Nanomaterial Removal and Transformation During Biological Wastewater Treatment

Engineered nanomaterials (ENMs) already occur in sewage and wastewater biosolids due to their release from commercial products (e. g., nanoscale titanium dioxide). Increasing levels and diversity of nanomaterials may enter sewage and wastewater treatment plants (WWTPs) in the future as they are released from products containing nanomaterials (e. g., coatings) embedded in products, or from industrial processes that use nanomaterials (e. g., polishing). Some metallic nanomaterials may dissolve (e. g., silver-, zinc-, or 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 nanomaterials throughout WWTPs and biosolids treatment to assure they are not released into the environment where they may pose human or ecological risks.