Effect evaluation of microplastics on activated sludge nitrification and denitrification

Area of Science:

• Environmental Science
• Environmental Microbiology
• Water Treatment Technologies

Background:

• Conventional wastewater treatment plants (WWTPs) receive substantial microplastic pollution.
• Limited research exists on microplastic impacts on activated sludge nitrification and denitrification.
• Understanding these effects is crucial for effective wastewater management and environmental protection.

Purpose of the Study:

• To investigate the effects of five common microplastics (PVC, polypropylene, polyethylene, polystyrene, PES) on activated sludge nitrification and denitrification.
• To evaluate microplastic toxicity and impact on nitrogen removal processes at varying concentrations (0–10,000 particles/L).
• To assess the influence of microplastics on nitrous oxide (N2O) emissions during denitrification.

Main Methods:

• Experimental study using activated sludge microcosms.
• Exposure to five microplastic types at concentrations of 0, 1000, 5000, and 10,000 particles/L.
• Monitoring of nitrification (ammonia and nitrite oxidation) and denitrification rates, and N2O emissions over 3 hours.

Main Results:

• Microplastics exhibited negative effects on ammonia oxidation rates but minimal impact on nitrite oxidation during nitrification.
• Denitrification rates were positively affected, particularly by PVC and PES at 5000 particles/L.
• High concentrations of PVC microplastics significantly increased N2O emissions, up to 4.6 times higher than controls.

Conclusions:

• Microplastics at concentrations below 10,000 particles/L generally have low toxicity to nitrification and denitrification in activated sludge within a 3-hour timeframe.
• PVC microplastics pose a significant risk by substantially elevating nitrous oxide (N2O) emissions during the denitrification process.
• Wastewater treatment strategies need to consider the potential for increased N2O emissions due to microplastic contamination.