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Effects of CeO2 nanoparticles on biological nitrogen removal in a sequencing batch biofilm reactor and mechanism of toxicity

Hou, Jun, You, Guoxiang, Xu, Yi, Wang, Chao, Wang, Peifang, Miao, Lingzhan, Ao, Yanhui, Li, Yi, Lv, Bowen
Bioresource technology 2015 v.191 pp. 73-78
ammonia monooxygenase, bacteria, biofilm, ceric oxide, confocal laser scanning microscopy, image analysis, lactate dehydrogenase, nanoparticles, nitrate reductase, nitrites, nitrogen, nitrogen content, reactive oxygen species, scanning electron microscopes, toxicity, viability
The effects of CeO2 nanoparticles (CeO2 NPs) exposure on biological nitrogen removal in a sequencing batch biofilm reactor (SBBR) were investigated. At low concentration (1mg/L), no significant effect was observed on total nitrogen (TN) removal. However, at high concentrations (10 and 50mg/L), the TN removal efficiency reduced from 74.09% to 64.26% and 55.17%, respectively. Scanning electron microscope imaging showed large amounts of CeO2 NPs adsorbed on the biofilm, which increased the production of reactive oxygen species. The exposure at only 50mg/L CeO2 NPs measurably affected the lactate dehydrogenase release. Confocal laser scanning microscopy showed that high concentrations of CeO2 NPs reduced bacterial viability. Moreover, after a short-term exposure, extracellular polymeric substances (EPS) were observed to increase, forming a compact matrix to protect the bacteria. The activities of nitrate reductase and ammonia monooxygenase were inhibited, but there was no significant impact on the activity of nitrite oxidoreductase.