Impact of iron-based nanoparticles on microbial denitrification by Paracoccus sp. strain YF1

•Impact of iron-based nanoparticles on microbial denitrification by Paracoccus.•Adding Fe or Fe/Ni led to a decrease in cell growth and denitrification.•The solution pH and temperature impacted on the nitrate removal and bacterial growth.•SEM, XRD and EDS used for the characterization of change of surface of Fe or Fe/Ni. This study investigates the effects of Fe and Fe/Ni nanoparticles on biological denitrification when using Paracoccus sp. strain YF1. Results show that adding Fe and Fe/Ni nanoparticles to the cells decreased their growth and denitrification rate. Compared to that of free cells (control 89.47%), a decrease (64.33%) in the presence of 1000mg/L Fe/Ni nanoparticles was observed, while a small decline in the denitrification rate (76.36%) was obtained when the concentration of Fe nanoparticles was 1000mg/L. These were further confirmed by adding Fe2+, Fe3+, Fe3O4, Fe2+/Ni2+ and Fe3+/Ni2+ individually to the free cell system. Furthermore, Fe and Fe/Ni nanoparticles influenced the nitrate removal and bacterial growth under different pH and temperature conditions. SEM, XRD and EDS demonstrated that iron oxides formed as a result of nanoparticles corrosion in biological medium. Finally the presence of nanoparticles around some bacteria was observed.