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New insights of NaClO induced polyvinyl chloride microplastics affect sewage treatment in activated sludge

Jin Xu1, Xiuhong Liu1, Yimai Zhou1

  • 1Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing University of Technology, Beijing, 100124, China; National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Beijing University of Technology, Beijing, 100124, China.

Journal of Environmental Management
|May 30, 2025
PubMed

Insights

Sodium hypochlorite (NaClO) and microplastics (MPs) together harm activated sludge in wastewater treatment. This co-exposure inhibits crucial enzymes and bacteria, impairing nutrient removal and damaging cell membranes.

Area of Science:

  • Environmental Science
  • Environmental Chemistry
  • Microbiology

Background:

  • Microplastics (MPs) accumulate in wastewater treatment plant (WWTP) bioreactors, particularly membrane bioreactors (MBRs).
  • Sodium hypochlorite (NaClO), a common cleaning agent, contacts MPs during MBR membrane cleaning.
  • Understanding the combined toxicity of NaClO and MPs on activated sludge is crucial for WWTP operation.

Purpose of the Study:

  • To investigate the toxicity mechanisms of co-exposure to NaClO and MPs on activated sludge.
  • To assess the impact on nutrient removal efficiencies and key microbial enzymes.
  • To elucidate the role of oxidative stress and additive release in the toxicity.

Main Methods:

  • Activated sludge was exposed to NaClO and PVC-MPs under simulated MBR conditions.
  • Chemical Oxygen Demand (COD), Total Nitrogen (TN), and Total Phosphorus (TP) removal efficiencies were monitored.
  • Enzyme activities related to nutrient metabolism and microbial community composition were analyzed.
  • Oxidative stress levels and microplastic leachate composition were examined.

Main Results:

  • Co-exposure to NaClO and MPs initially decreased COD, TN, and TP removal, with no recovery under NaClO stress.
  • Key enzymes involved in nitrogen metabolism (AMO, NXR, NIR, NAR) and dominant nitrogen-removing bacteria were inhibited.
  • NaClO stress altered MP leachate, enhancing the release of additives like BPA.
  • Combined exposure increased oxidative stress, leading to activated sludge cell membrane damage.

Conclusions:

  • NaClO and MPs co-exposure significantly impairs activated sludge performance and microbial community structure.
  • The primary toxicity mechanism involves enhanced oxidative stress, independent of additive release.
  • This highlights the need to manage MP accumulation and NaClO use in WWTPs to prevent operational disruptions.
Keywords:
LeachatesMicroplasticsNutrients removalOxidative stressToxicity

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