Research Of Applying Coaxial Falling Film Reactor Combined With Electrical Field/Discharge On Safe Sterilization Of Drinking Water

Disinfection is an important process in the drinking water treatment. Currently the disinfection of drinking water is commonly completed though dosing chemical disinfectant, resulting disinfection by-products inevitably, which has potencial risk to human health. In this study, an air insulated-coaxial falling-film reactor was applied in drinking water safe sterilization.The space of the coaxial electrodes is14mm and the inner electrode is a cylinder made of stainless steel.The difference of electrical field and discharge system lies in the pattern of outer electrodes:a stainless steel cylinder for electrical field system and a copper solenoid for discharge system.The high voltage (HV) electrode (outer electrode) is located in the air while the ground electrode (inner electrode) is covered with water film. The effective processing area lies on the air-water surface where the electrical field strenth can be as high as10kV/cm. Compared with the conventional reactors, the air surrounding the HV electrode avoids directive contract between the HV electrode and the water, effectively controls the leakage current, thus reducing energy loss caused by joule heating, meanwhile alleviating electrodes corrosion.The sterilization efficiency test results indicated that under the operational condition of10kV input voltage,10kHz frequency and50s treatment time, the sterilization efficiency of saprophytic bacteria could achieve3.5log reduction for corona discharge and2.1log reduction for electric field, and the efficiency of E.Coli. could achieve3.82log reduction for corona discharge and2.23log reduction for electric field.The power consumption results indicated that in the condition of sterilization efficiency of saprophytic bacteria achieve1log reduction, the power consumption were8.61kW·h/m3for corona discharge and18.89kW·h/m3for electrical field. The safety assessment of drinking water sterilization was also conducted by radical generation measurements. Our results showed that no radicals were generated during electric field sterilization. Both of those sterilization applications did not cause obvious tempetature rise, controled within5℃.Furthermore, flow cytometer (FCM) and fluorescence microscope tests were utilized to reveal the sterilization mechanism. The results confirmed that both discharge and electric field sterilization can cause protein damage. However, in the case of electric field sterilization, the membrane damage was reversible, which resulted in the existence of sub-lethal cells. While in the case of discharge sterilization, the inactivation was the combination of electrical field and free radicals, so that the membrane damage was irreversible. Thus, based on all above mentioned results, electric field sterilization is a promising drinking water sterilization technology.