Comprehensive analysis of the impacts of iron-based nanoparticles and ions on Anammox process

Abstract

The short- and long-term effects of 5 mg L−1 iron-based nanoparticles (NPs) and ions on Anammox sludge were comparatively investigated in the present study, including Fe3O4 NPs, Fe2O3 NPs, Fe NPs, Fe (II) and Fe (III). Results showed that short-term exposure to Fe (II) obviously increased the Anammox activity, while Fe2O3 NPs and Fe (III) both decreased it (p < 0.05), and Fe3O4 and Fe NPs presented slight impacts. After long-term exposure, the TN removal efficiencies varied to 89.4%, 42.5%, 74.8%, 91.3% and 56.2%, respectively, while that in the control was 82.6%. The OTUs showed the highest difference from others in the sludge exposed to Fe2O3 NPs, while the microbial biodiversity in the iron exposed reactors all increased. The relative abundance of Candidatus Kuenenia varied to 11.67%, 3.99%, 10.07%, 13.89% and 8.07%, respectively, from the abundance as 11.26% in the control. Denitrifying bacteria, including Arenimonas and Denitritisoma were enhanced by the iron. The impacts (positive (+) or negative (-)) of the irons on Anammox process were in the order Fe (II)(+)>Fe3O4 NPs(+)>Fe NPs( ± )> Fe (III)(-)>Fe2O3 NPs(-). Fe (II) and Fe3O4 NPs could be adopted for stimulating Anammox activity, while using Fe NPs need to pre-cultivate the sludge or optimize the dosing strategy.