Review: Issues of Silver Nanoparticles in Engineered Environmental Treatment Systems

Silver nanoparticles (AgNPs) have been developed and broadly used for various applications, especially biocidal purpose. This could lead to contamination of AgNPs in engineered environmental treatment systems. This review conveys basic knowledge of AgNPs including synthesis techniques, fate, contamination and toxicity mechanism. The work emphasizes on the influence of AgNPs on the wastewater treatment and environmental remediation system performances. AgNPs could be synthesized using physical or chemical methods. After production or utilization, AgNPs distribute in the wastewater treatment and remediation systems via wastewater and excess sludge. Toxicity of AgNPs including cell surface defection, cell metabolism inhibition and protein damage by AgNPs, released silver ions or reactive oxygen species is reviewed. In the engineered environmental treatment systems, silver (ions and particles) may influence chemical and biological processes. For the chemical processes, silver species are able to lessen the process performance by chemical interaction while silver could be toxic to organisms in biological processes and fail the process performance later on. Previous works presented inconsistent results on influence of AgNPs to the engineered environmental treatment systems because of difference in AgNP properties, tested conditions and environmental conditions.