Influence of wastewater type on the impact generated by TiO 2 nanoparticles on the oxygen uptake rate in activated sludge process

Physicochemical characteristics of wastewater have a relationship with the stability of TiO nanoparticles (NPs). This in turn has an effect on the toxicity of TiO NPs in microorganisms. In this work, the effect of TiO NPs on activated sludge process was evaluated using three different types of wastewater: synthetic, raw, and filtered. The results showed that aggregate size of TiO NPs and their specific adsorption of substrates were influenced by the type of substrates and the presence of suspended solids in the wastewater. It was also shown that TiO NPs in raw wastewater severely inhibited oxygen uptake by microorganisms as compared to uptake in synthetic or filtered wastewater. The attachment of TiO NP aggregates on cell membranes was observed for all types of wastewater. However, the internalization of TiO NPs by microorganisms was observed only for raw and filtered wastewater. These results indicate that the effects caused by TiO NPs on activated sludge were different depending on the wastewater used for the experiment.