Power source for inactivation of micro-organisms with partial high voltage discharge in a continuous process

An electrical discharge technology is investigated as a nonthermal method for inactivation of microorganisms. Potential applications include treatment of drinking water (e.g. legionella) and liquid food pasteurization (e.g. fruit juices). A strong interest exists in mild food conservation processes without the loss of food quality that results from elevated temperatures. The electrical discharge method, alternatively named nonthermal plasma method, is investigated as one of the opportunities. Fast rising high voltage pulses have been applied to a corona electrode geometry producing filamentary, fast propagating discharges, called streamers. The energy per pulse is kept very low in order to prevent the thermal arcing phase. The presented research activities are directed to a better control and understanding of the discharge for a range of conditions (electrical, electrode geometry, process conditions). Different pulse shapes and treatment chambers have been applied to achieve a uniform treatment of continuous liquid flow. The paper presents a parameter study of the electrical circuit, simulated electrical field conditions and microbiological test results. A 6 log inactivation of Lactobacillus Plantarum in a 0.1 S/m phosphate buffer with pH = 5.5, has been demonstrated under continuous flow conditions with 14 degrees temperature increase. However, the inactivation of spores (Bacillus subtilis) after treatment in the discharge chamber, has not been observed.