Occurrence, Removal and Regulation of Nanomaterials at Publicly Owned Sewage Treatment Works

Westerhoff, Paul
(Arizona State University)

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Engineered nanomaterials already occur in sewage and wastewater biosolids due to their release from commercial products (e.g., nano-scale titanium or silica dioxide in foods) and industrial processes (SiO2 in CMP polishing). Increasing levels and diversity of nanomaterials may enter sewage and wastewater treatment plants (WWTPs) in the future as they are released from products containing NMs (e.g., coatings, embedded in products or from industrial processes that use nanomaterials (e.g., for polishing). Some metallic nanomaterials may dissolve (e.g., silver, zinc, copper based) or biodegrade (e.g., fullerenes) in wastewater, and subsequently sorb to settable biomass, precipitate as inorganic solids or form stable aqueous complexes. Nanomaterials themselves sorb onto bacterial biomass in WWTPs, leading to their removal from water but accumulation in biosolids that are disposed to land surface spreading fields, landfills, or incineration where their fate needs to be further considered. Because of the dense biological communities in WWTP unit processes, under typical conditions >90% of the nanomaterials may attach to biomass which is removed within the WWTP. Inclusion of membrane filtration to augment gravity settling has the potential to increase nanoparticle removals. At expected production/use levels, the presence of nanomaterials in biomass appears unlikely to influence current biosolids treatment processes (e.g., anaerobic digestion) or landfill biogas production. Additional research is needed to be able to monitor the transformation and removal of engineered nanomaterials throughout WWTP and biosolids treatment to assure they are not released into the environment where they may pose human or ecological risks. We are working with the USEPA and OECD to assess rapid nanoparticle removal assessments that could be used to facilitate regulatory approval of nanomaterials in commerce.

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