| The main objective of this study was to assess the impacts of single-walled carbon nanotubes (SWCNTs) on the activated sludge process. Both batch-scale reactors and a continuous-flow reactor were used to evaluate the effects of 95% purified SWCNTs on the performance of activated sludge reactors and activated sludge properties.; Through the batch-scale study, we found that the SWCNTs adsorbed 22% of the soluble COD (sCOD, chemical oxygen demand). One-way ANOVA analysis revealed that only four experimental parameters, i.e., surface charge, sCOD, mixed liquor suspended solids (MLSS) and sludge volume index (SVI) were significantly impacted by the addition of SWCNTs. Other parameters such as pH, dissolved oxygen (DO), specific resistance to filtration (SRF), and relative hydrophobicity were not significantly impacted. Further data analysis demonstrated that better sCOD removal was achieved in the SWCNTs-added reactors than that in the control reactors (80% vs. 62%). The addition of the SWCNTs also improved sludge settleability and made the surface of the activated sludge flocs less negatively charged. Overall the SWCNTs showed positive impacts on the reactor performance and sludge properties.; The continuous-flow reactor was shock loaded resulting in a concentration of 270 mg/L of 95% purified SWCNTs after the reactor reached a quasi-steady state and the reactor was monitored for 18 days after the shock loading. Various experimental parameters were measured and compared. Overall the addition of SWCNTs did not negatively impact the performance of the activated sludge reactor; on the other hand, SWCNTs improved sludge settleability and sludge dewaterability. The cake solids of the sludge were increased and the activated sludge flocs became less negatively charged. Phase I was the initial reactor control period before the addition of SWCNTs. The positive impacts were more significant in Phase II (after running the reactor for a period of one solids retention time, SRT) than that in Phase III (after running for an additional 1.5 SRT).; The protection of bacteria by the extracellular polymeric substances (EPS) against the direct contact with SWCNTs is a possible explanation why no significant negative impacts were observed with respect to reactor performance. |
