Surface DBD plasma microbubble reactor for degrading methylene blue

Abstract

Water contaminants such as endocrine inhibitors, pharmaceuticals, and chlorine treatment by-products are only recently being identified as significant hazards to human health. Since current chlorine treatment does not address many of these compounds and conventional ozone processing is not seen as an economic alternative, water adjacent plasma treatment has been investigated as a more efficient and effective decontamination method. This work investigates the use of a surface dielectric barrier discharge electrode as a reduced discharge voltage portable plasma water treatment method. The gas passes through holes in the electrodes, normal to the discharge surface, so that the entire cross-sectional area of the feed gas is exposed to plasma, prior to passing through a hydrophobic filter and bubbling into the water. The decontamination effectiveness is quantified by measuring the degradation of methylene blue with absorption spectroscopy. Studies of the different processing parameters (treatment time, solution volume, initial concentration, electrode-filter distance, and gas flow rate) clarify the potential range of performance for this plasma treatment configuration. The setup has a yield energy of 0.45 g/kW·h at 25 ml of 1 mg/100 ml methylene blue treated over 5 minutes for a 92% degradation. The degradation rate is dependent upon the volume ratio of air to methylene blue solution, suggesting a first order chemical reaction process. The reaction rate is increased by increasing the quantity of either reactant. There is no change in the degradation between when the plasma is 1 mm or 1 cm from the water surface.