Degradation of azo dye active brilliant red X-3B by composite ferrate solution

UV light and Fe2+ catalysed COD removal of AO 8 using NaOCl as oxidant

The present study aims to establish NaOCl as a potential oxidant in the COD removal of Acid Orange 8 using UVC light (λ = 254 nm) and Fe2+ as catalysts. The different systems used in this study are NaOCl, Fe2+/NaOCl, UV/NaOCl, and Fe2+/NaOCl/UV. All these process were found to be operative in acidic, neutral and basic medium. The initial decolorisation and COD removal efficiency (CODeff) for different systems follow the order: Fe2+/NaOCl/UV > UV/NaOCl > Fe2+/NaOCl > NaOCl. Nevertheless, NaOCl can alone be used in the treatment process considering its CODeff to the extent of 95% in 90 min. The change in pH of the solutions after treatment is an important observation - for non-UV systems it remained around 11.0 and 7.0 in other systems. Thus, UV systems are environmental benign. The effect of various anions on CODeff was tested in Fe2+ systems. Presence of F- ions were found to accelerate CODeff in both the systems. However, the effect is more pronounced in Fe2+/ NaOCl/UV, where complete CODeff was observed in the presence of 9.0 gl-1 of F-. The COD removal kinetics for all systems was studied using zero-order, first-order, second-order, and BMG kinetic models. BMG model was found to be more suitable among all and is in good agreement with CODeff of all systems. It is, therefore, established that NaOCl can serve as a powerful oxidant in the advanced oxidation process.

Oxidation of selected fluoroquinolones by ferrate(VI) in water: Kinetics, mechanism, effects of constituents, and reaction pathways

In this work, the oxidation of gatifloxacin (GAT), fleroxacin (FLE) and enoxacin (ENO) in aqueous solution by ferrate (Fe(VI)) was systemically investigated. Weak alkaline and high oxidant doses were favorable for the reaction. The pseudosecond-order rate constants were 0.18055, 0.29162, and 0.05476 L/(mg·min), and the activation energies were 25.13, 15.25, and 11.30 kJ/mol at pH = 8.00 and n(Fe(VI)):n(GAT) = 30:1, n(Fe(VI)):n(FLE) = 20:1, n(Fe(VI)):n(ENO) = 40:1 and a temperature of 25 °C. The maximum degradation rates of the GAT, FLE and ENO were 96.72%, 98.48% and 94.12%, respectively, well simulated by Response Surface Methodology. During the oxidation, the contribution of hydroxyl radicals (HO•) varied with time, whereas the final contribution was approximately 20% at 30 min. The removal efficiency was inhibited by anions by less than 10%, and cations by less than 25%, and significantly inhibited by high concentrations of humic acid. Moreover, two or three dominant reaction pathways were predicted, and the ring cleavages of quinolone and piperazine were mainly achieved through decarboxylation, demethlation and hydroxylation, and some pathways ended up with monocyclic chemicals, which were harmless to aquatic animals and plants. Theoretical calculations further proved that the reactions between FeO4- and neutral fluoroquinolone antibiotics were the major reactions. This work illustrates that Fe(VI) can efficiently remove fluoroquinolone antibiotics (FQs) in aqueous environments, and the results may contribute to the treatment of wastewater containing trace antibiotics and Fe(VI) chemistry.

The efficient degradation of diclofenac by ferrate and peroxymonosulfate: performances, mechanisms, and toxicity assessment

In this study, the degradation efficiency and reaction mechanisms of diclofenac (DCF), a nonsteroidal anti-inflammatory drug, by the combination of ferrate (Fe(VI) and peroxymonosulfate (PMS) (Fe(VI)/PMS) were systematically investigated. The higher degradation efficiency of DCF in Fe(VI)/PMS system can be obtained than that in alone persulfate (PS), Fe(VI), PMS, or the Fe(VI)/PS process at pH 6.0. DCF was efficiently removed in Fe(VI)/PMS process within a wide range of pH values from 4.0 to 8.0, with higher degradation efficiency in acidic conditions. The increasing reaction temperature (10 to 30 ℃), Fe(VI) dose (6.25 to 100 µM), or PMS concentration (50 to 1000 µM) significantly enhanced the DCF degradation. The existences of HCO₃¯, Cl¯, and humic acid (HA) obviously inhibited the DCF removal. Electron paramagnetic resonance (EPR), free radical quenching, and probing experiments confirmed the existence of sulfate radicals (SO₄^•¯), hydroxyl radicals (^•OH), and Fe(V)/ Fe(IV), which are responsible for DCF degradation in Fe(VI)/PMS system. The variations of TOC removal ratio reveal that the adsorption of organics with ferric particles, formed in the reduction of Fe(VI), also were functioned in the removal process. Sixteen DCF transformation byproducts were identified by UPLC-QTOF/MS, and the toxicity variation was evaluated. Consequently, eight reaction pathways for DCF degradation were proposed. This study provides theoretical basis for the utilization of Fe(VI)/PMS process.

