Initial Acid Orange 7 Concentration Research Articles

Extraction of acid orange 7 from water by emulsion liquid membrane using Tri-dodecyl-amine as extractant

The main objective of this study was to investigate the feasibility of extracting Acid Orange 7 (AO7), a complex reactive dye, from aqueous solutions using a stabilized emulsion liquid membrane (ELM) technique. The ELM formulation comprised tri-dodecylamine (TDA) as the extracting agent, kerosene as the diluting medium, and SPAN 80 as the surfactant. We systematically examined various experimental variables that affect the extraction of AO7. These variables included the concentrations of the extractant and surfactant, internal phase concentrations, the ratio of the membrane phase to the internal phase, the choice of diluting medium and its grade, stirring speed, treatment ratio, and the initial concentration of AO7. Furthermore, we investigated the impact of sodium chloride concentration in the external phase. Our research findings indicate that the optimal conditions for AO7 extraction using the ELM method were as follows: a TDA concentration of 3% (w/w), a SPAN 80 concentration of 9% (w/w), an oil-to-aqueous phase ratio (O/A) of 1:1, kerosene as the diluting medium, H2SO4 as the internal phase, a stirring speed of 200 rpm, a treatment ratio of 1:10, and an initial AO7 concentration of 10 mg/L. Under these precise conditions, an exceptional extraction efficiency of 98.49% was achieved in just 15 min. Under these carefully controlled conditions, an exceptional extraction efficiency of 98.49% was achieved in just 15 min. Consequently, the emulsified liquid membrane extraction process demonstrates significant potential as an advanced separation technique for removing hazardous dyes, particularly in dilute solutions.

One-pot hydrothermal synthesis of FeNbO4 microspheres for effective sonocatalysis.

FeNbO4 sonocatalysts were successfully synthesized by a simple hydrothermal route at pH values of 3, 5, 7, 9 and 11. The catalysts were characterized by XRD, XPS, TEM, SEM, N2 adsorption and DRS to analyse the effect of pH parameters on the physicochemical properties of the materials during hydrothermal synthesis. The sonocatalytic activity of FeNbO4 microspheres was evaluated by using acid orange 7 (AO7) as the simulated contaminant. The experimental results showed that the best sonocatalytic degradation ratio (97.45%) of organic dyes could be obtained under the conditions of an initial AO7 concentration of 10 mg L-1, an ultrasonic power of 200 W, a catalyst dosage of 1.0 g L-1, and a pH of 3. Moreover, the sonocatalysts demonstrated consistent durability and stability across multiple test cycles. After active species capture experiments and calculation of the energy band, a possible mechanism was proposed based on the special Fenton-like mechanism and the dissociation of H2O2. This research shows that FeNbO4 microspheres can be used as sonocatalysts for the purification of organic wastewater, which has a promising application prospect.

Performance and mechanism of sulfite mediated oxidation of organic contaminants using iron(III) titanium oxide as catalyst

As sulfite has been employed currently in the catalytic degradation of various pollutants, the construction of more suitable and cheaper catalytic systems is required. Herein, a heterogeneous system for S(IV) activation by iron(III) titanium oxide (Fe2TiO5) was proposed to proceed the removal of acid orange 7 (AO7) and seven typical pharmaceutical and personal care products (PPCPs). Typically, the AO7 (10 mg L−1) can be degraded up to 67% within 60 min ([Fe2TiO5] = 0.8 g L−1, [S(IV)] = 2.0 mM, pH = 6.0). The effects of initial AO7 concentration, pH, Fe2TiO5 dosage, S(IV) concentration, and co-existing anions (HCO3− and H2PO4−) were examined to explore the application conditions and resistance of Fe2TiO5 −S(IV) system. Moreover, the stability of Fe2TiO5 −S(IV) system was tested by sequential runs, while XRD was also performed for the robustness evaluation of catalyst. The scavenging experiment showed that the active species in the system mainly include SO5•−, HO•, and SO4•−, while SO4•− being the dominant one. Through the competitive experiments of EDTA, the density functional theory (DFT) computation and the XPS analysis, a sensible mechanism was proposed that the electron transfer within Fe(III)−SO32− complex and the Fe(III)−Fe(II)−Fe(III) redox process were crucial for the sulfite activation. Meanwhile, a quantitative structural-activity relationship (QSAR) model for pseudo-first-order rate constants (kobs) was established with a high significance (R2 = 0.991, p = 0.006) by using four descriptors. This work provides an innovative strategy of sulfate radical-based advanced oxidation processes (SR−AOPs) for organic contaminants degradation using metal oxide catalysts.

