Quantitative ecology associations between heterotrophic nitrification-aerobic denitrification, nitrogen-metabolism genes, and key bacteria in a tidal flow constructed wetland

Abstract

This study explored the quantitative mechanisms of heterotrophic nitrification-aerobic denitrification (HN-AD) in a pilot-scale two-stage tidal flow constructed wetland (TFCW). The TFCW packed shale ceramsite (SC) and activated alumina (AA) at each stage, respectively, and aimed to improve decentralized wastewater treatment efficiency. In start-up phases, AA-TFCW accelerated NH4+-N decline, reaching transformation rates of 6.68 mg NH4+-N/(L·h). In stable phases, SC-AA-TFCW resisted low-temperatures (<13 °C), achieving stable NH4+-N and TN removal with effluents ranging 6.36–8.13 mg/L and 9.43–14.7 mg/L, respectively. The dominant genus, Ferribacterium, was the core of HN-AD bacteria, simultaneously removing NH4+-N and NO3–-N by nitrate assimilation and complete denitrification (NO3–-N → N2), respectively. The quantitative associations highlighted importance of nitrification, nitrate assimilation, and denitrification in nitrogen removal. HN-AD bacteria (e.g., Lactococcus, Thauera, and Aeromonas) carried high-weight genes in quantitative associations, including napAB, nasA and gltBD, implying that HN-AD bacteria have multiple roles in SC-AA-TFCW operation.