Nitrogen removal performance and mechanism of low-carbon sewage by airlift internal loop sequencing batch bio-microcapsule reactor

In this study, bio-microcapsules (PSCF) embedded with corncobs, zero-valent iron (ZVI) and Acinetobacter pittii SY9 were prepared, and the airlift internal loop sequencing batch reactor (AILP-SBR) was constructed with PSCF as filler. Results showed that the TN removal ratios of AILP-SBR were affected by HRT, C/N ratio and NH4+-N concentration, the NH4+-N, TN and COD removal efficiency of AILP-SBR reached 97.46 ± 2.18%, 90.67 ± 3.53% and 76 ± 7.43%, respectively under appropriate conditions (HRT of 10–12 h, C/N of 2–3, the influent COD concentration of 162.75 ± 16.02 mg/L, influent NH4+-N of 50 ± 0.92 mg/L, and pH of 7.00 ± 0.02), and the maximum first-order rate constant of TN removal was 0.2563 h−1. Moreover, carbon and total Fe (TFe) release characteristics, enzyme activity, functional genes and microbial community structure were used to explore the mechanisms of PSCF to enhance nitrogen removal. These results indicated that PSCF could release 98.15 mg COD/g and 1.15 mg/g TFe, provide electron donors for denitrification, and improve enzyme activity of nitrogen conversion. In addition, the addition of zero-valent iron (ZVI) could promote the abundance of nitrogen removal genes and functional bacteria in the AILP-SBR. In AILP-SBR, the dominant genera for nitrogen removal included Acinetobacter (10.57%), Dechloromonas (4.09%) and Hydrogenophaga (4.09%).