Insights into long-term effects of low-dose cerium on partial-nitrification process: Accelerating nitrite supply by...

Cerium (Ce(III)) is ubiquitously quantified in many rivers (up to 4.48 mg/L), especially in nitrogen-rich streams affected by rare earth mining. This study investigated effects and mechanisms for long-term (123 d) low-dose (0.5-5.0 mg/L) Ce(III) on partial-nitrification (PN) process. In this study, Ach1 and PrpE were upregulated by 1.0 mg/L Ce(III), which increased the proportion of acetate in metabolic products and enriched Pseudofulvimonas. Moreover, PN/endogenous nitrification partial denitrification (PN/ENPD) process established via the synergy of Pseudofulvimonas and Nitrosomonas, which increased specific nitrite production rate (60 %) and decreased N₂O (95 %). Furthermore, the "biotic/abiotic synergistic detoxification mechanism" activated when Ce(III) concentration reached 1.0 mg/L, which increased abundance of Nitrosomonas, performance, and secretion of biomolecules. Finally, PN/ENPD process collapsed when Ce(III) concentration reached 5.0 mg/L due to Ce(III) accumulated toxicity. Overall, this study advances the understanding of long-term risks of low-dose Ce(III) to PN process and provides novel insights into accelerating nitrite supply.