Biodegradation and Detoxification of Azo Dyes by Halophilic/Halotolerant Microflora Isolated From the Salt Fields of Tibet Autonomous Region China

This study aimed to decolorize azo dyes in high-salt industrial wastewater under high-salt and low oxygen conditions using extreme halophilic/halotolerant bacteria screened from the salt fields of Tibet, which consisted of Enterococcus, unclassified Enterobacteriaceae, Staphylococcus, Bacillus, and Kosakonia. Under the optimal conditions, 600 mg/l Congo red, Direct Black G (DBG), Amaranth, methyl red, and methyl orange could be completely decolorized in 24, 8, 8, 12, and 12 h, respectively. When the DBG concentration was 600 mg/l, NADH–DCIP, laccase, and azo reductase were confirmed to be the primary reductase and oxidase during the degradation process, and the degradation pathways were verified. The microflora could not only tolerate changes in salt concentrations of 0–80 g/l, but also displayed strong degradative ability. Under high-salt concentrations (≥ 60 g/l NaCl), NADH–DCIP reductase was primarily used to decolorize the azo dye. However, under low salt concentrations (≤ 40 g/l NaCl), azo reductase began to function, and manganese peroxidase and lignin peroxidase could cooperate to participate in DBG degradation. Additionally, the halophilic/halophilic microflora was shown to convert the toxic DBG dye to metabolites of low toxicity based on phytotoxicity analysis, and a new mechanism for the microflora to degrade DBG was proposed based on intermediates identified by liquid chromatography-mass spectrometry (LC–MS). This study revealed that the halophilic/halophilic microflora has effective ecological and industrial value for treating wastewater from the textile industry.

Disintegration of waste activated sludge with composite ferrate solution: Sludge reduction and settleability

Sludge reduction has been a key issue in waste activated sludge (WAS) treatment. In this study, composite ferrate solution (CFS) has been used to disintegrate WAS. The results showed that CFS could effectively disrupt sludge flocs and cells and caused the release of intracellular matter such as SCOD, cations and organic acids. These results showed that the sludge disintegration process could be divided into a rapid reaction stage (0-2 h) and a slow reaction stage (2-24 h). It was determined that at a CFS dosage of 50 mg Fe/g SS and a reaction time of 24 h, the sludge reduction was 55.4% and SV and SVI were reduced by 12.1% and 46.4%, respectively. The Fe(VI), ClO^- and OH^- in CFS all played important roles in sludge decomposition, but they did not have synergistic effects. The small-particle sludge, in situ formed Fe³⁺ and released Ca²⁺ could improve the sludge settleability.

A highly ordered honeycomb-like nickel(III/II) oxide-enhanced photocatalytic fuel cell for effective degradation of bisphenol A

The honeycomb-like nickel(III/II) oxide interpenetrated framework arrays labelled as H-NiO_x are used as cathode catalysts for the degradation of bisphenol A (BPA) in visible light-excited fuel cells. The nanoparticle close-packed NiO_x aggregates (C-NiO_x) and H-NiO_x are prepared by conventional electrodeposition (ED) and advanced oxidation-associated electrodeposition (AO-ED) strategies, carried out by multiple voltammetry controlled in the potential ranges of 0 to -1.3 V and 1.3 to -1.3 V (vs. SCE), respectively. Compared with C-NiO_x, the H-NiO_x frameworks with smaller charge transfer resistance and higher surface-confined redox-active centers exhibit larger cathode electrocatalytic activity for the photocatalytic degradation of BPA. The NaClO can act as a sacrificial agent to sustain the integrity and stability of H-NiO_x cathode. The H-NiO_x-assisted BPA degradation conditions are optimized by changing process variables. The BPA is degraded by 48.5% within 120 min in photocatalytic BPA (1.0 mmol L^-1, pH 13) fuel cell employing H-NiO_x cathode, CdS/TiO₂ photoanode and 0.2 mol L^-1 NaClO catholyte, and its degradation rate conforms to the first-order reaction kinetic model. The H-NiO_x can remarkably enhance the performances of the photocatalytic fuel cell, achieving a 4.1-fold or 15.2-fold increase in the short circuit current and maximum power density compared with that using bare cathode.

