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Nitrogen Removal Efficiency and Control of Bio-Denitrification Process of Aquatic Plants

ZHANG Fang;YI Neng;DI Pan-pan;WANG Yan;ZHANG Zhen-hua;TANG Wan-ying;YAN Shao-hua;GAO Yan;Institute of Agricultural Resources and Environment,Jiangsu Academy of Agricultural Sciences;College of Chemical Engineering of Nanjing University of Science & Technology;  
Eutrophication of water bodies has become a worldwide problem in recent years.So far,little has been reported on differences between types of aquatic plants in nitrogen(N) removal efficiency and function of controlling bio-denitrification processes,and variation of the function with growth stage of the plants.This will put us at a disadvantage when it comes to choose appropriate plant species and to further improve efficiency of the phytoremediation technology.With regard to this situation,an experiment was carried out to have four different types of aquatic plants(Eichhornia crassipes,Pistia stratiotes,Trapa bicornis,Hydrilla verticillata) to construct separately four microcosms for treating eutrophied water in an attempt to explore their N enrichment capacities,N removal efficiencies and functions of controlling bio-denitrification processes at different plant growth stages,i.e.initial growth period(June to July),rapid growth period(July to August)and slow growth period(September).Results show that the four types of aquatic plants differed significantly in NH_4~+-N,NO_3~--N and TN removal efficiency.The two types of floating plants,E.crassipes and P.stratiotes,were the highest in N removal efficiency and N enrichment capacity at all the growth stages with TN removal rate reaching(99.67± 0.27) % at the initial growth stage,(96.26±0.88) % at the rapid growth stage and(63.86± 3.77) % at the slow growth stage,while the type of submerged plant,H.verticillata,was the lowest in N removal efficiency.Among the three growth stages,the rapid growth stage witnessed the highest N removal efficiency for all the types of plants,and was followed by the initial growth stage.In terms of N enrichment capability,the four types of aquatic plants displayed an order of E.crassipes P.stratiotesTrapa bicornisHydrilla verticillata.However,the type of submerged plants released significantly more N2 and N_2O through bio-denitrification than all the others and so was its total gas release.The present study reveals that the aquatic plants differ in efficiency,pathway and mechanisms of N removal in eutrophied water with type and growth stage of the plants.It is,therefore,expected that all the findings in this experiment could provide some useful information on how tochoose appropriate aquatic plants and improve efficiency of the phytoremediation technology in treating eutrophied water.
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