Along with the recent development of industries, the demand for safety of drinking water has increased as the number of cases of detecting environmental impact of pharmaceuticals and personal care products (PPCPs) and pathogenic microorganisms increases. Therefore, there is a growing interest in advanced oxidation (including disinfection) process that replaces the existing disinfection process, and research on alternative disinfection technology is continuously on the increase. In this study, we evaluated the inactivation efficiency and mechanism of pathogenic microorganism by alternative disinfection technologies, such as 1) plasma discharge, 2) plasma discharge/Cu(II) system, 3) Cu(II)/H2O2 system, and 4) nZVI/PDS system.

The inactivation experiments were performed for MS-2 phage and rotavirus by plasma discharge in buffer solution. The inactivation efficiency was increased at a high applied voltage as 120 V. Also, the groundwater conditions were able to inactivate the MS-2 phage. The results show that the inactivation of MS-2 phage was more rapid than was that of rotavirus. This is likely because rotavirus has a more complex structure of molecular clouds than MS-2 phage. The inactivation mechanisms of MS-2 phage were confirmed that ROS (H2O2, O3, OH radical) and UVC were not affected by plasma discharge. These results indicate that a shockwave can directly inactivate the MS-2phage, resulting in protein or RNA damage. In the results, BSA showed no significant change, indicating that the protein was not damaged by SDS-PAGE analysis. Also, extraction of RNA after MS-2phage inactivation experiment, primers 2 and 8 were increased ΔCt by real-time PCR analysis, and it is damaged to RNA by shockwave. In addition, the results of bio-TEM confirmed the critical damage to the MS-2 phage by a shockwave.

Inactivation studies were carried out that applied to disinfection process of groundwater used as raw water of bottled water on E. coli by plasma discharge with Cu(II) system. The E. coli showed 1.2 log inactivation within 2 min of the alone treatment with plasma discharge for groundwater and showed an improved efficiency to 2.2 log inactivation at the addition of trace amount of Cu(II). These enhanced inactivation efficiencies are believed to be due to oxidants (e.g. OH radical, Cu(III)) generated via Fenton-like reaction with Cu(II) added with H2O2 produced during plasma discharge. As a result of the inactivation efficiency by addition of copper chelating agent and OH radical scavenger, it was concluded that Cu(III) is produced by Fenton-like reaction as a factor for inactivating E. coli. In addition, the plasma discharge/Cu(II) system produced more Cu(I) than the conventional Cu(II)/H2O2 system (w/o plasma discharge), which eventually promoted the production of Cu(III) and enhanced the collapse of cell-membrane integrity, resulting in fatal damage to E. coli.

The Cu(II)/H2O2 system was applied for inactivation of ARB and to degrade the ARG at neutral pH. Although the inactivation of ARB was observed as a possible condition of Cu(II) alone, the inactivation efficiency was increased significantly when H2O2 was added. In the Cu(II)/H2O2 system, ARB inactivation was not achieved due to blockage of the Cu(II)/Cu(I) redox cycle by adding the copper-chelating agents EDTA and DMP. In addition, when t-BuOH was added, the inactivation efficiency was not inhibited, indicating that there is no influence by the OH radical. From these results, it can be concluded that Cu(III) is the predominant oxidant responsible for the inactivation of ARB. PI staining confirmed that Cu(III) could change the cell membrane integrity, and the cell-permeability test established that it caused oxidative damage both intracellularly and extracellularly. The removal efficiency of Cu(II) was about 5.5% after 20 min in the removal experiment of ARG. The combined system of Cu(II)/H2O2 exhibited a removal efficiency of about 85% of ARG within 20 min. It has also been verified that ARG is directly damaged by the Cu(II)/H2O2 system through agarose gel electrophoresis experiment and that a linear form is generated. Our data suggest that the Cu(II)/H2O2 system can be used in water treatment processes for ARB inactivation and ARG degradation at neutral pH.

The nZVI/PDS system was applied to confirm inactivation kinetics for L. monocytogenes, and evaluated the role and factors (PDS concentration, pH) that influence inactivation. After applying the nZVI/PDS system to neutrality conditions, an inactivation efficiency of about 2.4 log was found within 20 min, and a synergy effect that was even higher than the sum of the inactivation efficiency from PDS alone and nZVI alone had occurred. And as the added PDS concentration increased, inactivation efficiency improved, and as pH decreased, inactivation efficiency also improved. Upon confirming the changes inactivation patterns according to the addition of t-BuOH and EtOH, which are ROS scavengers as factors that influence inactivation, the major oxidant was SO4- radicals and the minor oxidant was OH radicals. On the other hand, corrosion occurred when nZVI was under water, and FeSO4 (or Fe2(SO4)3) may be created on the surface of nZVI due to PDS. This is known to perform the function of coagulants that are used in the coagulation/precipitation process, and after conducting a test using bentonite, a high turbidity elimination rate was found. In this way, the nZVI/PDS system was confirmed to be able to serve various functions such as the coagulation/precipitation processes in addition to oxidation/sterilization processes.