Kinetics and mechanism of diclofenac removal using ferrate(VI): roles of Fe3+, Fe2+, and Mn2

In this study, the effect of Fe³⁺, Fe²⁺, and Mn²⁺ dose, solution pH, reaction temperature, background water matrix (i.e., inorganic anions, cations, and natural organic matters (NOM)), and the kinetics and mechanism for the reaction system of Fe(VI)/Fe³⁺, Fe(VI)/Fe²⁺, and Fe(VI)/Mn²⁺ were investigated systematically. Traces of Fe³⁺, Fe²⁺, and Mn²⁺ promoted the DCF removal by Fe(VI) significantly. The pseudo-first-order rate constant (k_obs) of DCF increased with decreasing pH (9-6) and increasing temperature (10-30 °C) due to the gradually reduced stability and enhanced reactivity of Fe(VI). Cu²⁺ and Zn²⁺ ions evidently improved the DCF removal, while CO₃^2- restrained it. Besides, SO₄^2-, Cl^-, NO₃^-, Mg²⁺, and Ca²⁺ almost had no influence on the degradation of DCF by Fe(VI)/Fe³⁺, Fe(VI)/Fe²⁺, and Fe(VI)/Mn²⁺ within the tested concentration. The addition of 5 or 20 mg L^-1 NOM decreased the removal efficiency of DCF. Moreover, Fe₂O₃ and Fe(OH)₃, the by-products of Fe(VI), slightly inhibited the DCF removal, while α-FeOOH, another by-product of Fe(VI), showed no influence at pH 7. In addition, MnO₂ and MnO₄^-, the by-products of Mn²⁺, enhanced the DCF degradation due to catalysis and superposition of oxidation capacity, respectively. This study indicates that Fe³⁺ and Fe²⁺ promoted the DCF removal mainly via the self-catalysis for Fe(VI), and meanwhile, the catalysis of Mn²⁺ and the effect of its by-products (i.e., MnO₂ and MnO₄^-) contributed synchronously for DCF degradation. Graphical abstract ᅟ.

Degradation of tetrabromobisphenol A by ferrate(VI) oxidation: Performance, inorganic and organic products, pathway and toxicity control

This study systematically investigated the degradation of tetrabromobisphenol A (TBBPA) by ferrate (VI) oxidation. The reaction kinetics between ferrate (VI) with TBBPA were studied under pseudo-first-order conditions in the pH range 5.5-10.5. Then, a series of batch experiments were carried out to investigate other factors, including the ferrate (VI) dosage, temperature and interfering ions. Additionally, the generation of inorganic products (bromide ion and bromate) was evaluated. The organic intermediates were identified, and possible pathways were proposed. In addition, the toxicity variation was analyzed with marine luminous bacteria (V. fischeri). Degradation of TBBPA by ferrate (VI) oxidation was confirmed to be an effective and environmentally friendly technique. The reaction was fitted with a second-order rate model. With a ferrate (VI) dosage of 25.25 μmol/L, TBBPA concentration of 1.84 μmol/L, an initial pH of 7.0, and a temperature of 25 °C, a 99.06% TBBPA removal was achieved within 30 min. The evaluation of inorganic products showed that the capacity of ferrate (VI) oxidation to yield bromide ions was relatively strong and could prevent the formation of bromate compared to photocatalytic and mechanochemical techniques. Eleven intermediates were identified, and the proposed degradation pathway indicated that TBBPA might undergo debromination, beta scission, substitution, deprotonation and oxidation. The results of toxicity testing showed that ferrate (VI) could effectively control the toxicity of the treated samples, although the toxicity increased in the initial reaction stage due to the accumulation and destruction of more toxic intermediates.

Biodegradation and detoxification of Direct Black G textile dye by a newly isolated thermophilic microflora

The biodegradation and detoxification of azo dye - Direct Black G (DBG) with a newly isolated thermophilic microflora was investigated in the present study. It was found this microflora can decolorize DBG at a wide range of pH from 5 to 10, and grow well under high concentration of dye (600 mg·L^-1) and salinity (50 g·L^-1). Its decolorization ratio could reach 97% with 8 h of incubation at optimal conditions. The induction of laccase, manganese peroxidase, lignin peroxidase and azoreductase suggests their synergetic involvements in the degradation process of DBG. In addition, the phytotoxicity analysis indicated the thermophilic microflora converted toxic dye DBG into low toxicity metabolites. PCR-DGGE analysis revealed that there are nine different bacteria presented in this microflora. Furthermore, a new degradation pathway of DBG degradation by this microflora was proposed based on the intermediates identified by LC-ESI-MS/MS.

