Removal Of Acid Orange Research Articles

Removal of Acid Orange 7 in simulated wastewater using a three-dimensional electrode reactor: Removal mechanisms and dye degradation pathway

The removal of Acid Orange 7 (AO7) in simulated wastewater was experimentally investigated using a three-dimensional electrode reactor with granular activated carbon as the particle electrode, ACF (activated carbon fiber)/Fe as the anode, and ACF/Ti as the cathode. Particular attention was paid to the reaction mechanisms and the dye degradation pathway in the system. The removal of AO7 in the system was mainly dependent on the oxidation by the produced active substances ( OH, etc.) and the coagulation by Fe(II) or Fe(III) dissolved from the anode. The former mechanism was predominant. A possible pathway for AO7 degradation was proposed by monitoring the temporal evolution of intermediates in the solution, with the use of some techniques including GC/MS, FTIR and HPLC. The AO7 molecule was observed to be firstly decomposed to aromatic intermediates, further degraded to ring opening products and finally mineralized to CO 2, H 2O and inorganic salts. The intermediates increased the biodegradability of the wastewater, which was proved by the increase of the BOD/COD value after electrolysis treatment. The three-dimensional electrode method can be considered an effective alternative to dye wastewater pretreatment prior to the biological process.

Simultaneous removal of color, organic compounds and nutrients in azo dye-containing wastewater using up-flow constructed wetland

Combination of aerobic and anaerobic processes in constructed wetlands can enhance the treatment performance in textile wastewater. This study assessed the treatment of azo dye Acid Orange 7 (AO7) and nutrients using five laboratory-scale up-flow constructed wetlands (UFCW) with and without supplementary aeration, and with different emergent plants. Supplementary aeration controlled the size of aerobic and anaerobic zones in the UFCW reactors as evidenced by the oxidation–reduction potential (ORP) and dissolved oxygen (DO) profile of the UFCW. The AO7 removal efficiency was above 95% in all UFCW reactors and most of the color was extensively removed in the anaerobic region of the UFCW beds. The intermediates produced through the breakage of azo bond were significantly reduced in the UFCW reactors with supplementary aeration. The results indicated the applicability of the UFCW reactors to the treatment of azo dye-containing wastewater. The removals of T-N and T-P were in the range of 60–67% and 26–37%, respectively, among the UFCW reactors. The COD and NH 4-N removals in the aerated reactors were about 86 and 96%, respectively. On the other hand, the COD and NH 4-N removals were in the range of 78–82% and 41–48%, respectively, in the non-aerated reactors. The supplementary aeration enhanced the removal efficiencies in organic matter, NH 4-N and aromatic amines in the UFCW reactors.

Removal of Acid Orange 7 from water by electrochemically generated Fenton's reagent

The removal of azo dye Acid Orange 7 (AO7) from water was investigated by the electro-Fenton technology using electrogenerated hydroxyl radicals (OH) which leads to the oxidative degradation of AO7 up to its complete mineralization. H(2)O(2) and Fe (II) ions are electrogenerated in a catalytic way at the carbon-felt cathode. AO7 decay kinetics and evolution of its oxidation intermediates were monitored by high-performance liquid chromatography. The absolute rate constant of AO7 hydroxylation reaction has been determined as (1.20+/-0.17)x10(10)M(-1)s(-1). The optimal current value for the degradation of AO7 was found as 300 mA. AO7 degradation rate was found to decrease by increase in Fe(3+) concentration beyond 0.1mM. Mineralization of AO7 aqueous solutions was followed by total organic carbon (TOC) measurements and found to be 92%. Based on TOC evolution and identification of aromatic intermediates, short-chain carboxylic acids and inorganic ions released during treatment, a plausible mineralization pathway was proposed.

Evaluation of energy transfer and utilization efficiency of azo dye removal by different pulsed electrical discharge modes

The degradation of an azo dye, acid orange 7 (AO7), caused by different high voltage pulsed electrical discharge modes (spark, streamer and corona discharge) induced by the various initial conductivities was investigated. A new type of pulsed high voltage source with thyratron switch and Blumlein pulse forming net (BPFN) was used. The typical discharge waveforms of voltage, current, power, pulse energy and the pictures of spark, streamer and corona discharge modes were presented. The results indicated that pulsed electrical discharges led to complete decolorization and substantial decrease of the chemical oxygen demand (COD) of the dye solution. The main intermediate products were monitored by GC-MS. The discharge modes changed from spark to streamer and to corona discharge, and the streamer length decreased with the liquid conductivity increasing. At a constant input power, the peak voltage, peak current, peak power and energy per pulse of the three discharge modes ranked in the following order: spark > streamer > corona. The effective energy transfer efficiency of AO7 removal was higher for spark discharge (57.2%) than for streamer discharge (40.4%) and corona discharge (27.6%). Moreover, the energy utilization efficiency of AO7 removal for spark discharge was 1.035×109 mol/J, and for streamer and corona discharge they were 0.646×10−9 and 0.589×10−9 mol/J. Both the energy transfer efficiency and the energy utilization efficiency of spark discharge were the highest.

