Experimental Study On Water Disinfection By Pulsed Electric Field And Plasma

The application of high voltage pulse technology in the field of water disinfection includes Pulse Electric Field (PEF) and Pulse Non-Thermal Palsma (NTP). They have been promising technologies for fast effective and environmental friendly disinfection for liquid treatments, In this paper, home-made pulsed power sources are used for PEF and NTP studies. Escherichia coli and Candida albicans are selected as test samples. The effects of operation parameters (constructional, electrical and aqueous parameters) on disinfection efficiency and energy efficiency are investigated in terms of the energy density, initial cell concentrations, and specifications of pulse power sources. The aim is to get deep fundamental insights for further optimization of the PEF/NTP disinfection processes.For the PEF disinfection, experiments are performed with a 500 mL cylindrical reactor. Average electric field intensity of 3-12 kV/cm is applied and the pulsed frequency is from 1 Hz to 20000 Hz. The water temperature is always below 40 ℃ during PEF treatment. Optimized high voltage electrode consists of 6 equally distributed mesh electrodes with diameters of 40 mm. Both the disinfection efficiency and energy efficiency are enhanced by increasing the pulse duration and decreasing the electrode gap. With the increase of conductivity, the sterilization efficiency of PEF firstly rises and then dropes. When the conductivity is equal to 50μS/cm, the disinfection efficiency reaches its maximum. For 3 min treatment, the reduction order is 2.1 for the Escherichia coli. Both pulsed frequency and pulse voltage give identical results in terms of the energy consumption and the efficiency. When the initial bacterial density is around 104-106 cfu/mL, the disinfection is not very sensitive to the the cell density. For the density of below 1250 cfu/mL, almost all cells can be sterilized after 144,000 pulses.For the NTP water disinfection process, a similar reactor is used but with another power source. NTP disinfection efficiency can be improved by increasing the injected energy density either via raising the pulse voltage or the energy storage capacitor as well as treatment time. When the storage capacitor is increased to 5.2 nF, disinfection efficiency of Escherichia coli reaches 100% after 5min treatments. When the conductivity is inbetween 1.5 μS/cm and 50 μS/cm, the conductivity does not significantly affect the disinfection efficiency. With raising it from 50 μS/cm to 200μS/cm, the disinfection efficiency drops. When the the forced air-flow increases from 1 L/min to 8 L/min, the sterilization efficiency of NTP firstly rises and then dropes. The maximum disinfection efficiency is achieved at the flow rate of around 3.5 L/min. In comparsion with the Escherichia coli, the treatment of Candida albicans shows a smaller efficiency. The reduction orders for Escherichia coli and Candida albicans are usually 3.2 and 2.2, respectively. The disinfection efficiency is almost same for the initial bacterial density of 104-107 cfu/mL. The reduction order is about 3.2 after 3 min treatment. TEM showed that intracellular cell structure is severely damaged after the NTP treatment.