Development of a functional assay for the prediction of NP net removal rates in WWT

Within recent years the growing application of nanoparticles (NPs) in products of everyday life caused raising concerns about their potential risks for humans and environment. Environmental concentrations of manufactured nanoparticles are predicted to be low, but significant. Key players in regulating NP influx into the environment are wastewater treatment plants (WWTP). The development of removal guidelines and a NP classification based on their likely fate in wastewater treatment (WWT) is mandatory to support WWTP operating companies and regulating agencies.
A potential approach based on suitable functional assays is developed within the project NanoSuppe in cooperation with an US-EPA initialized round robin test with various partners in the US. The idea is to use a simple test program to establish NP affinity coefficients with activated sewage sludge to predict net removal rates during WWT.
Within NanoSuppe, different NPs, such as TiO2, CeO2, MWCNT and Quantum dots, are radiolabeled for easy and highly sensitive detection and employed in batch sorption experiments with activated sludge from a local WWTP. Based on the theory developed by Barton et al., NP affinities for NP hetero-aggregation with the activated sludge are measured from the time-dependent sorption behavior and used as a means of categorizing NP in different groups.
We found that the results of such functional assays depend very much on the experimental setup, such as composition of the dispersion medium (or matrix solution) and consequently NP surface modification (which is to be expected). There is also a significant influence of mixing times and, more dominant, shaking intensity. One of the key parameters is the initial colloidal stability of the NPs in the used media. A suitable procedure that best reflects the situation during WWT is desirable and the predictive strength concerning net removal rates during WWT is to be verified in WWTP model experiments.