Decolorization Of Acid Orange Research Articles

Enhanced removal of organic contaminants in water by the combination of peroxymonosulfate and carbonate

In this study, a favorable CO32−/PMS system for efficient degradation of organic contaminants (acid orange 7 (AO7), acetaminophen, para-aminobenzoic acid, phenol, methylene orange, methylene blue) in water was firstly reported. Under optimal conditions, the decolorization ration of AO7 was 100% within 40 min. Data fitting showed that the AO7 decolorization could be described by the pseudo-first-order kinetics, and the rates constant values ranging from 0.0006 to 0.2297 min−1 depending on the operating parameters (initial PMS, CO32−, AO7 concentrations). Radical scavenging studies revealed that superoxide anion radical (O2−) and singlet oxygen (1O2) rather than sulfate (SO4−) nor hydroxyl (HO) were the dominant oxidants might be responsible for AO7 degradation. The presence of NO3−, HPO42− and low concentration of Cl−, NO2−, HCO3−, H2PO4−, HA had no significantly effect on the decolorization of AO7. Adding a higher Cl− concentration displayed favorable effects on the removal efficiencies of AO7, but adding a higher NO2−, HCO3−, H2PO4− and HA concentration apparently inhibited this process. The decolorization of AO7 was lower in wastewater in comparison to other natural waters and ultrapure water, which was probably due to the presence of higher concentration of colloids in wastewater. Nevertheless, up to 94.8%, 97.0% and 85.1% of AO7 were degraded from the filtrate, permeate, and retentate phases of wastewater within 60 min, respectively. Consequently, CO32−/PMS would be promising for removal methodology for AO7 in wastewater containing considerable colloids. Finally, three intermediates were identified and degradation pathways of AO7 were proposed.

Sol-Gel Hydrothermal Synthesis and Visible Light Photocatalytic Degradation Performance of Fe/N Codoped TiO₂ Catalysts.

Using Ti(OC4H9)4 as a precursor, Fe(NO3)3⋅9H2O as the source of iron, and NH4NO3 as the source of nitrogen, an Fe/N codoped TiO2 catalyst was prepared using a sol-gel hydrothermal method. The as-prepared powders were characterized using X-ray powder diffraction, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectrophotometry. Fe and N codoping resulted in decreased crystallite size and increased specific surface area. Results of the photocatalytic degradation of acid orange 7 (AO7) in a continuous-flow fluidized-bed reactor indicated that the maximum decolorization (more than 90%) of AO7 occurred with the Fe/N-TiO2 catalyst (dosage of 20 g/L) when a combination of visible light irradiation for 10 h HRT (hydraulic retention time), and a heterogeneous system was used. The AO7 degradation efficiency was considerably improved by increasing the hydraulic retention time from 2.5 to 10 h or by reducing the initial AO7 concentration from 300 to 100 mg/L. The reaction rate increased with the light intensity and the maximum value occurred at 35 mW/cm2; moreover, the efficiency of the AO7 degradation increased when the pH decreased with maximum efficiency at pH 3.

Reductive decolorization of azo dyes via in situ generation of green tea extract-iron chelate.

In this study, rapid decolorization of azo dyes was achieved by in situ-generated green tea extract-iron (GTE-Fe) chelate for the first time. When changing reaction conditions from the aerobic condition to the anaerobic condition, the decolorization efficiencies of two azo dyes, i.e., acid orange 7 (AO7) and acid black 1 (AB1), increased from 46.38 and 83.17 to 90.13 and 95.37%, respectively. The recalcitrant AO7 was then selected as the targeting pollutant in subsequent optimization and mechanism studies. Experimental evidences showed that the initial concentrations of AO7, Fe(III), and GTE are the key factors to optimize the decolorization efficiency. Further characterization studies by spectroscopic analysis, including FESEM, FTIR, and XPS, suggested that the major mechanism of AO7 decolorization is the nucleophilic attack of the oxygen in green tea polyphenols (GTP), and this attack could be facilitated by the organometal chelation. This study provided an efficient and environmental friendly strategy to decolorize azo dyes via in situ generation of the GTE-Fe chelate, as well as its mechanistic insights, shedding lights on in situ remediation of azo dye pollution. Graphical abstract ᅟ.

