Nitrogen removal processes in deep subsurface wastewater infiltration systems

•In the deep subsurface wastewater infiltration systems with a height of 2.0m, the overall performances were superior to previous research at same the hydraulic load.•Above 1.30m, 30.55% of the nitrogen was removed. 47.54% of the NH4+N participated in the CANON process, and the rest played a role in nitration.•At 1.30–2.00m, the denitrification process occurred and the removal of TN was mainly via denitrification.•Refractory organics could be used as a carbon source for denitrification. To determine nitrogen removal methods and the factors that limit denitrifying reactions during the sewage purification processes in deep subsurface wastewater infiltration systems, an organic glass column with a radius of 0.30m and a height of 2.00m was loaded with layers of soil from the Shunyi district of Beijing. Good performance was achieved under a hydraulic loading of 8cm/d. In addition, TP was nearly removed, and the effluent NH4+–N, TN, and COD concentrations were 0.14, 11.2, and 16.0mgL−1, respectively. Correspondingly, the removal efficiencies of NH4+–N, TN, COD and TP were 99.77, 83.68, 95.86 and 99.98%, respectively. According to the nitrogen variations with depth, 30.55% of the nitrogen missed at depths of up to 1.30m. A mass-balance and phylogenetic analysis indicated that completely autotrophic nitrogen-removal over nitrite (CANON) occurred. Furthermore, 47.54% of the NH4+–N participated in CANON, and the remaining NH4+–N played a role in nitrification. At depths of more than 1.30m, nitrogen was mainly removed by denitrification. In the process of denitrification, the change in the COD and the three-dimensional fluorescence spectra indicated that refractory organics could be used as a carbon source for denitrification.