS

The authors declare no competing financial interests.

Non-radical activation of H2O2 by surface-disordered WO3 for efficient and selective pollutant degradation with weak matrix effects

Heterogeneous catalysis is promising for water treatment. Solid catalysts play governing roles. Herein, the surface-disordered WO₃, D-WO₃, engineered with surface and sub-surface defective sites from NaBH₄ reduction was proven to be an effective catalyst for H₂O₂ activation. The defective degree and defects amount on WO₃ were regulated by NaBH₄. More than 95% of two typical azo dyes, RhB and MG, were selectively degraded in D-WO₃/H₂O₂ system during 3.0 h, while no significant activity was observed for MO as well as bisphenol A, roxarsone, phenol, 4-chlorophenol, p-nitrophenol, o-aminophenol, urea, and 2,4-dichlorophenol in comparison under the identical conditions (mainly less than 20%). Both ESR and radical scavenging tests indicated the minor role of ·OH from H₂O₂ activation on D-WO₃. The superior activity of D-WO₃ could be mainly attributed to the surface and sub-surface defects with finely tailored local atomic configurations and electronic structures of central metal sites. Surface and sub-surface defective sites could serve as the reactive sites of interfacial adsorption, dissociative activation, and catalytic decomposition for both oxidant and pollutants, with high adsorption energy, strong structural activation, and superior catalytic activity. Our findings provided a new chance for non-selective radical catalysis based on transition metal oxides and a promising catalyst with high performance, low cost, and no toxicity for pollutant degradation with weak matrix effects in wastewater and surface water.

Continuous degradation of Direct Red 23 by calcium pectate-bound Ziziphus mauritiana peroxidase: identification of metabolites and degradation routes

In the present study, oxido-reductive degradation of diazo dye, Direct Red 23, has been carried out by Ziziphus mauritiana peroxidases (specific activity 17.6 U mg^-1). Peroxidases have been immobilized via simple adsorption and cross-linking by glutaraldehyde; adsorbed and cross-linked enzyme retained 94.28% and 91.23% of original activity, respectively. The stability of peroxidases was enhanced significantly upon immobilization; a marked widening in both pH and temperature activity profiles were observed. Adsorbed peroxidases exhibited similar pH and temperature optima as reported for the free enzyme. Thermal stability was significantly enhanced in case of cross-linked enzyme which showed 80.52% activity even after 2 h of incubation at 60 °C. Packed bed reactors containing adsorbed and cross-linked peroxidases were run over a period of 4 weeks; adsorbed peroxidases retained 52.86% activity whereas cross-linked peroxidases maintained over 77% dye decolorization ability at the end of the fourth week of its continuous operation. Gas chromatography coupled with mass spectrometry was used to analyze the degradation products; it showed the presence of four major metabolites. Degradation of dye starts with the 1-Hydroxybenzotriazole radical attack on the carbon atom of the phenolic ring bearing azo linkage, converting it into cation radical which underwent nucleophilic attack by a water molecule and results in cleavage of chromophore via symmetric and asymmetric cleavage pathways. Intermediates undergo spontaneous removal of nitrogen, deamination, and oxidation reactions to produce maleic acid as the final degradation product. Graphical abstract.

Azonaphthalene dyes decolorization and detoxification by laccase from Trametes versicolor

The aim of the present study was to investigate the dye decolorization ability of laccase from Trametes versicolor. Five azonaphthalene dyes (Acid Violet 7, Acid Red 1, Allura Red AC, Orange G and Sunset Yellow FCF) were used to evaluate dye decolorization. Laccase from T. versicolor is capable of decolorizing dyes, namely Acid Violet 7 (53.7±2.3 %) and Orange G (46.0±2.2 %). The less effective ability of laccase was observed at the decolorization of other selected dyes (6.9 - 18.6 %). The presence of redox mediator (1-hydroxybenzotriazole) increased decolorization percentage for all tested dyes (≥ 90.5 %). Toxic effect of azo dyes and their degradation products after laccase treatment was observed on the growth of selected bacteria (Micrococcus luteus, Bacillus subtilis, Pseudomonas syringae and Escherichia coli), yeasts (Candida parapsilosis and Saccharomyces cerevisiae) and algae (Chlorella vulgaris and Microcystis aeruginosa). It was confirmed that degradation products showed lower inhibition effect compared to initial dyes. These findings suggest that laccase from T. versicolor are able to decolorize and detoxify selected azonaphthalene dyes.

