High Power DC Diaphragm Discharge Excited in a Vapor Bubble for the Treatment of Water

Novel apparatus for the generation of underwater plasma based on DC diaphragm discharge excited in a vapor bubble has been developed for decontamination and disinfection of conductive water. The apparatus allows deposition of relatively high applied power into the discharge (order of kW) and the treatment of a relatively large volume of liquid (order of L/min). The apparatus is operated at the quasi-pulse regime with self-terminating discharge pulses (with a repetition rate of 15–20 Hz) generated upon the formation of the vapor bubble inside the diaphragm (capillary) and its subsequent breakdown. The effects of input power, solution conductivity and the method of liquid flow through the reactor on the plasmachemical yield of H2O2 production and degradation of phenol have been determined. The biocidal effects of the apparatus were evaluated on inactivation of bacteria E. coli and E. faecalis suspended in aqueous NaCl solutions and on growth inhibition of the cyanobacterium Planktothrix sp. in natural lake water. The apparatus proved to be capable of efficiently reducing biological contamination in water, especially when operated in the plug-flow regime (up to a 5-log reduction in bacteria after 3 passes through the reactor). In the case of cyanobacteria, the growth inhibition further proceeded after exposure to the discharge and one pass of the biomass through the reactor was sufficient to reduce the algae in the water.