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Background and purpose: Nitrate contamination in aqueous solution has become an increasingly serious environmental problem. Hence, in this study removal of nitrate in aqueous solution was reviewed using electrocoagulation (EC) and electro-fenton (EF) processes for Fe electrodes. Materials and methods: In the present study, an EC and EF reactor in a lab scale to an approximate volume of 1 liter was proposed for removing of nitrate polluted water which was equipped with four Fe-Fe electrodes with dimensions 200 × 20 × 2 mm. The effects of operating parameters such as initial nitrate concentration, applied voltage (10-30 V), initial pH of the solution (3-12), different initial hydrogen peroxide (for EF process) and reaction times (5-30 minutes) were evaluated. Results: The batch experimental results showed that initial nitrate concentration, initial pH of the solution, different applied voltages, initial H2O2 concentration and reaction times were highly effective on the nitrate removal efficiency in these processes. Based on the results, over 88% of nitrate in optimum condition (pH = 8, applied voltage = 30 V, initial nitrate concentration of 100 mg/l) have been removed in EC process. In addition, the application of EF process can remove 93% of nitrate at pH = 3, applied voltage = 30 V, initial nitrate concentration of 100 mg/l and 5 ml H2O2/l. Conclusion: Both EC and EF technologies can highly remove nitrate in aqueous solution. However, it was found that much better nitrate removal efficiency could be achieved by EF process than by EC process at the same condition.

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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.