Sono-advanced Fenton decolorization of azo dye Orange G: Analysis of synergistic effect and mechanisms

Analysis of factors influencing on Electro-Fenton and research on combination technology (II): a review

The principle of Fenton reagent is to produce ·OH by mixing H2O2 and Fe2+ to realize the oxidation of organic pollutants, although Fenton reagent has the advantages of non-toxicity and short reaction time, but there are its related defects. The Fenton-like technology has been widely studied because of its various forms and better results than the traditional Fenton technology in terms of pollutant degradation efficiency. This paper reviews the electro-Fenton technology among the Fenton-like technologies and provides an overview of the homogeneous electro-Fenton. It also focuses on summarizing the effects of factors such as H2O2, reactant concentration, reactor volume and electrode quality, reaction time and voltage (potential) on the efficiency of electro-Fenton process. It is shown that appropriate enhancement of H2O2 concentration, voltage (potential) and reaction volume can help to improve the process efficiency; the process efficiency also can be improved by increasing the reaction time and electrode quality. Feeding modes of H2O2 have different effects on process efficiency. Finally, a considerable number of experimental studies have shown that the combination of electro-Fenton with ultrasound, anodic oxidation and electrocoagulation technologies is superior to the single electro-Fenton process in terms of pollutant degradation.

Electro-Fenton mineralization of real textile wastewater by micron-sized ZVI powder anode

The diverse compositions and complex nature of the textile wastewater make it imperative to find an economical and suitable degradation pathway. The degradation of real textile wastewater on a novel heterogeneous electro-Fenton system was carried out with a composite anode of magnetically fixed micron ZVI coupling with a Ti/RuO₂-IrO₂ sheet. The influences of different variables such as mZVI dosage, H₂O₂ amount, applied voltage and pH value on both total organic carbon and chemical oxygen demand removal efficiencies and energy consumption were investigated. The optimized parameters were simultaneously verified by using electrochemical workstation Tafel curves and Nyquist plots. The optimal operating conditions for evaluating the wastewater treatment were H₂O₂ dosage of 0.10 mol·L^-1, applied voltage of 5.0 V, mZVI amount of 1.0 g·L^-1 and initial pH value of 3.0. The high TOC and COD removal efficiencies of 92.44 and 82.84% could be achieved simultaneously in 60 min, respectively. XRD, XPS and SEM-EDS were used to investigate the interaction between the pollutant and the mZVI. GC-MS analysis was performed on untreated and treated wastewater to determine the degradation of pollutants in dyeing wastewater during the electro-Fenton process and to effectively propose a suitable degradation mechanism for this system.

Possibilities and Limitations of the Sono-Fenton Process Using Mid-High-Frequency Ultrasound for the Degradation of Organic Pollutants

Mid-high-frequency ultrasound (200-1000 kHz) eliminates organic pollutants and also generates H₂O₂. To take advantage of H₂O₂, iron species can be added, generating a hybrid sono-Fenton process (sF). This paper presents the possibilities and limitations of sF. Heterogeneous (a natural mineral) and homogeneous (Fe²⁺ and Fe³⁺ ions) iron sources were considered. Acetaminophen, ciprofloxacin, and methyl orange were the target organic pollutants. Ultrasound alone induced the pollutants degradation, and the dual competing role of the natural mineral (0.02-0.20 g L^-1) meant that it had no significant effects on the elimination of pollutants. In contrast, both Fe²⁺ and Fe³⁺ ions enhanced the pollutants' degradation, and the elimination using Fe²⁺ was better because of its higher reactivity toward H₂O₂. However, the enhancement decreased at high Fe²⁺ concentrations (e.g., 5 mg L^-1) because of scavenger effects. The Fe²⁺ addition significantly accelerated the elimination of acetaminophen and methyl orange. For ciprofloxacin, at short treatment times, the degradation was enhanced, but the pollutant complexation with Fe³⁺ that came from the Fenton reaction caused degradation to stop. Additionally, sF did not decrease the antimicrobial activity associated with ciprofloxacin, whereas ultrasound alone did. Therefore, the chemical structure of the pollutant plays a crucial role in the feasibility of the sF process.