Effective and Efficient Porous CeO2 Adsorbent for Acid Orange 7 Adsorption.

A porous CeO2 was synthesized following the addition of guanidine carbonate to a Ce3+ aqueous solution, the subsequent addition of hydrogen peroxide and a final hydrothermal treatment. The optimal experimental parameters for the synthesis of porous CeO2, including the amounts of guanidine carbonate and hydrogen peroxide and the hydrothermal conditions, were determined by taking the adsorption efficiency of acid orange 7 (AO7) dye as the evaluation. A template-free hydrothermal strategy could avoid the use of soft or hard templates and the subsequent tedious procedures of eliminating templates, which aligned with the goals of energy conservation and emission reduction. Moreover, both the guanidine carbonate and hydrogen peroxide used in this work were accessible and eco-friendly raw materials. The porous CeO2 possessed rapid adsorption capacities for AO7 dye. When the initial concentration of AO7 was less than 130 mg/L, removal efficiencies greater than 90.0% were obtained, achieving a maximum value of 97.5% at [AO7] = 100 mg/L and [CeO2] = 2.0 g/L in the first 10 min of contact. Moreover, the adsorption-desorption equilibrium between the porous CeO2 adsorbent and the AO7 molecule was basically established within the first 30 min. The saturated adsorption amount of AO7 dye was 90.3 mg/g based on a Langmuir linear fitting of the experimental data. Moreover, the porous CeO2 could be recycled using a NaOH aqueous solution, and the adsorption efficiency of AO7 dye still remained above 92.5% after five cycles. This study provided an alternative porous adsorbent for the purification of dye wastewater, and a template-free hydrothermal strategy was developed to enable the design of CeO2-based catalysts or catalyst carriers.

Synthesis of CaMoO4 microspheres with enhanced sonocatalytic performance for the removal of Acid Orange 7 in the aqueous environment

• Synthesis pH had great influence on morphology and catalytic performance of CaMoO 4 . • CaMoO 4 -7 had excellent sonocatalytic performance to the removal of Acid Orange 7. • CaMoO 4 -7 had good stability and reusability during the degradation process. Herein, a series of CaMoO 4 microspheres were prepared at different pH values by the hydrothermal method. The sonocatalytic performances of the prepared CaMoO 4 microspheres were estimated by the removal of Acid Orange 7 (AO7) as a model of organic pollutants. The results showed that the synthesis pH had a great influence on the morphology and the sonocatalytic performance of CaMoO 4 . The CaMoO 4 microspheres prepared at pH = 7 (CaMoO 4 -7) exhibited superior sonocatalytic performance. The removal ratio of AO7 using CaMoO 4 -7 as a sonocatalyst was 97.02 ± 0.65%. The sonocatalytic removal of AO7 in the presence of CaMoO 4 -7 was mainly attributed to the generation of hydroxyl radical (•OH), superoxide anion radical (•O 2 − ) and holes ( h + ). The optimized operational conditions, such as CaMoO 4 -7 dose, initial concentration of AO7, initial pH of AO7, ultrasonic power and ultrasonic time were 1.0 g/L, 5 mg/L, pH = 5, 200 W and 120 min, respectively. In addition, CaMoO 4 -7 had excellent reusability and stability in the sonocatalytic removal process. These results indicated that CaMoO 4 -7 had the potential as the sonocatalyst to apply in the environmental remediation.