A critical review of ferrate(VI)-based remediation of soil and groundwater

Over the past few decades, diverse chemicals and materials such as mono- and bimetallic nanoparticles, metal oxides, and zeolites have been used for soil and groundwater remediation. Ferrate (Fe^VIO₄^2-) has been widely employed due to its high-valent iron (VI) oxo compound with high oxidation/reduction potentials. Ferrate has received attention for wide environmental applications including water purification and sewage sludge treatment. Ferrate provides great potential for diverse environmental applications without any environmental problems. Therefore, this paper provides comprehensive information on the recent progress on the use of (Fe^VIO₄^2-) as a green material for use in sustainable treatment processes, especially for soil and water remediation. We reviewed diverse synthesis recipes for ferrates (Fe^VIO₄^2-) and their associated physicochemical properties as oxidants, coagulants, and disinfectants for the elimination of a diverse range of chemical and biological species from water/wastewater samples. A summary of the eco-sustainable performance of ferrate(VI) in water remediation is also provided and the future of ferrate(VI) is discussed in this review.

Degradation pathway and mechanism of Reactive Brilliant Red X-3B in electro-assisted microbial system under anaerobic condition

The degradations of Reactive Brilliant Red X-3B (RBRX-3B) in an electric-assisted microbial system (EAMS), a microbial system (MS) and an electrochemical system (ECS) were compared. The degradation efficiency of RBRX-3B in EAMS (99.8%) was 10.8% higher than the sum in MS (61.9%) and ECS (27.1%) at 24h at the optimal voltage of 0.4V, indicating that there was a synergistic effect between the electrode reaction and the biodegradation. The RBRX-3B degradation in EAMS followed first-order kinetic model. The activation energy of RBRX-3B degradation in EAMS was calculated to be 60.53kJmol^-1 by the Arrhenius equation, showing that the degradation rate of RBRX-3B mainly depended on bio-chemical reaction. RBRX-3B was degraded to both low-strength toxic compounds and nontoxic compounds in EAMS and those intermediates were easier to be further degraded. The pathway of RBRX-3B degradation in EAMS was different from that in MS.

Degradation of fluoroquinolone antibiotics by ferrate(VI): Effects of water constituents and oxidized products

The degradation of five fluoroquinolone (FQ) antibiotics (flumequine (FLU), enrofloxacin (ENR), norfloxacin (NOR), ofloxacin (OFL) and marbofloxacin (MAR)) by ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) was examined to demonstrate the potential of this iron-based chemical oxidant to treat antibiotics in water. Experiments were conducted at different molar ratios of Fe(VI) to FQs at pH 7.0. All FQs, except FLU, were degraded within 2 min at [Fe(VI)]:[FQ] ≤ 20.0. Multiple additions of Fe(VI) improved the degradation efficiency, and provided greater degradation than a single addition of Fe(VI). The effects of anions, cations, and humic acid (HA), usually present in source waters and wastewaters, on the removal of FLU were investigated. Anions (Cl(-), SO4(2-), NO3(-), and HCO3(-)) and monovalent cations (Na(+) and K(+)) had no influence on the removal of FLU. However, multivalent cations (Ca(2+), Mg(2+), Cu(2+), and Fe(3+)) in water decreased the efficiency of FLU removal by Fe(VI). An increase in the ionic strength of the solution, and the presence of HA in the water, also decreased the percentage of FLU removed by Fe(VI). Experiments on the removal of selected FQs, present as co-existing antibiotics in pure water, river water, synthetic water and wastewater, were also conducted to demonstrate the practical application of Fe(VI) to remove the antibiotics during water treatment. The seventeen oxidized products (OPs) of FLU were identified using solid phase extraction-liquid chromatography-high-resolution mass spectrometry. The reaction pathways are proposed, and are theoretically confirmed by molecular orbital calculations.

