From the editors´ desk

In this issue there are five articles. The first is "Pulsed Arc Electrohydraulic Discharge Characteristics, Plasma Parameters, and Optical Emission During Contaminated Pond Water Treatments" by Oi Lun Helena Li, Jen-Shih Chang, and Yiping Guo from McMaster University in Hamilton, Ontario, Canada. This article describes a pulsed arc electrohydraulic discharge reactor for the treatment of contaminated pond water, a technology that has been used in the dislodgement of mussels and removal and prevention of biofilms on cooling and water-intake pipes. The pulsed arc system described in the article operates at 10^-2 to 10 Hz, with peak current above 10 to 10² kA with a microsecond order voltage rise. It injects energy directly into an aqueous solution through a plasma channel formed by a high-current/ high-voltage electrical discharge between two submersed electrodes. The process generates UV radiation, radical reactions, ionic and electronic reactions, thermal dissociation, and strong pressure waves. The liquid-phase electrical discharge facilitates removal of chemical contaminants and inactivation of viruses and bacteria, and the acoustic emission impulse is sufficient to cause mortality of most pathogens and bacteria. The OH and H radicals in the discharge arc zone alter the pH of the solution, and treatment for trace ammonia compounds and phenol showed that the treated solution changed acidic and alkaline pH values, respectively. This suggests that pulsed-arc treatment could result in neutralized pH values. A detailed study of fundamental characteristics, including plasma parameters, pressure wave propagation, optical emission spectrum, and the decay time of the radicals is given in the article.