Effects of pulse frequency of input power on the physical and chemical properties of pulsed streamer discharge plasmas in water

Positive high-voltage pulses of 20 kV with repetition rates of up to 1 kHz were used to generate discharge in water using point-to-plane electrode geometry.By varying the pulse repetition rate, two distinct modes of discharge plasma were formed in water. The first was characterized by the formation of corona-like discharge propagating through the water in the form of streamer channels.The second mode was formed typically above 500 Hz, when the formation of streamer channels in water was suppressed and all plasma occurred inside a spheroidal aggregate of very fine gas bubbles surrounding the tip of the high-voltage electrode.The production of H2O2, degradation of organic dye Acid Orange 7, and inactivation of bacteria E. coli by the discharge were determined under different plasma modes in dependence with the pulse repetition rate.The efficiency of both chemical and biocidal processes induced by plasma in water decreased significantly using pulse repetition rates above 500 Hz.