Long-term performance of enhanced biological phosphorus removal with increasing concentrations of silver nanoparticles and ions

Abstract

The wide use of silver nanoparticles (AgNPs) and silver ions (Ag⁺) as antimicrobial agents have caused concerns about their potential effects on the environment, such as wastewater treatment plants. This paper reports the effects of increasing the influent AgNPs and Ag⁺ from 1 to 5 mg L⁻¹ on the performance of enhanced biological phosphorus removal (EBPR). The increase of AgNPs showed no significant influence on EBPR in both short-term and long-term experiments. Phosphorus removal, however, was decreased by a sudden increase in Ag⁺ concentration and it was gradually recovered after long-term culture. The mechanism studies showed that the transformation of polyhydroxyalkanoates and glycogen and the activity of exopolyphosphatase declined when Ag⁺ was increased suddenly, but they were recovered after long-term culture. The denatured gradient gel electrophoresis and fluorescence in situ hybridization analyses indicated that the bacterial community structure and the abundance of polyphosphate accumulation organisms were not changed by AgNPs or Ag⁺. Further investigations revealed that the long-term exposure of Ag⁺ increased the amount of sludge extracellular polymeric substances, which accounted for the mitigation of Ag⁺ toxicity to the EBPR key enzyme and microbes.