Enhancing the electrochemical oxidation of acid-yellow 36 azo dye using boron-doped diamond electrodes by addition of ferrous ion

Photocatalytic degradation of acid yellow 36 with calcined titania-hydroxyapatite-cuo xerogels

Advanced oxidation processes (AOP), using semiconductor (SC) and hydroxyapatite (HA) composites, are promising due to the synergy of photocatalytic and adsorption properties. Still, dye removal efficiency of composites based on HA-SC remains low, because most of the research reported consider single SC materials. In this work, nanocrystalline xerogels of titanium oxide (TiO2) with copper oxide (CuO) and HA were synthesized by the sol-gel process. HA was obtained by the precipitation method without heat treatment and calcined in the range of 200-1000 °C. TiO2 and copper precursors were added to a sol containing HA in a 12:1 mol ratio, obtaining HA-TiO2 and HA-CuO-TiO2 nanomaterials. The xerogels were characterized by X-ray diffraction, scanning electron microscopy, emission field scanning electron microscopy and photoresponse. Their performance in the photocatalytic discoloration of an aqueous solution acid yellow dye 36 (AY36) was evaluated, using visible and UV light. The best discoloration was achieved with HA-CuO-TiO2 xerogels with HA calcined at 600 °C, showing a degradation kinetic constant of 0.24 min-1. In contrast, HA-TiO2 materials showed little or no photocatalytic activity, but strong dye adsorption/desorption. The thermal treatment of HA determines the filament-like morphology and degree of compaction of the nanomaterials, which are relevant in the crystallite size and sensitization of the SC matrix. Further studies must address the surface chemistry and rectifying properties of the best SC composite to have a more complete understanding of the mechanisms involved.

Synergistic effects of oxidation, coagulation and adsorption in the integrated fenton-based process for wastewater treatment: A review

Fenton process is the most popular for wastewater treatment among all available advanced oxidation processes (AOPs). Numerous endeavors have been devoted to improving the oxidation efficiency of Fenton reaction in terms of promoting ·OH generation, accelerating iron redox cycle and extending applicable pH range. However, in addition to oxidation, coagulation and adsorption also simultaneously occur in the Fenton process, which play important role in the removal of pollutants. Rapid progress has revealed the synergistic effects of oxidation, coagulation and adsorption in the Fenton process, providing new ideas for the treatment of complex and refractory wastewater. Based on available studies, this review is the first to systematically summarize the research progress regarding the synergistic effects of oxidation, coagulation and adsorption in the integrated Fenton-based processes for wastewater treatment. The involved mechanism of the synergistic effects in different Fenton processes (homogeneous Fenton, heterogeneous Fenton and physical field-assistant Fenton coupling process) are critically reviewed. Furthermore, special attention has been paid to the representative applications of the synergistic effects in wastewater treatment (such as industrial organic wastewater, landfill leachate and heavy metal-organic complexes, etc.), particularly focusing on the operation parameters and removal performance. Finally, a conclusion of the review and subsequently, perspectives are given for possible research directions. We believe this review can provide useful information for researchers and end-users involved in the development and application of the Fenton process in wastewater treatment.

Simultaneous Electrochemical Generation of Ferrate and Oxygen Radicals to Blue BR Dye Degradation

In this study, electro-oxidation (EOx) and in situ generation of ferrate ions [Fe(VI)] were tested to treat water contaminated with Blue BR dye (BBR) using a boron-doped diamond (BDD) anode. Two electrolytic media (0.1 M HClO4 and 0.05 M Na2SO4) were evaluated for the BDD, which simultaneously produced oxygen radicals (•OH) and [Fe(VI)]. The generation of [Fe(VI)] was characterized by cyclic voltammetry (CV) and the effect of different current intensity values (e.g., 7 mA cm−2, 15 mA cm−2, and 30 mA cm−2) was assessed during BBR degradation tests. The discoloration of BBR was followed by UV-Vis spectrophotometry. When the EOx process was used alone, only 78% BBR discoloration was achieved. The best electrochemical discoloration conditions were found using 0.05 M Na2SO4 and 30 mA cm−2. Using these conditions, overall BBR discoloration values up to 98%, 95%, and 87% with 12 mM, 6 mM, and 1 mM of FeSO4, respectively, were achieved. In the case of chemical oxygen demand (COD) reduction, the EOx process showed only a 37% COD reduction, whereas combining [Fe(VI)] generation using 12 mM of FeSO4 achieved an up to 61% COD reduction after 90 min. The evolution of reaction byproducts (oxalic acid) was performed using liquid chromatography analysis.