Sono-degradation of Reactive Blue 19 in aqueous solution and synthetic textile industry wastewater by nanoscale zero-valent aluminum

Reactive dyes, which are commonly used in the textile industry, are toxic and carcinogenic for the ecosystem and human health. The objective of this study was to investigate the removal of Reactive Blue 19 (RB19) from aqueous solution and synthetic textile industry wastewater using nanoscale zero-valent aluminum (nZVAl), ultrasonic bath (US-40 kHz), and combined US/nZVAl through the consideration of varying experimental parameters such as pH, nZVAl dosage, contact time, and initial RB19 dye concentration. The acidic pH value was an effective parameter to degrade RB19. As the nZVAl dosage and contact time increased, the degradation of RB19 dye from aqueous solution and synthetic textile industry wastewater increased using combined US/nZVAl process. A similar result was obtained for RB19 removal with combined US/nZVAl using 0.10 g dosage at 30 min, whereas it was obtained with nZVAl alone using 0.20 g dosage at 60 min. The sono-degradation process activated the nZVAl surface depending on US cavitation effect and shock waves, and increased RB19 dye uptake capacity with a shorter contact time and lower nZVAl dosage. Increasing the initial dye concentration decreased the removal efficiency for RB19. According to the obtained reusability results, nZVAl particles could be reused for four and two consecutive cycles of combined US/nZVAl and nZVAl alone, respectively.

A review of the new multifunctional nano zero-valent iron composites for wastewater treatment: Emergence, preparation, optimization and mechanism

Nano zero-valent iron (NZVI) with high chemical reactivity and environmental friendliness had recently become one of the most efficient technologies for wastewater restoration. However, the unitary NZVI system had not met practical requirements for wastewater treatments. Expectantly, the development of NZVI would prefer multifunctional NZVI-based composites, which could be prepared and optimized by the combined methods and technologies. Consequently, a systematic and comprehensive summary from the perspective of multifunctional NZVI-composite had been conducted. The results demonstrated that the advantages of various systems were integrated by multifunctional NZVI-composite systems with a more significant performance of pollutant removal than those of the bare NZVI and its composites. Simultaneously, characteristics of the product prepared by the incorporation of numerous methods were superior to those by a simple method, resulting in the increase of the entirety efficiency. By comparison with other preparation methods, the ball milling method with higher production and field application potential was worthy of attention. After combining multiple technologies, the effect of NZVI and its composite systems could be dramatically strengthened. Preparation technology parameters and treatment effect of contaminants could be further optimized using more comprehensive experimental designs and mathematical models. The mechanism of the multifunctional NZVI system for contaminants treatment was primarily focused on adsorption, oxidation, reduction and co-precipitation. Multiple techniques were combined to enhance the dispersion, alleviating passivation, accelerating electron transfer efficiency or mass transfer action for optimizing the effect of NZVI composites.

Modeling azo dye removal by sono-fenton processes using response surface methodology and artificial neural network approaches

Textile industry wastewaters, which cause serious problems in the environment and human health, include synthetic dyes, complex organic pollutants, surfactants, and other toxic chemicals and therefore must be removed by advanced treatment methods. Determination of appropriate treatment conditions for efficient use of advanced treatment methods is an important and necessary step. In the last thirty years, the Artificial Neural Network-Genetic Algorithm (ANN-GA) and Response Surface Methodology (RSM) have emerged as the most effective empirical modeling and optimization methods especially for nonlinear systems. Reactive Red 195 azo dyestuff was chosen as the target pollutant. The color removal efficiency was modeled and optimized as a function of Sono-Fenton conditions such as H₂O₂ dosage, Fe²⁺ dosage, initial pH value, ultrasound power, and ultrasound frequency, using ANN-GA and RSM. The generalization and predictive ability of these methods were compared using the results of the 46 experimental sets generated by the Box-Behnken design. The mean square errors for these models are 3.01612 and 0.00295, and the regression coefficients showing the superiority of ANN in determining nonlinear behavior are 0.9856 and 0.9164, respectively. In optimal conditions, the prediction errors with hybrid ANN-GA and RSM models are 0.002% and 3.225%, respectively.

