Removal of ammonia nitrogen from black and odorous water by macrophytes based on laboratory microcosm experiments

In recent years, the removal mechanism of ammonia nitrogen in black and odorous water (BOW), especially in the process of phytoremediation, has been a research "hotspot". Here, the migration process of ammonia nitrogen in macrophytes (Acorus calamus, Canna indica and Eichhornia crassipes) was detected by Fourier transform infrared (FT-IR) spectroscopy. Experiments revealed that the concentration of ammonia nitrogen (NH₄ ⁺-N) was reduced significantly. Maximum reduction in the NH₄ ⁺-N concentration was obtained in 75% BOW: the absorption of NH₄ ⁺-N was >90% in A. calamus and C. indica, and >80% in E. crassipes. After two 10 days cultivations, in the culture dishes of A. calamus and C. indica, absorption of NH₄ ⁺-N was >90% whereas, in the culture dishes of E. crassipes, absorption of NH₄ ⁺-N was ∼50% and ∼60%. FT-IR spectroscopy showed that NH₄ ⁺-N, NO₂ ^--N and NO₃ ^--N could be absorbed by the root and migrate to the stem and leaf of macrophytes. NH₄ ⁺-N and NO₂ ^--N were transformed, and the direction was NH₄ ⁺-N → NO₂ ^--N → NO₃ ^--N. The migration rate of NH₄ ⁺-N in C. indica was faster because of its regular and smooth capillaries according to scanning electron microscopy. Our study on the removal and transformation mechanism of ammonia nitrogen in BOW could be an important reference for other bodies of water.