Study of acid orange 7 removal from aqueous solutions by powdered activated carbon and modeling of experimental results by artificial neural network

In this work, removal of acid orange 7 (AO7) by powdered activated carbon, from aqueous solutions with initial concentrations of 150 ppm to 350 ppm and initial pH values of 2.8, 5.8, 8.0 and 10.5 at 25°C was studied. Experiments were done in batch mode and the experimental solutions were agitated periodically. All concentrations were measured spectrophotometrically at 483 nm and three times replicated. In most cases, after 75 min contact time, the most of AO7 removal is performed. The maximum equilibrium removal of acid orange 7 (AO7) was 96.24% for its initial concentration of 150 ppm at pH i = 2.8, and minimum equilibrium removal was 48.05% for initial concentration of 350 ppm at pH i = 5.8. At the similar experimental conditions, application of different initial pH values altered the AO7 removal percent no more than 9.06%. It is found that the adsorption system follows the second-order adsorption rate expression and the constants of the rate expression at different conditions were calculated which are comparable and often higher than other adsorbents in adsorption of other dyes. The constants of Langmuir equation, Q and b, and constants of Freundlich equation, K f and 1/n, were calculated and results show that the adsorption process is favorable. Comparison of R 2 values shows that fitting of Freundlich equation to experimental data is better than Langmuir equation. The experimental results were also modeled by artificial neural network with mean relative error of 5.81%. This model was developed in Matlab 6.5 environment using a 3-layer feed forward backpropagation network with 3, 2 and 1 neurons in first, second and third layers, respectively.

Removal of C.I. Acid Orange 7 from aqueous solution by UV irradiation in the presence of ZnO nanopowder

The removal of C.I. Acid Orange 7 (AO7) from aqueous solution under UV irradiation in the presence of ZnO nanopowder has been studied. The average crystallite size of ZnO powder was determined from XRD pattern using the Scherrer equation in the range of 33 nm. The experiments showed that ZnO nanopowder and UV light had a negligible effect when they were used on their own. The effects of some operational parameters such as pH, the amount of ZnO nanopowder and initial dye concentration were also examined. The photodegradation of AO7 was enhanced by the addition of proper amount of hydrogen peroxide, but it was inhibited by ethanol. From the inhibitive effect of ethanol, it was deducted that hydroxyl radicals played a significant role in the photodegradation of the dye. The kinetic of the removal of AO7 can be explained in terms of the Langmuir–Hinshelwood model. The values of the adsorption equilibrium constant, K AO7, and the kinetic rate constant of surface reaction, k c, were 0.354 (mg l −1) −1 and 1.99 mg l −1 min −1, respectively. The electrical energy consumption per order of magnitude for photocatalytic degradation of AO7 was lower in the UV/ZnO/H 2O 2 process than that in the UV/ZnO process. Accordingly, it could be stated that the complete removal of color, after selecting desired operational parameters could be achieved in a relatively short time, about 60 min.

Aerobic degradation of acid orange 7 in a vertical-flow constructed wetland

Biological, aerobic degradation of an azo dye and of the resultant, recalcitrant, aromatic amines in a constructed wetland (CW) was demonstrated for the first time. A vertical-flow CW, planted with Phragmites sp. was fed with 127 mg l −1 of acid orange 7 (AO7) at hydraulic loads of 28, 40, 53 and 108 l m −2day −1. Color removal efficiencies of up to 99% clearly demonstrate cleavage of the azo bond, also confirmed by the similar AO7 removal and SO 4 2− release rates revealing that adsorption onto the matrix was constant. The positive redox potential at the outlet demonstrates that aerobic conditions were present. Chemical oxygen demand and total organic carbon removal efficiencies of up to 93% were also indicative of AO7 mineralization. The degradation of sulfanilic acid was confirmed by the presence of NO 3 −, SO 4 2− and secondary metabolites, which suggest at least two degradation pathways leading to a common compound, 3-oxoadipate.

Anaerobic treatment of azo dye Acid Orange 7 under fed-batch and continuous conditions

Acid Orange 7 (AO7) was treated anaerobically under fed-batch and continuous conditions. Fed-batch assays carried out with and without cosubstrate showed that the removal rate of this dye is highly favourable when glucose is added as cosubstrate. In addition, some intermediates generated after the reductive breakdown of AO7, such as 1-amino-2-naphthol (1A2N), seem to play a significant role as redox mediators, thus increasing the degradation rate of the dye. This effect is evidenced by the fact that, during the first feeding, the maximum AO7 removal rate was achieved after a lag phase, whereas for further AO7 feedings this phase was not observed. This can be explained by the presence of 1-amino-2-naphthol in the medium. During the continuous treatment with UASB reactors, AO7 loading rates of 1.7 mM d(-1) (590 mg l(-1)d(-1)) were achieved, with 92% AO7 removal efficiencies, operating with an influent comprised of AO7 (0.58 mM) and glucose (2 gl(-1)). In addition, when the cosubstrate was limiting (AO7 0.3 mM and glucose 0.25 gl(-1)), AO7 removal was significantly lower (78%).