Heterogeneous Fenton reaction for elimination of Acid Yellow 36 in both fluidized-bed and stirred-tank reactors: Computational fluid dynamics versus experiments

Heterogeneous Fenton process is a kind of advanced oxidation processes (AOPs) that is significant for wastewater treatment. In the first part of this study, acid yellow 36 (AY36) degradation process has occurred in two kinds of reactors: fluidized-bed and stirred-tank reactors. Performances of these two semi-pilot reactors are compared by evaluating the removal ratio of the dye and pH changes during the process. Pyrite has been used as a heterogeneous catalyst. For obtaining the characteristics of pyrite, XRD, SEM, and FT-IR analysis have been carried out. In the second part of this study, a modified computational fluid dynamics (CFD) method has been utilized to solve the momentum and mass balances for heterogeneous Fenton process in both reactors. In AOPs, free radicals are reactive and have a short lifetime, so that turbulence mixing would be a limiting factor for the reactions that radicals are involved. By introducing a new parameter, named turbulence mixing rate, as a reaction rate for reactive species like hydroxyl radicals, the results of removal ratio and pH changes during the process showed a good agreement between the experiments and the CFD simulations, compared with not including the mixing rate in the CFD simulations (conventional kinetic modeling). In addition, the results revealed the high performance of the fluidized-bed reactor for this process in both experiments and CFD simulation.

Optimization and toxicity assessment of a combined electrocoagulation, H2O2/Fe2+/UV and activated carbon adsorption for textile wastewater treatment

In this study, the potential application of sequential Electrocoagulation + Fenton (F) or Photo-Fenton (PF) + Active carbon adsorption (EC + F/PF + AC) processes were analyzed as alternatives for the treatment of an industrial textile wastewater resulting from an industrial facility located in Medellín (Colombia). In order to maximize the organic matter degradation, each step of the treatment was optimized using the Response Surface Methodology. At first, the optimal performance of EC was achieved with Fe electrodes operating at pH = 7, j_EC = 10 mA/cm² and 60 rpm, during 10 min of electrolysis. At these conditions, EC let to remove 94% of the dye's color, 56% of the COD and 54% of the TOC. Next, sequentially applied Fenton or photo-Fenton process (i.e., EC + F/PF), operating at the optimized conditions (pH = 4.3, [Fe²⁺] = 1.1 mM, [H₂O₂] = 9.7 mM, stirring velocity = 100 rpm and reaction time = 60 min.), improved the quality of the treated effluent. The EC + F let to achieve total color reduction, as well as COD and TOC removals of 72 and 75%, respectively. The EC + PF reached 100% of color, 76% of COD and 78% of TOC reductions. The EC + F/PF processes were more efficient than EC in elimination of low molecular weight (<5 kDa) compounds from wastewater. Moreover, the BOD₅/COD ratio increased from 0.21 to 0.42 and from 0.21 to 0.46 using EC + F and EC + PF processes, respectively. However, EC + F/PF were not fully effective for the removal of acute toxicity to Artemia salina: 20% and 60% of reduction in toxicity using EC + F and EC + PF, respectively, comparing to very toxic (100%) raw textile wastewater. Thus, activated carbon adsorption was applied as an additional step to complete the treatment. After AC adsorption, the acute toxicity decreased to 10% and 0% using EC + F and EC + PF, respectively. The total operational costs, including chemical reagents, electrodes, energy consumption and sludge disposal, were of 1.65 USD/m³ and 2.3 USD/m³ for EC + F and EC + PF, respectively.

Enhancing ferrate(VI) oxidation process to remove blue 203 from wastewater utilizing MgO nanoparticles

The aim of this study is to investigate the beneficial effect of utilizing MgO nanoparticles on the performance of ferrate(VI) oxidation process to remove blue-203 dye from wastewater. It was also made an attempt to assess the effects of pH, temperature, and MgO nanoparticle dosage on this oxidation process performance. Several sets of batch experiment were conducted to find out the effects of temperature ranging from 25 to 65 °C, pH ranging from 1.5 to 13, ferrate(VI) concentration ranging from 0.5 to 5.9 mg/L and MgO nanoparticles dosage ranging from 0.01 to 0.05 g in 150 mL solution on the removal efficiency. The results showed that adding MgO nanoparticles can improve the performance of ferrate(VI) oxidation removal method significantly, spec. at basic conditions. This synergistic effect can be attributed to the simultaneous adsorption of ferrate(VI) and dye molecules on the surface of nanoparticles. The results also revealed that the reaction between blue-203 dye and ferrate(VI) takes place rapidly at high mixing rate. It means that the required time to complete the removal process is controlled by mixing rate. It was finally concluded that adding MgO nanoparticles was an efficient means to enhance the performance of ferrate(VI) to oxidize blue-203 dye, esp. under basic conditions.

