Effect of Different Nanomaterials on the Metabolic Activity and Bacterial Flora of Activated Sludge Medium

In this study, the dominant and representative bacteria of activated sludge before and after the addition of different nanomaterials (NMs) (multiwalled carbon nanotube, MWCNT, silicon dioxide nanoparticle, nSiO₂, titanium oxide nanoparticle, nTiO₂, aluminum oxide-nanoparticle, nAl₂O₃, and silver nanoparticle, nAg) were separately isolated, enumerated, and identified. In total, 17 different representative isolates were identified by using 16S rDNA gene sequence analysis. The effects of NMs on the growth (viable counts), biological oxygen demand (BOD) removal performances, respiration mechanism, and extracellular polymeric substances (EPS) production of bacteria were also investigated. Both BOD removal capacity and respiration rate of bacterial medium decreased after NMs exposure. Most toxic NMs were MWCNT (46.15%) and nAg (42.30%) related with BOD removal capacity and nAg (62%) and nTiO₂ (56%) for respiration mechanism. Therefore, the protein content of soluble EPS (sEPSp) increased with addition of nAg, nTiO₂, and nAl₂O₃. NMs also have negative effect on the structure of community of activated sludge in both diversity and density.