Electrochemical degradation of Mordant Blue 13 azo dye using boron-doped diamond and dimensionally stable anodes: influence of experimental parameters and water matrix

In this work, the electrooxidation as environmentally clean technology has been studied to the degradation of Mordant Blue 13 azo dye (MB13) using boron-doped diamond (p-Si/BDD) and oxide ruthenium titanium (Ti/Ru_0.3Ti_0.7O₂ (DSA)) anodes in various water matrices: distilled water (DW), hot tap water (HTW), and simulated wastewaters with (SWS) and without surfactant (SW). The influence of experimental parameters, such as current density, initial dye concentration, electrolysis time/specific charge, and pH on the MB13 degradation rate, current efficiency, and energy consumption, has been determined. The enhanced rate of both color and chemical oxygen demand (COD) removal in sulfate aqueous solutions with BDD was observed, which indicates that sulfate (SO₄^-•) radicals along with ^•OH ones might be responsible for the degradation process. The MB13 decolorization process obeyed a pseudo-first-order reaction kinetics with the apparent rate constant from 7.36 × 10^-2 min^-1 to 4.39 × 10^-1 min^-1 for BDD and from 9.2 × 10^-3 min^-1 to 2.11 × 10^-2 min^-1 for DSA depending on the electrolysis conditions. The effect of water matrix on the decolorization and COD removal efficiency has been evaluated. Inorganic ions, mordant salt, and surfactant contained in simulated effluents decelerated the COD decay compared to DW and HTW for the both anodes; meanwhile, they differently affected the discoloration process. A comparison of the specific energy consumption for each electrocatalytic material under different experiment conditions has been made. The BDD electrode was more efficient than the DSA to oxidize the MB13 dye in all kinds of water.

Ferrocene-catalyzed heterogeneous Fenton-like degradation mechanisms and pathways of antibiotics under simulated sunlight: A case study of sulfamethoxazole

Readily-available and efficient catalyst is essential for activating oxidants to produce reactive species for deeply remediating water bodies contaminated by antibiotics. In this study, Ferrocene (Fc) was introduced to establish a heterogeneous photo-Fenton system for the degradation of sulfonamide antibiotics, taking sulfamethoxazole as a representative. Results showed that the removal of sulfamethoxazole was effective in Fc-catalyzed photo-Fenton system. Electron spin resonance and radical scavenging experiments verified that there was a photoindued electron transfer process from Fc to H₂O₂ and dissolved oxygen resulting in the formation of OH that was primarily responsible for the degradation of sulfamethoxazole. The reactions of OH with substructure model compounds of sulfamethoxazole unveiled that aniline moiety was the preferable reaction site of sulfamethoxazole, which was verified by the formation of hydroxylated product and the dimer of sulfamethoxazole in Fc-catalyzed photo-Fenton system. This heterogeneous photo-Fenton system displayed an effective degradation efficiency even in a complex water matrices, and Fc represented a long-term stability by using the catalyst for multiple cycles. These results demonstrate that Fc-catalyzed photo-Fenton oxidation may be an efficient approach for remediation of wastewater containing antibiotics.

Decolorization of Basic Turquise Blue X-GB and Basic Blue X-GRRL by the Fenton’s Process and its Kinetics

Textile industries use dyes to color their products and release waste water containing dyes, causing water pollution which is a serious problem for survival of human life on earth. The decolorization of basic turquise blue X-GB (BTB X-GB) 250% and basic blue X-GRRL (BB X GRRL) 250% dyes was examined by advanced (Fenton process) oxidation process. The effects of different parameters (initial dye concentration, pH, concentrations of hydrogen peroxide (H2O2) and reaction time) have been examined and optimum conditions were determined. It has been noted that percentage decolorization of both dyes (50 mg/L) increases with increase in concentration of H2O2. At optimum conditions (pH=3.0, H2O2=4.8 mM, temperature=50°C, time=80 min of BTB X-GB, and pH=5.0, H2O2=5.6 mM, temperature=40°C, time=60 min of BB X-GRRL) the decolorization obtained by Fenton process was 85.83% of BTB X-GB and 74.98% for BB X-GRRL. 1st order, 2nd order and BMG kinetic models were used to analyze the data. BMG model gives us the higher values of correlation coefficients for all data. Results showed that Fe2+/H2O2 are most effective for oxidation treatment of waste water effluents containing dyes as main pollutants.

