Configuration-driven microplastic fate in full-scale sewage sludge treatment and opportunities for system-level...

Area of Science:

• Environmental Science
• Environmental Engineering
• Polymer Science

Background:

• Microplastic (MP) accumulation in sewage sludge poses risks to land application and biosolid sustainability.
• Understanding MP fate during wastewater treatment is crucial for environmental management.

Purpose of the Study:

• To investigate how different sludge treatment configurations (thickening, digestion, dewatering) affect MP abundance, size, and polymer profiles.
• To identify key stages and configurations influencing MP enrichment and removal in wastewater treatment plants.

Main Methods:

• Analysis of microplastics in sludge across three wastewater treatment plants with varying treatment configurations.
• Characterization of MP abundance, size distribution (e.g., >10-100 μm, <100 μm), and polymer types (e.g., PE, PP, PVC, PU, PET).

Main Results:

• Treatment configuration significantly influenced MP fate, with concentrations ranging from 617 to 936 MP/g dry solids.
• Fibrous MPs dominated initially, shifting to fragments in dewatered sludge. Later WAS entry enriched low-density polymers (PE, PP).
• Dewatering converged final sludge MP concentrations, dominated by fine MPs (<100 μm), with total loads of 1.36-3.59 × 10^8 MP/d.

Conclusions:

• Sludge treatment configuration critically shapes microplastic profiles in biosolids.
• Mechanical dewatering modifies MP characteristics, but feed composition and entry point are key.
• Centrate management during dewatering is vital for reducing terrestrial microplastic transfer.