Ultrasound assisted zero valent iron corrosion for peroxymonosulfate activation for Rhodamine-B degradation

In this work, ultrasound (US) irradiation assisted powder zero valent iron (ZVI) corrosion was conducted for peroxymonosulfate (PMS) activation. PMS activation activity was evaluated by Rhodamine-B (Rh B) degradation efficiency. The other US/PMS, ZVI/PMS, Fe²⁺/PMS and US/PMS/Fe²⁺ systems were performed to investigate the synergistic effects of US and ZVI on PMS activation activity. US/PMS/ZVI system performed the highest activity of Rh B degradation. 99.76% of Rh B was removed within 12 min under the optimum condition (pH = 4.5, ZVI dosage = 1 g/L, PMS = 1 mM, US power = 50 W). A comparison of US/PMS/ZVI system with PMS/ZVI and homogeneous US/PMS/Fe²⁺ systems for Rh B degradation was conducted, indicating that ultrasound irradiation contributed to acceleration of ZVI corrosion and removal of passive films. Besides, the electrons transformation from Fe⁰ to PMS made main contribution to the generation of sulfate radical, which resulted in the ability of degradation of Rh B. ZVI could be reused for five cycles with efficient activity of PMS activation. Exhaustion of ZVI led to the decrease in PMS activation at the sixth recycle. Thus, this work presents important information on understanding reuse of iron fillings for PMS/PS activation in practical application of pollution remediation.

Sonochemical and sonoelectrochemical production of hydrogen

Reserves of fossil fuels such as coal, oil and natural gas on earth are finite. The continuous use and burning of these fossil fuel resources in the industrial, domestic and transport sectors has resulted in the extremely high emission of greenhouse gases, GHGs (e.g. CO₂) and solid particulates into the atmosphere. Therefore, it is necessary to explore pollution free and more efficient energy sources in order to replace depleting fossil fuels. The use of hydrogen (H₂) as an alternative fuel source is particularly attractive due to its very high specific energy compared to other conventional fuels and its zero GHG emission when used in a fuel cell. Hydrogen can be produced through various process technologies such as thermal, electrolytic, photolytic and biological processes. Thermal processes include gas reforming, renewable liquid and biooil processing, biomass and coal gasification; however, these processes release a huge amount of greenhouse gases. Production of electrolytic hydrogen from water is an attractive method to produce clean hydrogen. It could even be a more promising technology when combining water electrolysis with power ultrasound to produce hydrogen efficiently where sonication enhances the electrolytic process in several ways such as enhanced mass transfer, removal of hydrogen and oxygen (O₂) gas bubbles and activation of the electrode surface. In this review, production of hydrogen through sonochemical and sonoelectrochemical methods along with a brief description of current hydrogen production methods and power ultrasound are discussed.

Sono-advanced Fenton-like degradation of aromatic amines in textile dyeing sludge: efficiency and mechanisms

In this paper, a novel strategy integrating ultrasound (US) with a Fenton-like (zero-valent iron/EDTA/air, ZEA) process was proposed for the removal of the refractory and carcinogenic aromatic amines (AAs) in textile dyeing sludge for the first time. The operating condition was optimized as 1.08 W/cm³ ultrasonic density, 15 g/L ZVI, and 1.0 mM EDTA, which could reach degradation efficiencies of 51.79% in US, 72.88% in ZEA, and 92.40% in US/ZEA system after 90-min reaction. Quenching experiments showed that electron transfer reactions generated by the iron ligands in ZEA brought about various reactive oxidative species (ROS), in which Fe (IV), O₂˙^-, and ˙OH dominated the degradation. US induced sludge disintegration by ultrasonic shear, proven by particle size decrease and supernatant organic matter upsurge, which helps ROS contact with those pollutants in the sludge cavities. Besides, US facilitated the iron redox cycle for oxygen activation by promoting the corrosion of ZVI and stripping considerable ferric ions from sludge iron oxides which were verified by SEM, XRF, and XPS. Graphical abstract.