Study on the degradation mechanism and pathway of benzene dye intermediate 4-methoxy-2-nitroaniline via multiple methods in Fenton oxidation process

Benzene dye intermediate (BDI) 4-methoxy-2-nitroaniline (4M2NA) wastewater has caused significant environmental concern due to its strong toxicity and potential carcinogenic effects. Reports concerning the degradation of 4M2NA by advanced oxidation process are limited. In this study, 4M2NA degradation by Fenton oxidation has been studied to obtain more insights into the reaction mechanism involved in the oxidation of 4M2NA. Results showed that when the 4M2NA (100 mg L-1) was completely decomposed, the TOC removal efficiency was only 30.70-31.54%, suggesting that some by-products highly recalcitrant to the Fenton oxidation were produced. UV-Vis spectra analysis based on Gauss peak fitting, HPLC analysis combined with two-dimensional correlation spectroscopy and GC-MS detection were carried out to clarify the degradation mechanism and pathway of 4M2NA. A total of nineteen reaction intermediates were identified and two possible degradation pathways were illustrated. Theoretical TOC calculated based on the concentration of oxalic acid, acetic acid, formic acid, and 4M2NA in the degradation process was nearly 94.41-97.11% of the measured TOC, indicating that the oxalic acid, acetic acid and formic acid were the main products. Finally, the predominant degradation pathway was proposed. These results could provide significant information to better understand the degradation mechanism of 4M2NA.

Treatment of real benzene dye intermediates wastewater by the Fenton method: characteristics and multi-response optimization

Benzene dye intermediates (BDI) wastewater has caused major environmental concern due to its potential carcinogenic, teratogenic, and mutagenic effects.

Persulfate oxidation assisted hydrochar production from Platanus Orientalis Leaves: Physiochemical and combustion characteristics

Platanus Orientalis Leaves (POL), a widely planted tree in parks and along streets, was employed by sequential persulfate oxidation (Fe²⁺and persulfate) and hydrothermal treatment (HTC) to improve the thermal stability, energy yield and combustion behavior of hydrochars (HCs). Higher heating values (HHVs) of HCs derived from persulfate pretreated POL was increased by 30.5% at mild HTC temperature (i.e., 210°C) as compared to char without pretreatment. Elevating Fe²⁺/persulfate ratio to 0.2 enables HCs with high fractions of lignin, thus promoting the energy yield going up to 64.4%. The ultimate and proximate analysis, N₂ adsorption-desorption isotherms, FT-IR spectroscopy and thermogravimetric analysis were conducted to probe into chars' physiochemical and combustion characteristics. Results indicated that persulfate pretreatment on POL strengthened efficient HTC conversion from volatile matter to fixed carbon, increasing the ignition temperature of HCs from 261.5 to 404.3°C as compared to the char obtained with only HTC.

Effects of chloride on PMS-based pollutant degradation: A substantial discrepancy between dyes and their common decomposition intermediate (phthalic acid)

A considerable effort has been devoted to elucidating the roles of chloride in oxidative degradation and chlorination of dyes. However, few investigations are available on kinetic analysis and transformation pathways of secondary degradation byproducts of dyes in saline wastewater treatment. Here the impact of chlorine on the degradation rate of phthalic acid, a typical dye degradation intermediate, by the Co²⁺/peroxymonosulfate (PMS) process was examined. Degradation efficiency, intermediate products, AOX (adsorbable organic halogen) formation and mineralization were considered. An overall negative impact was observed within the concentration of Cl^- up to 100 mM, differing from the dual effect of chloride on dye degradation process as previously observed. The presence of high levels of Cl^- led to a low production of AOX and a reduction of the formation of chlorinated by-products. The mineralization was also restrained when the Cl^- concentration was increased. Degradation pathways for these processes are proposed. These findings provide valuable information about the degradation pathways of dyes and about the formation mechanism of chlorinated by-products in industrial saline wastewater treatment.

