Insights into the short-term effects of CeO₂ nanoparticles on sludge dewatering and related mechanism

As CeO₂ nanoparticles (NPs) are used in many applications, the released particles eventually enter wastewater treatment plants, influencing sludge dewatering and increasing the disposal costs. We conducted tests to gain insight into the sludge dewatering performance and the potential mechanism related to the distribution and production of extracellular polymeric substances (EPS). In addition, we conducted single-factor tests with six concentrations of CeO₂ NPs in sequencing batch reactors containing matured activated sludge. Overall, the specific resistance to filtration (SRF) improved with an increase in the CeO₂ NPs dosage. The SRF significantly increased from 1.460 × 10¹² to 1.632 × 10¹² m/kg after the addition of 5 mg/L CeO₂ NPs (p < 0.05). The bound water content was enhanced from 2.43 to 2.75 kg/kg dry solid, indicating a deteriorated dewaterability. We found that the increased EPS production, especially the dominant protein (r = 0.987, p < 0.01), was correlated significantly with the SRF. This is ascribed to the inhibited activity of leucyl aminopeptidase and the reduced adenosine 5'-triphosphate concentrations after exposure to CeO₂ NPs. The fluorescence region integration technique and protein secondary structures revealed the reasons for the poor dewatering performance in the presence of CeO₂ NPs. These are the enhanced amount of soluble microbial by-product-like material and the low value of the α-helix/(β-sheet + random coil). These results could potentially expand the knowledge on sludge dewatering in the presence of NPs.