## 4 Water Sterilization and Disinfection
On the contrary, \({}^{1}\)O\({}_{2}\) can effectively diffuse into the cell layer and initiate peroxidation of lipid due to its lifetime being longer than that of OH. Moreover, the results illustrated that in plasma devices (e.g., DBD plasma and plasma micro jets), the \({}^{1}\)O\({}_{2}\) concentration is often greater than the OH radicals concentration. Nevertheless, O\({}_{2}\)\({}^{-}\) requires a greater oxidation ability to remove H\({}_{2}\) from the phospholipids and consequently can only enter the cell hydrophobic area with significant effort. However, by the Haber-Weiss reaction [90], O\({}_{2}\)\({}^{-}\) can be changed into OH radicals and converted into hydroperxyl (HOO) radicals by protonation when the pH is less than 4.7. Hence, these species can easily enter the cell hydrophobic area. Moreover, it has been demonstrated that plasma acid is a significant factor in the inactivation of plasma-liquid media. It is a vital parameter in enabling plasma species to pass into cell walls and in decreasing the resistance of cells versus acidic media [91; 92; 93; 94]. To enhance the effects of sterilization, it is important to develop a device in which most components in the liquid (microorganisms) could come into direct contact with the plasma. The results showed that NTAPP performs sterilization much more effectively, because the concentrations of RONS causing sterilization are quite high in NTAPP, and the probability of reaction between _Escherichia coli_ and the plasma-generated RONS increases [50]. Both nitrous and nitric acid are formed through the interaction of NO and NO\({}_{2}\) with water by hydrolysis. Meanwhile, NO\({}_{x}\) is produced by reaction with the air, but when plasma interacts with liquid and thus does not have the opportunity to contact air, NO\({}_{x}\) generation barely occurs. Furthermore, air plasma jet have a greater sterilization effect than nitrogen plasma jet due to the generally huge number of reactive species causing bacterial inactivation [50]. Moreover, the radical concentration affects the sterilization in proportion to the plasma length (e.g., it increases with increasing gas flow rate). In another study [86], the behavior of the surface potential of bacteria was investigated as a function of the applied energy by analyzing the molecular levels of DNA and proteins. The applied pulse voltage (23 kV) and frequency (25 Hz) in the experiments enabled rapid disinfection. In a treatment time of 6 min, complete disinfection was achieved. This result indicated that plasma could increase the protein leakage via the membrane of bacteria. It is interesting that in this case, approximately 70% of all proteins were leaked during the first 8 min of treatment. The plasma spark method is another important approach for water disinfection. [PERSON] et al. [95] investigated water disinfection (_Escherichia coli_ and _Enterococcus faecalis_ inactivation) using the plasma spark technique and compared the results with those of ordinary methods. In this research, some of the chemical and physical parameters of the water were evaluated. The results demonstrated that _Escherichia faecalis_ and _Escherichia coli_ decrease by 8 log CFU after 12 and 15 min, respectively. Moreover, this research showed that major bacteria inactivation in water is achievable using electric fields and H\({}_{2}\)O\({}_{2}\) molecules produced using plasma. NTAPP also has a powerful ability to remove bacteria. A concentration reduction of 8 log CFU was observed in all samples. In this method, some plasma species (e.g., H\({}_{2}\)O\({}_{2}\), OH radicals, O\({}_{3}\)) are strong oxidizers with the necessary ingredients of bacterial invasions, including lipids, proteins, and DNA, as summarized in Figure 7.  
After applying plasma to drinking or wastewater, the effects of different types of organic and inorganic matter on the disinfection process have been investigated. The results have shown that the concentrations of inorganic and organic compounds in tap water can change after treatment [70].