Promoting effect of polylactic acid biodegradable plastic on denitrification and co-metabolic degradation of quinoline

Quinoline is a typical refractory nitrogen heterocyclic organic matter found in industrial wastewater. Our previous studies have shown that poly lactic acid (PLA) could increase the abundance of denitrifying microorganisms in the short term, based on which we hypothosized that they could improve the anaerobic degradation efficiency of quinoline by enhancing the denitrification co-metabolism process. To test this hypothesis, we explored the performance of PLA and magnetically modified PLA (Fe₃O₄@PLA) fillers in enhancing the anaerobic degradation of quinoline. The results showed that PLA significantly improved the degradation rate of quinoline at concentrations of 50 mg/L, 100 mg/L, and 150 mg/L, and Fe₃O₄@PLA exhibited the optimal promoting effect with a quinoline degradation rate of 94.84%, 88.63%, and 82.09%, respectively. The abundance of denitrifying nirS gene was significantly higher in wastewater added with PLA and Fe₃O₄@PLA than in the control group, which was 6.07±0.08×10⁷ copies/g and 3.20±1.22×10⁸ copies/g; 1.36±0.06×10¹¹ copies/g and 1.48 ±0.03×10¹¹ copies/g; 2.61±0.72×10⁷ copies/g and 8.22±0.58×10⁷ copies/g at above-mentioned 3 quinoline concentrations, respectively, indicating that these two fillers enhanced the denitrification process, thereby improving the anaerobic degradation of quinoline. This study confirms that PLA can significantly improve the degradation of quinoline, and our findings expand the application fields of biodegradable plastics.