Disinfection of E. coli in conducting solution by nonthermal microplasma electrolysis

Summary form only given.Disinfection of liquids is an important issue and remains a major problem in many countries. The major electrical techniques to inactivate microorganism in liquids include electrochemical inactivation1, pulsed electric field2, and pulsed corona (streamer) discharge3. In this study, we have developed an alternative method to inactivate microorganism in conducting liquids by means of microplasmas. The device consists of single powered electrode with a sharp tip and a ground electrode. Both electrodes are immersed into normal saline solution. The powered electrode is made of Titanium wire (-100 I????m in diameter) covered by a glass tube and the tip is exposed. The typical magnitude of the applied voltage is around 500 V. The power consumption of the device (~108 J/m3) is comparable with other conventional methods. We employed asymmetric square wave at 1-10 kHz. The device configuration and operation conditions are designed based on a previous report by K. Stalder et al4. On applying the high voltage, small bubbles are generated at both electrodes, suggesting the electrolysis occurs. Then, repetitive light emission is observed in the vicinity of the sharpened tip. We employed E. coli as an indicator bacterium. 105 colony forming unit of E. coli in 0.4 ml saline solution was exposed to the microplasma for 0-180 s. After the treatment, the number of viable cells was measured using the spread plate method on agar incubated at 37 deg.C for 12 h. The survival curve shows that more than 99% of E. coli is disinfected in 180 s. Thus, the nonthermal microplasma electrolysis is potentially applicable for practical use. The possible inactivation agents in the experiments are thought to be reactive chemical species (OH, HCIO, etc.) and UV light.