Evaluation of nanocopper removal and toxicity in municipal wastewaters

Bench scale studies were performed to evaluate removal and toxicity of copper nanoparticles (CuNPs) and copper ions in activated sludge biomass. The data indicated that, under the test conditions, copper nanoparticles were removed more effectively (∼95%) than copper ions (30-70%) from the wastewater. Mechanisms of CuNP removal were further investigated by equilibrating CuNP and copper ion in activated sludge filtrate (0.45 μm). The predominant mechanisms of copper removal appear to be aggregation and settling (CuNP) or precipitation (copper ion) rather than biosorption. Most probable number (MPN) test data indicated that addition of 10 mg/L of copper ion was toxic to both coliform and ammonia oxidizing bacteria in the wastewater while no inhibitory effects were observed with the addition of the same amount of copper nanoparticles. Respirometry data indicated a 55% decrease in respiration rate when 10 mg/L ionic copper was added. However, no significant decrease in respiration rate was observed in the presence of copper nanoparticles. The toxicity of copper to activated sludge microorganisms appears to be a function of the concentration and characteristics of copper remaining in solution/suspension.