Visible light active Fe-N codoped TiO2 synthesized through Sol Gel Method: Influence of operating conditions on photocatalytic performances

Acid Orange 7 (AO7) is an azo dye present in the effluents coming from the textile industry. It is a coloring agent consisting of an azo group bonded to aromatic rings. This azo dye can react with other chemical substances producing aromatic amines which cause toxic and carcinogenic effects in the environment. For this reason, it is necessary to eliminate this compound from aqueous discharges. Recently, the scientific research has focused the attention on heterogeneous photocatalysis based on semiconductor oxides because it is a technology able to completely degrade many organic pollutants to carbon dioxide and water at ambient temperature under UV/visible light irradiation. In photocatalysis, the most used semiconductor is titanium dioxide (TiO2). TiO2 presents various crystalline phase and a wide band gap (3.2 eV for anatase), therefore, it can be activated only under UV light irradiation. In order to make TiO2 active under visible light, in this work TiO2 doped with metallic (Fe) and non-metallic element (N) was synthetized through sol-gel method. The photocatalytic tests on discoloration of AO7 aqueous solution were carried in a photoreactor surrounded by visible-LEDs strip. To determine the optimum conditions for the photodegradation, the influence of photocatalyst dosage (1.5 - 6 g L-1), initial AO7 concentration (5 - 20 mg L-1), initial pH of the solution (3-8) and the incident visible light intensity (3.25 to 13 mW cm-2) was investigated. It was observed that the Fe-N-TiO2 photocatalyst reached about 90% of AO7 discoloration and 83% of mineralization efficiency under the optimized working conditions, in a very short time (60 min) using a photocatalyst dosage of 3 g L-1 and AO7 initial concentration of 10 mg L-1.

Adsorption of Acid orange 7 dyes from aqueous solution using Polypyrrole/nanosilica composite: Experimental and modelling

ABSTRACT The adsorption of Acid orange 7 (AO7) by Polypyrrole/nanosilica composite (PPN/SiO2) was studied and various parameters have been investigated, more than 99.4% of the adsorption efficiency was obtained under the optimal conditions (PPN/SiO2 mass = 1 g/L, contact time = 90 min, Initial AO7 concentration = 10 mg/L, shaking speed = 200 rpm and temperature = 328 K and pH = 3).PPN/SiO2specifications were determined using FTIR, XRD, TGA, pHzpc,TEM and SEM analysis. The kinetic data were fitted by the pseudo-second-order kinetic; the rate constant K increased when temperature increased indicating the adsorption was endothermic in nature. The studies related to the adsorption mechanism illuminated that the AO7 adsorption process was complex and obeyed both surface adsorption and particle diffusion. Moreover, based on the results, the adsorption happens through film diffusion at low concentrations while the particle diffusion is the rate-determining step at higher concentration. The isotherm equations showed that the equilibrium data followed more than the Langmuir isotherm with a maximum adsorption capacity of 181.4 mg/g. The thermodynamic parameters were calculated, and their negative value of ΔG° and positive value of ΔS° and ΔH° showed that the adsorption was spontaneous and endothermic.

Acid Orange-7 uptake on spherical-shaped nanocarbons

Acid-dyes, typically used in textile productions, could infer poisoning harmful effects on the environment as well as on human health, if not properly treated during their disposal. Henceforth, there is an absolute necessity to achieve new efficient low-cost techniques to remove these dyes from industrial chemical waste. Here, the leaves of oil palm, which are abundant in tropical countries, were used as precursor in the development of carbon nanospheres (adsorbent) to remove hazardous acid Orange-7 (AO-7) dye (C16H11N2NaO4S). The removal efficacy of spherical-shaped nanocarbons was investigated as a function of contact period, by varying their dose (0.5, 1, 1.5, 2 and 2.5 mg), pH (acidic, native and basic), and initial AO-7 concentration (10, 15, 20, 25 and 30 μM). Amazingly, the oil palm leaves–based carbon nanospheres removed acid-dye up to an efficiency of about 99%. Pseudo second-order kinetics governs the adsorption mechanism and the Redlich–Peterson isotherm model fits well to the adsorption results, with regression co-efficient close to unity. This study suggests the importance of natural biowaste-based carbon nanoparticles in sustainable recycling, within the worldwide demanded circular economy.

