| Summary: | In engineering application, a two-stage biological aerated filter (BAF) has been deployed to achieve the steady nitrogen removal of the wastewater from the mining area of ionic rare earth with a low carbon to nitrogen (C/N) ratio. However, the cost-efficiency of the medium and carbon source casts a shadow over further development. In this study, the influences of four media (i.e., volcanic, zeolite, quartz, and ceramisite) and three soluble carbon sources (i.e., acetate, glucose, and methanol) on the N removal were systematically compared. Applying volcanic and quartz showed a favorable start-up performance due to the biophilic surface and dense packing, respectively. However, regardless of medium type, with [NH<sub>4</sub><sup>+</sup>-N]<sub>0</sub> = 50 and [NO<sub>3</sub><sup>−</sup>-N]<sub>0</sub> = 30 mg/L, the C/N ratio of 3 was required to meet the discharge standards of NH<sub>4</sub><sup>+</sup>-N, TN, and COD, and acetate was confirmed applicable for all the selected medium-packed BAFs. Introduction of sweet potato residues as the solid carbon source decreased the amount of added acetate by more than 13%. The 16S rRNA high-throughput gene sequencing revealed that <i>Sphingomonas</i> and <i>Nitrospira</i> were abundant in the aerobic stages of the volcanic and zeolite-packed BAFs, respectively. Such a community integrated with the extensively distributed <i>Thauera</i>, <i>Clostridium_sensu_stricto</i>, and <i>Proteiniclasticum</i> in the anoxic stage accounted for the efficient N removal. Thus, deploying volcanic as the medium and acetate as the soluble carbon source was proposed. These findings will provide valuable references for the selection of medium and carbon source and, consequently, further optimize the operational performance.
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