Treatment of Anionic Surfactant Solution Using Nanosecond Pulsed Power Discharges

Recently, improvements of drainage water treatment technology have been required. The streamer discharges generated by nanosecond pulsed power was applied to treat surfactant solution as a persistent chemical. Radicals with a high redox potential, as especially hydroxyl radical, is expected for degradative treatment of the persistent chemical. In using a coaxial cylindrical reactor, streamer discharges were generated in gas phase and progressed towards the liquid surface. Oxygen gas was used as a surrounding gas, and ozone was generated in gas phase. Treatment was carried out by a combined effect of direct action of streamer discharge on the water surface and ozone generated in the air. In comparison with a system using external ozonizer, an effect of streamer discharges was investigated. The voltage pulses of 1.5-ns pulse-width were applied on treatment of 1-L solution of purified water dissolved with 0.1 g of sodium dodecyl benzene sulfonate (DBS) as an anionic surfactant for 80 minutes. The concentration of anionic surfactant was evaluated with a methylene blue visual colorimetric method. The concentration of the surfactant decreased with treatment time in both systems. Treatment by pulsed power system decomposed the surfactant faster than treatment by external ozonizer system, especially for first 20 minutes of treatment. Dissolved ozone was confirmed from spectral absorbance change. The characteristic absorbance spectrum of DBS didn't change with treatment by external ozonizer system but decreased with treatment by pulsed power system. It was suggested that the decomposition intermediates having a benzene ring was formed and could not be decomposed by ozone treatment alone. It was considered that ozone was decomposed by effect of streamer discharge, generation of radicals as hydroxyl radical was promoted, and a benzene ring of intermediates was opened.