Fate and biological effects of silver, titanium dioxide, and C₆₀ (fullerene) nanomaterials during simulated wastewater treatment processes

As engineered nanomaterials (NMs) become used in industry and commerce their loading to sewage will increase. In this research, sequencing batch reactors (SBRs) were operated with hydraulic (HRT) and sludge (SRT) retention times representative of full-scale biological WWTPs for several weeks. Under environmentally relevant NM loadings and biomass concentrations, NMs had negligible effects on ability of the wastewater bacteria to biodegrade organic material, as measured by chemical oxygen demand (COD). Carboxy-terminated polymer coated silver nanoparticles (fn-Ag) were removed less effectively (88% removal) than hydroxylated fullerenes (fullerols; >90% removal), nano TiO₂ (>95% removal) or aqueous fullerenes (nC₆₀; >95% removal). Experiments conducted over 4 months with daily loadings of nC₆₀ showed that nC₆₀ removal from solution depends on the biomass concentration. Under conditions representative of most suspended growth biological WWTPs (e.g., activated sludge), most of the NMs will accumulate in biosolids rather than in liquid effluent discharged to surface waters. Significant fractions of fn-Ag were associated with colloidal material which suggests that efficient particle separation processes (sedimentation or filtration) could further improve removal of NM from effluent.