Readers involved with industrial and commercial uses of nanomaterials may be interested in the Water Environment Research Foundation’s new report, Impacts of Silver Nanoparticles on Wastewater Treatment.
According to the report, silver nanoparticles from manufacturing and consumer products enter sewers and wastewater treatment plants in unknown quantities. For example, because silver nanoparticles are water soluble, as much as 100 percent of these particles might be able to leach out of clothing in just a few washes. In areas where industrial processes use these materials, concentrations of 0.1mg/L have been observed in municipal wastewater treatment plants.
Wastewater treatment processes generally reduce effluent levels to 10 percent or less of influent concentrations. This means that very low concentrations of silver may be reaching the receiving waters. However, because nanoparticles are more reactive than other forms of silver, many scientists and environmentalists are concerned about toxicity and environmental impacts. (See e.g., Silver Nanoparticles and Silver Nitrate Cause Respiratory Stress in Eurasian Perch, Aquatic Toxicology, January 2010; Nanometals Induce Stress and Alter Thyroid Hormone Action in Amphibia at or below North American Water Quality Guidelines, Environ. Sci. Technol., October 2010; Silver Nanotechnologies and the Environment: Old Problems or New Challenges, Project on Emerging Nanotechnologies, 2008)
WERF investigated the effects of these particles on activated sludge and anaerobic digestion. The research found that the nitrifying bacteria essential to removing ammonia from wastewater treatment systems were especially susceptible to inhibition by silver nanoparticles. Silver ions and silver nanoparticles concentrations as low as 0.4 mg/L inhibited the growth of nitrifying bacteria. In addition, anaerobic microbial activity in biomass (i.e., sewage sludge) was inhibited at silver nanoparticles concentrations of 19 mg/L.
WERF notes that the presence of nanoparticles during sludge treatment can have beneficial results. Recent WERF research has found that nanomaterials reduce the potential for odors in wastewater treatment and improve solids processing. (See Use of Nanomaterials for Biosolids Odor Reduction and Improved Dewaterability.)