## 3 Results and Discussion
### Mechanisms of B/C Improvement  
#### 3.3.1 GC-MS Analysis of Wastewater  
Table 2 lists the GC-MS composition analysis of wastewater, Fenton, and ozone oxidation. The wastewater composition is relatively complex and contains a variety of large  
Figure 2: Effect of H\({}_{2}\)O\({}_{2}\) concentration on (**a**) COD removal; (**b**) B/C values; (**c**) BOD\({}_{5}\) variation during Fenton oxidation. Conditions are as follows: Fe\({}^{2+}\) concentration 120 mg/L; 250 mL wastewater; pH = 3.0.  
organic pollutants, such as tripropylene glycol methyl ether, Di-tert-butylphenol, and large organic acids. The relative abundance of organic pollutants in the wastewater samples is shown in Figure 4a. It can be seen that the relative abundance of Di-tert-butylphenol, 2-Amino-4,5,6-methylbenzoic acid and 2-Methyl-2-Pentanol are higher, at 25.31%, 33.45%, and 15.50% respectively. This result suggests that the main microscopic composition of their organic load is large-molecule organic pollutants, from which it can be inferred the COD composition of wastewater may be large polar organic pollutants that are difficult to biodegradable, organic acids, phenols, and other organic substances [27]. Because of the high content of macromolecular organic pollution in wastewater, it is difficult or not biodegradable.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**Molecular Structure**} & **Elemental** & **t\({}_{\mathbf{q}}\)** & **[Min]** & **[M + H] + m/z** & **Wastewater** & **Fenton** & **Ozone** \\  & & & & & & & **Oxidation** & **Oxidation** \\ \hline \multirow{2}{*}{A} & Ethanethioamide,N,N-dimethyl- & \multirow{2}{*}{\(\begin{array}{c}\text{S}\\ \text{C}_{4}\text{H}_{9}\text{NS}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{C}_{4}\text{H}_{9}\text{NS}\end{array}\)} & \multirow{2}{*}{4.173} & \multirow{2}{*}{103.19} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} \\ \hline \multirow{2}{*}{B} & Acetamide,N-(aminocarbony)- & \multirow{2}{*}{\(\begin{array}{c}\text{O}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} & \multirow{2}{*}{\(\begin{array}{c}\text{\surd}\\ \text{\surd}\end{array}\)} \\ \end{tabular}
\end{table}
Table 2: GC–MS analysis of petrochemical wastewater.  
Figure 3: Effect of ozone flow rate on **(a)** COD removal; **(b)** B/C values; **(c)** BOD\({}_{5}\) variation during Fenton oxidation. Conditions are as follows: ozone concentration 1 g/L; 250 mL wastewater; pH = 6.26.