Pulsed Corona in Water: Pulse Generation and Applications

Summary form only given. Removal of organic pollution from water is of increasing concern for drinking water as well as for many industrial processes. Application of pulsed corona discharges is a known possibility to attack that problem by producing highly active radicals in-situ, without using additional chemistry. To investigate the efficiency of submerged pulsed corona discharges in water we have built a laboratory scale, parallel-plate, flow-type reactor that is part of a closed loop water circulation system. A pulsed voltage is applied across the electrodes. One of the electrodes is coated with a porous ceramic layer in order to create local field enhancements to initiate corona discharges. For energisation of the plasma reactor a pulse generator has been developed which is based on a capacitor discharge initiated by a semiconductor switch. A pulse transformer, followed by two magnetic pulse compression stages, produces voltage pulses with amplitudes of up to 37 kV at a pulse width of 0.3 mus. Simulation of the circuit behavior leads to good agreement with voltage and current measurements. Details of the pulse generator and first experimental results concerning the efficiency of radicals production are presented. Depending on the conductivity of the water to be treated, pulse currents of > 600 A at a voltage of 37 kV are obtained for electrode sizes of around 50 cm2. The efficiency of the radical production is measured in terms of the hydrogen peroxide (H₂O₂) concentration, which is formed by recombination of hydroxyl radicals (OH) at sufficiently high concentrations downstream of the plasma reactor. At pulse repetition rates of 20 to 100 Hz, H₂O₂ concentrations of up to several mg/l are produced. Production efficiencies have been measured to be in the range of up to ap1 g/kWh.