Tubular reactor-enhanced ecological floating bed achieves high nitrogen removal from secondary effluents of wastewater treatment

Excessive nitrogen emission is a common problem in the secondary effluents of rural wastewater treatment facilities. Nitrogen could be removed by constructed wetlands and ecological floating beds, but these techniques have low purification capacity in practice. Here, a novel tubular reactor-enhanced ecological floating bed was developed to enhance nitrogen removal of secondary effluents. We tested the feasibility of this system during a long-term operation. Results show that our system achieves a removal efficiency of secondary effluent N of 82.2% for 30 days after start-up and then maintains this efficiency for an additional 220 days. Dissolved oxygen was reduced from 2.92 to 0.23 mg L⁻¹, and the COD_Cr/TN (C/N) ratio increased from 2.6 to 13.1 along the reactor channel. This finding is explained by the synergy between the unique tubular reactor configuration and the mixed filler: palm fiber and bagasse. This environment enhances the spatial distribution of nitrifiers and denitrifiers along the channel, which was further demonstrated by scanning electron microscopy and high-throughput sequencing.