Oxidation-coagulation of β-blockers by K2FeVIO4 in hospital wastewater: assessment of degradation products and biodegradability

This study investigated the degradation of atenolol, metoprolol and propranolol beta-blockers by ferrate (K2FeO4) in hospital wastewater and in aqueous solution. In the case of hospital wastewater, the effect of the independent variables pH and [Fe(VI)] was evaluated by means of response surface methodology. The results showed that Fe(VI) plays an important role in the oxidation-coagulation process, and the treatment of the hospital wastewater led to degradations above 90% for all the three β-blockers, and to reductions of aromaticity that were close to 60%. In addition, only 17% of the organic load was removed. In aqueous solution, the degradation of the β-blockers atenolol, metoprolol and propranolol was 71.7%, 24.7% and 96.5%, respectively, when a ratio of 1:10 [β-blocker]:[Fe(VI)] was used. No mineralization was achieved, which suggests that there was a conversion of the β-blockers to degradation products identified by liquid chromatography/mass spectrometry tandem. Degradation pathways were proposed, which took account of the role of Fe(VI). Furthermore, the ready biodegradability of the post-process samples was evaluated by using the closed bottle test, and showed an increase in biodegradability. The use of the ferrate advanced oxidation technology seems to be a useful means of ensuring the remediation of hospital and similar wastewater.

Oxidation of nitrogen-containing pollutants by novel ferrate(VI) technology: a review

Nitrogen-containing pollutants have been found in surface waters and industrial wastewaters due to their presence in pesticides, dyes, proteins, and humic substances. Treatment of these compounds by conventional oxidants produces disinfection by-products (DBP). Ferrate(VI) (Fe(VI)O(4)(2-), Fe(VI)) is a strong oxidizing agent and produces a non-toxic by-product Fe(III), which acts as a coagulant. Ferrate(VI) is also an efficient disinfectant and can inactivate chlorine resistant microorganisms. A novel ferrate(VI) technology can thus treat a wide range of pollutants and microorganisms in water and wastewater. The aim of this paper is to review the kinetics and products of the oxidation of nitrogen-containing inorganic (ammonia, hydroxylamine, hydrazine, and azide) and organic (amines, amino acids, anilines, sulfonamides, macrolides, and dyes) compounds by ferrate(VI) in order to demonstrate the feasibility of ferrate(VI) treatment of polluted waters of various origins. Several of the compounds can degraded in seconds to minutes by ferrate(VI) with the formation of non-hazardous products. The mechanism of oxidation involves either one-electron or two-electrons processes to yield oxidation products. Future research directions critical for the implementation of the ferrate(VI)-based technology for wastewater and industrial effluents treatment are recommended.

Treatment of simulated wastewater containing Reactive Red 195 by zero-valent iron/activated carbon combined with microwave discharge electrodeless lamp/sodium hypochlorite

A comparative study of treatment of simulated wastewater containing Reactive Red 195 using zero-valent iron/activated carbon (ZVI/AC), microwave discharge electrodeless lamp/sodium hypochlorite (MDEL/NaClO) and the combination of ZVI/AC-MDEL/NaClO was conducted. The preliminary results showed the two steps method of ZVI/AC-MDEL/NaClO had much higher degradation efficiency than both single steps. The final color removal percentage was nearly up to 100% and the chemical oxygen demand reduction percentage was up to approximately 82%. The effects of operational parameters, including initial pH value of simulated wastewater, ZVI/AC ratio and particle size of ZVI were also investigated. In addition, from the discussion of synergistic effect between ZVI/AC and MEDL/NaClO, we found that in the ZVI/AC-MEDL/NaClO process, ZVI/AC could break the azo bond firstly and then MEDL/NaClO degraded the aromatic amine products effectively. Reversing the order would reduce the degradation efficiency.

Application of ferrate(VI) in the treatment of industrial wastes containing metal-complexed cyanides : a green treatment

Ferrate(VI) was employed for the oxidation of cyanide (CN) and simultaneous removal of copper or nickel in the mixed/complexed systems of CN-Cu, CN-Ni, or CN-Cu-Ni. The degradation of CN (1.00 mmol/L) and removal of Cu (0.095 mmol/L) were investigated as a function of Fe(VI) doses from 0.3-2.00 mmol/L at pH 10.0. It was found that Fe(VI) could readily oxidize CN and the reduction of Fe(VI) into Fe(III) might serve efficiently for the removal of free copper ions. The increase in Fe(VI) dose apparently favoured the CN oxidation as well as Cu removal. Moreover, the pH dependence study (pH 10.0-13.0) revealed that the oxidation of CN was almost unaffected in the studied pH range (10.0-13.0), however, the maximum removal efficiency of Cu was obtained at pH 13.0. Similarly, treatment was carried out for CN-Ni system having the initial Ni concentration of 0.170 mmol/L and CN concentration of 1.00 mmol with Fe(VI) dose 2.00 mmol at various pH values (10.0-12.0). Results showed a partial oxidation of CN and partial removal of Ni. It can be observed that Fe(VI) can partially degrade the CN-Ni complex in this pH range. Further, Fe(VI) was applied for the treatment of simulated industrial waste/effluent waters treatment containing CN, Cu, and Ni.