Polyvinyl Chloride Microplastics Facilitate Nitrous Oxide Production in Partial Nitritation Systems

Area of Science:

• Environmental Science
• Environmental Engineering
• Microbiology

Background:

• Partial nitritation (PN) is crucial for treating high-strength wastewater in sidestream systems.
• PN systems are increasingly affected by microplastic pollution, particularly polyvinyl chloride microplastics (PVC-MPs).
• Understanding microplastic impacts on PN is vital for mitigating nitrous oxide (N2O) emissions.

Purpose of the Study:

• To investigate the effects of PVC-MPs on N2O emission pathways in PN systems.
• To quantify the influence of PVC-MPs on ammonia oxidation rates (AORs) and N2O production.
• To elucidate the mechanisms behind PVC-MP-induced alterations in PN performance and N2O emissions.

Main Methods:

• Long-term experiments to assess PN performance under varying PVC-MP concentrations (0.5 and 5 mg/L).
• Batch tests to measure AORs and N2O production rates at different dissolved oxygen levels.
• Site preference analysis and metabolic inhibitors to identify N2O production pathways.
• Analysis of bisphenol A leaching and reactive oxygen species (ROS) production.

Main Results:

• Low-dose PVC-MPs (0.5 mg/L) had minimal impact, while high-dose (5 mg/L) significantly impaired PN performance.
• PVC-MPs reduced AORs by 5.78-21.94% and stimulated aerobic N2O production by 9.22-88.36%.
• Increased dissolved oxygen mitigated N2O stimulation but worsened AOR inhibition.
• Hydroxylamine oxidation and heterotrophic denitrification pathways were enhanced contributors to N2O at low DO.
• Bisphenol A leaching and ROS production were identified as key mechanisms leading to cell death and community shifts.

Conclusions:

• PVC-MPs pose a significant threat to PN system efficiency and contribute to elevated N2O emissions.
• Microplastic pollution is an underestimated factor in wastewater treatment systems, necessitating further research and mitigation strategies.
• The study highlights the complex interactions between microplastics, microbial processes, and greenhouse gas emissions in aquatic environments.