Bacterial decontamination of water by means of pulsed-corona discharges

By using a tungsten wire with 75-mum diameter, 2 cm apart from a plane cathode, and applying a 600-ns, 120-kV square wave pulse, we were able to obtain a pulsed-water corona discharge (PWC). The effect of these discharges on bacteria was studied using water contaminated with Escherichia coli or Bacillus subtilis, the latter in both the vegetative and spore state. The strongest effect was obtained on E. coli. The concentration of E. coli could be reduced by three orders of magnitude after applying eight corona discharges to the water. The corresponding energy expenditure is 10 J/cm(3). The decontamination rate had the largest values at the beginning, and decreased considerably after 15 electrical discharges, reaching a constant residual concentration value of 10(-4) of the initial concentration. For B. subtilis in the vegetative state, it took almost 30 discharges to reach the same result, corresponding to an energy expenditure of 40 J/cm(3). There was no effect on B. subtilis spores. Comparisons with the pulsed-electric field (PEF) method indicate that the decontamination efficiency of the PWC method is slightly higher than that of the PEF method.