Abstract
The purpose of this study is to reduce the seasonal fluctuation and enhance the efficiency of nitrogen removal in vertical flow-horizontal subsurface flow (VF-HSF) constructed wetlands. Two sets of VF-HSF constructed wetlands were built, VF1-HSF1 and VF2-HSF2, and a zeolite section was placed in VF2. The results showed that VF2-HSF2 compared to VF1-HSF1 was not only a more reliable nitrogen removal method, but also enhanced the nitrogen removal efficiency by 50%. The average apparent rate of nitrogen removal in VF2-HSF2 reached to 2.52 gN·m ·d , which doubled the rate in VF1-HSF1. Plant uptake and organic nitrogen sediment accounted for 12% and 6% of the total nitrogen removal in VF1-HSF1, respectively, and 10% and 4% in VF2-HSF2, respectively. Biologic nitrogen removal was the dominant mechanism, which accounted for 79% and 87% of the total nitrogen removal in VF1-HSF1 and VF2-HSF2, respectively. Ammonia adsorbed by zeolite during the cold seasons was desorbed, and then nitrified in warm seasons, which resulted in a bioregeneration efficiency of 91%. Zeolite in VF was capable of transferring ammonia from cold seasons to warm seasons as well as enhancing nitrification, which was accompanied by high potential denitrification in HSF that reinforced the efficiency and relieved seasonal fluctuation of nitrogen removal in VF-HSF.
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