Water purification by electrical discharges

Abstract

There is a continuing need for the development of effective, cheapand environmentally friendly processes for the disinfection and degradation oforganic pollutants from water. Ozonation processes are now replacingconventional chlorination processes because ozone is a stronger oxidizingagent and a more effective disinfectant without any side effects. However, thefact that the cost of ozonation processes is higher than chlorinationprocesses is their main disadvantage. In this paper recent developmentstargeted to make ozonation processes cheaper by improving the efficiency ofozone generation, for example, by incorporation of catalytic packing in the ozonegenerator, better dispersion of ozone in water and faster conversion ofdissolved ozone to free radicals are described. The synthesis of ozone inelectrical discharges is discussed. Furthermore, the generation and plasma chemicalreactions of several chemically active species, such as H2O2, O•, OH•, HO2•,O3*, N2*, e-, O2-, O-, O2+, etc, which are produced in the electricaldischarges are described. Most of these species are stronger oxidizers thanozone. Therefore, water treatment by direct electrical discharges may providea means to utilize these species in addition to ozone. Much research anddevelopment activity has been devoted to achieve these targets in therecent past. An overview of these techniques and important developments thathave taken place in this area are discussed. In particular, pulsed coronadischarge, dielectric barrier discharge and contact glow dischargeelectrolysis techniques are being studied for the purpose of cleaning water. Theunits based on electrical discharges in water or close to the water level arebeing tested at industrial-scale water treatment plants.}