Facile synthesis of magnetic sludge-based carbons by using Electro-Fenton activation and its performance in dye degradation

Highly stable iron based magnetic carbon were prepared by sequential Electro-Fenton (EF) activation and pyrolysis of sewage sludge. The applied voltage exerts great influence on EF treated sludge flocs and thus poses significant effect on physiochemical properties of the as-prepared carbons. High insertion rate of iron into sludge from EF activation resulted in carbons with highly dispersed iron oxides, which had average size of iron nanoparticles being 4.77nm. The carbon also presented well developed porosity which had Brunauer-Emmett-Teller (BET) surface area attaining 341m²/g. Carbons prepared by traditional Iron Impregnation (IM) were used as comparison to gain further insight into their catalytic role as Fenton-like catalyst. Results showed that EF-activated sludge carbon could yield 96.1% of Methyl Orange (MO) removal in 60min together with only 1.4% of iron leaching. After three cycles, the MO removal can still reach 80% with EF-activated carbons.

Adsorption behavior of benzenesulfonic acid by novel weakly basic anion exchange resins

Two novel weakly basic anion exchange resins (SZ-1 and SZ-2) were prepared via the reaction of macroporous chloromethylated polystyrene-divinylbenzene (Cl-PS-DVB) beads with dicyclohexylamine and piperidine, respectively. The physicochemical structures of the resulting resins were characterized using Fourier Transform Infrared Spectroscopy and pore size distribution analysis. The adsorption behavior of SZ-1 and SZ-2 for benzenesulfonic acid (BA) was evaluated, and the common commercial weakly basic anion exchanger D301 was also employed for comparison purpose. Adsorption isotherms and influence of solution pH, temperature and coexisting competitive inorganic salts (Na₂SO₄ and NaCl) on adsorption behavior were investigated and the optimum desorption agent was obtained. Adsorption isotherms of BA were found to be well represented by the Langmuir model. Thermodynamic parameters involving ΔH, ΔG and ΔS were also calculated and the results indicate that adsorption is an exothermic and spontaneous process. Enhanced selectivity of BA sorption over sulfate on the two novel resins was observed by comparison with the commercial anion exchanger D301. The fact that the tested resins loaded with BA can be efficiently regenerated by NaCl solution indicates the reversible sorption process. From a mechanistic viewpoint, this observation clearly suggests that electrostatic interaction is the predominant adsorption mechanism. Furthermore, results of column tests show that SZ-1 possesses a better adsorption property than D301, which reinforces the feasibility of SZ-1 for potential industrial application.

Accelerating biodegradation of a monoazo dye Acid Orange 7 by using its endogenous electron donors

Biodegradation of a monoazo dye - Acid Orange 7 (AO7) was investigated by using an internal circulation baffled biofilm reactor. For accelerating AO7 biodegradation, endogenous electron donors produced from AO7 by UV photolysis were added into the reactor. The result shows that AO7 removal rate can be accelerated by using its endogenous electron donors, such as sulfanilic and aniline. When initial AO7 concentration was 13.6mg/L, electron donors generated by 8h UV photolysis were added into the same system. The biodegradation rate 0.4mg^0.05h^-1 was enhanced 60% than that without adding electron donor. Furthermore, sulfanilic and aniline were found to be the main endogenous electron carriers, which could accelerate the steps of the azo dye biodegradation.

Degradation of Reactive Yellow X-RG by O3/Fenton system: response surface approach, reaction mechanism, and degradation pathway

O₃/Fenton for the treatment of effluent containing Reactive Yellow X-RG is investigated. The response surface methodology is applied to study the main and interactive effects of the parameters. With the initial dye concentration being controlled at 300 mg L^-1, the optimized conditions for wastewater treatment are 3.68, 29.19 and 18.49 mg min^-1 for initial pH, mole ratio of [H₂O₂]/[Fe²⁺] and ozone dosage, respectively. The regression quadratic model well describing the degradation efficiency of O₃/Fenton process is developed and validated by the analysis of variances, respectively. In addition, a possible pathway for Reactive Yellow X-RG degradation is proposed by detecting the temporal evolution of intermediates in the solution, with the use of some techniques including ultraviolet spectrophotometric method (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and gas chromatography-mass spectrometry (GC/MS). Meanwhile, every reaction step is given to explain the degradation mechanisms.