Diazo dye Congo Red degradation using a Boron-doped diamond anode: An experimental study on the effect of supporting electrolytes

Diazo dye Congo Red (CR) solutions at 100mg/L, were degraded using different supporting electrolytes in an electrochemical advanced oxidation process (EAOPs), like the anodic oxidation (AOx/BDD). All experiments were carried out in a 3L flow reactor with a Boron-doped diamond (BDD) anode and stainless steel cathode (AISI 304), at 7.5, 15, 30 and 50mA/cm(2) current densities (j). Furthermore, each experiment was carried out under a flow rate of 7L/min. Additionally, HClO4, NaCl, Na2SO4, and H2SO4 were tested as supporting electrolytes at a 50mM concentration. The degradation process was at all times considerably faster in NaCl medium. Solutions containing SO4(2-) or ClO4(-) ions were less prompted to degradation due to the low oxidation power of these species into the bulk. Dissolved organic carbon (DOC) analysis, was carried out to evaluate the mineralization of CR. The degradation of CR, was evaluated with the HPLC analysis of the treated solutions.

Ferrate(VI) as a greener oxidant: Electrochemical generation and treatment of phenol

Ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) is a greener oxidant in the treatment of drinking water and wastewater. The electrochemical synthesis of Fe(VI) may be considered environmentally friendly because it involves one-step process to convert Fe(0) to Fe(VI) without using harmful chemicals. Electrolysis was performed by using a sponge iron as an anode in NaOH solution at different ionic strengths. The cyclic voltammetric (CV) curves showed that the sponge iron had higher electrical activity than the grey cast iron. The optimum current density was 0.054mAcm(-2) in 10M NaOH solution, which is much lower than the electrolyte concentrations used in other electrode materials. A comparison of current efficiency and energy consumption was conducted and is briefly discussed. The generated ferrate solution was applied to degrade phenol in water at two levels (2mgL(-1) and 5mgL(-1)). The maximum removal efficiency was ∼70% and the optimum pH for phenol treatment was 9.0. Experiments on phenol removal using conventional coagulants (ferric chloride (FeCl3) and polyaluminium chloride (PAC)) were performed independently to demonstrate that removal of phenol by Fe(VI) occurred mainly by oxidative transformation. A combination of Fe(VI) and coagulant may be advantageous in enhancing removal efficiency, adjusting pH, and facilitating flocculation.

Complete removal of AHPS synthetic dye from water using new electro-fenton oxidation catalyzed by natural pyrite as heterogeneous catalyst

The mineralization of a new azo dye - the (4-amino-3-hydroxy-2-p-tolylazo-naphthalene-1-sulfonic acid) (AHPS) - has been studied by a novel electrochemical advanced oxidation process (EAOP), consisting in electro-Fenton (EF) oxidation, catalyzed by pyrite as the heterogeneous catalyst - the so-called 'pyrite-EF'. This solid pyrite used as heterogeneous catalyst instead of a soluble iron salt, is the catalyst the system needs for production of hydroxyl radicals. Experiments were performed in an undivided cell equipped with a BDD anode and a commercial carbon felt cathode to electrogenerate in situ H2O2 and regenerate ferrous ions as catalyst. The effects on operating parameters, such as applied current, pyrite concentration and initial dye content, were investigated. AHPS decay and mineralization efficiencies were monitored by HPLC analyses and TOC measurements, respectively. Experimental results showed that AHPS was quickly oxidized by hydroxyl radicals (OH) produced simultaneously both on BDD surface by water discharge and in solution bulk from electrochemically assisted Fenton's reaction with a pseudo-first-order reaction. AHPS solutions with 175 mg L(-1) (100 mg L(-1) initial TOC) content were then almost completely mineralized in 8h. Moreover, the results demonstrated that, under the same conditions, AHPS degradation by pyrite electro-Fenton process was more powerful than the conventional electro-Fenton process.

