Effect of cerium dioxide, titanium dioxide, silver, and gold nanoparticles on the activity of microbial communities intended in wastewater treatment.

Growth in production and use of nanoparticles (NPs) will result increased concentrations of these in industrial and urban wastewaters and, consequently, in wastewater-treatment facilities. The effect of this increase on the performance of the wastewater-treatment process has not been studied systematically and including all the microbial communities involved in wastewater treatment. The present work investigates, by using respiration tests and biogas-production analysis, the inhibitory effect of four different commonly used metal oxide (CeO(2) and TiO(2)) and zero-valent metal (Ag and Au) nanoparticles on the activity of the most important microbial communities present in a modern wastewater-treatment plant. Specifically, the actions of ordinary heterotrophic organisms, ammonia oxidizing bacteria, and thermophilic and mesophilic anaerobic bacteria were tested in the presence and absence of the nanoparticles. In general, CeO(2) nanoparticles caused the greatest inhibition in biogas production (nearly 100%) and a strong inhibitory action of other biomasses; Ag nanoparticles caused an intermediate inhibition in biogas production (within 33-50%) and a slight inhibition in the action of other biomasses, and Au and TiO(2) nanoparticles caused only slight or no inhibition for all tested biomasses.