Notice of Retraction: Effects of Nano Zero-Valent Iron on the Performance of Denitrification of Alcaligenes eutrophus

Abstract

Being a strong redox agent, when nano zero-valent iron (NZVI) is much applied in the environmental remediation, it is important to understand if the functions of indigenous microorganisms have been affected. For this purpose, in this paper, effects of NZVI on the performance of denitrification of autotrophic denitrifying bacteria especially Alcaligenes eutrophus and possible toxicity mechanism were studied. The results showed that: when OD422 of the culture in the reactors was 0.0033±0.0002, in the reactor system without any electron donor, the process of denitrification can not been maintained. While in the reactor that almost exclusively on H2 as the only electron donor, the nitrate can be degraded rapidly and completely degraded into N2 in 4d. By comparison, after adding NZVI, the rate and products of denitrification were inhibited significantly. To degrade the same amount of nitrate, it needed 8d and the proportion of nitrogen decreased to 30%. For this, we studied the change of pH value, oxidation-reduction potential (ORP) and cell morphology to explore the possible toxicity mechanism after NZVI was added in the reaction system. Results showed that the cell membrane of the bacterial treated with NZVI was damaged significantly. The pH value had increased rapidly from around 7.2 to around 9.1, meanwhile the oxidation-reduction potential decreased rapidly from around 18.3 mV to around -490.3 mV after 24 hours. All these were unsuitable to denitrification. But with the reaction progressing, the pH value trended to be stable at 9.3~9.6 and ORP increased to 107.5mv, which was suitable to the denitrification and decreased the activity and toxicity of NZVI to Alcaligenes eutrophus.