Enhanced removal of basic violet 10 by heterogeneous sono-Fenton process using magnetite nanoparticles

The removal of basic violet 10 (BV10), which is known as a cationic dye, from aqueous solution was studied by employing a heterogeneous sono-Fenton process over the nano-sized magnetite (Fe₃O₄) which had been prepared by the milling of magnetite mineral using a high-energy planetary ball milling process. The magnetite samples were characterized using the X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FTIR), and inductively couple plasma mass spectrometer (ICP-MS). It was found that the catalytic activity of the ball-milled magnetite sample was enhanced along with the improvement in its physicochemical properties; also, the ball-milled magnetite of 6 h displayed the highest catalytic activity in BV10 removal by the heterogeneous sono-Fenton process as compared with that for 4 h (66.12% after 120 min) and 2 h (48% after 120 min).The effect of operational parameters, namely, pH solution, catalyst dosage, the initial H₂O₂ concentration, ultrasonic power and the initial BV10 concentration, on the removal efficiency (RE%) of BV10 was investigated. The optimum conditions for the BV10 RE% were: the pH value of 3, the catalyst dosage of 1.5 g L^-1, the initial H₂O₂ concentration of 36 mM, the ultrasonic power of 450 W L^-1, and the initial BV10 concentration of 30 mg L^-1. The RE% of BV10 was 75.94% at these conditions after the reaction time of 120 min. The trapping experiments revealed that OH radicals were the dominant oxidative species, but O₂^-/HO₂ radicals also had a partial role in the removal of BV10.The reusability of the magnetite nanoparticles revealed about 28% decrease in the removal efficiency within five consecutive runs. The results obtained through GC-MS analysis also confirmed the efficient removal of BV10 molecules in the aqueous solution during the process.

Synthesis of iron-based metal-organic framework MIL-53 as an efficient catalyst to activate persulfate for the degradation of Orange G in aqueous solution

A series of MIL-53(Fe) materials were synthesized using a solvothermal method under different temperature and time conditions and were used as catalysts to activate persulfate and degrade Orange G (OG). Influences of the above conditions on the crystal structure and catalytic behavior were investigated. Degradation of OG under different conditions was evaluated, and the possible activation mechanism was speculated. The results indicate that high synthesis temperature (larger than 170 °C) leads to poor crystallinity and low catalytic activity, while MIL-53(Fe) cannot fully develop at low temperature (100 or 120 °C). The extension of synthesis time from 5 h to 3 d can increase the crystallinity of the samples, but weakened the catalytic activity, which was caused by the reduction of BET surface area and the amount of Fe (II)-coordinative unsaturated sites. Among all the samples, MIL-53(Fe)-A possesses the best crystal structure and catalytic activity. In optimal conditions, OG can be totally decolorized after degradation for 90 min, and a removal rate of 74% for COD was attained after 120 min. The initial solution pH had great influence on OG degradation, with the greatest removal in acidic pH environment. ESR spectra showed that sulfate radical (SO_4^- ·), hydroxyl radical (OH·), persulfate radical (S₂O_8^- ·), and superoxide radical (O₂·) exist in this system under acidic conditions. Furthermore, with the increase of pH, the relative amount of O₂· increases while that of OH· and SO_4^- · decreases, resulting in a reduced oxidizing capacity of the system.

Ultrasound-enhanced nanosized zero-valent copper activation of hydrogen peroxide for the degradation of norfloxacin

Commercial nanosized zero-valent copper (nZVC) was used as hydrogen peroxide (H₂O₂) activator in conjunction with ultrasonic irradiation (US) for the oxidative degradation of norfloxacin (NOR) in this study. Compared with silent degradation system, a significantly enhanced NOR removal was obtained in sono-advanced Fenton process, which involved a synergistic effect between sonolysis and Fenton-like reaction. Almost complete removal of NOR was achieved at 30min when the operating conditions were 0.25g/L nZVC and 10mM H₂O₂ with ultrasound power of 240W at 20kHz. The released Cu⁺ during the nZVC dissolution was the predominant copper species to activate H₂O₂ and yield hydroxyl radicals (OH) in US/nZVC/H₂O₂ system. According to the radical quenching experiments and electron paramagnetic resonance technique, hydroxyl radicals in solution (OH_free) were verified as the primary reactive species, and superoxide anion radicals (O₂^-) were regarded as the mediator for the copper cycling by reduction of Cu²⁺ to Cu⁺. NOR removal efficiencies were improved in various degrees when increased nZVC dosage, ultrasound power, hydrogen-ion amount and H₂O₂ concentration. Moreover, the inhibitory effect of different inorganic salts on NOR degradation followed the sequence of Na₂SO₄>NaNO₃≈no salt>NaCl>NaHCO₃. Finally, eleven intermediates were identified and five oxidation pathways were proposed, the cleavage of piperazine ring and transformation of quinolone group seemed to be the major pathway.

