Nanostructured materials as hazardous wastewater micropullutants: Sources, behavior, and impact on functional bacterial community of activated sludge

Unique properties of nanoscale materials make them attractive for industrial, medical, agricultural, and environmental applications. Nevertheless, the release of nanoparticles into the environment is a major concern due to the lack of knowledge about their behavior in the environment and potential widespread environmental impacts. On the one hand, nanomaterials are perceived as pollutants that may affect activated sludge microorganisms and, consequently, the efficiency of wastewater treatment processes. On the other hand, some nanomaterials can be intentionally added to activated sludge systems to improve their performance in terms of, e.g., sludge settling and removing heavy metals or organic pollutants. As a result, nanoparticles are frequently accumulated in wastewater, which is considered to be a major source of nanoparticle release to the surrounding environment. Processes that involve the action of activated sludge are used worldwide in wastewater treatment plants due to their excellent capacity of removing nutrients, degrading toxins, and retaining biomass. High concentrations of nanoparticles entering activated sludge systems can affect their growth and metabolism. The research studies, which are reviewed in the present article, show that nanoparticles significantly reduce the relative abundance of the activated sludge microbial community associated with nitrification, denitrification, and phosphorus removal. The knowledge about the structure of the activated sludge microbial community with an assessment of nanomaterial toxicity can contribute to optimizing the sludge population and improving the performance of wastewater treatment plants.