Magnetic Fe₃O₄ nanoparticles induced effects on performance and microbial community of activated sludge from a sequencing batch reactor under long-term exposure

The performance and microbial community of activated sludge from a sequencing batch reactor (SBR) were investigated under long-term exposure of magnetic Fe₃O₄ nanoparticles (Fe₃O₄ NPs). The COD removal showed a slight decrease at 5-60mg/L Fe₃O₄ NPs compared to 0mg/L Fe₃O₄ NPs, whereas the NH₄⁺-N removal had no obvious variation at 0-60mg/L Fe₃O₄ NPs. It was found that 10-60mg/L Fe₃O₄ NPs improved the denitrification process and phosphorus removal of activated sludge. The microbial enzymatic activities of activated sludge could be affected by Fe₃O₄ NPs, which had similar variation trends to the nitrogen and phosphorus removal rates of activated sludge. The reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release demonstrated that Fe₃O₄ NPs led to the toxicity to activated sludge and destroyed the integrity of microbial cytomembrane. High throughput sequencing indicated that Fe₃O₄ NPs could obviously affect the microbial richness and diversity of activated sludge.