Degradation of acid orange 7 (AO7) by a bacterium strain Flavobacterium mizutaii L-15.

Acid orange 7 (AO7) is an azo dye widely used in the dyeing and direct printing industry. AO7 is an environmental pollutant because the cleavage of azo bonds produces aromatic amines, which are considered mutagenic and carcinogenic. Microbial degradation is one of the most effective methods to remove environmental pollutants. A bacterium strain L-15 was isolated from the wastewater treatment system of a dye manufacturer. This strain is capable of decolorizing AO7. The strain was identified as Flavobacterium mizutaii based on its morphological, physiological and biochemical characteristics, and the sequence of 16S rDNA. The AO7-degrading characteristics and the effects of culture condition on the degrading efficiency of the strain were investigated by shake-flask culturing. The optimal degradation condition of L-15 was 30 °C and pH 7.0. After culturing at 30 °C for 3 days with the initial AO7 concentration of 20 mg/L, the degradation rate of AO7 was 60.45%. The optimal salt concentration was lower than 2%.

Synergistic degradation of acid orange 7 dye by using non-thermal plasma and g-C3N4/TiO2: Performance, degradation pathways and catalytic mechanism

In order to harness the full capability of ultraviolet and visible light in the dielectric barrier discharge induced non-thermal plasma (DBD-NTP) process, g-C3N4/TiO2 catalysts were prepared and utilized in this process. Synergistic degradation of acid orange 7 (AO7) dye by DBD-NTP and g-C3N4/TiO2 was conducted, and the performance, degradation pathways and synergistic catalytic mechanism were investigated. The results showed that the degradation rate of AO7 in the DBD-NTP and g–C3N4–15/TiO2 process increased by 39.1% compared with that in the single DBD-NTP process at 12 min discharge time. At 20 W input power, initial concentration of AO7 was 5 mg/L, catalytic dosage was 0.5 g/L, initial pH value was 10.0 and air flow rate was 52 L/h, the degradation rate of AO7 reached 100.0% after 12 min discharge time. Higher discharge power and initial concentration of AO7 inhibited AO7 degradation, whereas increasing the air flow rate and initial pH value of the solution promoted AO7 degradation. The degradation pathways of AO7 consisted of azo structure destruction, ring opening reaction, hydroxylation, carboxylation and mineralization reaction. The results of radical trapping experiment showed that O2−, h+, OH, O3 and H2O2 were the main reactive species for AO7 degradation in the DBD-NTP and g–C3N4–15/TiO2 process. The Z-scheme photocatalytic mechanism for the g-C3N4/TiO2 catalyst was proposed.

Adsorption of textile dye in activated carbons prepared from DVD and CD wastes modified with multi-wall carbon nanotubes: Equilibrium isotherms, kinetics and thermodynamic study

The purpose of the present work was to prepare activated carbon (AC) from low-cost wastes, such as digital versatile discs (DVDs) and compact discs (CDs), coated with carbon nanotubes (CNTs) for adsorption of Acid Orange 7 (AO7) from dye-containing solutions. The surface morphology of the activated carbons from DVDs (DVDsAC), CDs (CDsAC), CNTs, CNTs/DVDsAC and CNTs/CDsAC was determined by XRD and SEM techniques. SEM micrographs of adsorbents clearly show a heterogeneous porous surface with irregular pores in the structure of the activated carbons. Results showed that CNTs/DVDsAC (30.3mg/g) and CNTs/CDsAC (32.8mg/g), in comparison with DVDsAC (15.1mg/g) and CDsAC (9.9mg/g), were more efficient adsorbents for the adsorption of AO7. The dye adsorption amount (qe) increases with a reduction in the solution pH, adsorbent dosage and an increase in the initial concentration of AO7 for these two more efficient adsorbents. Pseudo-second order model and Langmuir isotherm fitted with the experimental data. The spontaneous and endothermic processes were analyzed by the thermodynamic studies for the adsorption of AO7. The negative values of ΔG, and the positive values of ΔH and ΔS parameters indicate that the adsorption of AO7 onto CNTs/CDsAC and CNTs/DVDsAC was spontaneous and endothermic, respectively.

