Investigation of the mechanism of inactivation of E. coli in water using a pulsed spark plasma discharge

Abstract

Summary form only given. According to WHO-UNICEF Joint Monitoring Programme on Water Supply and Sanitation (JMP), more than 1 billion human beings, use potentially harmful sources of water. Certain viruses and parasites like Giardia and Cryptosporidium are resistant to conventional sterilization methods like chlorination and are easily transported to the point of use. Hence, there arises the need for a robust, effective and improved water purification technology for inactivating microorganisms in drinking water. Pulsed plasma discharges have proved to be very effective in killing microorganisms in water. Experiments were conducted using a high voltage pulsed spark plasma discharge having the following parameters: peak-to-peak voltage 30kV, peak-to-peak current 80A, pulse duration 2µs, frequency 1-50Hz and energy per pulse 1.7-2J. It has already been demonstrated that a rather low energy input of 85J/L and 150J/L of water respectively are required for complete inactivation of Escherichia coli and Bacillus cereus spores of initial concentration 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Colony Forming Units(CFU)/ml of water. The different factors considered by many researchers to be responsible for the microbicidal action of pulsed discharges in water include the production of ultraviolet radiation, active chemical species including ozone, hydrogen peroxide, hydroxyl and superoxide free radicals and shock waves [1]. The present study shows that ultraviolet radiation produced by a pulsed spark plasma discharge in water plays a dominant role in the inactivation of E. coli in water. Disinfection of E. coli in water is completely suppressed by adding ∼50mg/L of Benzophenone-9, a non-toxic ingredient in commercial water-soluble sunscreens. Further experiments with reactive oxygen species scavengers are being conducted to determine if there is a synergy between ultraviolet radiation and hydrogen peroxide produced in water by pulsed spark plasma discharge.