Aiming at the problem of high concentration of total nitrogen (TN) and low available carbon source for microorganisms in municipal secondary effluent, the vertical flow constructed wetland associated with iron-carbon internal electrolysis (ICIE-VFCW) was applied to investigate the removal efficiencies of pollutants in municipal secondary effluent. Moreover, the mechanism for enhanced nitrogen removal was primarily discussed by the applications of UV visible spectrum (UV-VIS) and gel filtration chromatography (GFC). The results showed that the ICIE-VFCW could improve the COD removal efficiencies and the effluent COD of less than 30 mg·L-1could be stably obtained. The average COD removal efficiencies of the whole year, warm months, and cold months could be increased by 10.16%, 9.81%, 11.22%, respectively, compared to the control group. The effluent TN of the ICIE-VFCW could be maintained below 10 mg·L-1, and the average TN removal efficiencies of the whole year, warm months and cold months could be increased by 13.72%,12.90%,16.17%, respectively. Besides, compared to the influent, the humification, aromaticity and average relative molecular weight (Mr) in the effluent obviously decreased, and the Mr decreased more significantly in the ICIE-VFCW. The ICIE-VFCW could promote the conversion of refractory organics in municipal secondary effluent to the small and readily biodegradable molecules, which could enhance the utilization of organic compounds by microorganisms, thus improving the removal efficiency of nitrogen.
Keywords: deep denitrification; distribution of molecular weight; iron-carbon internal electrolysis; municipal secondary effluent; vertical flow constructed wetland.