Effects of chronic exposure to different sizes and polymers of microplastics on the characteristics of activated sludge

Wastewater treatment plants (WWTPs) have become an important source of microplastics (MPs) contamination and most MPs remain in the sludge inducing potential impacts on sludge disposal. However, little is known about the influence of MPs on the characteristics of sludge, which is essential for sludge disposal. In this study, the dewaterability of activated sludge in response to chronic exposure (60 days) to MPs of different sizes (213.7nm similar to 4.2mm) and polymers (polystyrene, polyethylene, and polyvinyl chloride) were investigated. Overall, different particle sizes caused more evident effects on sludge dewatering than different polymer types did. Millimeter MPs (similar to 4 mm) dramatically reduced the dewaterability of sludge by 29.6% similar to 47.7%. These effects were mainly caused by the physical crushing of MPs on sludge flocs, except polyvinyl chloride (PVC)-MPs, possibly containing additives, induced toxicity on sludge. Moreover, 100mg/L nano-sizeMPs (213 nm) also reduced the dewatering performance of sludge. The potential mechanism is that nano-size MPs inhibited sludge activity and decreased the abundance of key microorganisms, which subsequently altered the composition and spatial distribution of extracellular polymeric substances (EPS), and finally impeded sludge dewatering. Our results highlight the impacts of different sizes of MPs on the characteristics of sludge, affecting the final disposal of sludge. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study revealed that microplastics have a significant impact on the dewaterability of sludge, with millimeter-sized microplastics causing more notable effects. Nano-sized microplastics inhibited sludge activity and altered the composition of extracellular polymeric substances, ultimately affecting sludge dewatering.