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.

Activation of Peroxymonosulfate by CuNi@C Derived from Metal–Organic Frameworks Precursor

Calcined Cu-based metal–organic frameworks impregnated with nickel nitrate catalysts (CuNi@C) were synthesised. X-Ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy techniques were applied for the characterisation of the synthesised catalyst, which revealed an octahedral particle shape, rough surface, and metallic copper (Cu, CuO) and nickel (Ni, NiO) particles. CuNi@C was fabricated as a novel peroxymonosulfate (PMS) activator for the oxidative degradation of Acid Orange 7 (AO7) in aqueous media. Results showed that the CuNi@C/PMS system can efficiently degrade nearly 100 % of 0.02 mmol L−1 AO7 within 60 min. In addition, the trapping experiments confirmed the participation of sulfate radicals (SO4•−) and hydroxyl radicals (HO•) as reactive species in the system. Furthermore, the effects of parameters including catalyst and PMS dosages, initial concentration of AO7, and pH were studied. Results showed that the decolourisation efficiency increased with the increase of catalyst dosage, but decreased with the increase of AO7 concentration. The optimal PMS concentration was 0.675 mmol L−1, and initial pH showed no significant effect on the degradation of AO7. Moreover, the CuNi@C could be reused four times with good activity and reusability. Findings revealed that the CuNi@C/PMS system shows potential for degrading contaminants in the environment, due to its catalytic activity and non-negligible adsorption.

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

The mechanism and efficiency of MnO2 activated persulfate process coupled with electrolysis

Pure three-dimensional manganese oxides (MnO2) were successfully synthesized by a simple one-step hydrothermal process. The obtained particles were characterized via XRD, BET, SEM, XPS and FTIR techniques. To enhance the efficiency of heterogeneous catalytic process, a facile and effective electrochemical method was introduced. The degradation of C. I. Acid Orange 7 (AO7) as the target pollutant in aqueous solution by an oxidation system involving MnO2 activated peroxydisulfate (PDS) coupled with electrochemical method is reported herein. Influences of some key reaction parameters such as initial pH (pH0), current density, initial AO7 concentration, dosage of MnO2 and anions (Cl−, NO3−, HCO3− and H2PO4−) were investigated. The cyclic voltammetry (CV) was performed to investigate the charge transfer process occurred at the surface of catalyst. LC-MS/MS analysis was applied to identify degradation intermediates and a plausible degradation mechanism is proposed accordingly. Activated sludge inhibition tests were carried out to evaluate the change of toxicity of the dye solution in the oxidation process. The inorganic by-products such as NO2−, NO3−, and NH4+ along with AO7 degradation were also identified. The stability of MnO2 catalyst was evaluated by recycling experiments and the electrical energy consumption was also investigated. Radical quenching tests with several scavengers (methanol, tert-butyl alcohol, 1,4-benzoquinone and phenol) were performed to clarify the dominating reactive species participating in this oxidation process and the underlying mechanisms involving the generation of radical from the proposed electro-assisted heterogeneous activated PDS system were identified.

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.

