Effects of CeO2 nanoparticles on sludge aggregation and the role of extracellular polymeric substances - Explanation based on extended DLVO

Abstract

The extended DLVO (XDLVO) theory was applied to elucidate the potential effects of CeO₂ nanoparticles (CeO₂ NPs) on sludge aggregation and the role of extracellular polymeric substances (EPS). In this study, seven different concentrations of CeO₂ NPs were added to activated sludge cultured in sequencing batch reactors (SBRs) and compared with a control test that received no CeO₂ NPs. After exposure to 50mg/L CeO₂ NPs, a negligible change (p>0.1) occurred in the sludge volume index (SVI), whereas the flocculability and aggregation of the sludge decreased by 18.8% and 11.2%, respectively, resulting in a high effluent turbidity. The XDLVO theory demonstrated that the adverse effects of the CeO₂ NPs on sludge aggregation were due to an enhanced barrier energy. Compared to the van der Waals energies (W_A) and the electric double layer (W_R), the acid-base interaction (W_AB) markedly changed for the various concentrations of CeO₂ NPs. The EPS played a decisive role in the sludge surface characteristics, as the removal of EPS equals to the negative effects induced by 5-10mg/L CeO₂ NPs on the sludge flocculability and aggregation. The presence of CeO₂ NPs induced negative contributions to the tight boundary EPS (TB-EPS) and core bacteria while positive contributions to the total interaction energy of the loose boundary EPS (LB-EPS).

Keywords: CeO(2) nanoparticle; Extended DLVO theory; Extracellular polymeric substances; Sludge aggregation; Total interaction energy.