Discharge characteristics of plasma induced by water drop and its potential for water treatment

Water surface discharge is an effective water treatment method. However, the industrial application of this technology is limited by some problems including the difficulty to get a large area of uniform discharge plasma and the insufficient durability of high voltage electrodes. To solve these problems, the water to be treated was dispersed as droplets and sprayed to the high voltage electrodes to make a water drop induced discharge system. The discharge photographs indicated that when dripping down in the discharge gap, water drops can induce the happening of discharge. The discharge channels concentrated near the water drops and the discharge intensity changes with water flow rate. This feature could reduce the requirement for the uniformity of electrodes as the uniform discharge could be obtained by making a uniform water distribution. In addition, both the discharge channels and active species were concentrated on or very close to the water drops to be treated. The transfer distance of active species was shortened, and then both the chemical reaction efficiency and the energy efficiency could be increased. Ibuprofen degradation results showed that the ibuprofen can be removed exceeding 99% after 1 h treatment. The maximum energy yield exceeded 10 g/kWh. Factors including discharge voltage, water flow rate, water conductivity and electrode gap distance influenced the ibuprofen removal. (C) 2017 Elsevier B.V. All rights reserved.