The use of artificial neural network for modeling the decolourization of acid orange 7 solution of industrial by ozonation process

Acid Orange 7 (AO7) is one of the synthetic dye in the dyeing process in the textile industry. The use of this dye can produce wastewater which will be endangered if not treated well. Ozonation method is one technique to solve this problem. Ozonation is a waste processing techniques using ozone as an oxidizing agent. Variables used in this research is the ozone concentration, the initial concentration of AO7, temperature, and pH. Based on the experimental result that the optimum value decolourization percentage is 80% when the ozone concentration is 560 mg/L, the initial concentration AO7 is 14 mg/L, the temperature is 390 °C, and pH is 7,6. Decolourization efficiency of experimental results and predictions successfully modelled by the neural network architecture. The data used to construct a neural network architecture quasi newton one step secant as many as 31 data. A comparison between the predicted results of the designed ANN models and experiment was conducted. From the modeling results obtained MAPE value of 0.7763%. From the results of this artificial neural network architecture obtained the optimum value decolourization percentage in 80,64% when the concentration of ozone is 550 mg/L, the initial concentration AO7 is 11 mg/L, the temperature is 41 °C, and the pH is 7.9.

Optimization of a textile dye degradation in a recirculating fluidized-bed reactor using magnetite/S2O82− process

ABSTRACTOptimization of Acid Orange 7 (AO7) treatment using heterogeneous Fenton-like method in a recirculating fluidized-bed reactor (FBR) was investigated by using central composite design (CCD). Natural magnetite (NM) as Fenton-like catalyst was characterized using scanning electron microscopy. A nonlinear CCD model was obtained for the prediction of dye degradation as a function of experimental variables such as peroxydisulfate concentration (0.1–0.5 mmol/L), initial AO7 concentration (5–25 mg/L), pH (3–9) and NM dosage (0.25–1.25 g/L) after 105 min of treatment. The calculated results by the model were consistent with the experimental results (R2 = 0.959). Furthermore, the model is suitable to estimate the optimum operational conditions and determine the effects of the parameters for maximum AO7 degradation. Eventually, gas chromatography–mass spectroscopy was used for the recognition of the dye degradation by-products.

Activated carbon adsorptive removal of azo dye and peroxydisulfate regeneration: from a batch study to continuous column operation.

The performance of activated carbon (AC) for the adsorption of Acid Orange 7 (AO7) was investigated in both batch and column studies. The optimal conditions for adsorption process in batch study were found to be a stirring speed of 500rpm, AC dosage of 5g/L, and initial AO7 concentration of 100mg/L. The spent AC was then treated with peroxydisulfate (PDS), and the regenerated AC was used again to adsorb AO7. Both pseudo-first-order and pseudo-second-order rate models for adsorption kinetics were investigated, and the results showed that the latter model was more appropriate. The effects of regeneration time, PDS concentration, and stirring speed on AO7-spent AC regeneration were investigated in batch studies, and the optimal conditions were time 2h, stirring speed 700rpm, and PDS concentration 10g/L. Under the same adsorption conditions, 89% AO7 could be decolorized by adsorption using regenerated AC. In the column studies, the effect of flow rate was investigated and the adsorption capacity was nearly the same when the flow rate rose from 7.9 to 11.4mL/min, but it decreased significantly when the flow rate was increased to 15.2mL/min. The performance of regenerated AC in the column was also investigated, and a slight increase in the adsorption capacity was observed in the second adsorption cycle. However, the adsorption capacity decreased to some extent in the third cycle due to the consumption of C-OH group on the AC surface during PDS regeneration.

Accelerating biodegradation of a monoazo dye Acid Orange 7 by using its endogenous electron donors

Biodegradation of a monoazo dye – Acid Orange 7 (AO7) was investigated by using an internal circulation baffled biofilm reactor. For accelerating AO7 biodegradation, endogenous electron donors produced from AO7 by UV photolysis were added into the reactor. The result shows that AO7 removal rate can be accelerated by using its endogenous electron donors, such as sulfanilic and aniline. When initial AO7 concentration was 13.6mg/L, electron donors generated by 8h UV photolysis were added into the same system. The biodegradation rate 0.4mg0.05h−1 was enhanced 60% than that without adding electron donor. Furthermore, sulfanilic and aniline were found to be the main endogenous electron carriers, which could accelerate the steps of the azo dye biodegradation.