Impact of titanium dioxide nanoparticles on the bacterial communities of biological activated carbon filter intended for drinking water treatment

Titanium dioxide nanoparticles (TiO₂ NPs) are inevitably present in the aquatic environment owing to their increasing production and use. However, knowledge of the potential effects of TiO₂ NPs on the treatment of drinking water is scarce. Herein, the effects of two types of anatase TiO₂ NPs (TP1, 25 nm; TP2, 100 nm) on the bacterial community in a biological activated carbon (BAC) filter were investigated via quantitative polymerase chain reaction (Q-PCR) analysis, ATP quantification, and 454 pyrosequencing analysis. Both TP1 and TP2 significantly inhibited the bacterial ATP level (p < 0.01) and induced a decrease in the abundance of bacterial 16S rDNA gene copies at doses of 0.1 and 100 mg L⁻¹. Simultaneously, the diversity and evenness of the bacterial communities were considerably reduced. The relative abundances of bacteria annotated to OTUs from Nitrospira class and Betaproteobacteria class decreased upon TiO₂ NP treatment, whereas those of Bacilli class and Gammaproteobacteria class increased. TiO₂ NP size showed a greater effect on the bacterial composition than did the dose based on Bray-Curtis distances. These findings identified negative effects of TiO₂ NPs on the bacterial community in the BAC filter. Given the fact that BAC filters are used widely in drinking water treatment plants, these results suggested a potential threat by TiO₂ NP to drinking water treatment system.