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Background and purpose: Indirect electro-oxidation method with H2O2 electrogeneration is an electrochemical process for wastewater treatment based on the production of hydroxyl radicals by means of H2O2 generation in the presence of transition metals such as copper. Materials and methods: The electrogenerated hydrogen peroxide process was performed in an open and undivided cell to be assessed for degradation of real textile wastewater using graphite felt (cathode) and Pt (anode) in the presence of copper ions. The effect of major parameters such as dissolved oxygen concentration, initial pH, applied current, copper concentration and time reaction on the decolorization was investigated. Results: 67.9% decolorization and 56.3% chemical oxygen demand (COD) removal were achieved after 210 minutes reaction under the conditions 7.8-7.9 mg/l dissolved oxygen, 250 mA applied current, 7 mM copper concentration and pH=4. Conclusion: The electrogenrated H2O2 process in presence of copper ions could degrade real textile wastewater. Moreover, due to generation of hydrogen peroxide, this process can be economically important.

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Background and purpose: Using catalysts to enhance the efficiency of the ozonation process (known as catalytic ozonation process) has received much attention in recent years. This study aimed at examining the overall feasibility of using catalysts ozone as catalyst in ozonation process for decolorization and mineralization of a real textile wastewater in presence of persulfate.

Materials and methods: This experimental study was conducted on a laboratory scale reactor using a semi-batch mode. The effect of persulfate, ozone flow rate, reaction time and catalytic dose in dye and COD was investigated in an optimal state of textile wastewater. To obtain optimization test, the experiment was performed by fractional factorial method at three-level factorial (3k−p) with a high resolution (VI).

Results: In this study, 15 min contact time (P = 0.006) and 0.5g/L dose of catalyst (P=0.029) had the best effect on color removal. Moreover, the interaction of these parameters were found to be significant (P= 0.025). The optimum condition for color removal was achieved at 15 min reaction time, ozone flow rate of 2 L/min, 1.5 mM persulfate and catalyst dosage of 0.5 g/L. Optimum efficiency removal for color and COD in textile wastewater were 96% and 75%, respectively.

Conclusion: Application of nano-magnesium oxide with ozone in presence of persulfate showed synergistic effect and buffering property in decolorization and mineralization of textile wastewater. It also increases the efficacy of color removal and improves mineralization so, there would be no need for pH adjustment.

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Background and purpose: Due to the poor performance of industrial dye settings about 50% of the washing dye liquor is discharged into the environment. Inappropriate discharge of dye-containing effluents is undesirable because of their color, resistance to biological treatment systems, toxic, and their carcinogenic or mutagenic nature to life forms. In the present study we investigated the photocatalytic degradation of reactive yellow 147 using magnetic Fe₃O₄@SiO₂@TiO₂.

Materials and methods: A central composite design (CCD) under response surface methodology (RSM) was employed to study the interaction between some parameters, including photocatalyst dose, solution pH, and temperature in order to optimize the removal condition of Reactive Yellow 147 via photocatalytic process. Therefore, 20 tests were designed in Design Expert Software (version 7.0.0). All of these Factors were classified in 5 levels +α, +1, 0, -1, -α.

Results: There was an increase in removal efficiency with increase in the photocatalyst dosage of Fe₃O₄@SiO₂@TiO₂ and with decrease in the temperature. Under acidic conditions, the photocatalytic process was more efficient than that under alkaline conditions. The results also indicated that the application of RSM method not only helped to find the optimum levels of experimental parameters, but also proved that the role of initial pH of the solution and temperature were much more dominant than that of photocatalyst dosage in the photodegradation Reactive Yellow 147 under UV light exposure.

Conclusion: Current study showed that photocatalytic process with optimization of effective
operational factors, is highly efficient in removal of Reactive Yellow 147. The regenerated as-synthesized photocatalyst shows high stability and high efficiency in the degradation of Reactive Yellow 147 even after ten times of successive reuse without a significant drop in removal efficiency which makes this process economical.

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Background and purpose: Azo dyes are present in the wastewater of most textile factories, and if they enter water resources, they pose risks to the health of humans and the living environment due to the effects of toxicity, biological accumulation, and mutagenicity. This study aimed to determine the removal of azo dye by a biological method using wastewater treatment plant sludge in aerobic and anaerobic conditions and isolation and identification of bacteria.
Materials and methods: This experimental study, was conducted in the faculty of health, at Mazandaran University of Medical Sciences. In this study, the removal of reactive red azo dye 195 in the wastewater of textile factories was investigated using the activated sludge of the wastewater treatment plant. Experiments were carried out in batch mode in both aerobic and anaerobic conditions with 192 samples. The concentrations of azo dye in the range available in the wastewater of textile factories were 50, 65, and 80 mg/liter. The culture medium used in this study was a mineral medium containing glucose. Bottles containing culture medium, sludge, and azo dye were kept at 30°C in an incubator in aerobic and anaerobic conditions for 8 days. The effect of factors including contact time, amount of sludge, and concentration of color was investigated. Sampling was done at the contact times of 1, 2, 4, and 8 days and after centrifuge, the color concentration was measured by spectrophotometric method at a wavelength of 545 nm. The total organic carbon (TOC) concentration of the samples was measured by a TOC analyzer. After removing the color, the bacteria in the bottles were identified by the differential diagnosis method and using special culture media, gram staining techniques, and biochemical tests.
Results: In anaerobic conditions and contact time of 8 days, the removal of azo dye in concentrations of 50 and 80 mg/liter by using 5 ml of biomass was obtained by 93 and 82%, respectively. In the aerobic condition, the removal of the dye was achieved to more than 90% within two days, and after that, the removal efficiency reached 100% with a gently increasing slope up to 8 days. By increasing the concentration of dye from 50 to 80 mg/liter, the removal efficiency decreased by about 10%. Increasing the volume of sludge from 5 to 10 ml in both cases did not have a significant effect on increasing the amount of dye removal. The amount of azo dye removal was higher in aerobic than in anaerobic conditions. In aerobic conditions, for all dye concentrations, the TOC removal rate was about 85-90%. There was no significant difference in the amount of TOC removal for 5 and 10 ml of sludge. The average TOC removal in aerobic was about 10% higher than in anaerobic conditions. In the aerobic condition, the identified bacteria included Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aerogenosa, and in the anaerobic condition, the identified bacterial species were Lactobacillus, Enterococcus faecalis, and Bacillus cereus.
Conclusion: Complete removal of azo dye from textile wastewater by sludge biomass under microaerophilic culture conditions is possible with a contact time of 8 days or more. The dye removal efficiency was higher in partial aerobic than in absolute anaerobic conditions. The identified azo dye-removing bacteria were mainly facultative anaerobic and microaerophilic.