Selective conversion of organic pollutant p-chlorophenol to formic acid using zeolite Fenton catalyst

Effective remediation technologies which can converse the harmful organic pollutants to high-value chemicals are crucial both for wastewater treatment and energy regeneration. This study provides an evidence that extracting useful chemicals from wastewater is feasible through selective conversion of p-chlorophenol to high value formic acid as an example. The reported system works with a readily available Fe-containing ZSM-5 catalyst, water as the solvent and hydrogen peroxide as the oxidant. The yield of formic acid reached up to 50.7% when the Si/Al ratio of ZSM-5 was 80 and the Fe-content was 1.4%. By X-ray adsorption fine structure (XAFS), NH3 temperature-programmed desorption (NH3-TPD) technique, the pyridine adsorption Fourier-transition infrared (Py-IR) spectroscopy and adsorption measurements, it was concluded that the controllable degradation of p-CP could be approached through selective adsorption, the moderate Brønsted acid sites for H2O2 activation and the properly selective conversion control due to extra-framework coordination unsaturated sites (CUS) of Fe. This approach might provide a new avenue for the field of organic pollutant remediation.

Heterogeneous activation of H2O2 by defect-engineered TiO(2-x) single crystals for refractory pollutants degradation: A Fenton-like mechanism

The heterogeneous catalyst plays a key role in Fenton-like reaction for advanced oxidation of refractory pollutants in water treatment. Titanium dioxide (TiO2) is a typical semiconductor with high industrial importance due to its earth abundance, low cost and no toxicity. In this work, it is found that TiO2 can heterogeneously activate hydrogen peroxide (H2O2, E°=1.78 eV), a common chemical oxidant, to efficiently generate highly-powerful hydroxyl radical, OH (E(0)=2.80 eV), for advanced water treatment, when its crystal shape, exposed facet and oxygen-stoichiometry are finely tuned. The defect-engineered TiO2 single crystals exposed by high-energy {001} facets exhibited an excellent Fenton-like activity and stability for degrading typical refractory organic pollutants such as methyl orange and p-nitrophenol. Its defect-centered Fenton-like superiority is mainly attributed to the crystal oxygen-vacancy, single-crystalline structure and exposed polar {001} facet. Our findings could provide new chance to utilize TiO2 for Fenton-like technology, and develop novel heterogeneous catalyst for advanced water treatment.

Rapid degradation of p-arsanilic acid with simultaneous arsenic removal from aqueous solution using Fenton process

Although banned in some developed countries, p-arsanilic acid (p-ASA) is still used widely as a feed additive for swine production in many countries. With little uptake and transformation in animal bodies, nearly all the p-ASA administered to animals is excreted chemically unchanged in animal wastes, which can subsequently release the more toxic inorganic arsenic species upon degradation in the environment. For safe disposal of the animal wastes laden with p-ASA, we proposed a method of leaching the highly water-soluble p-ASA out of the manure first, followed by treatment of the leachate using the Fenton process to achieve fast oxidation of p-ASA and removal of the inorganic arsenic species released (predominantly arsenate) from solution simultaneously. The effects of solution pH, dosages of H2O2 and Fe(2+), and the presence of dissolved organic matter (DOM) on the treatment efficiency were systematically investigated. Under the optimum treatment conditions (0.53 mmol L(-1) Fe(2+), 2.12 mmol L(-1) H2O2, and initial pH of 3.0), p-ASA (10 mg-As L(-1)) could be completely oxidized to As(V) within 30 min in pure water and 4 natural water samples, and at the final pH of 4.0, the residual arsenic levels in solution phase were as low as 1.1 and 20.1-43.4 μg L(-1) in the two types of water matrixes, respectively. The presence of humic acid significantly retarded the oxidation of p-ASA by scavenging HO, and inhibited the As(V) removal through competitive adsorption on ferric hydroxide. Due to the high contents of DOM in the swine manure leachate samples (TOC at ∼500 mg L(-1)), much higher dosages of Fe(2+) (10.0 mmol L(-1)) and H2O2 (40.0 mmol L(-1)) and a longer treatment time (120 min) were required to achieve near complete oxidation of p-ASA (98.0%), while maintaining the levels of residual arsenic in the solution at <70.0 μg L(-1). The degradation pathway of p-ASA in the Fenton process was proposed based on the major degradation products detected. Together, the results demonstrate that the Fenton process is promising as an efficient, robust, and low-cost treatment method for controlling the risk of p-ASA in the animal wastes generated at factory farms.

