## 3 Results and Discussion
### Effect Analysis of Environmental Factors on Degradation  
Although the P&A bacterial consortium had been constructed, the degradation rates of NAP, PHE, and PYR also depend on environmental factors, bacteria, and PAHs 'initial  
Figure 4: Degradation rates of mixed PAHs by bacteria consortium with different ratio (\(\Delta\): PHE degradation rate; \(\hat{\varkappa}\): PYR degradation rate). Figure 3: Degradation rates of mixed PAHs by purebred strain (\(\Delta\): PHE degradation rate; \(\hat{\varkappa}\): PYR degradation rate). concentrations. The effects of temperature, pH, bacteria, and PAHs' initial concentrations on the degradation of PAHs were studied by single variable method. Since 500 mg/L NAP was completely degraded by bacterium in experiment 3.2.2, the PAHs mixture contained 2000 mg/L NAP, 20 mg/L PHE, and 40 mg/L PYR in the following test, except Experiment (c). The PAHs initial concentrations in Figure 5c are shown in Table 3 as follows. The results are shown in Figure 5.  
The effects of environmental conditions on NAP, PHE, and PYR degradation efficiency are shown in Figure 5. It can be seen from Figure 5a that temperature is one of the most important environmental factors that is affecting the growth and survival of microorganisms; when the degradation temperature is 35 \({}^{\circ}\)C, the comprehensive degradation rates of NAP, PHE, and PYR are higher than others (99.51%, 92.60%, and 91.71%), and when it is higher or lower than 35 \({}^{\circ}\)C, a considered decrease of degradation rate could be observed. Within the appropriate temperature range, the enzymatic reaction efficiency, the solubility and mass transfer rates of PAHs are increased [43; 44]. Based on the Figure 5b, the higher degradation rates of NAP, PHE, and PYR could be achieved (93.86%, 78.98%, and 77.08%) when pH is  
Figure 5: Effects of environmental conditions on the degradation rate of PAHs (\(\Diamond\): NAP degradation rate; \(\Delta\): PHE degradation rate; \(\%\): PYR degradation rate). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**NO.** & **1** & **2** & **3** & **4** & **5** \\ \hline NAP/mg/L & 1000 & 2000 & 3000 & 4000 & 5000 \\ PHE/mg/L & 10 & 20 & 30 & 40 & 50 \\ PYR/mg/L & 20 & 40 & 60 & 80 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The PAHs initial concentrations in Figure 5c. about 7. However, the NAP, PHE, and PYR degradation rates would be decreased at other pH, proving that the enzyme activity will be reduced if pH is out of the optimum pH range of 6.5-7.5 [45]. With the increasing initial concentration (IC) of NAP, PHE, and PYR in the degradation system, the degradation rates showed a downward trend (Figure 5c). However, when the IC values of NAP, PHE, and PYR were 1000, 10, and 20 mg/L (Table 3), respectively, NAP and PHE were degraded by the P&A bacterial consortium completely, and the degradation rate of PYR was as high as 85.55%. In order to carry out the follow-up experiment and observe the experimental phenomenon, the dosages of NAP, PHE, and PYR in the follow-up experiment were determined as 2000, 20, and 40 mg/L, and the degradation rates of NAP, PHE, and PYR under this IC were 95.23%, 88.13%, and 70.72%, respectiveiy. The lower initial concentration of PAHs made it not only difficult to provide sufficient carbon source but also difficult to induce microorganisms to produce corresponding degrading enzymes. High-concentration PAHs have toxicity to microorganisms [29], and suitable initial concentration also is the important consideration factor for further analysis. It can be observed from Figure 5d that when the bacterial inoculum is 5% (volume percent), the degradation rates of NAP, PHE, and PYR were 96.37%, 88.54%, and 73.82%, respectively, which were higher than others. The accumulation of biomass would take a long time when the bacterial inoculum is lower than the appropriate amount, but higher bacterial inoculation will lead to a large number of cell deaths because of nutrient deficiency.