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

Abstract

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.