Synthesis of microsize Fe/Cu bimetallic particles using in situ acid‐mediated coating: Application on decolorization of azo dye acid orange 7

Iron‐based bimetallic particle has become an attractive material in environmental remediation, particularly for wastewater treatment. However, it is yet to be applied in large scale processes, mainly due to the requirement of multistep syntheses for the desired materials, as well as the rigorous control of the conditions for its synthesis. This study introduces a facile methodology to synthesize micro‐size iron/copper bimetallic particles (mFe/Cu‐BPs) by in situ coating of Cu on the surface of Fe in an acidic media for the removal of azo dye Acid Orange 7 (AO7) in aqueous media. Morphological analyses showed that Cu planted on the surface of the particles exhibit a dense leaf‐like structure with great connectivity and electron movement between Fe0 core and Cu shell. In addition, the effects on the decolorization of AO7 via key parameters such as theoretical Cu mass loading (TMLCu), initial pH, dosage, and initial AO7 concentration were assessed. Experimental results revealed that the decolorization efficiency of AO7 was highly dependent on the operational conditions. Under optimal conditions (TMLCu of 0.6 g Cu/g Fe, initial pH of 3.0, mFe/Cu‐BP dosage of 45 g/L, and initial AO7 concentration of 1000 mg/L), decolorization of AO7 as a function of reaction time was investigated via UV‐vis spectrometry, which confirmed that the azo bond of AO7 successfully cleaved by mFe/Cu‐BPs. The maximum decolorization, COD, and TOC removal efficiencies were found to be 99.55, 83.91, and 73.81% after 30 min of reaction time, respectively. Lastly, the potential mechanism for the decolorization of AO7 is proposed. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1901–1907, 2018

Biodegradation of Acid Orange 7 in a combined anaerobic-aerobic up-flow membrane-less microbial fuel cell: Mechanism of biodegradation and electron transfer

A distinctive combination of anaerobic-aerobic in a single chambered up-flow membrane-less microbial fuel cell (UFML MFC) was developed to explore the interrelation and mechanism between Acid Orange 7 (AO7) biodegradation and bioelectricity generation. The performance of AO7 biodegradation in UFML MFC was evaluated by various operating configurations. This study demonstrated that the UFML MFC capable to sustain high decolorization efficiency throughout a long term operation. Besides, the obtained results illustrated that the AO7 decolorization would compete with exoelectrogens and other anaerobic microbial activities for electrons that released from the substrate. The decolorization efficiency of AO7 was ranging from 89% to 96% during operated in various configurations. However, the voltage output was highly affected as the AO7 dosage was increased. Therefore, these results indicated that most of the available electrons were more prone to be used by AO7 decolorization rather than voltage output. Moreover, the results suggested that the high AO7 dosage and continuous 24-h flow pattern could inhibit the other anaerobic microbial activities, and consequently more electrons can be used for AO7 decolorization and electricity generation. Furthermore, AO7 decomposition intermediates were further identified by using high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC–MS). The results demonstrated that the residual aromatic compounds from decomposition of AO7 were recalcitrant to be biodegraded in anaerobic region. However, the aromatic compounds can be further biodegraded in aerobic region. Therefore, the proposed biodegradation pathway showed the AO7 can be completely mineralized by using a combination of anaerobic-aerobic UFML MFC.

Carbonate-activated hydrogen peroxide oxidation process for azo dye decolorization: Process, kinetics, and mechanisms

