Inhibitory effects of titanium dioxide, silver and fullerene nanoparticles on activated sludge from a municipal wastewater treatment plant

V. Aude Luppi, M.M. Fidalgo de Cortalezzi
Instituto Tecnologico Buenos Aires, AR

Keywords: activated sludge, nanomaterials, respiratory inhibition


The possibility of negative impacts of three nanomaterials on an aerobic heterotrophic microbial community (activated sludge) was investigated through respiratory inhibition tests (OECD 209 protocol). Titanium dioxide (TiO2NP, Evonik P25), silver (AgNP, synthesized in the laboratory), and fullerene (C60, Sigma Aldrich) nanoparticles were considered, since they have reached or are expected soon to reach consumers in significant quantities through nano-enabled products. All materials tested showed respiratory inhibition at concentrations between 10 mg/l and 100 mg/l (Fig.1), although ionic silver resulted significantly more toxic with a LC50 below 5 mg/l. A particular effect for TiO2NP was detected when exposed to light, resulting in an increased oxygen consumption, although experiments in the dark revealed respiratory inhibition. Preliminary results indicate that this behavior is due to the presence of live organisms. Transmission Electron Microscopy of the activated sludge after the tests showed the nanoparticles adsorbed on to the bacteria. The concentrations considered in this study are higher than normally expected in a domestic effluent nevertheless the evidence of acute toxicity and adsorption on the activated sludge hints that negative impacts may also occur at lower concentrations but extended exposure times in a full scale activated sludge system.