## 4 Conclusions  
An optimal PAHs degradation bacterial consortia (_P. aeruginosa_ and _A. faecalis_) and their volume ratio (1:1) were screened out by this study from 10 bacterium in local oily sludge. The PAHs solution degradation efficient of P&A bacterial consortium under different environmental conditions, bioaugmentations, and exogenous stimulations were studied by UV-vis spectrophotometer and GC-MS. The result shows that, after 8 days degradation under 35 \({}^{\circ}\)C, pH 7, with 5% (volume percent) of the inoculation amount, the degradation  
Figure 11: Chromatogram analysis of oily sludge. (**a**) Chromatographic analysis of oily sludge before degradation; (**b**) chromatographic analysis of degraded oily sludge; 1. Naphthalene; 2. Acenaphthylene; 3. 1H-Phenalene; 4. Phenalene; 5. 4H-Cyclopenta[d,e,f]phenanthrene; 6. Fluoranthene; 7. Pyrene; 8. Triphenylene; 9. 9H-Cyclopenta[a]pyrene; 10. Benzo[k]fluoranthene). Figure 10: Degradation of PAHs in oily sludge by PA bacterial consortium. rates of 2000 mg/L NAP, 20 mg/L PHE, and 40 mg/L PYR were higher than 90%, 80%, and 70%, respectively. In the report of [PERSON] et al. and [PERSON] et al., the highest biodegradation rates of PHE and PYR were only 74% and 60% [56, 57], although [PERSON] et al. used _C. versicolor_ and _F. palustris_, which could degraded 93.7% of PYR, but its degradation term was as long as 28 d [58]. In contrast, the P&A bacterial consortium has more advantages in degradation efficiency and degradation term. Additionally, the experimental results also show that the additional crude oil further improved the degradation efficiency of P&A bacterial consortium. The MIC values of Cu\({}^{2+}\), Zn\({}^{2+}\), and Pb\({}^{2+}\) to bacterium were 2.002, 17.388, and 9.435 mM, respectively. The addition of surfactants had a negative or limited positive effect on the PAHs degradation rate. Furthermore, the average degradation rates of NAP, PHE, and PYR in oily sludge by P&A bacterial consortium also reached above 80%. Based on GC-MS test result before and after incubation, PAHs degradation ability of P&A bacterial consortium is not only limited to NAP, PHE, and PYR, but also includes others such as Acenaphthylene, 1H-Phenalene, 4H-Cyclopenta[d,e,f]phenanthrene, Fluoranthene, Triphenylene, 9H-Cyclopenta[al]pyrene, and Benzo[k]fluoranthene. However, there are few reports on the degradation of PAHs mixture in oily sludge by bacterial consortium. The P&A bacterial consortium has outstanding performance on PAHs degradation activity in oil sludge and high concentration heavy metal ion environment. Based on this advantage, the P&A bacterial consortium can be prepared into immobilized microorganisms to improve the microbial cell density in unit volume medium and further improve its anti-toxic ability. At the same time, the carrier material can act as a loosening agent. It also can wrap the nutrients by microorganisms to play a stable role in complex environment, which means that the P&A bacterial consortium has prospects in the application in oily sewage, oily sludge, and soil treatment. Formal analysis, C.Q. and F.Q. ; investigation, A.M.; resources, T.Y. ; data curation, L.Z. and B.Y. ; writing--original draft preparation, L.Z. and B.Y. ; writing--review and editing, G.C. and F.Q. All authors have read and agreed to the published version of the manuscript. The open project of the State Key Laboratory of Petroleum and Petrochemical Pollutant Control and Treatment Study on the Mechanism of Supercritical Hydrothermal Catalytic Oxidation of Oily Sludge' (subject number PPC2019001); The Open Project of Shaanxi Key Laboratory of Oil and Gas Field Environmental Pollution Control Technology and Reservoir Protection' Study on Ecological Safety Evaluation of Oily Sludge Residue after Treatment'; Major low-carbon project of PetroChina: Research on pyrolysis catalyst and catalytic process conditions of oily sludge (School No. 240113001). Not applicable.