A comparative study on the toxicity of nano zero valent iron (nZVI) on aerobic granular sludge and flocculent activated sludge: Reactor performance, microbial behavior, and mechanism of toxicity

Abstract

The increasing use and release of nanoscale zero-valent iron (nZVI) to the environment have aroused serious concerns about their environmental behavior and the potential ecological impacts. In this study, short-term (7 days) and long-term (60 days) effects of nZVI on the performance of flocculent activated sludge (FAS) and aerobic granular sludge (AGS) were investigated. FAS and AGS were exposed to 5–100mg/L of nZVI in SBRs and their response were estimated through the monitoring of reactor performance, microbial enzymatic activity, integrity of cell membrane and generation of reactive oxygen species (ROS) tests as well as bacterial community analysis. In FAS, the COD, nitrogen (TN) and phosphorus (TP) removal efficiencies were more remarkably affected, compared to AGS; also, short-term effects were more momentous. In AGS, integrity of membrane and enzymatic activities were not affected by NPs and generation of ROS was slightly reduced in contrast to FAS. Metagenomic analysis revealed little changes in microbial community diversity, suggesting that bacterial community in AGS was relatively more stable than FAS. The bacterial diversity in AGS were not obviously impacted at the phylum, class and genus levels. This study reports the possible toxicity of nZVI to biological wastewater treatment systems, particularly FAS.