Design, synthesis of uniform Au nanoparticles modified Fe2O3–TiO2 coaxial nanotubes and their enhanced thermal stability and photocatalytic activity

Au nanoparticles are loaded on Fe₂O₃/TiO₂ nanotubes by a one-pot strategy using lysine as both a linker and a capping agent.

Enhanced adsorptive removal of naphthalene intermediates from aqueous solution by introducing reed straw into sewage sludge-based activated carbon

The disposal of sewage sludge (SS) and reed straw (RS) has becoming a critical issue due to their rapid production. In this study, the SS-based activated carbon (SSC) was produced by introducing the RS as a component material. Properties including BET surface area, pore volume, surface chemical groups, and morphologies were characterized. The adsorption of 1-diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid) and 2-Naphthol (2-Nap), which differs in their physicochemical properties, on as-prepared carbons were investigated. The overall adsorption was found to be jointly controlled by external mass transfer and intraparticle diffusion, and the optimal pH was found to be 5 due to their electrostatic attraction. Further study revealed that the SS- and RS-based carbons (SC and RSC, respectively) exhibited different adsorption behavior toward 1,2,4-Acid and 2-Nap. The calculated adsorption capacity from Langmuir–Freundlich model of SC and RSC for the two intermediates was 141.0, 84.6 mg g(-1) and 48.2, 110.2 mg g(-1), respectively, whereas their hybrid product (SSC) showed comparable capacity for 1,2,4-Acid (117.8 mg g(-1)), as well as higher capacity for 2-Nap (157.5 mg g-1). It was found that the presence of meso- or macropores facilitates the precipitation of mineral phases of inorganic substances during carbonization, attracting the molecules with polar functional groups, while the introduction of C-rich RS to SS enhances the adsorption of hydrophobic molecules

Influence of generated intermediates' interaction on heterogeneous Fenton's degradation of an azo dye 1-diazo-2-naphthol-4-sulfonic acid by using sludge based carbon as catalyst

Sewage sludge based carbons have recently been used as novel catalyst in heterogeneous Fenton's reactions to degrade azo dye molecules. The carbons, functioning as both catalyst and adsorbent, play an important role in pollutants elimination, especially for those simultaneously generated organic intermediates. Different factors, i.e., H2O2 concentration, may influence the type and properties of those intermediates and may have great impacts on their elimination through the interactions with catalysts' surface. Thus, techniques including Temperature Programmed Desorption-Mass Spectrometer (TPD-MS), N2 adsorption isotherm and Scanning Electron Microscope (SEM) were used to probe the ways of the interaction between oxidation products and catalyst by using different initial H2O2 concentrations (10 and 20mM). The higher Chemical Oxygen Demand (COD) removal with 20mM H2O2 was found to be related not only to the higher hydroxyl radicals but also the specific interactions between the intermediates and catalyst' surface. The deep oxidation occurred in the conditions with higher oxidant amount enhances the intermediates' adsorption on catalyst, thus increasing the COD removal by large margin. Simulated adsorption experiments by using six primarily formed intermediates and three deeply mineralized products on three different catalysts also confirmed the assumption. Results suggested close relations between adsorption capacities and intermediates' properties such as polar surface area and octanol-water partition coefficient.

Environmental mass spectrometry

Environmental mass spectrometry is an important branch of science because it provides many of the data that underlie policy decisions that can directly influence the health of people and ecosystems. Environmental mass spectrometry is currently undergoing rapid development. Among the most relevant directions are a significant broadening of the lists of formally targeted compounds; a parallel interest in nontarget chemicals; an increase in the reliability of analyses involving accurate mass measurements, tandem mass spectrometry, and isotopically labeled standards; and a shift toward faster high-throughput analysis, with minimal sample preparation, involving various approaches, including ambient ionization techniques and miniature instruments. A real revolution in analytical chemistry could be triggered with the appearance of robust, simple, and sensitive portable mass spectrometers that can utilize ambient ionization techniques. If the cost of such instruments is reduced to a reasonable level, mass spectrometers could become valuable household devices.

