## 3 Plasma Application to Eliminate Organic Pollutants in Water
### Organic Chemical Reagents  
Phenol is a widespread pollutant in wastewater; it has teratogenic and carcinogenic activity. [PERSON] et al. [69] looked into the plasma treatment's ability to degrade phenol. When phenol liquids are subjected to plasma, reaction products can be identified using high-performance liquid chromatography (HPLC). Further research has shown that hydroxylated degradation products of phenol (catechol, hydroquinone, 1,4-benzoquinone and hydroxy-1,4-benzoquinone, see Table 3) were detected for APP. In this case, however, nitrated phenol degradation by-products (4-nitrophenol, 2-nitrophenol, 4-nitroatechol and 4-nitrosophenol, see Table 3) were detected in addition to the hydroxylated products. Another earlier study found that the degree of phenol decomposition increased as solution thickness decreased under the impact of pulsed corona discharge in O\({}_{2}\)[95], and an identical effect was seen during glow discharge electrolysis [96]. Additionally, DBD discharge showed a decline in breakdown efficiency as phenol content rose [97]. In this case, most research, at least for the acid media wherein it occurs in our instance, presume that the principal events leading to the destruction are interactions of phenol with \(\cdot\)OH [96; 98] (reactions (1) and (2)). This points out the significance of plasma acids in the purification of effluents. \[\text{C}_{6}\text{H}_{5}\text{OH}+\cdot\text{OH}\rightarrow\text{H}_{2}\text {O}+\text{C}_{6}\text{H}_{4}\text{OH} \tag{1}\]\[\mathrm{C_{6}H_{4}OH}+\mathrm{OH}\to\mathrm{C_{6}H_{4}(OH)_{2}} \tag{2}\]  
According to earlier research [99], carboxylic acids are converted to aldehydes under discharge conditions. In particular, it has been mentioned that hydroxylated phenols and carboxylic acids are the breakdown byproducts [100]. One can assume that the main byproduct of the interaction between phenols and free radicals is the formation of acids from hydroxylated phenols. A recent study has confirmed that the products of plasma degradation of phenol are carboxylic acids; these acids are further transformed into aldehydes, which are then further degraded to CO\({}_{2}\) and H\({}_{2}\)O [101]. In addition, the degradation of a mixture consisting of phenol and other organic substances by plasma has been developed now. Each kind of runoff water contains chloride anions [102], so the authors performed a set of experiments with model solutions containing phenol and KCl to evaluate the overall degradation efficiency [103]. The results show it is evident that the part of chloride ions is converted into an available chlorine species via the plasma treatment of these model solutions. The available chlorine is able to increase the overall purification efficiency. Therefore, another pathway of organic pollutant degradation exists in this process, which involves available chlorine, in addition to the reaction of the organic matter with the active species of the O\({}_{3}\) and O\({}_{2}\) plasma. The major component of the acid in the water generated by oil and gas extraction is acetic acid [104]. The results demonstrated that adding O\({}_{3}\) significantly increased the degradation of the highly concentrated acetic acid solution [105]. Researchers have developed a simple multiple plasma generation system to achieve efficient decomposition of persistent organic compounds in water [106]. By altering the capacitance of the ballast capacitor, which establishes the plasma input power for each plasma treatment orifice, it is possible to regulate the rate of reaction of H\({}_{2}\)O\({}_{2}\) and O\({}_{3}\). The total organic carbon (TOC) reduction rate and efficiency increased significantly upon adding plasma-treated gas into the solution, which enhanced the reactivity of \(\cdot\)OH produced by H\({}_{2}\)O\({}_{2}\) and O\({}_{3}\). Despite the plasma approach's slower rate of decomposition being a disadvantage in comparison to these AOPs [106], the key benefit of the plasma technique over AOPs that use chemicals is that no chemical transportation or storage is required.