Advanced oxidation processes offer effective solutions in treating wastewater from various industries. This study is the first time to investigate the potential of carbonate-activated hydrogen peroxide (CAP) oxidation process for the removal of organic pollutant from highly alkaline wastewaters. Azo dye acid orange 7 (AO7) was selected as a model pollutant. The influences of various parameters on AO7 decolorization by the CAP oxidation were evaluated. Furthermore, the active species involved in AO7 degradation were explored using scavenger experiments and electron spin resonance analysis. Additionally, AO7 degradation products by the CAP oxidation were identified to elucidate possible transformation pathways. Results showed that the CAP oxidation had better AO7 decolorization performance compared to bicarbonate-activated hydrogen peroxide method. The AO7 decolorization efficiency augmented from 3.70 ± 0.76% to 54.27 ± 2.65% when carbonate concentration was increased from 0 to 50 mM at pH 13.0, and then changed slightly with further increasing carbonate concentration to 70 mM. It increased almost linearly from 5.95 ± 0.32% to 94.03 ± 0.39% as H2O2 concentration was increased from 5 to 50 mM. Moreover, trace amount of Co(II) could facilitate AO7 decolorization by the CAP reaction. Superoxide and carbonate radicals might be the main reactive oxygen species involved in the CAP process. Finally, a possible degradation pathway of AO7 by the CAP oxidation was proposed based on the identified products.

Increasing the bio-electrochemical system performance in azo dye wastewater treatment: Reduced electrode spacing for improved hydrodynamics

The electrodes spacing would exert a pronounced effect on bio-electrochemical systems (BESs) performance, especially for the scaling-up of reactors and practical applications. In this study, we traced the effect of electrode spacing on wastewater treatment performances from the aspects of hydrodynamics and electrochemical characteristics. Three series of folded stainless steel mesh (f-SSM) electrodes with electrode spacing of 2, 4 and 8mm were designed for azo dye (acid orange 7 (AO7)) wastewater treatment. Results showed that BES with electrode spacing of 2mm (RS2) obtained the highest efficiencies of AO7 decolorization (90.9±0.4%) and COD removal (36.8±3.8%) at HRT of 8h, which was 30.7% and 15.2% higher than that in BES with electrode spacing of 8mm (RS8), respectively. Moreover, the relationship between pollutants removal, internal resistance and hydrodynamics of BESs with different electrode spacing supported the hydrodynamics was significantly influence the pollutants removal performance.

Degradation of Acid Orange 7 using peroxymonosulfate catalyzed by granulated activated carbon and enhanced by electrolysis

Electrochemistry coupled with granulated activated carbon catalysis of peroxymonosulfate (electro/GAC/PMS) as a novel wastewater treatment process was performed for the degradation of Acid Orange 7 (AO7) in aqueous solution. The decolorization of AO7 was compared under different permutations and combinations of electro-oxidation, GAC and PMS. It showed that the electro/GAC/PMS process was the most effective and the decolorization of AO7 followed pseudo-first order kinetics. The surface chemistry of GAC samples was analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Compared with the fresh samples, π-electron density and hydroxyl group content decreased under the GAC/PMS system, but kept the similar values under the electro/GAC/PMS system. Electron paramagnetic resonance and radical scavenger studies were used to verify the formation of sulfate radicals (SO4−) and hydroxyl radicals (OH). The optimized conditions were found to be: current density 8 mA cm−2; PMS concentration 5 mM; GAC dosage 0.5 g L−1; and initial pH value 5.0. GAC recycling experiments over 4 runs showed some decrease in reactivity. Overall, the results indicate that 100% color removal was readily achieved and 50.4% of TOC was removed which shows high efficiency of the electro/GAC/PMS process.

Enhanced bio-decolorization of acid orange 7 and electricity generation in microbial fuel cells with superabsorbent-containing membrane and laccase-based bio-cathode

This study investigates the decolorization of the azo dye Acid Orange 7 (AO7) and the simultaneous generation of electricity in air-cathode microbial fuel cells (AC-MFCs) with a fungal bio-cathode. The laccase-producing white-rot fungus Ganoderma lucidum BCRC 36123 that was seeded on wood-chips around the cathode of the AC-MFCs functioned synergistically with an anaerobic microbial consortium in the anode chamber to degrade AO7. Superabsorbent polymer (SAP) was mixed with polyvinyl alcohol (PVA) to form a polymer electrolyte membrane (PEM) that separated the cathode from the anolyte of the AC-MFC to provide high proton transfer rate and water retention capacity, promoting the decolorization of AO7 and electricity generation. The solid-state cultivation of Ganoderma lucidum yielded 17.3 times more laccase than did the liquid-state cultivation of the same fungus. A maximal open-circuit voltage of 699 mV and a 96.7% decolorization of AO7 at 500 mg/L were achieved in AC-MFCs that were equipped with a PEM with an optimal PVA/SAP ratio of 1:2. A maximal power density of 207.74 mW/m2, which was 10–15 times those obtained in similar studies in the literature, was obtained at an AO7 concentration of 500 mg/L. Over 84% of the by-products of AO7 decolorization were further degraded in the AC-MFC during a 30 day test period. This study reveals the feasibility of using both the improved PEM and a white-rot fungus in a solid-state culture on the cathode to increase considerably the pollutant removal efficiency of MFCs and the amount of electricity they generate.

