Higher nitrogen removal achieved in constructed wetland with polyethylene fillers and NaOH-heating pre-treated corn stalks for advanced treatment of low C/N sewage.

Advanced processing of low C/N sewage faces the carbon sources shortage, while quantities of agricultural biomass wastes need to be disposed. This study investigated the potential of quantitative modified biomass addition in constructed wetlands (CWs) filled with polyethylene fillers. Results showed that the lignin in NaOH-heating pretreated corn stalks (NH-CSs) was destroyed, and the wrinkles on the stalks increased and became more soft after pretreatment, which was more conducive to the utilization of carbon sources and attachment of microorganisms. Compared with glucose and sodium acetate, the denitrification with mixed carbon source (glucose and NH-CSs) had the highest effective utilization percentage (61.37%) and NH-CSs were expected to become stable and fast-release carbon sources. After adding 30 g NH-CSs to the rear unit of CW with polyethylene fillers (CW-A), TN removal efficiency was increased by 18.21%, and the average removal efficiency of COD, NH-N, TN, and TP reached 54.83%, 89.95%, 64.11%, and 45.04%, respectively. Compared with the traditional CW (CW-B), CW-A had a significant denitrification advantage (P < 0.05), but the removal efficiency and effluent stability of phosphorus were inferior to CW-B. These results indicate that the biomass carbon sources such as corn stalks and polyethylene fillers have a good potential to improve the denitrification in CWs.