Citation:

Luxton, T., E. Baumann, A. Gitipour, W. Platten, J. Clar, J. Kid, P. Westerhoff, D. Tobias, J. Unrine, C. Chen, A. Remsen, Z. Hu, AND R. Sierra. Study Report on a Test for Removal in Wastewater Treatment Plantsof Gold Manufactured Nanomaterial (Mn): Activated Sludge SorptionIsotherm. OECD Press, Paris, France, 2021.

Impact/Purpose:

The Office of Chemcial Safety and Pollution Prevention (OSCPP), Office of Pollution Prevention and Toxics (OPPT) requested help with the development of guidelines and methods to provide screening level information for the biochemcial process of engineered nanomaterial (ENM) removal during waste water treatment. OPPT was interested in lab scale data on nanomaterial interactions with suspended solids present during wastewater treatment. The guideline/method would provide a basis for estimating removal that can be applied to waste water treatment plants (WWTPs). The guideline/method was requested to provide a clear bench-top based indication of the ENM removals to be anticipated in a typical WWTP. Lastly, OPPT requested the guideline developed be submitted to the Organisation for Economic Co-operation and Development (OECD) for review by the Expert Panel and adoption as a OECD approved Test Guideline (TG).

Description:

EPA ORD in conjunction with key university, Arizona State University, University of Kentucky, University of Missouri, University of Arizona, and program office partners, OCSPP tested the reproducibility of data produced using a protocol designed to estimate two key parameters: 1) removal in batch bench-scale experiments of ENMs under one set of conditions of MLSS, mixing, temperature and residence time selected to simulate removal in the clarifier of a WWTP and, 2) quantification of the affinity of ENMs for the MLSS that will allow for extrapolation to operating conditions that are outside of the test protocol. The test guideline/method developed is based upon the OPPTS 835.1110 method. Previous research has demonstrated the method to be ineffective for predicting the removal of MNs during wastewater treatment. The freeze-drying significantly alters the physical size and structure of the biofloc which reduces interaction with the MNs. In the method evaluated the biomass was used fresh within a 24 hour period for evaluating ENM removal. The conditions in the test were set to mimic waste water treatment (e.g., amount of biomass per volume of water). Measuring the percentage removal of nanomaterial at a small number of concentrations from the water phase will provide the risk assessor with a rough estimate of the percentage removal to be anticipated in WWTPs and will justify the release numbers used in the environmental exposure assessment. A 0% WWTP removal is currently used in assessments unless relevant data is available in the literature or produced by the manufacturer. Research groups have demonstrated the ability to use batch bench-scale ENM removal data to model and/or match continuous-flow lab-scale reactors or full-scale WWTP removals of ENMs. The benefits of the batch bench-scale protocol and simpler tests than continuous-flow reactors is the ability to simulate a larger range of site-specific conditions (temperatures, MLSS levels, hydraulic residence times, etc.) using a smaller mass of ENMs which may be developed by a company.

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