TiO2-SiO2/GAC particles for enhanced electrocatalytic removal of acid orange 7 (AO7) dyeing wastewater in a three-dimensional electrochemical reactor

Abstract In this work, granular activated carbon (GAC) supported TiO2-SiO2 oxide (TiO2-SiO2/GAC) was prepared and packed in a three-dimensional electrochemical reactor (3DER) for the removal of acid orange 7 (AO7) dyeing wastewater. The characteristics and the electrocatalytic performance of the prepared TiO2-SiO2/GAC were investigated to verify the feasibility of TiO2-SiO2/GAC application as particle electrodes. Results show that the TiO2-SiO2/GAC could significantly improve the AO7 removal efficiency, extend service life of particle electrodes, and enhance the stability of 3DER system. Orthogonal array was designed to optimize the operation parameters of 3DER, which was determined as electric field intensity 1 V/cm, filling amount of TiO2-SiO2/GAC particles 200 g/L, electrolytic concentration (Na2SO4) 0.07 mol/L, pH 3, treatment time 120 min. Under the optimal condition, the AO7 decolorization rate and COD removal efficiency are 83.20% and 48.95% respectively. The possible intermediates generated in 3DER during AO7 decomposition were identified and the biodegradability of the effluent was also estimated. Results suggest that the 3DER with TiO2-SiO2/GAC particle electrodes could be an alternative for the pretreatment of dyeing wastewater before biological treatment.

EFFECT OF RADICAL SCAVENGERS AND PROPOSED PATHWAYS FOR DEGRADATION OF AZO DYE IN AQUEOUS SOLUTION UNDER PRESENCE OF IRON(III) AND PERSULPHATE

The degradation process of Acid Orange 7 (AO7) in aqueous solutions by iron(III) under activation by persulfate (PS, S2O82-) oxidation and Visible (Vis) light (≥420 nm) exposure has been studied. The radical scavenging effect was examined by using ethanol (EtOH), tert-butyl alcohol (TBA) and sodium azide to state that the hydroxyl radical (·OH) is regarded as the predominant reactive oxidant for the AO7 decolorization, while the sulfate radical (SO4·-) and singlet oxygen(1O2) are also make their contribution to dye's degradation. The reaction intermediates were determined by electrospray ionization-mass spectrometry (ESI-MS) analysis, and a probable degradation pathway mechanism has been proposed. It was suggested, that firstly an initial successive radical attacks the N atom of the dye, which decompose to p-phenolsulfonic acid and 1,2-naphthaquinone through the contemporaneous break of two C-N bonds. Afterwards, subsequent oxidation of these products and loss of the −SO3− group are observed. Finally, the acyclic carboxylic acids are formed from the central ring-opening, and then the further oxidation to simple carboxylic acids is evident. The work can provide a simple, effective and economic system for the treatment of non-biodegradable azo dye. The recommendations were proposed on organization of an effective quality control of technological water discharge and products of its processing at the local wastewater treatment facilities of industrial plants for prevention of the ingress of hazardous biological substances to the hydrosphere.Forcitation:Heng Zhong, Hui Zhao, Jun Li, Lei Sun, Aihua Xu, Dongsheng Xia, Nevsky A.V. Effect of radical scavengers and proposed pathways for degradation of azo dye in aqueous solution under presence of iron (III) and persulphate. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 4. P. 88-94.

