Behavior of nanoscale titanium dioxide in laboratory wastewater treatment plants according to OECD 303 A

The fate assessment of nanomaterials in municipal sewage treatment plants (STP) is a crucial step for their environmental risk assessment and may be assessed by monitoring full scale STP, dosage to medium scale pilot STP or by laboratory testing. For regulatory purposes preferably standardised test protocols such as the OECD guidelines for testing of chemicals should be used. However, these test protocols have not yet been specifically designed for nanoparticles. Therefore, the fate and behavior of a TiO2 nanomaterial (P25, average hydrodynamic diameter <250 nm) was investigated in laboratory sewage treatment plants according to the OECD Guideline for the Testing of Chemicals 303 A. It is concluded that this guideline is applicable for the testing of nanomaterials if modifications regarding the dosage, nitrifying conditions, and a characterisation of the nanoparticles in the effluent are applied. A compilation of the cumulative mass balance by comparison of the total dosage added with the amount in the outflow and in the activated sludge is recommended. In this study, the majority of the TiO2 nanomaterial (>95%) was retained in the sewage sludge and only 3-4% was found in the effluent. No effect of the TiO2 nanomaterials on the biodegradation or nitrification was observed.