Adsorption and Fenton-like degradation of naphthalene dye intermediate on sewage sludge derived porous carbon

A sewage sludge derived porous carbon (SC), which was prepared by physicochemical activation and carbonization (600°C), was applied for the adsorption and degradation of 1-diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid) in the presence of H(2)O(2) and the performance was compared to that of pure Fe(3)O(4) magnetic nanoparticles (MNPs). The prepared SC showed mesoporous structure with magnetic property, which made it favorable for solid-liquid separation application. Further experiments revealed that SC had a higher adsorption capacity and degradation efficiency of 1,2,4-Acid than bare Fe(3)O(4). The Langmuir and Freundlich model fitted the isotherm data and illustrated that the equilibrium adsorption amount of 1,2,4-Acid onto SC (95.1 mg g(-1)) was quadruple as large as that on Fe(3)O(4) (26.4 mg g(-1)). The subsequent degradation experiments were conducted at conditions (pH 5.0 in the presence of 15 mM H(2)O(2)) with regard to 1,2,4-Acid degradation efficiency and metal ions leach. The 120 min's treatment in SC/H(2)O(2) system achieved 94% of 1,2,4-Acid (from 150 mg L(-1) after adsorption equilibrium to 9 mg L(-1)) and 48.1% TOC reduction, far higher than the efficiency of 46% and 24.3% by using Fe(3)O(4) MNPs. Further analysis evidenced the co-catalytic effect of iron, carbon, silicon and aluminum, which existed in large quantities in sludge derived SC. The carbonaceous phase along with silica contributes to an increase in the dispersion of catalytic centers and an adsorbent to concentrate organic pollutant whereas the iron oxide as well as alumina provides the catalytic centers for a Haber-Weiss initiated reactions.

Stabilization of hydrogen peroxide using phthalic acids in the Fenton and Fenton-like oxidation

The stabilization of hydrogen peroxide was evaluated in Fenton reaction with phthalic acid as a stabilizer. The stabilization effect was high at a low pH<pK(a1) and the effect was negligible at a high pH above pK(a2) in both Fenton and Fenton-like reactions. While the lifetime of hydrogen peroxide was prolonged by phthalic acid, the stabilization could not contribute on the increase of the reaction rate in the current Fenton and Fenton-like experimental systems because the systems were all well mixed systems. The interaction between dissolved iron and phthalic acid was spectroscopic monitored in variable pH over pK(a1) and pK(a2) of phthalic acid. Ferrous iron was well stabilized and the initial concentration was kept after mixing with phthalate while ferric iron was removed from the aqueous phase by the phthalic acid. It could be concluded that the stabilization by phthalic acid is due to inhibition of catalytic activity of dissolved iron and minimizes the self-decomposition of hydrogen peroxide. The stabilization is affected by ionization state of the organic acid.

Impacts of operating parameters on oxidation-reduction potential and pretreatment efficacy in the pretreatment of printing and dyeing wastewater by Fenton process

An experiment was conducted in a batch reactor for a real printing and dyeing wastewater pretreatment using Fenton process in this study. The results showed that original pH, hydrogen peroxide concentration and ferrous sulfate concentration affected ORP value and pretreatment efficacy greatly. Under experimental conditions, the optimal original pH was 6.61, and the optimal hydrogen peroxide and ferrous sulfate concentrations were 1.50 and 0.75 gL(-1), respectively. The relationship among ORP, original pH, hydrogen peroxide concentration, ferrous sulfate concentration, and color (COD or BOD(5)/COD) was established, which would be instructive in on-line monitoring and control of Fenton process using ORP. In addition, the effects of wastewater temperature and oxidation time on pretreatment efficacy were also investigated. With an increase of temperature, color and COD removal efficiencies and BOD(5)/COD ratio increased, and they were in proportion to the exponent of temperature reciprocal. Similarly, color and COD removal efficiencies increased with increasing oxidation time, and both color and COD removal obeyed the first-order kinetics. The BOD(5)/COD ratio could be expressed by a second-degree polynomial with respect to oxidation time, and the best biodegradability of wastewater was present at the oxidation time of 6.10h.