Activated sludge community and flocs morphology in response to aluminum oxide particles in the wastewater treatment system

Abstract

This work aims at comparing the response of activated sludge on the exposure either to aluminum oxide microparticles (Al2O3 MPs) or aluminum oxide nanoparticles (Al2O3 NPs) in the activated sludge system operating in the continuous mode. It was for the first time made with regard to three issues: composition of the microbial community, morphology of activated sludge flocs and settling properties of the sludge. It occurred that the addition of Al2O3 MPs or NPs to activated sludge did not reduce either richness or diversity of the bacterial community. Proteobacteria was the dominant phylum in each activated sludge system studied, however the presence of Al2O3 MPs or NPs caused to the decrease of Betaproteobacteria and the increase of Alphaproteobacteria. The most abundant genera identified in the control run, i.e. without addition of Al2O3 particles, were KD1-23, Caldilinea, Dechloromonas and Pseudomonas, whereas in the runs with Al2O3 MPs or NPs these were Caldilinea, Pseudomonas, Brevundimonas, Terracoccus or Caldilinea, Rhodobacter, Dokdonella, Terracocus, respectively. It was found that Al2O3 MPs or NPs contributed to the reduction of the denitrifying bacteria representing the genera Dechloromonas and KD1-23. Regarding the flocs morphology it occurred that Al2O3 NPs influenced it stronger than Al2O3 MPs did. Al2O3 NPs made the activated sludge flocs bigger and more circular compared to those exposed to Al2O3 MPs or not exposed to any Al2O3 particles. These changes of flocs morphology influenced positively the settling properties of activated sludge and contributed to the limitation of sludge bulking.