Effect of Persulfate on the Degradation of Acid Orange 7 (AO7) by Dielectric Barrier Discharge Plasma

A novel process for decolorization of Acid Orange 7 (AO7) dye wastewater by dielectric barrier discharge plasma coupled with persulfate (PS) was investigated, and the enhancing performance of PS on the AO7 decolorization efficiency and energy efficiency were examined under different molar ratio of AO7 to PS (MR), gas discharge gap, initial concentration of AO7 and gas discharge atmosphere. The experimental results indicate that the decolorization efficiency (ƞ) and the energy efficiency (γ) increased with the addition dosage of PS until the MR of 1:100, and an increment in the decolorization efficiency and energy efficiency reached 60.5% and 0.33 g/(kW h) respectively at an MR of 1:100. An increase in the gas discharge gap and in the initial concentration of AO7 greatly decreased the decolorization efficiency of AO7, but the increment in energy efficiency due to PS addition increased with the AO7 initial concentration and discharge gap except for the discharge gap of 8 mm, and the highest increment in energy efficiency of 0.75 g/(kW h) was obtained at a gas discharge gap of 6 mm and an initial concentration of 30 mg/L. Moreover, higher AO7 decolorization efficiency was achieved in air than in Ar atmosphere, while the increment in decolorization efficiency and energy efficiency due to PS addition was not influenced by the gas discharge atmosphere. The experimental results imply that PS was activated into stronger radical species such as sulfate radical and hydroxyl radical, which contributed to a higher decolorization performance. The possible motivator of PS was tentatively concluded as UV irradiation, Joule heating effect, etc.

Decolorization of azo dye and generation of electricity by microbial fuel cell with laccase-producing white-rot fungus on cathode

Wood-degrading white-rot fungi produce many extracellular enzymes, including the multi-copper oxidative enzyme laccase (EC 1.10.3.2). Laccase uses atmospheric oxygen as the electron acceptor to catalyze a one-electron oxidation reaction of phenolic compounds and therefore has the potential to simultaneously act as a cathode catalyst in a microbial fuel cell (MFC) and degrade azo dye pollutants. In this study, the laccase-producing white-rot fungus Ganoderma lucidum BCRC 36123 was planted on the cathode surface of a single-chamber MFC to degrade the azo dye acid orange 7 (AO7) synergistically with an anaerobic microbial community in the anode chamber. In a batch culture, the fungus used AO7 as the sole carbon source and produced laccase continuously, reaching a maximum activity of 20.3±0.3 U/L on day 19 with a 77% decolorization of the dye (50mg/L). During MFC operations, AO7 in the anolyte diffused across a layer of polyvinyl alcohol-hydrogel that separated the cathode membrane from the anode chamber, and served as a carbon source to support the growth of, and production of laccase by, the fungal mycelium that was planted on the cathode. In such MFCs, laccase-producing fungal cathodes outperformed laccase-free controls, yielding a maximum open-circuit voltage of 821mV, a closed-circuit voltage of 394mV with an external resistance of 1000Ω, a maximum power density of 13.38mW/m2, a maximum current density of 33mA/m2, and a >90% decolorization of AO7. This study demonstrates the feasibility of growing a white-rot fungal culture with continuous laccase production on the cathode of MFCs to improve their electricity generation and azo dye removal efficiency.

Synergetic degradation of Acid Orange 7 (AO7) dye by DBD plasma and persulfate

The synergetic degradation performance of Acid Orange 7 (AO7) by dielectric barrier discharge plasma (DBDP) and persulfate (PS) was examined. Addition of PS in AO7 solution hardly degraded any AO7 in 50min, but when DBDP was initiated over the solution surface, PS greatly enhanced the decolorization efficiency of AO7, and the improvement efficacy depended on the addition dosage of PS, the applied voltage, the air discharge gap and the gas discharge atmosphere. An increase in AO7 decolorization efficiency of 60% was obtained for AO7 solution of 5mg/L at a PS addition dosage of 100:1 (molar ratio of PS to AO7) and a discharge power of 3.6W, correspondingly, the decolorization rate of AO7 was accelerated by 6.7 times. The improvement on AO7 degradation mainly attributes to the enhanced production of sulfate radical (SO4−) and hydroxyl radicals (OH) which are produced from the activated PS by DBD plasma. The activators of PS were tentatively speculated as the UV irradiation and heat released in discharge channels, and hydrated electrons may also play a role in the activation process of PS. The intermediates identified by GC–MS and the TOC measurement show that addition of PS into AO7 solution had little effect on the degradation pathways of AO7, but greatly improved the mineralization of AO7, which was mainly due to the increased production of SO4− and OH.

