Investigation of the rheological behavior of activated sludge in response to CeO2 nanoparticles and potential mechanism

With the rapid development of CeO2 nanoparticles (NPs), the released CeO2 NPs entering into wastewater treatment plants might bring the challenges for sludge pumping and mixing. In this study, we firstly elucidated the rheological behavior of 4.0 wt% sludge at various concentrations of CeO2 NPs. With the increase of CeO2 NPs to 5 mg/L, the shear stress at any given shear rate was reduced and the limiting viscosity was also decreased, indicating the sludge became more flowability. The dynamic sweep tests further demonstrated the decreased elastic behavior and weakened internal structure in response to low concentrations of CeO2 NPs (≤ 5 mg/L). However, 20 mg/L CeO2 NPs had negative effects on the rheological evolution of sludge, namely, better solid-like property and higher elastic structure. These results were mainly attributed to the combination of the decreased β-d-glucopyranose polysaccharides which support the rigid structure of sludge and the dramatically increased protein content (especially in 20 mg/L CeO2 NPs). These results can potentially provide novel information for the efficient design of sludge treatment when coped with CeO2 NPs.