Ozonation-based decolorization of food dyes for recovery of fruit leather wastes

Commercial manufacture of fruit leathers (FL) usually results in a portion of the product that is out of specification. The disposition of this material poses special challenges in the food industry. Because the material remains edible and contains valuable ingredients (fruit pulp, sugars, acidulates, etc.), an ideal solution would be to recover this material for product rework. A key practical obstacle to such recovery is that compositing of differently colored wastes results in an unsalable gray product. Therefore, a safe and scalable method for decolorization of FL prior to product rework is needed. This research introduces a novel approach utilizing ozonation for color removal. To explore the use of ozonation as a decolorization step, we first applied it to simple solutions of the commonly used food colorants 2-naphthalenesulfonic acid (Red 40), tartrazine (Yellow 5), and erioglaucine (Blue 1). Decolorization was measured by UV/vis spectrometry at visible wavelengths and with a Hunter colorimeter. Volatile and semivolatile byproducts from ozone-based colorant decomposition were identified and quantified with solid phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC-MS). Removal of Yellow 5, Red 40 and Blue 1 of about 65%, 80%, and 90%, respectively, was accomplished with 70 g of ozone applied per 1 kg of redissolved and resuspended FL. Carbonyl compounds were identified as major byproducts from ozone-induced decomposition of the food colorants. A conservative risk assessment based on quantification results and published toxicity information of potentially toxic byproducts, determined that ozone-based decolorization of FL before recycling is acceptable from a safety standpoint. A preliminary cost estimate based on recycling of 1000 tons of FL annually suggests a potential of $275,000 annual profit from this practice at one production facility alone.

Decolorization of sulfonated azo dye Metanil Yellow by newly isolated bacterial strains: Bacillus sp. strain AK1 and Lysinibacillus sp. strain AK2

Two different bacterial strains capable of decolorizing a highly water soluble azo dye Metanil Yellow were isolated from dye contaminated soil sample collected from Atul Dyeing Industry, Bellary, India. The individual bacterial strains Bacillus sp. AK1 and Lysinibacillus sp. AK2 decolorized Metanil Yellow (200 mg L(-1)) completely within 27 and 12h respectively. Various parameters like pH, temperature, NaCl and initial dye concentrations were optimized to develop an economically feasible decolorization process. The maximum concentration of Metanil Yellow (1000 mg L(-1)) was decolorized by strains AK2 and AK1 within 78 and 84 h respectively. These strains could decolorize Metanil Yellow over a broad pH range 5.5-9.0; the optimum pH was 7.2. The decolorization of Metanil Yellow was most efficient at 40°C and confirmed by UV-visible spectroscopy, TLC, HPLC and GC/MS analysis. Further, both the strains showed the involvement of azoreductase in the decolorization process. Phytotoxicity studies of catabolic products of Metanil Yellow on the seeds of chick pea and pigeon pea revealed much reduction in the toxicity of metabolites as compared to the parent dye. These results indicating the effectiveness of strains AK1 and AK2 for the treatment of textile effluents containing azo dyes.

Mineralization of Acid Yellow 36 azo dye by electro-Fenton and solar photoelectro-Fenton processes with a boron-doped diamond anode

The degradation of the Acid Yellow 36 (AY36) azo dye is studied by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a recirculation flow plant with an undivided cell containing a boron-doped diamond anode and an air-diffusion cathode for H₂O₂ electrogeneration, coupled with a solar photoreactor. A solution of 2.5L with 108 mg L⁻¹ of the dye and 0.5 mM Fe²(+) at pH 3.0 was comparatively treated at constant current. Hydroxyl radicals formed from Fenton's reaction and at the anode surface are the main oxidants. Total mineralization is almost achieved in SPEF, while EF yields poor TOC removal. Both processes are accelerated with increasing current. AY36 decays with similar rate in EF and SPEF following a pseudo first-order reaction, but the solution is more slowly decolorized because of the formation of conjugated byproducts. NH₄(+) ion is released in SPEF, while NO₃⁻ ion is mainly lost in EF. Tartronic, maleic, fumaric, oxalic, formic and oxamic acids are detected as generated carboxylic acids. Fe(III)-oxalate complexes are largely accumulated in EF and their quick photodecomposition in SPEF explains its higher oxidation power. The SPEF method yields greater current efficiency and lower energy cost as current decreases, and then it is more viable at low currents.