Bioelectrochemical reduction of an azo dye by a Shewanella oneidensis MR-1 formed biocathode

Presently there is great interest to develop pure culture cathodes in bioelectrochemical systems (BES) for achieving decolorization/reduction of azo dyes. In this study, we investigated the decolorization of a model azo dye, acid orange 7 (AO7) in a biocathode inoculated with a model electrogenic microorganism Shewanella oneidensis MR-1 (MR-1). The decolorization efficiency of AO7 reached 95.8 ± 4.6%, 86.4 ± 2.0%, and 77.8 ± 1.0% in 46 h in the biocathode fed with lactate, in the biocathode without lactate, and in the abiotic cathode respectively. Thus, enhanced decolorization of AO7 occurred in the biocathode, compared to the abiotic cathode, regardless of the presence of lactate. To further investigate the AO7 reduction mechanism and electron transfer between the electrode and S. oneidensis, the cathode potential was controlled such that hydrogen was not produced. In the absence of lactate, the AO7 decolorization efficiency (78.5 ± 0.8%) and sulfanilic acid (SA) production efficiency (70.9 ± 1.5%) in the biocathode were higher than the AO7 decolorization efficiency (63.7 ± 3.6%) and the SA production (56.1 ± 1.9%) efficiency in the abiotic cathode. This suggests that the reduction of AO7, with electrode as the sole electron donor, was enhanced by electron transfer between the cathode and the S. oneidensis formed biofilm on the cathode surface. This study demonstrated that S. oneidensis enhanced the capture of electrons from the cathode electrode for the reduction of the organic pollutant AO7.

Activation of periodate by granular activated carbon for acid orange 7 decolorization

This study investigated the activation of periodate (IO4−) by granular activated carbon (GAC) for acid orange 7 (AO7) decolorization at ambient temperature. It was found that there existed a remarkable synergistic effect in the GAC/IO4− system. Some influential parameters, including periodate concentration, GAC dosage, initial solution pH and anions (Cl− and CO32−) were examined and analyzed. The results from radical scavenging experiments (with ethanol and tert–butyl alcohol) and electron spin resonance (ESR) analysis revealed that hydroxyl radical (•OH) made a minor contribution to AO7 decolorization. Furthermore, the increasing formation of iodate (IO3−) as the reaction proceeded in the presence of excessive ethanol indirectly suggested that iodyl radical (IO3•) was likely to be the dominating reactive species that controlling the oxidation process. In the reuse experiments, the efficiencies of AO7 decolorization enhanced surprisingly and remained 100% when the dried-GAC (GAC collected from the former cycle experiment and dried at 105°C for 24h) was reused for over ten cycles, which indicated that the dried-GAC showed remarkable catalytic ability and sustainable reuse capability. Besides, a series of experiments were conducted to testify the main contributor to the strong enhancement of AO7 decolorization with the dried-GAC.

Decolorization of azo dye by peroxymonosulfate activated by carbon nanotube: Radical versus non-radical mechanism

Carbon nanotube (CNT) has been shown to effectively activate peroxymonosulfate (PMS) to remove contaminants, whereas controversial activation mechanisms (radical vs non-radical mechanism) were previously proposed. Here we report that radical-induced decolorization of acid orange 7 (AO7) dominated in the CNT activated PMS system, but non-radical mechanism was also involved at high Cl⿿ concentration. CNT exhibited high activity in activating PMS to decolorize AO7. The decolorization rate of AO7 increased with increasing PMS dosages and CNT loadings, rising temperature and higher pH. Radical quenching and photoluminescence techniques confirmed the decolorization of AO7 in the CNT/PMS system was caused by the radical oxidation, which dominantly took place on the surface of CNT, rather than the bulk solution. The presence of Cl⿿ exhibited a dual effect on AO7 decolorization. Low concentration of Cl⿿ slightly inhibited AO7 decolorization, but further raising the concentration to above 0.1M significantly accelerated its decolorizaition. Cl⿿ was confirmed to react with PMS to generate HClO, which effectively bleached AO7 through non-radical process rather than radical process. The decolorization of AO7 induced from the non-radical process exhibited different degradation products and less mineralization in comparison to that derived from radical process.

