Magnetite nanoparticles influence the ammonium-oxidizing bacteria activity during nitritation process

With nanotechnology dissemination, nanomaterials' (NMs) release into the environment is inevitable and may adversely affect the wastewater treatment processes. Among the NMs, the iron oxide nanoparticles have a considerable commercial potential, mainly because their magnetic properties, high catalytic ability and antimicrobial activity. However, few studies have examined their potential effect on the biological wastewater treatment. In this process, ammonium-oxidizing bacteria (AOB) are sensitive to the presence of inhibitory compounds and are useful as biosensors to assess contaminant toxicity information. Thus, this work aimed to assess the effect of commercial magnetite nanoparticles (Fe₃O₄-NPs) on AOB activity. Kinetic experiments were carried out where AOB were exposed in a short-term period (14 h) to different concentrations (from 0.2 to 1.0 g L⁻¹) of Fe₃O₄-NPs. A decrease of the 61.33% in the NO₂⁻-N production rate was observed to the highest concentration of Fe₃O₄-NPs studied, compared with the control sample. The Fe₃O₄-NPs concentration that reduces 50% of NO₂⁻-N production rate (IC-50) was estimated 0.483 g Fe₃O₄-NP L⁻¹. Scanning electron microscopy images revealed that NPs remained incorporated in the biomass (sludge). These results suggest that NPs can reach the environment through sludge disposal, mainly in cases of the reuse as soil fertilizer.