Hydrodynamic cavitation as a strategy to enhance the efficiency of lignocellulosic biomass pretreatment

Hydrodynamic cavitation (HC) is a process technology with potential for application in different areas including environmental, food processing, and biofuels production. Although HC is an undesirable phenomenon for hydraulic equipment, the net energy released during this process is enough to accelerate certain chemical reactions. The application of cavitation energy to enhance the efficiency of lignocellulosic biomass pretreatment is an interesting strategy proposed for integration in biorefineries for the production of bio-based products. Moreover, the use of an HC-assisted process was demonstrated as an attractive alternative when compared to other conventional pretreatment technologies. This is not only due to high pretreatment efficiency resulting in high enzymatic digestibility of carbohydrate fraction, but also, by its high energy efficiency, simple configuration, and construction of systems, besides the possibility of using on the large scale. This paper gives an overview regarding HC technology and its potential for application on the pretreatment of lignocellulosic biomass. The parameters affecting this process and the perspectives for future developments in this area are also presented and discussed.

Decolorization of reactive azo dyes using a sequential chemical and activated sludge treatment

Textile wastewater contains high concentrations of organic substances derived from diverse dyes and auxiliary chemicals, some of which are non-biodegradable and/or toxic. Therefore, it is essential that textile wastewater is treated and that these substances are removed before being discharged into the environment. A combination of advanced oxidation processes (AOPs) to obtain partial dye degradation followed by a biological treatment has been suggested as a promising method for cost-effective decolorization of wastewater. The aim of this study was to develop and evaluate a combined method of partial Fenton's oxidation and biological treatment using activated sludge for decolorization of azo dyes, which represent an important group of recalcitrant, toxic textile dyes. Using Reactive Violet 5 (RV5) as a model dye, color removal was significantly higher when the combined Fenton treatment/activated sludge method was used, as opposed to separate application of these treatments. More specifically, pretreatment with Fenton's reagent removed 52.9, 83.9 and 91.3 % of color from a 500 mg l^-1 RV5 aqueous solution within 60 min when H₂O₂ concentrations of 1.0, 1.5, and 2.0 mM were used, respectively. Subsequent biological treatment was found to significantly enhance the chemical treatment, with microbial decolorization removing 70.2 % of the remaining RV5 concentration, on average. Molecular analysis of the microbial community within the activated sludge revealed that exposure to RV5 shifted the community composition from diverse towards a highly-specialized community harboring taxa with azo dye degrading activity, including Trichosporon, Aspergillus and Clostridium species.

Novel bio-electro-Fenton technology for azo dye wastewater treatment using microbial reverse-electrodialysis electrolysis cell

Development of sustainable technologies for treatment of azo dyes containing wastewaters has long been of great interest. In this study, we proposed an innovative concept of using microbial reverse-electrodialysis electrolysis cell (MREC) based Fenton process to treat azo dye wastewater. In such MREC-Fenton integrated process, the production of H₂O₂ which is the key reactant of fenton-reaction was driven by the electrons harvested from the exoelectrogens and salinity-gradient between sea water and fresh water in MREC. Complete decolorization and mineralization of 400mgL^-1 Orange G was achieved with apparent first order rate constants of 1.15±0.06 and 0.26±0.03h^-1, respectively. Furthermore, the initial concentration of orange G, initial solution pH, catholyte concentration, high and low concentration salt water flow rate and air flow rate were all found to significantly affect the dye degradation. This study provides an efficient and cost-effective system for the degradation of non-biodegradable pollutants.