Abstract
The imminent arrival of nanoparticles (NPs) to the wastewater treatment plants (WWTP) brings concern about their effects. In this work, the effects of titanium dioxide (TiO2) NPs in the removal of carbon, nitrogen, and phosphorus by activated sludge bioreactors during the treatment of synthetic, raw and filtered wastewater were evaluated. The floc size, compaction of sludge, and morphological interactions between sludge and NPs were also evaluated. The main effect was observed in the ammoniacal nitrogen removal, which was inhibited up to 22% for all types of wastewater in the presence of TiO2 NPs. While nitrite production deficiencies were observed for real wastewaters experiments, nitrate formation was mainly affected for synthetic wastewater. The removal of organic matter was affected by TiO2 NPs in lower level (up to 6%) than nitrogen removal, especially during treatment of raw wastewater. The removal of orthophosphate was improved in presence of NPs 34%, 16% and 55% for synthetic, raw, and filtered wastewater, respectively. The compaction of the sludge was also a positive effect, which enhanced as the concentration of NPs increased without alterations in the floc size for all types of wastewater. Based on TEM and STEM imaging, the main interaction of TiO2 NPs with activated sludge flocs was mainly the adsorption of NPs on the cell membrane. This means that NPs can disrupt the cell membrane during aerobic wastewater treatment. The effects of NPs on macronutrient removal depended on wastewater characteristics. The use of realistic matrices is highly encouraged for ecotoxicological experiments.
Influence of wastewater type in the effects caused by titanium dioxide nanoparticles in the removal of macronutrients by activated sludge