Degradation of methylene blue dye as wastewater pollutant by atmospheric pressure plasma: A comparative study

Abstract

The industrial application of non-thermal plasma has been a research field in the last few years. One of the potential applications of non-thermal plasma is in treating dye effluents of textiles industries which are considered as one of environmental pollutants. Before scaling up plasma technology at the industrial level, it is required to understand the interaction of non-thermal plasma with a synthetic dye-containing solution in laboratory experiments. A detailed comparative study of MB dye degradation using an atmospheric pressure air plasma (corona discharge) source is carried out in this report. Different concentrations (5 mg/L, 10 mg/L, and 40 mg/L) of MB solutions were treated with plasma and were observed various chemical parameters (pH, TDS, EC, etc.) as well as degradation percentages. We observed nearly 80 % MB degradation in about 100 min, 110 min, and 130 min treatment times for 5 mg/L, 10 mg/L, and 40 mg/L MB solutions respectively. With increasing the volume of the MB sample solution (15 ml to 30 ml), nearly double the plasma treatment time is required to decompose the same amount of MB dye. We observed a higher degradation percentage (∼ 90 %) of MB solution (10 mg/L) in 100 minutes when iron material (sheet) is used as cathode. However long time treatment (170 to 180 minutes) to degrade ∼ 90 % MB dye in the case of copper or aluminium cathode is reported. The MB degradation percentage can be increased from ∼ 60 % to 90 % if the pH of the MB solution is changed from mild basic (pH ∼ 8.5) to acidic (pH ∼ 3.5) in the case of the aluminium cathode in nearly 60 min. The pH of the MB solution is changed by adding low pH treated dye solution instead of any external chemicals. The results show that acidic MB solution takes less time, about 90 minutes instead of 180 minutes to degrade approximately 90 % MB dye. The pH of the solution decreases during plasma treatment but the TDS and EC of MB solution increases during plasma treatment irrespective of dye concentration, the volume of solution, and different types of cathodes (iron, copper, and aluminium). The results are qualitatively discussed in line with the available theoretical and experimental background of plasma-water interaction.