Copper-spent activated carbon as a heterogeneous peroxydisulfate catalyst for the degradation of Acid Orange 7 in an electrochemical reactor.

The exhausted activated carbon generated from the adsorption of heavy metal wastewater needs further treatment/disposal. In this study, a new application of copper-spent activated carbon (Cu-AC) was proposed. Cu-AC was used to activate peroxydisulfate (PDS) for the decolorization of Acid Orange 7 (AO7) and electrical current was introduced to enhance the process. The decolorization followed a pseudo-first-order kinetic pattern well (R(2) > 0.95). 92.4% of color removal at 60 min and 38.3% of total organic carbon removal at 180 min were achieved when initial pH value was 9.0, current density was 16 mA/cm(2), PDS concentration was 5 mM and Cu-AC dosage was 0.25 g/L. The radical scavengers including methanol, tert-butanol and phenol, as well as electron paramagnetic resonance test, were employed to investigate the oxidizing species responsible for AO7 decolorization. The stability of Cu-AC was confirmed by three recycle experiments.

Enhanced decolorization efficiency of acid orange 7 by electric field granular‐activated carbon combined system and its statistical optimization by response surface methodology

In this study, the decolorization of Acid Orange 7 (AO‐7), a model pollutant, was experimentally investigated by combining granular‐activated carbon (GAC) in an electrochemical treatment system, which in this investigation is called an EF‐GACC (Electric Field and Granular Activated Carbon‐Combined) system. The results of preliminary testing showed that the EF‐GACC system exhibited a greatly higher decolorization performance for AO‐7 than did either the individual electric field or GAC adsorption system. This is mainly due to the dual action of GAC in the system as adsorbent and moving conductor. Subsequently, to statistically optimize the key parameters (applied voltage, GAC concentration, initial pH, and reaction time) in the EF‐GACC system and thereby maximize the decolorization efficiency, a response surface methodology with a Box‐Behnken design was used. In terms of the results, the overall performance revealed that the decolorization was well fitted by a quadratic regression model developed in this study and that the selected independent variables had significant interactive effect on the decolorization efficiency. Through numerical optimization, the complete decolorization and destruction of the parent molecule were obtained under statistically optimized conditions: an applied voltage of 28 V, a GAC concentration of 30 g/L, an initial pH of 5.0, and a reaction time of 40 min. The scale‐up and semicontinuous sequencing batch reactor system was satisfactorily tested and found to have an average decolorization of 99.7% ± 0.3%. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1674–1682, 2015

Decolorization of Acid Orange 7 by an electric field-assisted modified orifice plate hydrodynamic cavitation system: Optimization of operational parameters

In this study, the decolorization of Acid Orange 7 (AO-7) with intensified performance was obtained using hydrodynamic cavitation (HC) combined with an electric field (graphite electrodes). As a preliminary step, various HC systems were compared in terms of decolorization, and, among them, the electric field-assisted modified orifice plate HC (EFM-HC) system exhibited perfect decolorization performance within 40min of reaction time. Interestingly, when H2O2 was injected into the EFM-HC system as an additional oxidant, the reactor performance gradually decreased as the dosing ratio increased; thus, the remaining experiments were performed without H2O2. Subsequently, an optimization process was conducted using response surface methodology with a Box–Behnken design. The inlet pressure, initial pH, applied voltage, and reaction time were chosen as operational key factors, while decolorization was selected as the response variable. The overall performance revealed that the selected parameters were either slightly interdependent, or had significant interactive effects on the decolorization. In the verification test, complete decolorization was observed under statistically optimized conditions. This study suggests that EFM-HC is a useful method for pretreatment of dye wastewater with positive economic and commercial benefits.