Corncobs addition enhances the nitrogen removal in a constructed wetland for the disposal of secondary effluent from wastewater treatment plants

Secondary effluent from wastewater treatment plants poses a persistent threat to the aquatic ecosystems owing to substantial nitrogen residues. For efficient nitrogen removal, this study explores the utilization of agricultural waste (corncob) to promote nitrogen removal in an up-flow constructed wetland (CW). Meanwhile, the corncob dosage and nitrogen transformations in CW are investigated. A proper dosage (70 g center dot m(-2)) of corncobs was determined, resulting in efficient and stable nitrogen removal, with average total nitrogen (TN), ammonia (NH4+-N) and nitrate (NO3--N) removals of 99.22%, 99.25% and 99.54%, respectively. During an addition cycle, equivalent of 2648.17 mg chemical oxygen demand (COD) of organics was released from corncobs, and most organics were effectively utilized. After adding corncobs in the CW, the main dominant genera were norank_Chloroplast, unclassified_Comamonadaceae, and norank_SBR1031. Functional genes predictions highlighted that organic degradation predominantly occurred in the lower region of CW, with the enhancement of nitrification and denitrification simultaneously in the CW. Findings in this research provide the theoretical reference for proper dosage and adding strategy of biomass recycling in CWs.